Wire antennae lengths, loops etc. - Page 1
Forum section: electronics / rf-microwave

author: CJay
author_rank: Super Contributor
timestamp: October 03, 2017, 12:40:18 pm
content: I have a 22M long garden, over which I can suspend a wire antenna at a height of 7-9M, one end will be terminated with an Icom AT-130 tuner and I can spread some radials for grounding at the bottom of the support pole, the other will be moored to a conventional brick built house with the necessary insulator etc.However it occurs to me that because the garden is 7M wide, I could potentially have double that length plus 7M.What's the error in my thinking, would it 'perform' better than a single 22M length of wire for transmit or am I wasting my time and materials?A beam is out of the question and an HF vertical would probably also be tricky, masts will have to be fibreglass and removable so no towers or winch ups.

author: cdev
author_rank: Super Contributor
timestamp: October 03, 2017, 01:37:42 pm
content: One approach would simply be to make a big loop. Maybe use blue jacketed, thin, woven wire.. which blends in to surroundings.. Balanced antennas - especially loops of all kinds, are less noisy too.For your feed, maybe feed it near to your shack using ladder line.and then use a balanced tuner like PA0FRI's "S-match"..You could also have multiple kinds of antennas - either enabled outside with a relay switch box at the antenna end or multiple ladder lines running into your shack.Ladder line = less loss.Or maybe even just have banana plugs on the wire and switch them that way.Its always good to have choices.Would make up to some extent for the lack of space for a beam..Also to start out, for lower bands, a dipole suspended up high between two poles with a balun at its center can have its feedline and center tied together at the shack end and become a capacitive loaded vertical that way, with the feedline as a vertical element and the dipole as its "hat".You could then use a unun at its base..If you have a decent ground system. Or try multiple loops.You could try using eznec or similar to try to model the effects?A good mag loop might outperform many of these antennas but not the best designed ones. But at the start it might be the best option. Because you can rotate it. If your shack is outside you will already be there. Lots of hams go outdoors with their rig and set up on a picnic table in their yerds and make QSOs from a mag loop and it works well for them just turning and tuning it by hand. Or you could motorize both.It all depends on your neighbors and how much wire your family and neighbors will put up with IMHO. Also on how well you make it blend in.I don't know what the general theme in your area is..Would a loop that rotated (you could rotate it by hand) be less obtrusive? If you make it well and incorporate it into the existing environment/decor - maybe that would be best.I think that a big but somewhat subtle looking double loop made of copper tubing in a perfect circle in the shape of a flattened spiral (Like the one Jeri Ellsworth has) with a gamma match is compatible with more environments than most HF antennas.. it seems almost "art like".That would help a lot with acceptability in some neighborhoods.

