Antenna positioning system: active feedback (2-axis) - Page 1
Forum section: electronics / projects

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 21, 2016, 08:20:28 am
content: Good morning everybody.I've came across an interesting problem it turns out I can't find an easy answer to!I am currently building a 2-axis antenna positioning system (for the purpose of tracking satellites with a directional antenna): I had opted for a fairly simple design with 3D printed and plate-metal parts - stuff that I can easily work in the lab.The system will have a 180 degree traverse on the x-axis (antenna elevation: allowing me to point it from one horizon to the other) and 270 degree traverse on the z-axis (azimuth): this keeps the wiring simple (I can probably increase the azimuth actually, just by using a longer wire, but obviously twisting the cabling repeatedly won't be good for it!My original plan was to use stepper motors with some reduction gearing to control the axis (the antenna(s) would be mounted on an axle and counterbalanced to minimise the torque needed to position them) - and during the planning and design stage I've started to question my intention to use a relative positioning system.In an ideal world were cost was not an issue, I'd have everything on active feedback loops so that the controller knows exactly where the antenna is pointing - unfortunately, costisan issue!I was just wondering, what sort of absolute positioning have people used for things like this? In my admittedly brief research I've seen everything from accelerometers to optical interrupters, hall effect sensors and even simple potentiometers. It doesn't need to betooaccurate, but +/-1 degree would be great, even less would be terrific: and at a push I can just use a relative positioning system with a number of clutches to reduce unwanted movement (but this is not ideal!)Do any of the below ideas carry any merit? If you were making something like this, how wouldyoubuild it?-Servomotors (may lack the torque needed)-Stepper motors (relative positioning: if wind moves the antenna accuracy will be lost)-Optical interrupters (feasible: may lack the accuracy required)-Potentiometers (feasible: would require mechanical linkage; may lack the accuracy required)-Accelerometer (may not have accuracy required for the azimuth (z-axis) rotation (BUT I've not looked into these much))-Hall-effect sensors (has the potential to be fairly complex)

author: C
author_rank: Super Contributor
timestamp: October 21, 2016, 05:49:48 pm
content: First are you going to make a fancy tracking system or keep it simple?Using the amplitude difference from two antennas can give you output on what direction to move. Need a min of three antennas for satellites where two axis output needed. Difference gives zero output when pointed correctly and magnitude of direction to move when not.Servos can make it easy.Think of a dish on a ship where the ship is also moving.Think of what a simple servo is. Position less then commanded position rotate clock wise, position greater then commanded position rotate counter clock wise, with hysteresis. Fancy uses distance from commanded position to adjust speed. Any type of motor can be usedTwo ways to control movement.Rotary axis movement & jack screw providing axis movement.For satellites, jack screws are often used to remove need for heavy gearbox for some axis..The antenna rotor's you can find for sale are probably using a single phase reversible AC motor with gear reduction with some thing that gives a pulse per revolution or more before gear reduction. Limit switches that turns off the command to rotate in one direction so that it all coasts to a stop before mechanical stop is reached.You can use a radio signal to calibrate this to absolute position. It is also cheap to make it better.To make above better you just need some spot you can find on axis, A spot on main rotation that is anded with above pulse per revolution output. Think of main spot being a window that you are selecting one pulse out of all.QuoteNo size or torque limits. Can be any type of motor.QuoteThe faster you want to move the bigger the motor, costs increase.QuoteDo not use just one. Use many attached to different points in gear train.QuoteWorked with a system where the Potentiometer was optical. A slot to restrict light with the ratio of light on two sensors making a Potentiometers like output. This simple sensor was used to control servo with direction, speed and tension of very thin mag tape going on a large heavy mag tape reel. Tape movement was input control here.QuoteQuoteFancy would use many Hall-effect sensors picking up gear teeth for example. The sensor close to motor gives a high rate output while the output of many at same time gives you a fixed position.If you put this all together, If you can do a raw point to get a signal from a satellite, you can lock on to that satellite's position even if it is moving. If you know this satellite's position you now have all you need to calibrate system.Note that a directional antenna has a broad amplitude peak as you move to and past a signal. The differential signal from two antennas makes a sharp notch when both antennas are pointed correctly, easy to see & use.For two antennas an in phase combiner to add signals. Differential is an out of phase combiner for two antennas.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 21, 2016, 06:50:58 pm
content: One could combine absolute and incremental position reading. E.g. coarse but accurate absolute readings to zero in the incremental readings. So only a little movement is needed to reset the incremental positioning.Optical decoders can be quite accurate - it depends on the construction.Stepper motors with gears might still be a good solution as they don't move easy even if turned off. Servo motors are more useful at high power or if high speed is needed.

author: Howardlong
author_rank: Super Contributor
timestamp: October 21, 2016, 07:20:04 pm
content: Is this for fast LEO tracking, or repositioning for geostationary selection?What frequency bands are you interested in and what antenna gains (i.e. what are the typical beamwidths)?How big are the antennas, and what are the torque requirements and wind loading limits?If it's for LEO tracking, does it need to flip (i.e., mid pass does it need to be able to cover 180 degree elevation, or is 90 degree elevation enough)?For simple geostationary repositioning, simple single screw actuators are commonly used.The low end az-el rotators use simple pots for feedback, and these are easily suitable for reasonably small arrays with beamwidths of, say, ten degrees or more.The higher end mounts are often adjustable polar mounts rather than simple az-el.

author: viperidae
author_rank: Frequent Contributor
timestamp: October 21, 2016, 07:51:38 pm
content: If you're going to use a reduction gear, why not a attach a multi turn pot to one of the gears?

