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160 and Small Antennas




 
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N3DRB The Derb
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« Reply #125 on: April 27, 2007, 06:13:54 AM »

thats cool, I never seen that done b4.....how did it work?
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KF1Z
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Are FETs supposed to glow like that?


« Reply #126 on: April 27, 2007, 07:50:43 AM »

thats cool, I never seen that done b4.....how did it work?

Works fine,

As I said, I have no idea how much loss there is....

I found the idea on a corntester site a few years ago.


There's about 110' of the double coax, and 75 ish feet of 450 ohm 16 guage up to the ant.

Would have gone all the way with the coax....but that stuff is HEAVY!!


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The Slab Bacon
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« Reply #127 on: April 27, 2007, 08:16:38 AM »

I guess its time to throw my $.02 in the mix. Due to having a postage stamp sized yard, I have been forced to run a short, non resonant antenna for many years now, and no one seems to have any problem hearing me. (unless I'm running piss-weak low power)

I am running 100w in the early evenings, and full legal limit in the later nights when the going gets rough. I am using a 60' long center fed flat top, fed with 14ga crappy brown stuff. It works just fine from 80m all the way up to 10. I can even get it to work reasonably on 160. It puts out a very good signal on 80 and 40, and is tollerable on 160. I have no other choice, its either use a short skyhook or buy another home.
Since verticals suck for close in work due to the low angle takeoff angle, a flat top was the only choice.

The tuna and all of the other accessories were optimized for the short antenna / high feedline current scenario, and it was an interesting learning experience. The tuna is strapping and HB and engineered to hamdle the high current WITHOUT HEATING UP!.  Remember that anything that is getting hot is dissapating power. The biggest priority is simply to get absloutely as much of the transmitter's output as you can to the antenna. Minimize your I-R losses as much as possible and it will work.

Putting the tuna at the antenna's feedpoint would be ideal, BUT, lets face it it is really not practical. The small amount of loss in the balanced line really makes it pretty much a moot point. Why bother!!
It simply has to just make the complex impedance at the end of the feedline look appealing to the transmitter. Thats it- game, set, and match!!

Letz face it .5-1db is a pretty neglible amount of loss, no one is going to see that on the receiving end. Just not worth the bother to worry about. Sometimes you hit the "point of diminishing return" and its really not worth pulling your hair out to improve things any further. Also sometimes it is just easier to accept the fact that something works instead of wasting your brain trying to figger out how it works.

                                                       The Slab Bacon 
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WA1GFZ
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« Reply #128 on: April 27, 2007, 08:41:34 AM »

double coax will force a balance but feedline loss comes in two flavors. Dielectric and resistive. The idea of a shielded line is a big help snaking it through the house and #9 wire is pretty good but a high VSWR will drive up dielectric losses. Still "race what you brung."
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AF9J
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« Reply #129 on: April 27, 2007, 09:08:08 AM »

Yes that's quite true about dielectric losses, especially since (assuming the tuner, is at the radio point) you are having some radiation from the feedline, due to the antenna system being non resonant .  Since the the center conductors are being used for the feedline, the braid has now become a part of your dielelctric losses.  I would assume that this affects radiation efficiency for the system.  I've read about using twin coaxes for a balanced feedline.  Years ago (remember people, I corntest too), it was sort of flavor of the month for contesting.  You don't hear as much about it anymore.   I think the losses, and that fact that the feedline is so heavy have a lot to do with that.  The company I work for uses twin coax assemblies (some are as long as 350 feet), made out of RG-59 for transmission lines from ultrasonic transducers, to the readouts.  That stuff is clunky enough as it is, much less making it out of RG-8.

Antennas are always interesting to me.  Due to my being challenged for space, I've done a fair amount of expirimenting with short, non-resonant antennas.

73,
Ellen - AF9J 
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The Slab Bacon
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« Reply #130 on: April 27, 2007, 09:31:31 AM »

there is really no substitute for a really good skyhook,BUT.......

