Measuring an event timing - Page 1
Forum section: electronics / beginners

author: jhall
author_rank: Newbie
timestamp: February 24, 2015, 12:57:02 am
content: Hi,I'm new to the forum and just bought a Siglent SDS1102CML. I'm working on an issue with the antenna tuner in my Yaesu amplifier. The amplifier was designed to work with Yaesu radios and I'm trying to adapt it to work with my Flexradio. The tune cycle of the amplifier is initiated by pushing a button on the amp which in turn closes a contact that, on a Yaesu radio causes the radio to emit a carrier the tuner then uses to tune the antenna input. Unfortunately, my radio doesn't have a port that will accept the contact closure. What I have been able to do is use a computer serial port to read the contact closure and issue computer commands(CAT) to the radio to have it emit the carrier. While it works(sort of) it is not reliable. I believe the problem is that there is too much delay from the time the tune button is pushed closing the contact until my computer gets the radio to emit the tuning carrier.Okay, that's the background on my problem. What I want to do is use my new oscilloscope to measure the time from the contact closure to the RF tune signal being generated. I have an RF sampler that I can use to provide a -50db rf tap to measure the carrier, but I don't know how to make the scope trigger on the contact closure. For that matter, I obviously don't know the best way to setup to measure what I am looking for.Any help will be greatly appreciated.Jon

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 24, 2015, 01:19:38 am
content: You will need two probes, or one plus a BNC cable or whatever.Probe Ch1, serial pin to GND. Should be doing 0/5V or something like that, so 2V/div.Check that it's reading the probe multiplier correctly, too, if applicable; the choice of 1x or 10x won't matter for this.Ch2, RF input somehow. A 50dB coupler may be too quiet. How much does the radio key up when it's doing the test? Is that like some little pilot tone, or is it freaking full blast on a 100W transmitter? Mind that the inputs can't take more than maybe a watt, and that's probably pushing it. (my Tektronix actually has a thermistor to sense the temperature of the internal termination resistor, and disable it if it gets too hot... but I don't know if they bother with such features on a cheap scope like that.)Trigger mode: single or normal; edge; source Ch1; whichever +/- slope you need (you'll know better, having wired the contact closure); threshold/level halfway between voltage/logic levels.Horizontal: probably 2ms/div is a good starting point. Repeat the test a few times until you see what you're looking for.Display mode / acquisition: peak detect mode. Not High Res, or bandwidth limiting, or smoothing, or averaging, or any of that. (BW settings are often under the vertical/channel menus too.)Also, obviously, your scope needs to be able to resolve the frequency you're running at. So, a 100MHz scope will see shortwave signals just fine, and probably won't be remarkably useful troubleshooting VHF radios (you don't have enough bandwidth to resolve harmonic distortion, if present) but will still detect it, and anything UHF+ will just buzz right on past without a clue. (For those cases -- you can use an RF detector probe, in which case your Ch2 will see a DC offset when RF is present, so Peak Detect mode won't matter.)Tim

author: jhall
author_rank: Newbie
timestamp: February 24, 2015, 02:09:24 am
content: Thanks Tim,I'm going to try this tomorrow evening. I'm working at frequencies under 30mhz so the scope should be able to keep up. The tuner requires 60-80 watts in order to tune so yes, there will be quite a lot of RF. I'll start out with my sampler and see what I get. I'll adjust the RF output lower until I'm sure the levels are safe for the scope.Jon

author: babysitter
author_rank: Frequent Contributor
timestamp: February 24, 2015, 06:26:42 am
content: Ahem... does the "give me rf for tuning" contact in the tuner stay closed as long as the rf is needed?Quote from: jhall on February 24, 2015, 12:57:02 amI bet you have those inputs. It is named "CW", "KEY" or similar but requires you to switch to CW mode before tuning (The only task for your software.). Setting to FM mode and using the PTT input is another chance. The manufacturer of the radio did a lot of things to keep the transmit delay low already. Leaving out the serial data part completely will always be quicker than your method.To prevent immediate connection of your scope to the tuner, you can either try clipping your ground wire to your probe tip to get a pick-up loop, or build a small field strength indicator (basically a AM detector like thing, lots of plans on the internet) which is a useful tool anyway, but can be connected to the scope too if you want to trigger on the presence of RF.To the other, trigger side of your problem:You can feed a voltage with a several K resistors to the contact and clip your scope probe to ground and the switched port. In case the switch is open you will measure the voltage applied (minus a little bit), when the switch is closed zero volt. Set your scope to normal trigger on falling edge. The trigger level must be set between those two levels.If you connect your radio "key in" to the "rf request" out of your amplifier, the radio will supply this voltage.Also, your radio might have a line that it uses to tell the amplifier "i want to transmit" - by closing a switch to ground, too, which you can hook up to your amplifier in turn so dont need to use the vox feature where the amplifier learns the hard way when its unexpectedly hammered with RF.This signal ground and "ptt out" or "amplifier on" can be hooked to your other scope channel.73