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 21, 2016, 09:52:10 pm
content: Quote from: viperidae on October 21, 2016, 07:51:38 pmThat's an interesting idea actually! I'll have to look into that!Quote from: Howardlong on October 21, 2016, 07:20:04 pmThis will be mostly for LEO on VHF and UHF: the current design is for two yagi-uda antennas - one for each band. Only the VHF will be mounted at first (2m boom length wighing in at 3.4kg with the counterbalance weight mounted) - torque requirement (for positioning) isn't too high - but it would need to resist any movement from wind loading.I am unsure of the wind loading specs on it, as it's a DIY antenna and will probably mutate the more I use it! Given that it's 2m long, I'd expect a >50 N-m motor would be required (these are just ballpark figures - given that I probably won't use it in high winds I can probably get away with less)I actually considered putting a third axis in to make it a polar mount (simply to tilt the existing elevation axis (which Ithinkis called "declination?")) but decided against it as the engineering for it was going to be awkward unless I reduced the mass of the antennas!As for the max elevation, my intention was to allow it to have the full 0-180 degree traverse, allowing it to be pointed in any direction if the azimuth is limited to 270 (just flip it around to add 180 to the azimuth) In principle, it's not actually needed - I was simply adding it to compensate for targets passing over or near the zenith and to make pointing it in any direction easier.Quote from: Kleinstein on October 21, 2016, 06:50:58 pmI must say, after I built my 3D printer, I was very fond of stepper motors for a while! They do have their downsides with something like this though (as I said, if they slip from wind loading the tracking software will have no idea it's happened!)As for the accuracy of optical decoders/interrupters/etc/etc - the construction was the problem, unless I was getting parts CNC'd, I'd doubt I could build it precisely enough to make it work - I could be wrong though, I've only looked at fairly simple encoders so far.Quote from: C on October 21, 2016, 05:49:48 pmOoft! Lots of good info there!I'm almost certainly going to keep it the tracking simple as I can - my garden can only support so much construction before the neighbours will complainI was thinking of keeping the tracking pretty much limited to software to begin with, relying on the antenna having a moderately wide beam width (I don't have any empirical data on the beam width as I built it myself - I only have the model data, which suggests it should be about 10 degrees off-centre... I'd err on the side of caution and say it's got a wider beam than that though, simply because I built it myself!) to compensate for any inaccuracies. The need for positional feedback was for my future plans of actually locking onto it using a mixture of telemetry data and/or signals, and more immidiately, if a gust of wind moved it I wouldn't have to re-home the entire system before re-tracking it!Tracking will (initially) just be "get the orbital path: follow where the satellite is predicted to be (and make corrections based on signal strength/telemetry/etc) - it won't be an "active" tracking system so to speak, as in it won't actually be locking on to the target (initially!)Another option is to get the orbital data and wait for a signal, and then follow the predicted orbital path at a set rate once a signal is acquired.I figured I had better get the mount built first before I worry about the details of tracking (my assumption being that if I can point it at a target and keep it pointed, I can actually figure out where the target is later)

author: C
author_rank: Super Contributor
timestamp: October 21, 2016, 11:08:34 pm
content: QuoteMight look at telescope mount for details.The third axis is more for tilt, You can use a jack screw drive to get this. The fact that a jack screw can make change of almost 2x it compact length and the length lets you attach out on an axis makes this great for strength.Think of a teeter totter with two axises mounted on it with the jack screw moving end. You are just making the top of tower have a lean.Some rotors use a worm gear drive. Makes it harder for wind to change position. On main shaft a hole in gear or a disk with a hole makes for a great index spot when combined with other sensors. If you had an optical encoder with index on motor shaft, Some encoder count & hole sense becomes very accurate main shaft index.You may be forgetting about gear reduction. How many degrees will main shaft move with one revolution motor shaft? A simple disk with a hole or slot mounted on motor shaft will give you that. If not enough two is still easy by hand to do. Easy to use output of 3D printer directly or as a drill guide. Just 3D print your encoders.Two of your home build antenna will let you create that notch signal drop. May not want this now but easy to plan ahead for this.Think of really nice system and what is needed for it, then allow for parts to be added easily to your simple start.

author: Howardlong
author_rank: Super Contributor
timestamp: October 22, 2016, 02:43:39 pm
content: Why is the Az limited to 270? Are the LEOs polar orbiting or something else?The reason I ask is that if you limit you Az you will frequently suffer loss of signal during passes while you wait for the El flip.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 22, 2016, 03:11:26 pm
content: Quote from: Howardlong on October 22, 2016, 02:43:39 pmI can see where you're coming from - the design actually allows for greater than 360 degree rotation: I had (rather arbitrarily) decided to limit it to avoid excessive cable movement, relying on the ability for the elevation to exceed 90 degrees to compensate for the loss of azimuth.The other thing is that because the array will be ground mounted (definitely not the best place for it!) that my house will be in the way for a portion of the traverse anyway!By lengthening the cable I can probably increase the rotational range; but because the cable will be going up the centre of the support, I can't increase it too much!Anyway - will get some cad drawings up shortly!

author: CM800
author_rank: Frequent Contributor
timestamp: October 22, 2016, 05:08:01 pm
content: The biggest issue you will have here is running it outside. You'd want IP67-IP69I'd recommend closed loop stepper motors Optical encoders are more precise then you will ever care to need, cheap run-of-the-mill ones are 1024 lines (4096 ppr) giving you a resolution of 0.09 degrees, you can easily find ones with resolutions as high as a few microns for not much.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 22, 2016, 05:21:50 pm
content: I've got a couple of tricks for waterproofing (which is one of the reasons he only has two axis) - the preferred method i've been looking at is a grease filled labyrinth seal and covers over the moving parts.If that is insufficient, I can also encase the entire thing in flexible cover (looks like a bag xD)

author: CM800
author_rank: Frequent Contributor
timestamp: October 22, 2016, 05:33:47 pm
content: -

author: C
author_rank: Super Contributor
timestamp: October 22, 2016, 08:33:47 pm
content: If you are going to use grease might add this trick of pressurized grease. Just a little pressure can replace grease that works out of shaft seals keeping the void out of the grease seal. You are just making the leak go the direction you want.Think about off the shelf parts. Using some of them is creating more problems then the part cures and can be a large cost. For example, for one axis things get better if the axis is hollow so you can have a pipe from one side to other. A lot of prebuilt gearboxes do not have this. A large ID gear can let this happen, Two of these gears can make it easer while supplying 2X strength if the gear box has outputs on both sides. This removes some places where you have to counter torque.Might want to think some on stepper motors. Think of a satellite that passes overhead. You go from stopped to very high speed when satellite is above and back to stopped. Not a big deal for antennas, but can the motor supply the torque and speed needed?Note that using a worm gear drive system may need no holding torque from motor to hold antenna position.You might want to think about ac motor and drive it like a computer fan does. A computer fan motor is just a two phase motor. A single phase capacitor run motor could be operated this way.Note that a Hall-effect sensors does not have to be expensive and will still function with grease in the area. Many cars use them for this reason. An index mark is just a missing or extra tooth sensed.