Sometimes you just gotta do what you gotta do! A short non resonant antenna is still better than no antenna at all. The fun of it all is getting it to work well. thats the challenge!


Long runs of coax at high swrs (high impedance mismatch) are too lossy. The capacitive reactance just acts like a sponge and soaks up all of the power. If you have to sin with high swr and coax i have found that a low impedance situation (low voltage / high current) is definately less lossy as long as the I-R losses dont eat you up. I have a SHORT run of coax (about 8') between my tuna and the balun at my back wall. That coax runs at an outrageous swr, but the losses are pretty minimal because it is running at a low impedance. The rest of the feeders are balanced line.

Use balenced line whenever and wherever you can and you will never regret it, especially if you want multi band operation with 1 antenna!

                                                       The Slab Bacon 
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Steve - WB3HUZ
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« Reply #131 on: April 27, 2007, 05:38:47 PM »

Frank, your antenna system is not non-resonant.
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W2VW
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« Reply #132 on: April 27, 2007, 06:52:02 PM »

Frank, your antenna system is not non-resonant.

Steve, you can repeat this on every hammy site until blue in the face. The average ham thinks resonance is necessary. Frank is only stating it the way I see everywhere. The antenna is non resonant but the system is. Maybe your approach will stick in a few minds. BTW coax heads, a full wave antenna is resonant and will show quite a bit of magic SWR when fed with cow-axe. 
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W4EWH
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« Reply #133 on: April 27, 2007, 06:58:40 PM »

Frank, your antenna system is not non-resonant.

Frank & Steve,

Let's talk about that: I was at Frank's post-Timonium party: I and Brent, W1IA, were debating exactly what antenna Frank has.

Frank's antenna is, IIRC, about 80 feet long, and it look like 6-inch ladder line turned on it's side, with the midpoint open on the top wire, fed at the midpoint of the bottom wire with ladder line.

I say it's a folded dipole, even though the top radiator is interrupted in the middle. Brent thinks it's a Bazooka, because he thinks the top half couples to the driven elements on the bottom and thus broadens the bandwidth.

Frank, what's the "Official" name of your antenna? Is it described online?

Steve, is this resonant? Why?

Bill
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Bacon, WA3WDR
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« Reply #134 on: April 27, 2007, 08:12:45 PM »

If the ends of the top and bottom lengths are tied together, I would call it a linear-loaded antenna.  I think that RF sees it as a 160 foot dipole with wierd cross-coupling on each wing.

I did something a little similar with 160 feet of that 450 ohm brown twin lead stuff.  But I made it into a 40 foot per side square loop.  Where the ends came together, I connected the left top to one side of the feedline and the right bottom to the other side of the feedline.  I did not tie the opposite corners together.  So it was like 320 feet of wire coiled into a 2-turn open loop (a solenoid), and center fed.

My thinking on this was that the current of the two wires would be in-phase this way, while with the doubled-back linear loading, the current is out of phase.  And it did work on 160, as well as anything I tried.  However, it needed to be vertical - when it was horizontal, it put a big fat null straight up where all the local signals were coming from, but it heard static from a thousand miles away just fine.

Some day I want to try this arrangement with the loop size self-resonant at the operating frequency.
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Steve - WB3HUZ
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« Reply #135 on: April 28, 2007, 11:25:01 AM »

The wires Frank has in the air are nothing more than a 120 foot long "full-sized" dipole folded in half. It's just a way to fit 120 feet of wire into a 60 foot space. I don't know if the set of wires he has in the air are resonant on 75 meters but they are resonent somewhere. From the reading I've done, this sort of antenna will resonate at about 0.6 or 0.7 times the "normal" resonant frequency for the antenna length. In Frank's case, the antenna is 60 feet from end to end. A single-wire dipole of this length would resonate at around 7.8 MHz, so Frank's wires would probably resonate in the 4.7 to 5.5 range. But a grid dipper would tell the real story.