author: jhall
author_rank: Newbie
timestamp: February 25, 2015, 04:51:16 pm
content: Tim,I seem to have a problem getting this to work. I connected Channel 1 to the lead going from the contact on the back of the tuner to the serial port on the computer. It works fine as a trigger but whenever the prob is connected to the serial line the computer never responds to the contact closure. To summarize, when I put a 10X probe on the serial line running from the amp to the computer, the computer doesn't respond to the contact closure. When I remove the probe it works normally. So, I assume the probe is interfering with the line levels. The RF Channel is working fine.Any ideas?Babysitter,"does the "give me rf for tuning" contact in the tuner stay closed as long as the rf is needed?"Well, that is really the problem I am wrestling with. When you push the tune button the cycle will normally fail almost instantly. About 1 in 10 tries it will "catch" and run a normal tune cycle. My suspicion is that the way I am initiating the tune cycle with the serial port is introducing too much delay and the tuner gives up.My original thought was to have the tuner contact also close the key line on the radio. Then all my program needs to do is bring up the RF level. The idea being to shorten the delay. Unfortunately, I had the same problem as the probe above. When I connected the key line with the serial port, the serial port stopped working.Jon...kf2e

author: babysitter
author_rank: Frequent Contributor
timestamp: February 25, 2015, 10:06:56 pm
content: Do it like this: Turn to CW mode first, press tune button, wire NEED-RFimmediatelyto KEY IN of radio without interaction with the serial interface. Oh, and get the serial line some ferrite, there is RF where it doesnt belong to. Not unexpected during untuned operation.

author: katzohki
author_rank: Frequent Contributor
timestamp: February 25, 2015, 10:13:38 pm
content: Wait a sec, the tuner in your amplifier requires 60-80 Watts to tune? That seems like a lot.

author: babysitter
author_rank: Frequent Contributor
timestamp: February 25, 2015, 10:20:36 pm
content: Ehm, yes, ... maybe everything works if you use less RF power? The RF where it doesn't belong would make less trouble then.

author: jhall
author_rank: Newbie
timestamp: February 25, 2015, 11:00:14 pm
content: From the user manual..."Drive power must be at least 50 watts for accurate SWR detection, and 70 to 80 watts for optimum tuner performance."I was shocked when I first got the amp as well. Just to be sure I have tried this at lots of other power settings. At anything less than about 65 watts I can't ever get the tuner to tune.Babysitter,I understand what you are recommending but what I really want to accomplish is to be able to just push the tune button and have the amp tune to the antenna. The method you are suggesting would require a mode change, then a drive power change, then a tune cycle, then another drive power change and then back to my original operating mode. This doesn't even take into account the additional changes necessary if I'm operating split or digital modes. What I have now is *almost* working. I'm really just trying to measure the delay for tune button push to RF showing up at the amp so I can compare it to the time it takes a Yaesu radio that works every time.FYI...the amp is a Yaesu VL1000 and my radio a Flex 6500 and the antenna is an OCF dipole.Jon

author: babysitter
author_rank: Frequent Contributor
timestamp: February 26, 2015, 05:35:47 am
content: Quote from: jhall on February 25, 2015, 11:00:14 pmI just want to tell you how to do it right and not punish that tuner with some "I want to introduce delay but know how much I can afford!" way. You will need to do some serial comms, but you just need someoutsidethe tune cycle not adding to the delay! Digimodes should give a nice carrier always, also FM. CW might need a key actually pressed down, SSB a tone generator. Split and that crazy power level setting - you will always need that, it is not my fault or that of the suggested method. It will always be better than your "all over serial" business, delay-wise.Now as you have told us out of grace what radios you have, its not just that babysitter guy on the forum who tries to tell you. Yaesu does, on page4of the manual.Also, chapter 7.4.4 and 7.4.10 of the flex-6000 hardware reference tells me that I was right regarding the TRX accepting this signal. Do it as suggested by me and them or stop complaining! [Additional rant redacted before publishing] Gee, both manuals could even use my drawing with adapting to their pin naming, don't they?Your setup has another problem, RF in the wrong places. Your rig not working when you connect the scope is the reason to suppose that, as it should work with the probe connected. So far, I guess you did measuring stuff correctly. Digital IO have (such as the key in or the handshake out) several diodes inside that rectify RF on the wire, the resulting DC could be responsible for messing up operations. I suggested using some ferrite on the cabling - if you want to scope the PTT signal, especially, but it could stop other unwanted mishaps.