author: Howardlong
author_rank: Super Contributor
timestamp: October 23, 2016, 07:43:52 am
content: Quote from: cprobertson1 on October 22, 2016, 03:11:26 pmIn my experience, dressing the cables on Yagi tracking arrays to avoid snagging will be easier with 450 Az and 90 El: as soon as you flip, the chance of cable snagging magnifies, with some nasty consequences! Been there, and have the bent metal to prove it ;-)If you can have both 360+ and 180, so much the better. Flipping usually happens at very high El passes which are the minority. Depending on how far the antennas are from your house, you might find that your actual El angles are much lower than you think: it's a trick of the eye, tall looking structures present lower El obstructions than you might think.I totally understand about restriction in antenna location. My first satellite contacts were done from a basement apartment with the antennas below ground level pointing up. Needless to say visibility pass times was fairly short, but it worked.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 23, 2016, 07:43:03 pm
content: Quote from: CM800 on October 22, 2016, 05:33:47 pmWould mind a couple of those - not sure I could afford them thoughDoing my best to keep the cost in the sub £100 regionQuote from: C on October 22, 2016, 08:33:47 pmPressurised grease is a good idea - not 100% sure how I'll stop backflow into the main unit though - I'll figure something out I'm sureI'm currently leaning towards stepper motors: still not sure on the exact arrangement though - still investigating a polar mount arrangement using some threaded bar for the declination, but struggling to keep the strength up (don't wan't it flexing too much if there's a gust of wind!)Actually, given that this will be mounted on a pole to get it above the brick wall on one side of my garden: this is probably when I'll find out that wind makes the entire thing oscillate...Hall effect sensors might be a viable solution; still looking into it though.Quote from: Howardlong on October 23, 2016, 07:43:52 amI've been considering just leaving a big loop of coax out the back of the yagi and onto a frame attached to the rotator - if I go with the aforementioned polar mount I can probably cut out a good amount of the elevation requirements (but again, my design doesn't place a physical limit on the elevation so I can extend it if the cabling allows for it (the mount is effectively a T shape, possibly with an extra axis for declination)I'm probably going to make a mock-up of the frame to get some idea of the torque requirements - will report back later in the week (once I get a new hole-cutter... I cut a hole in my soffit earlier today to put a coax through... and discovered that my fascias have random 4-inch wide bits of concrete inside it every nine feet(ish) along it.I don't know why, it's weird and it broke my hole saw...

author: C
author_rank: Super Contributor
timestamp: October 23, 2016, 09:13:57 pm
content: Pressurised greaseFor trailers here in USA they use what is called a "bearing buddy"It is nothing more then a piston with a spring pushing against grease side.Seals like these are used in car breaks and other places.just need a hole, a spring, a medal disk and above seal. then put pressure on grease. The "bearing buddy" mounts a grease zerk in disk with small hole in seal. For other seals, many things use press in seals.Just use two on each side, one to seal outside and one inside. Grease pressure will force them further apart and can be used here.outside, Seal, bearing, seal, inside,seal,bearing,seal, outside.EZ mountUse two pipes for your mask with a one pipe separation.Raise center pipe clear of ground and put a bolt through all three pipes close to top of two pipes. Antenna's and rotors mount higher then bolt on center pole. Moving center pipe out from between pipes at bottom gives you a tilt. The screw jack works great for adjustment.The above is simple and messy just to get idea across, hope you get idea, just make it fit and work better for you.Might think of a box with two pipes all the way through the box to use as axis.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 24, 2016, 10:24:55 am
content: Ooh! I didn't realise I could use off-the shelf parts for the grease seal: I had assumed the pressurised grease systems would have always been engineered onto the axle or the surrounding bushing.I'm actually wondering if I could just use sealed bearings as the water resistant seal, in conjunction with a simple cover to keep most of the water off - obviously if it gets submerged it won't hold up - but if my antenna system is being submerged I'm pretty sure water ingress would be the least of my worries.I think I've decided not to bother with a polar mount, for the simple reason that it's much simpler to build and program an Az-Al system. Sure, it may not be the best option - but I can always add a system to tilt the mast itself should I decide I want it in the future.So in short, simple Az-Al mount - probably going to use worm drives for the motion (I've estimated that with a stepper I can get a minimum of 300 rpm which works out at 14 to 20 degrees per second depending on the size of the spur gear.)I will aim for stepper motors, but might be able to get away with other types depending on torque requirements (I'll make a hand operated mock-up to make sure it will work, first of all!) and then take it from there (provided I use positional feedback - a simple optical encoder telling me how many rotations the worm drive has made should be enough due to the high reduction ratio)This brings us back round to the original problem - with a worm drive (i.e a very high holding torque), and stepper motors, reckon I could get away with a relative/incremental feedback system? Or would it be worth adding absolute feedback so that I don't need to re-home everything if it loses its calibration for whatever reason?In fact, I think somebody suggested earlier that I can get away without the feedback if steppers were used!

author: C
author_rank: Super Contributor
timestamp: October 24, 2016, 08:07:21 pm
content: Quote from: cprobertson1 on October 24, 2016, 10:24:55 amA sealed bearing is built to keep some stuff out while keeping grease in bearing. Could work a long time properly shielded. A few things could make this better. A press fit ring on shaft so that any water running along shaft is forced away from shaft. a greased/oiled felt ring next to bearing to keep air moisture out. Keep in mind that a shield leaks and plan for diverting the leaks to where they do little harm. The ring above would be better as a funnel shape except when acting like a liquid funnel. To cover this you could have two funnels with outside one with a drain hole.Quote from: cprobertson1 on October 24, 2016, 10:24:55 amYou are thinking of a stepper motor only as an output device. Think of it as an input device. Movement would cause voltages on terminals. If you think of this as optical encoder output, what you are missing is an index pulse.As a stepper, you need an index pulse per rotation to know where in rotation the stepper actually is. When you couple this to a gearbox, you need an index pulse on gearbox output shaft to know where in it's rotation it is.You now have equal of an optical encoder with gearbox setting counts per rotation.In both cases the index pulse could be several stepper motor steps wide, but this is a fixed value. With fixed steps here you just pick a step in the window(s) as actual index.For absolute position;You then have gearbox index & stepper index & specific stepper step in window giving a very accurate index to whole system. Note that you might need to rotate one of the index generators to make this happen at same time.When you know master index position you are absolute.The remaining problem is finding the index when this information is lost. You could use limit switches on axis to find this.Or you could have output from gear output shaft that gives direction to index output. Just a disk with 1/2 rotation a smaller diameter. At the speed here you could even use a switch like.With just one output here you have change with index or change and no index for axis that rotates 360 or more. Knowing that this is a direction output makes finding index easy.For an axis that you do not want full rotation on, just reduce the degrees for direction & no index. A stack of three disks makes this easy. You can use a nice ramp to change levels here.Would be simple to add, recalibrate system any time you pass system index.You might want to rethink system as if using large RC servos. On web is some microcontroller replacements for the electronics in the cheap RC servo you can copy from. Using a stepper motor is open loop control, while an RC servo is closed loop control. One simple step in this direction is not using stepper counts for position but relative position between index pulses from above. Any bad acts of stepper motor is then counseled at next index pulse.What motor to use then becomes which has lower cost of driver & motor.