author: cdev
author_rank: Super Contributor
timestamp: October 03, 2017, 01:48:41 pm
content: There are a ton of balanced tuner designs on PA0FRI's site.. good for wire loop antennas and balanced dipoles and similar.See what your "electrically rotateable" wire antenna options are.Also, keep in mind my lack of real world, practical experience.Get as many others advice as possible.Especially remember simple is often the best.As I said, a balanced antenna (or balanced mag loop, the simplest uses a double ganged variable capacitor to tune the loop with the center /body part grounded, and a shielded and/or balanced pickup loop) is said by many to offer big noise advantages. I only have experience with a not well balanced mag loop and my occasional (arguably lame) attempts to make a balanced antenna by using two wires in my back yard.. trees being used were/are not well placed for this..Still both were quieter than my long wire, even with its unun (which reduces noise quite substantially).Some lengths of wire (search term "end fed antenna") tune up easily on all bands because the length of wire and feed line are optimal for this. Sometimes the wire ends up being a manageable match on all ham bands using a 9:1 unun, so much that you don't need a counterpoise or can get by with a very basic one.With some lengths of wire and coax feed. A lot has been written about this and its worth reading.With the right length wire, a 9:1 unun and feed, you may find that your antenna "just works" with little fuss and only the rigs' own antenna tuner or a very basic tuner..Zap.. problem solved with very little effort..Misc links- hope some are helpful!:http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm(This is a huge article about mag loops - unique for its definitive list of loop coupling methods, especially)http://www.66pacific.com/calculators/small_tx_loop_calc.aspxAlso:https://m0ukd.com/static/homebrew/magnetic_loop/rjeloop1.exeandhttps://m0ukd.com/static/homebrew/magnetic_loop/rjeloop2.exehttp://www.aa5tb.com/loop.htmlhttp://www.pa0fri.com/(lots of antenna tuner info including "s-match" balanced tunerThis is kind of interesting.. very large loops designed for very low resistance..https://web.archive.org/web/20170108145422/http://www.g4hjw.metahusky.net:80/magloops.htmThere is also a long essay about "The Underestimated Magnetic Loop Antenna" by VK5KLT out there.. Google should find it.Also, I have a PDF "Chapter 10: Large Loop Antennas" - about wire loops (and their HF characteristics) that appears to be from a book on ham antennas.. Maybe Google can find it.--------End-fed/off center fed/Windomhttp://m0ukd.com/homebrew/antennas/homemade-carolina-windom-antenna/http://m0ukd.com/homebrew/baluns-and-ununs/end-fed-half-wave-antenna-tuned-coupler/

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: October 03, 2017, 08:00:29 pm
content: The answer depends on which bands you need to cover and the distances you wish to cover.Generally you can get away with antennas being down to 70% of full size before performance starts to suffer (without alternative techniques).Probably the critical question is whether you want to cover 3.5 or even 1.8 MHz as well (a good idea for the next few low sunspot years).You can cover both bands with an antenna that fits in 22m but it's going to be awkward.22m is just enough for a half wave antenna on 7 MHz.A loop is possible and may be low noise on receive but needs to be around 1 wavelength perimeter on its lowest frequency (though again you can get away with about 70% of that). And ideally it needs to be fairly open (ie nearer to a circle or square). Even on 7 MHz that may be hard.It's difficult to build an antenna much better than a 1/2 wave dipole and very easy to build one that's inferior.My own yard is 20 x 4m. I have a mast in the middle. On it is an inverted vee doublet with 15m of wire a side (with about 5m bent inwards). It uses open wire line. This works well on at least 80 & 40m (not much use with higher bands) and can be loaded up on 160 and even 630m with a large loading coil wound on a bucket.

author: CJay
author_rank: Super Contributor
timestamp: October 04, 2017, 08:18:50 am
content: Quote from: cdev on October 03, 2017, 01:48:41 pmPart of the problem is not that there's a lack of information, there's far far too much and a lot of it is contradictory or too vague for a newby to pick the substance out of, gather five antenna 'experts' together and there are five different opinions, lots of fun ahead experimenting I think.I think I'm going to go with wire down one side of the garden, across it and back up the other side which should give me ~50 metres to see how that performs, it should be a fairly simple matter to take out a 'side' or modify it.I also realise that my use of 'loop' was somewhat incorrect, I intended it to mean a length of wire that ran round the boundary of the garden and came back to the start point, not a magloop but mag loops also look worth investigating, I *might* be able to get away with a small one.

author: CJay
author_rank: Super Contributor
timestamp: October 04, 2017, 08:26:52 am
content: Quote from: vk3yedotcom on October 03, 2017, 08:00:29 pmMhm, I'm limited to 10 watts at the moment (50 when I pass intermediate, next month I hope) and I'm focused on 40M right now as it seems most active when I look at the various web connected SDRs but I think 80 might be interesting too. 160 would probably be out of reach for now.I've built many antennae that have performed similarly to a slightly damp length of twine so I'm hoping I can buck the trend with little advice and guidance.