But all the above really doesn't matter, just as it really doesn't matter for any set of wires feed with open-wire line and a tuner (except in the case where the open-wire line is used as a flat line). My point is that the SYSTEM, thatis the wires in the air, the feedline and the tuner ARE resonant. The system would not take power and radiate if it weren't.
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The Slab Bacon
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« Reply #136 on: April 29, 2007, 09:19:41 AM »

Frank, your antenna system is not non-resonant.

Actually this very true, just everybody doesnt see it that way. Any length of antenna is resonant on any frequency. it is just NOT a 1/2 wave / 50 ohm match. Any length is wire is some wierd fraction of a wavelength, if it is not a 1/2 wave  / 50 ohm match it just doesnt work with coax and plastic ricebox radios. You must use a tuna (transmatch if you must) to make it work. With balanced line feeders, SWR is no longer any real issue, you just have to have something to make the complex impedance that appears at the end of the feedline look like something that the transmitter wants to pump a little rf into.

Always remember that ladda line is your friend. If you are using balanced feeders on a balanced antenner and a good strapping tuna, you can just about always make it work.

I'm not saying that piss poor antenner is always the answer. there is no substitute for a good well designed and installed antenna. BUT...........................sometimes you just gotta do what you gotta do. Some of us just dont have the physical room for a real antenna. I just cant afford to move the QtH at this time. So in the true spirit of ham radio, I experimented until I found something that would work.

Bill, my antenna is 60' in length. Just like steve said, it is 120' of wire folded back on itself, but not forming a complete loop. The spreaders (spacers) are 12" and it is up about 33' off of the ground. It sure works a hell of a lot better than on antenna at all.

Always remember: you can tune a transmitter, you can tune an antenner,
but you cant tune a fish!!    Grin Grin

                                                                        the Slab Bacon
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W4EWH
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« Reply #137 on: April 29, 2007, 12:24:55 PM »


[snip]

Bill, my antenna is 60' in length. Just like steve said, it is 120' of wire folded back on itself, but not forming a complete loop. The spreaders (spacers) are 12" and it is up about 33' off of the ground. It sure works a hell of a lot better than (no) antenna at all. [snip]


Frank,

You know what they say about how Bumblebees can't fly, and your sky hook just keeps buzzing around in my brain. Huh

The next time I'm at Timonium, I'm going to bring some sand and concrete to the party. If you can find forty feet of flagpole, I'll be glad to help dig the hole: we'll get you a 120-foot span from back to front - and my head will stop trying to explode every time I think of your antennaWink

73, Bill
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AF9J
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« Reply #138 on: April 29, 2007, 12:50:23 PM »

Frank you silly goose!  You misquoted REO Speedwagon:

"You can tune a piano, but you can't tuna fish!" Wink  When I was expirimenting with what I call loopy dipoles (dipoles with each leg configured in a loop - pretty good on the hihg bands, lousy on the low bands) at the present QTH, I always used balanced line (although it was speaker wire, which can get pretty lossy above 40m [I had a short run, so it wasn't much of an issue]).  Because as people mentioned, it's the system that counts.  Remember, unless you have a balun right at the antenna itself, the further off of resonance you are, the more your feedline will radiate, hence, becoming a part of the (radiating) antenna.  Dielectric losses determine how much field strength this feedline radiation will have.  Since wire/twinlead type balanced lines have relatively low dielectric losses, they will radiate decently.  Hence the reason why balanced feed (and I don't mean twin coaxes) antennas such as the Zepp, original G5RV, and the original Windom, make decent multiband antennas.  You'll have a screwy radiation pattern, due to the feedline radiating, but you will radiate more RF, than a coax fed, non-resonant antenna.