author: C
author_rank: Super Contributor
timestamp: October 24, 2016, 08:12:02 pm
content: Normal build process is to use tools to build what you want. What is often forgotten is that what you are building can be used as a tool to help the build. You will have two axis that you control & have some need to test the axis motion. You could build a temporary x-y table with just threaded rod, nut, some hose & hose clamps. Two rotary axis like this can become a lathe using offsets between axis. Think of simple here as better than hand but less then real tool. When a lathe tool is replaced with a grinding tool, forces become low. You are trading high speed of real tool for slower speed of simple junk tool.You said 3D printer, use it. Make some plastic bearings for shafts but use as a seal.Do like old timers did, use what they have to build something better.You could probably use sleeve bearings for axis shafts. Remember that other parts of axis gets stronger by using hollow shaft axis, too big a hole through axis is not a problem and can be good. With too large you can use wedges to clamp and center smaller pipe inside larger pipe. Two pipes, one with taper on ID other OD cut in sections where needed so can change sizes. A plummer has tools to cut a taper thread on pipe. Your axis could look like a wire spool with what you build being in wire position, A pipe & two pipe flanges.You do not want two separate axis, as a system you want two axis that work together, A box with two axis holes through the box. A simple change from one set of axis control wires having to move to two sets.For wires think of a spiral between axis half's. The axis movement would change spiral wraps by 1 count while the spiral changes that amount in diameter. Support is something that flexes in one direction and not in other( a tape measure rule)If you want low cost, use what is low cost that will do job while not making it harder.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 26, 2016, 08:56:51 am
content: Quote from: C on October 24, 2016, 08:12:02 pm(sorry to long to quote it all)Lots of useful info there! Thanks a bunch!Quick question, what do you reckon the lowest maximum rotational rate I could get away with is? (absolute minimum, I always err on the side of caution and don't actually approach my minimina if I can help it!)At a guess, I would assume it to be 180 degrees (horizon to horizon, through the zenith) using the a very short pass time (3 minutes) gives us 180 degrees / 3 minutes = 60 degrees per minute = degree per second.Obviously most passes will be longer than that (and thus require a lower speed) and will be at a lower elevation (requiring even slower movement)My current design would have at the following maxima (the RPM is a minimum estimated value: it will likely be higher, but varies from motor to motor)Code:1:100 reduction, driven by 100 RPM motor with 200 stepsOutput Rotational rate = 1 RPM = 6 degrees per secondRange per drive revolution >= 3.6 degreesPrecision (max)= +/- 0.018 degrees per stepPrecision (min)= +/- 0.027 degrees per step, 50% step distance errorDo you reckon 6 degree/second is high enough to handle the fastest passes?

author: C
author_rank: Super Contributor
timestamp: October 26, 2016, 08:13:10 pm
content: What you want to point antenna at makes the difference here. But might want to think of the odd thing also.Think of a jet going over top of antenna.At little distance you have extreme speed when pointing strait up. As distance increases max speed drops. But you also have your 10 degree beam width working for you here. So you could go max speed before needed to use one side of beam to receive and jet moves in beam width and you are fine if jet does not get out of other side of beam width at max speed.This Idea can drop max speed needed for center to a lower max speed needed to stay in beam.I used over the top here because that is most extreme speed needed for an axis. 1000 feet up is same as 1000 feet to one side and low. just different axis.At 45 degrees you are using both axis to get needed speed and keep on something moving faster.LEO hight = speed, slower it falls out of sky, faster needs rocket motor. You need to think about a orbit that is not a circle. At low hight, you have rocket motor speed & max hight is fall out of sky speed. A low hight to think of is burn up hight or too much drag.my quick read is 160 kilometers (99 mi) strait up and about 7.8 km/s for circular orbit. And you need faster to cover the highly elliptical orbit (HEO).If my quick thinking is correct, you have a circle strait up where you will lose signal for and then pick it up again based on speed of object.A distance of 160 kilometers & 7.8 km/s gives you max angular rate for over top leo.Less then this angular rate, is covered some by beam width. Still slower and you have drop and pickup circle form.If you have a circle, the size would decrease as you start using a second axis for movement until you get to a min at 45 degrees on two axis.So throw some numbers in a spreed sheet. Play with beam width. Get a feel for distance vs speed while thinking on real object speed and what distance is normal to that object.When you add 5 to 10 degrees to 160 kilometers (99 mi) the 7.8 km/s peek drops some.So the over top axis horizon to horizon time is not what to think about, it is the peek speed needed at strait up. The horizontal rotation peek speed will be less for a LEO as the distance has increased.A pass over head jet is fastest axis movement and drops as distance to one side increases.Keep in mind that normal max speed for a stepper is limited prevent missing steps as it is open loop control. With index pulse for feedback it's less a problem or no problem.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 27, 2016, 08:54:54 am
content: QuoteAye, I was arbitrarily halving the max speed figures for estimations.I've just discovered, after two solid hours of degreasing, that the worm gear I was planning to use (salvage from an old industrial actuator of some sort) has quite a few chips in it's moving surfaces, it's currently in an alcohol bath to clean it up a bit (that prehistoric grease + prehistoric rust flakes + prehistoric swarf + prehistoric steel grindings has more than a few qualities that'd make a good cement!) - but I'm not confident it will have the nice smooth movement I was hoping!Any idea where I can get worm gear sets for around... say, £20? The only ones I can see in that price range are too small for my needs (40-teeth with a low mod value >> low overall diameter)Failing that I can of course use anything from pulleys, drive belts or spur gears.This topic has totally drifted off my original problem of how to determine the position of the gearing!