author: cdev
author_rank: Super Contributor
timestamp: October 04, 2017, 01:21:30 pm
content: If you can make a very basic loop antenna I would say that good quality signals on 40 meters is quite doable for you.Getting a decent counterpoise for a loop is much easier than a radial system. You could even use some kind of grating like chicken wire, if you could get a good electrical connection to it. But even just a few wires hanging on the ground will do.Look at Jeri Ellsworth's backyard antenna. You should build something like that. Note that it is a two turn loop. It looks roughly 1.5 meters in diameter. It uses copper tubing but not so large that you cannot find it. She probably used a tube bending jig made with three rollers. Using one of them you can make a very nice, graceful circular loop. A nice loop like that should last you decades if you take good care of it.Find a used tripod you can use to get it up a bit while you are using it. A wooden tripod such as used for old telescopes would be best.I would start with a shielded coupling loop made out of your coax connecting back to its own shield.The very long link I posted yesterday on magnetic loops has dozens of coupling/matching ideas in it.If you can find a nice vacuum variable that would be a good investment but then I would bring the loop inside when you are not using it.I suppose aluminum would have the advantage of not being as convertible into money by a potential thief but the electrical connections to aluminum are likely to be iffy from copper unless you take great care to make them properly.One interesting option instead of copper tubing is wide copper tape. You might be able to find some very light plastic piping (perhaps a hula hoop, or pool float made out of bendable foam, anything flexible and cylindrical.) and make what is essentially a torus out of it, by wrapping it loosely with the widest copper tape you can find; (It should look like a "barber pole" bare, but if it all works you likely could paint it.)At the ends, connect to thick copper flashing material large enough to act as a good low resistance connection and the two ends then get connected in the lowest resistive manner possible to the variable capacitor.A loop could get you on the air very quickly.You can make a very simple loop out of wire in minutes by simply taking a variable capacitor, attaching a length of 3 -5 meters of the thickest wire you can find to it to make a resonant circuit, and then connecting a coupling loop to your receiver, you could screw two hooks into your rooms ceiling to hold a wire. Put the coupling loop in the plane of the big loop near one of the wires. You should be able to find the peak on your receiver pretty easily or you are doing something wrong.Tune back and forth- Eventually you will find it.. You'll hear amarkedincrease in the signals (like from almost no signal to lots of signals.) when the capacitor/loop resonant frequency crosses the frequency the receiver is tuned to. (If you have an SDR with a waterfall display of several MHz available, use it, that is very very helpful in finding this peak.)Even poly-varicon caps work fine for this, on receive.With all magnetic loops, the tuning will likely be sharp. That means, the bigger the knob you can find, the better, because otherwise your peak may be hard to find. You may find you need to have a way to turn the knob much more slowly. A reduction gear.Since you now have your license, you might be able to use a loop to get on the air today with minimal fuss with just a few minutes work.(Check to make sure whatever capacitor you use won't arc over with your 10 watts! Maybe start out with even less power?)Ask hams who use loops, they would know what to expect there.

author: Hawke
author_rank: Contributor
timestamp: October 25, 2017, 03:01:57 pm
content: G'day I once lived in a town house many moons ago with a small yard and found it hard to use anything decent as an antenna. Then I found plans for a CCD Antenna and built it. It looped round the top of the fence, on the clothes hoist or anywhere I could put it and it worked great. It was in the ARRL handbook in the early 90's then I bought a commercially made unit the looked better than my home made job. Its a brilliant solution for small yards. Maybe look into them as a possible solution. Cheers

author: GreyWoolfe
author_rank: Unknown
timestamp: October 25, 2017, 05:59:17 pm
content: I have an 80M loop here. Thankfully, I have just enough space (272' of 14 GA THHN. I feed it with ladder line to the window of my shack and I have a transition balun made for ladder line to coax and about a 6' piece coming into the shack and to the radio. The radio's internal antenna tuner (Yaesu FT-1000MP) tunes easily on 80 to 10 with the exception of 17M I think, I really only play on 80, 40 and 20.