Coax feeds as we well know, will not radiate well, due to dielectric losses.  In some cases, the heating from these losses, can be enough to melt the dielectric at high RF voltage points, if you're running enough power.  As a result, coax fed antennas make lousy multiband/non-resonant antennas, unless you use traps, capacitive coupling, etc., AND a balun to keep that "evil" feedline radiation from occurring.  A coax fed antenna that tries to bypass the above provisos, with mediocre results, is the modern G5RV.  As I mentioned before, the original G5RV was an OK balanced feed antenna.  But, when internal tuners on radios like the TS-430 & 440 became the rage in the 80s, they encountered a little problem: the limited impedance range of these tuners couldn't deal too well with the complex impedances presented when using wire antennas for multiple bands.  It was noticed that by removing some of the balanced/ladder line feed from a G5RV, and replacing it with coax (sorry, I don't remember what the length is, I'm not a big fan of G5RVs), you could put the system impedance into a range that the internal tuner could handle, in effect making the G5RV an "all band" antenna.  Unfortunately adding the section of coax, turned the G5RV into not much more than an air cooled dummy load on some bands, due to feedline radiation in the coax, soaking up RF, in dielectric losses.  On some bands like 17m, a hamstick will radiate better than a modern G5RV.  In another group I belong to, another ham mentioned how during Field Day, the G5RV they were using on 40m with 100W was netting them no QSOs, while the 40m dipole he threw together in 15 minutes, was working like gangbusters.  In some cases (if your coax section is made from wimpy coax, or you're running serious power), system SWR conditions can be enough to melt the dielectric in the coax section of a G5RV.

Nope, the only advantage that coax has over balanced line is that it's physically  sturdier, and isn't affected much (impedancewise) by nearby metallic objects.

73,
Ellen - AF9J
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The Slab Bacon
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« Reply #139 on: April 29, 2007, 08:51:22 PM »

Bill,
      You dont have to worry about my antenner. It works just fine the way that it is. No one ever has any problem hearing me on 75m, even at a 100w power level. and even on 160 I usualy GET the same signal reports as I GIVE, which isnt too shabby for a 60' long antenna.
I have configgered the whole station for high angle rag chewing and am also heard quite well out into the midwest. I was talking with Skip, K7YOO last night with no problems. the only change that I plan for the antenner system is to make some new homebrew #12 or 10 ladda line feeders to help minimize the I-R losses a little better on 160. If it aint broke, dont fix it. Sometimes you just gotta accept the fact that something works instead of tearing your brain out trying to figger out why it workz.


Ellen,
         I am very familiar with that quote, I just figgered that the other references would be a little more apprepo here. I love that quote too! As far as feeding a balanced antenna goes, if it is not operating on the the frequency that it was cut for (1/2 wave) no one will ever convince me that coass is any better than ladda line. Coass is fine for feeding an unbalanced antenner (ground plane, vertical etc) but for a flat top antenner operating on any other than its 1/2 wave frequency ladda line kicks butt and takes names. As long as you keep your ladda line balanced it wont radiate because it is balanced. I was given a demonstration many years ago by the Derb that made me a believer.  When he was living at his mothers house in Columbia, Md. he had a small cheap P.O.S. b&w television ( with rabbit ears) sitting on a shelf in his radio room. His ladda line from the transmitter went up the wall not more than a few inches from the television. With the TV on and the transmitta fired off at full strap he didnt even put a line on the tv screen. That demonstration made a believer out of me!! I saw it with my own eyes.

Feeding an antenner with balanced line is the only REAL answer for multiband operation. Yea you can put up a fan dipole or lossy ass traps, but why botha if you dont have to!!
I feed my "non resonant" antenner with ladda line (14ga crappy brown stuff) and have used it from 160 all the way up to 10m without any "rf in the shack" problems. None at all!
Coass is fine for an unbalanced antenna operating on its resonant frequency, but anywhere else it getz lossy. Keeping the outer shield from becoming "hot" with rf can be a real challenge once the coax gets more than 1/4 wavelength in length.  Trust me it works, anyone who has ever worked me agrees that I put out a pretty good signal for using a compromised antenner. It is the end result of quite a bit of experimenting. If you feed it with ladda line, do everything possible to get as much of the rf as you can to the antenna (minimize I-R losses) and find a way to match its complex impedance to the transmitta, it will play!! Trust me on this one.

                                                                       the Slab Bacon
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