author: C
author_rank: Super Contributor
timestamp: October 27, 2016, 04:56:47 pm
content: Can not think of something that uses a worm gear that will have the strength needed.Keep in mind that the idea is to move the antenna's. You gain strength to weight by using pipe. You also gain strength by using a longer arm.If you are using a micro controller you have a 2 or 3 axis control input that that actually uses linear motion to make axis movement.When you think of motor jack screws, think of a hydraulic piston actuator with feedback. More length change is easer, your lever arm increases. You can use common ball joints for connections.You could use a rotary motion to cause a 90 degree tilt by a 45 degree rotary joint on axis.A change from simple two rotary axis to a harder to control thing with a large strength increase that allows antennas to be on a pipe with wide spaced support.Think of what a jack screw is. Your stepper motor with gears with the worm gear replaced with a threaded rod and nut rides on the threaded rod giving a length change. Wind will not move this.Put a chain sprocket on an axis. Attach the chain to the nut above. Add a idler sprocket to keep chain tight. You now have controlled linear motion moving axis many degrees, could easily be greater then 360. Easy to add a weather shield to protect chain. Note that a chain sprocket with large center hole is easy to find.EditNote that other things can replace chain hereA spool with a couple turns of cable for example.Import part is total system and being able to build it.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 28, 2016, 11:49:34 am
content: Urk! The drive system keeps changing!I've got a hold of some M12 threaded rod: I'll probably end up using that to drive a simple lever attached to the axle: should be give more than enough torque to move it a decent speed - and if it's not fast enough then I can upgrade the motors - this keeps the design fairly low profile as well so I can add extra axes in later on if I want!Other (azimuth) drive will be a simple pair of motors on a 1:5 (or higher) set of spur gears, with a rubber ligature to allow adjustment of the friction.I'll use 40mm x 3mm 6082T6 aluminium tube for the axle itself, bearing mounted horizontally in a silicone sealed wooden enclosure clad in overlapping aluminium sheeting and simple labyrinth seals on the axles, covered by a small canopy to keep direct rain of the seal. All that will be mounted on a piece of discarded downpipe, forming a T shape with the antennas at either end of the horizontal tubing.Materials:ItemUnit CostQtyLine CostSubtotal4-Axis Stepper Driver (module)£11.001£11.00£11.00Al 1050A Sheet (1000x1000x0.5mm)£10.001£10.00£21.00Al 6082T6 Tube (2500x40x3mm)£12.001£12.00£33.00Concrete (25kg)£5.001£5.00£38.00Controller (ATMega 128, input buffer, supporting circuitry)£7.001£7.00£45.00End Cap (40mm ID)£1.202£2.40£47.40NEMA-17£10.002£20.00£67.40PVC Reducer (40-44mm)£3.002£6.00£73.40PVC Reducer (48-52mm)£3.502£7.00£80.40Sand (Also 25kg)£6.001£6.00£86.401/2" Wood (salvage)£0.001£0.00£86.403D printed fixtures (consumables)£0.001£0.00£86.40Downpipe (salvage)£0.001£0.00£86.40M12 Nuts (salvage)£0.004£0.00£86.40M12 Threaded Bar (salvage)£0.001£0.00£86.40Total£86.40Now that I've *finally* decided how I'm going to build it, I can finally get a CAD drawing made up

author: C
author_rank: Super Contributor
timestamp: October 28, 2016, 01:19:46 pm
content: I know that a threaded rod can push some, but the strength is in pull mode.Force on that rod will not be good on some bearings. tapered roller bearings each end of threaded rod. Think of torque on nut and how to counter this easy.Don't forget the limit sensors, axis index & threaded rod indexYou can probably build two of one faster then two different.Plan out how you will build each thing.Have fun

author: cprobertson1
author_rank: Frequent Contributor
timestamp: October 31, 2016, 01:29:09 pm
content: Quote from: C on October 28, 2016, 01:19:46 pmI always doBasic design for the elevation drive is complete: motor will drive a threaded rod which will move a lever (attached to the elevation axis) forward and backwards. Drive rod will be able to rotate around the motor and will have a reinforcing bar going to the end and will have tapered roller bearings which will take the majority of force off the motor itself.The levers (attaching the drive rod to the axle) will be made of wood and cut by hand: they will be secured to the rod with a pin/bolt going through the axle and will also be tightened onto it. Finally, a strip of metal steel will be bent over it and bolted into place which should hopefully prevent the wood splitting. At the moment they're 1/2" thick, which might suffice, but I'll probably upgrade that to 1" thickness when I can be bothered changing the CAD models.Azimuth drive will be really easy - just going to use a radically shortened drivechain from a kiddies' 1-speed bike, with a motor on the smaller side and any tension taken up by an idler.I'll model the azimuth drive next actually, as it's going to be a pain to design since it will have the cable looming through it! I'm thinking about using another tapered bearing to keep the center of the axle hollow, which will allow me to loom the cables through it. There are a couple of things I can do for this actually - including just putting the cables on the outside of the mast (in a helix, as you suggested!) instead of inside a larger-diameter, hollow mast. In fact, that would make things very simple if I done that - I think I just made my decision!--EDIT--Ah, torque might be an issue if there's wind involved - with 2x 1.5m of Yagi-uda boom sticking out close to perpendicular to the axis (at low elevations) that could easily apply quite a bit of torque to the azimuth drive. This would have been a perfect use for that worm drive...)--EDIT--Offsetting the center of rotation for the Yagis (making the moving part an "H" shape) might reduce the torque from wind loading considerably (as any torque applied in one direction will be applied more or less equally in the other direction as well): this will also reduce the overall height of the system meaning I can mount them higher tooI think a hand-operated mockup is in order!

author: C
author_rank: Super Contributor
timestamp: October 31, 2016, 11:42:54 pm
content: Azimuth drive, You might think of pipe inside a pipe or pipe beside a pipe. In both cases you have made supporting points further apart. The drive's main job then is to rotate axis. You have option to have drive hold axis up with your tapered roller bearing.Think you have a weather problem here, A lot of threaded rod exposed.Many ways to cure this.Think you have threaded rod being used to push as well as pull. If you put the tapered roller bearings at each end of threaded rod then the rod will always be pulling against a tapered roller bearing and not want to bend.So to start fixing a lot of problems think of using two lengths of angle iron to hold the tapered roller bearings at each end apart. You are making a box out of angle iron but with a length gap between the two. You now have a long slot to connect to the nut on threaded rod. Now if you think of weather, that long slot is a problem. If you attach the nut to two more angle iron, You can get the motor at one end of threaded rod and the push/pull connection past the other end of threaded rod. You can now put this all inside a pipe and cover the exposed part as the length increases by an outside pipe. You might do nut to pipe.For some parts look at cheap plummer supplies.Hint use a very long threaded rod so torque & force is less. May need to shorten use of threaded rod to gain movement speed.AntennasStart with four antennas in an H with middle of H your support. If you do a band on each side of H, You have big antennas on one side. Mount the four antennas in form of X on the H and one big antenna on each side with good wind load. Moving cross bar of H up/down also helps balance.Have option for four but all still works for two antennas.Think what you said just in a different way.You need to make an H of the antennas, so you have cross bar pipe of H to a pipe with antennas. Same parts could be used to mount axis movement arm. This would also allow easy arm length change.

author: rs20
author_rank: Super Contributor
timestamp: November 01, 2016, 12:52:36 am
content: Just a drive-by post with two little ideas:-- If you set up your antenna to make little circular sweeps, and measure the signal strength/quality as a function of how far around that sweep you are, you can infer which direction the dish needs to be moved. It's a similar concept to MPPT in solar panels (continually shift voltage up/down to figure out the max power point of the V/I curve), in this case you'd be continually trying different dish positions. All that is required is a signal strength input into your controlling MCU/computer, and some incredibly simple software -- which might be easier to arrange for than 3 or more separate feeds.-- If money is no object (which I think you've already stated isnotthe case, but I'll continue), then I really like Teknic Clearpath motors -- like stepper motors, but stronger, more accurate (w.r.t. "step" resolution), can detect when they've been blown off-course by wind and will return to the original position (while asserting a "out-of-position" signal), and has built-in drivers so you can drive it directly from MCU I/O (takes 24-72V in as a separate input directly into the motor). It can auto-home on power-up, and has configurable maximum torque output as well (via a USB setup interface). You'd be looking at about US$0.5-1k for a couple of motors, but it's just such a complete solution I'd be strongly tempted.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: November 01, 2016, 03:10:00 am
content: You could also use a coax rotary joint in azimuth to give you unlimited rotation in that axis (assuming you have a single coax coming down from your LNB). You can find them for cheap on ebay.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 01, 2016, 06:45:20 am
content: Quote from: C on October 31, 2016, 11:42:54 pmOh sorry, that's just the mechanism, whole thing will be covered - only exposed parts will be the ends of the axle/pipe - the movement mechanism and electronics will all be inside a wooden enclosure, varnished and sealed with silicone - and then the whole thing will be clad in overlapping aluminium sheeting to keep the water off the treated wood. It will be a bit how-you-doing (damnit Dave, now you've got me saying it!) but it should keep water out - maintenance access will be provided by disconnecting a recessed plate on the bottom.Quote from: radar_macgyver on November 01, 2016, 03:10:00 amNae luck there I'm afraid, unless I'm very sneaky with how I handle the stepper motor signal and power, I'll have at least one extra cable going through it - I could, maybe (this is just conjecture) feed power through the coax and use a low frequency drive signal for the microcontroller and rely on a high pass filter to separate it from the radio signal - but it seems like a lot more trouble than it's worth.My original plan was one coax, one power cable for the motors and one duplexed data line - and just using a step-down SMPS to power the micro controller and keep all the electronics in a sealed casing right beside where it's needed.Quote from: rs20 on November 01, 2016, 12:52:36 amNow those are somenicemotorsCompletely out my price range though! (Like, almost 10x what I was hoping to spend on the motors!)If I had throwaway cash those would be nigh perfect =/ Oh well! At least this gives me the fun of building the system myself'C' mentioned a similar system using the differential signal from the two antennas to lock onto a satellite (see below)Quote

author: rs20
author_rank: Super Contributor
timestamp: November 01, 2016, 07:35:56 am
content: Quote from: cprobertson1 on November 01, 2016, 06:45:20 amThat's anentirelydifferent approach. He's suggesting using two (would actually need 3) feedhorns with no motion, I'm suggesting using a single feedhorn and using continuous motion.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 01, 2016, 08:38:46 am
content: Quote from: rs20 on November 01, 2016, 07:35:56 amAh, fair enough xD I thought he was referencing two yagi antennas moving along the predicted path of the satellite and using the differential signal between the two to figure out when it was pointed at the satellite and correct the position based on that (in one axis in this case?)Would your continuous-motion method work for short duration passes (<5 minutes)? I know it'd be perfect for geostationary satellites, but for LEO and MEO passes, would it be too slow, relatively speaking?My plan is to get the mechanics and electronics sorted before figuring out the actual tracking method - my figuring being that the tracking system will be primarily a programming issue. There will be a raspberry pi somewhere in this design, so I should definitely have the processing power available - and in addition to that there will be an ATMega128 (or higher) actually running the motors via some driver ICs, so that will have extra IO left over for running any tracking hardware I decide to install. I'm designing the hardware to be fairly modular so I can tack additional circuitry (and mechanics) to it as required as well.Initially, the goal is to be able to get it to reliably point at an Azimuth/Altitude programmatically - after that, getting it to move to another Az-Al at a particular rate should be child's play. Finally, once that is working, adding a correction system to track the signal itself is the stretch goal (instead of relying on the operator correcting it by hand) - the comparatively wide beamwidth of my yagis is probably to my advantage in that regard

author: rs20
author_rank: Super Contributor
timestamp: November 01, 2016, 09:14:22 am
content: Quote from: cprobertson1 on November 01, 2016, 08:38:46 amI didn't realise moving satellites were involved.Regarding LEO passes, if you were purely relying on the feedback from my method, then probably it'd not be able to keep up (the required rotation rate would be too violent). But if you knew the nominal path that the satellite was taking, and were using my method as a fine-adjust on top of that, then it'd probably still be quite effective (in my mind's simulation at least).Naturally, using three yagis would give more rapid feedback (more suitable for tracking totally unknown targets), but you have to weigh that up against needing 3 yagis and the associated signal strength measuring stuff.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 01, 2016, 09:39:08 am
content: QuoteLol - no worries, it was way back at the beginning of the thread I last mentioned it. I should probably have put it in the title actually.QuoteI believe if we used that system relative to existing movement - i.e if you start it moving along the nominal path and then add an offset to the slew rates to scan back and forth across the target, getting more accurate each time, then it should allow for increased accuracy in tracking - at the expense of hurting my head when I try to imagine programing thatQuoteThe initial plan is for a single yagi, which will then be arrayed with a second yagi allowing "locking" along the plane of the two antennas.Eventually, these will either be augmented with another pair of yagis in an H configuration, OR, replaced with two pairs of oppositely polarised helical antennas - but that's definitely a plan for another day!

author: C
author_rank: Super Contributor
timestamp: November 01, 2016, 09:50:12 am
content: elevation driveYour threaded rod is inside this. Notice the pipe inside pipe on right side. That black ring is weather seal. Right end has hole to attach to lever arm.Next think of how much weight you can drag or push across a table with a wire. Drag you move a lot of weight, push wire kinks.tapered roller bearings to take force at each end of threaded rod, keeps force in drag mode.Think you understand this.Think you need simple, easy to find cheap parts that are easy to use.It is easy to find two pipes that one fits inside other.Angle iron shape is stronger then a rod for same weight when force is push.google "pipe clamp 90 degree crossover"Use any place you can.

author: Howardlong
author_rank: Super Contributor
timestamp: November 01, 2016, 06:13:30 pm
content: For V/UHF where beamwidths are wide, practically speaking using a closed loop feedback mechanism will be extremely difficult. Determining the difference between fading due to off-pointing, and fading due to polarisation and relative satellite attitude (remember LEOs typically spin, and flip at the Poles as they orbit) will be a very difficult task to accomplish practically speaking.The "feedback" method works well when tracking by hand (i.e., a hand-held yagi) because (a) you correct for polarisation fading continuously as well as off-pointing and (b) you can make correct large corrections in a second or two. Doing this mechanically would be a very difficult undertaking, by the time the system has made its correction, the parameters will have already changed significantly.At mm-wave frequencies, it's far easier to accomplish a semi-closed loop feedback tracking system because of the ability to fabricate reasonably sized narrow beamwidth antennas.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: November 03, 2016, 05:22:57 pm
content: Howardlongis right. VHF/UHF yagi beamwidths aren't going to be much narrower than ~40 degrees, so you don't need precise positioning (I'massumingyou're planning this primarily for amateur satellites). However, Itotallyunderstand a desire for precision tracking because it makes the project immensely more fun & interesting!I've been tinkering with the same type of project in my head for a couple of years and want to thankRS20for the tip on Teknic motors.That would greatly simplify my design! Unfortunately, they're out of my price range, but considering the complexity they save, probably pay for themselves in design. The minimum for my app would be modelCPM-MCPV-3421S-RLS($411 USD). Maybe tackling the build in baby steps over time . . .My twist on the topic is a dual antenna system with circularly polarized VHF & UHF yagis that mounts in the back of a pickup truck and folds down for travel. The mast would need to self-level, then GPS plus a magnetometer could determine location & approximate orientation.It is possible to get slip ring connectors with multiple 50-ohm RF connections in addition to power & signal lines. They can be robust enough to handle modest transmit power. I found a company in China that can custom build them in single unit quantities for ~$100. Unfortunately, their web domain has been relinquished (www.amenlinker.com), but I'm sure there are others.I've already prototyped the tracking software to allow me to select a target and continuously compute its az-el in real time. That's running on a FEZ Panda. Just need to cough up bucks & time for the rest! LOL.One tip: Trying to build your own linear actuator is not worth it, IMO. Standard threaded rod is not appropriate for push/pull loads. You want acme threads for that. As expensive as they can be, a commercial sealed actuator with an internal position sensor is by far the best choice if you decide to go with a jack screw type of elevation gear. My preference is a stepper motor driving the horizontal shaft through a wide timing belt.

author: rs20
author_rank: Super Contributor
timestamp: November 03, 2016, 09:43:57 pm
content: No problem! I have one clearpath motor and it is as nice to use as it seems! Just a note of warning that the specific model you suggested, with MCPV in the name, is very different to a normal stepper motor, and can't move to arbitrary positions. You'd need the "stepper killer" models for that.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 04, 2016, 08:50:22 am
content: BREAKING NEWSNeighbours complain to council over "turret" in garden: turns out it's just a yagi on a wooden frame that a Ham was using to test torques... (with a force meter last calibrated in 1992! Meh, it seems to work)Council tell Ham to seek planning permissionPlanning Department tell Ham that this is a permitted development.Ham tells council. Council are down with that.Ham tells neighbour. Neighbour is down with that. Neighbour lied.Neighbour reported Ham to the police.What the actual f**kNo seriously, I had a knock on the door from some very concerned policemen: the neighbours had told them I was deliberately interfering with their television by pointing my antenna at their house. The police were very understanding actually: when I showed them that a wooden pole with some weights on it isn't a transmitter - and even if it was, it's not a police matter, it's an Ofcom matter and dutifully informed the neighbours.They were some pretty hoopy froods* actually - seemed genuinely interested when I explained that I was building a system to communicate with satellites, who knows, I might even encounter them in the Ham world some day*kudos if you get the referenceAnd now to return to the technical matters instead of worrying about the ignorant neighbour (it wasn't even my next door neighbour, it was somebody two doors down who could only see it when they put their face up against one of their upstairs windows! FFS!)QuoteI did suspect that might be an issue - which is partly why the lock-on and signal feedback systems weren't going into the initial build.As for precision-pointing ability, it does seem fun - though as you said, the wide beam width is in my favour here (can get away with a lot more). According to the antenna modelling software I was using I can thin the beam out a little, at the expense of losing some gain to sidelobes. But as you said, the wider beam means I've got more leeway when tracking!I also accidentally designed an antenna with a terrible (simulated) main lobe and massive side lobes: which could be fun for playing around with (maybe use it in conjunction with a "good" yagi? if the signal is in the sidelobe-antenna you know the target isn't being tracked correctly? Who knows, I'm not building that one anytime soon anyway xD)Are you using cross polarised yagis I take it? Also, I somehow hadn't heard of a Fez Panda before! My microcontroller prototyping went from arduino to standalone microcontrollers: which is a pity because there are quite a few pretty nice-looking prototyping boards out there!@C: I think I'm still leaning towards encasing everything in a DIY enclosure: keep everything closed up (and as I mentioned, I can also put a flexible nylon or vulcanised rubber bag over the moving parts (one of the benefits of being able to sew!) which will make everything pretty much airtight - add a desiccant and you get a dry atmosphere. Surprisingly simple as long as the stitches are done properly (triple-folding and taping them at the end - I can give you a quick tutorial on it if you want!)The bagging method is fairly simple as you can just secure it onto the axle with cable ties and caulk it in place, or use a rubber seal, or... etc - and if you fold it in particular ways you can get pretty wide movement range (a bit like twisting an accordion: don't do that btw, you'll ruin your accordion)Making the "bag" is tedious, as you need to sew every seam three times (seam>fold>sew>fold>sew>fold>sew>tape) - but I've used them before for outside parts without issue!

author: C
author_rank: Super Contributor
timestamp: November 04, 2016, 03:01:09 pm
content: Like the newsAs to the build, do your thing, no problem here. Just trying to give you some ideas that might be missed.As for bag, keep in mind that some things these days do not last as long in weather.Think I heard of something waterproof for your seam's. For a part you can cheat and use the iron glue sheet to hold in place for sewing. Think the waterproof was putting a sheet of something between what you are sewing together that changed when ironed.Ziplock bag seal might be handy in places.Have a old singer here.Your satellite tracking has a base of radio direction finding.For HF radio, something like AN/FRD-10https://en.wikipedia.org/wiki/AN/FRD-10which is built for tracking many signals at same time and supports fast direction change.RAF Edzell, Edzell, Scotland had one.https://www.google.com/maps/place/56%C2%B048'33.4%22N+2%C2%B036'20.0%22W/@56.8094582,-2.6066775,575m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d56.809282!4d-2.605551?hl=enWhen you have worked a place like this, you pickup some things.Think of the 180 degree antenna combiner I mentioned. Said amplitude but is that all that is happening? To get more aptitude when combining two antennas you phase add the signals with coupler/combiner. Different cable lengths lets you change a broadside array to an end-fired array. You can swing where the beam points by changing cable.When you rotate two antennas you are changing the length of air cableUsing difference vs sum here gives easer use.Most of the time to do better direction finding, you need a separate path to listen and direction find.In addition to time of arrival combining the signals you can switch between antennas in a way to get a signal you can hear.https://www.eevblog.com/forum/projects/radio-direction-finding/If you put together what Howardlong & I have said, You need to be able to get access to cable to each antenna cable. That building above had a huge room with antenna couplers used to make up beams.

author: Howardlong
author_rank: Super Contributor
timestamp: November 04, 2016, 05:41:55 pm
content: A question for the OP: have you tried listening for ham LEO satellites before?Although it's not the optimum setup (what is?) it's really reasonably easy to receive many ham LEOs with just a quarter wave antenna mounted on a reasonable ground plane such as a magmount on the roof of a car.Once you've done this, try it with a handheld directional antenna (I can highly recommend the dual band Arrow yagi for example, although I am sure these days there are more modern equivalents).For homebrew, you can make a dual band handheld antenna based on Kent Britain's (WA5VJB) Cheap Yagis, I had a lot of success with this combination, his antenna designs are examples of how to do it right, they are cheap and easy to fabricate, and are forgiving of the kind of imperfections made by real people when experimenting.By using a handheld setup you get a really good feel for what's expected practically speaking from a more permanent mechanically pointed setup.When I set up my first permanent ham satellite antenna array, I spent a lot of time messing about with rotators, power splitters, phasing harnesses, remote polarisation switches, preamps etc: these are all complications that you simply don't need with a handheld setup.My intention when I started was to set up a completely autonomous system providing a store-and-forward gateway, that gives you an idea of how long ago it was! What I found was though once I'd achieved that goal I got bored and moved onto other aspects within the same domain. That's the way I am, I have projects and once they're done and achieved my completion adrenaline shot, and I tend to move on to the next project. In my case that's led to making a career out of it, including designing and building satellites, particularly the RF, DSP and embedded aspects, something I still find very fulfilling, and not at all how I expected my career to unfold.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 04, 2016, 06:04:19 pm
content: Quote from: Howardlong on November 04, 2016, 05:41:55 pmYup- currently have a 1/2 wave vertical colinear which picks up LEO CW pretty well.Also have a 2-meter DIY Yagi which I've pointed skyward a few times (but never transmitted because the dipole was inches from the back of my head and I don't fancy radiation burns to the scalp will be very fun) - just used a phone with the Heavens Above app for aiming. Seemed to work pretty decently (until I dropped it and bent half the directors - then it only worked intermittently (loose connection to the dipole inside the aluminium frame: I can hear it creaking when I move the coax going into the back of it - haven't got round to taking it apart to fix it yet (I was just going to build new, lighter duplicates of the design when the time came!))I really need to stop using nested parenthesis in normal postsI might make a yagi with a smaller boom (actually handheld instead of shoulder-mounted) at some point as well - last time I made one I just used an online calculator and then played around on MMANA-GAL with it before building anything.QuoteHaha! I understand completely

author: Howardlong
author_rank: Super Contributor
timestamp: November 04, 2016, 08:44:57 pm
content: I'm sure how much power you are running, but back in the HEO days of AO-13 and AO-40 it wasn't uncommon for me to operate 50W into a hand held yagi, and those were long passes, several hours, with long overs. Maybe that might explain a few things ;-)Anyway, if you're only running 5W or so I certanly wouldn't worry about it, that's about the same as the average PMR handheld.

author: cprobertson1
author_rank: Frequent Contributor
timestamp: November 05, 2016, 09:59:11 am
content: Quote from: Howardlong on November 04, 2016, 08:44:57 pmThat is a very good point!Apparently (according to the RSGB website) you can get away with pretty low powers for LEO work.I've just generally, as a rule of thumb, decided never to stand in front of a yagi while it's transmitting! (or inside the yagi in this case!) - as you said though, at five or even ten watts, even if I'm standing behind it I'll be in the back lobe!I might repair that yagi today actually and see what I can work tonight - on the other hand... I do technically have a house to tidy and a garden shed to fix... i.e I have to choose between "fun DIY" and "boring DIY. Decisions, decisions!

author: Howardlong
author_rank: Super Contributor
timestamp: November 05, 2016, 04:25:14 pm
content: Indeed, you can work even the FM LEOs with <50mW and a hand held yagi, done that many times during quieter periods.