HFU HF Underground

Technical Topics => Equipment => Topic started by: John Poet on October 08, 2015, 0241 UTC

Title: Cyclone fence (sort of - loop) antenna?
Post by: John Poet on October 08, 2015, 0241 UTC
Anybody ever tried hooking up to the top-rails of their cyclone fence for a receiving antenna?

I've got about 160 feet of fence surrounding the yard, with additional sections going off the backside on both ends for god knows how far (backs of the neighboring yards).

As an experiment, I'm thinking about tapping into both ends of the section surrounding this yard with normal insulated wire, just what I need to reach them, in a sort of loop configuration through the section surrounding the yard.  Feedline would be 300 ohm into an antenna tuner (or possibly a dual coax using the center-wires only, to try to shield away some of the noise around here).  Of course it wouldn't be an actual loop with all the extra sections going off the back-corners for as far as they may be electrically continuous..

Although not high off the ground, if the rails are well-connected enough, it would end up being a hell of a large.... metal thing, sort of like an antenna....  Not sure what the grounding effect would be, with all the support rails going into the ground, but it seems like a very large surface area in a sort of fishbone pattern for receiving signals....

OK, so... Who's tried it?   Anyone?   Anyone?  Bueller?


Since a falling pine tree finished off my other antenna, I'm looking into some other things, but the possible antenna support situation isn't very good in this yard-- everything high is too close to the house.
Ideally I'd like a wire loop in the air, but that would be difficult here without a new bunch of "eyesore masts"...





Title: Re: Cyclone fence antenna?
Post by: Pigmeat on October 08, 2015, 2032 UTC
I've used a chain link fence with good results as receiving antenna in the summer months. Cuts the Hell out of the static.

A hundred feet of wire or so on the ground is good in the same type of situation. Both seem to cut back on fading.
Title: Re: Cyclone fence antenna?
Post by: John Poet on October 29, 2015, 2115 UTC
OF COURSE Pigmeat has tried it!   I should have guessed   ;)

I did it, and have  loop continuity between the terminals, with all kinds of extra fences going off to the sides, of course...

It does work, and maybe reduced my noise somewhat.
Can't say if it's improved anything around 43 meters, (although CHU 7850 is kicking ass on it early tonight), but I think it's improved things on the lower bands.
Title: Re: Cyclone fence antenna?
Post by: ChrisSmolinski on October 29, 2015, 2151 UTC
Poet, I'm curious, what are the (rough) dimensions of it?
Title: Re: Cyclone fence antenna?
Post by: John Poet on October 30, 2015, 0748 UTC
The closed part of the loop is about 250 feet or so around, maybe a bit more.... 
about 70 feet of wire that's around 12 feet off the ground, (the remains of my doublet),
and 180 feet of fence rail around the three sides of the backyard.

So about 2 wavelengths at 7 MHz and near 1 wavelength around 90m.

The superfluous sections going off in both directions from the back is at least a couple hundred feet; I don't really know how far they go or stay connected.  Could be down the entire block, up to 900 feet.  Dunno what effect that would have, if any.

At first I only had one side connected to the fence, and it was extremely noisy.  Made a huge difference when I closed the loop.



Title: Re: Cyclone fence antenna?
Post by: ChrisSmolinski on October 30, 2015, 1127 UTC
At first I only had one side connected to the fence, and it was extremely noisy.  Made a huge difference when I closed the loop.

Yep, it is amazing how much lower the noise is from a loop antenna. I find this both with my sky loop, as well as with a folded dipole (vs a regular dipole of the same dimensions).

How are you feeding the antenna?
Title: Re: Cyclone fence antenna?
Post by: Pigmeat on October 30, 2015, 1530 UTC
The closed part of the loop is about 250 feet or so around, maybe a bit more.... 
about 70 feet of wire that's around 12 feet off the ground, (the remains of my doublet),
and 180 feet of fence rail around the three sides of the backyard.

So about 2 wavelengths at 7 MHz and near 1 wavelength around 90m.

The superfluous sections going off in both directions from the back is at least a couple hundred feet; I don't really know how far they go or stay connected.  Could be down the entire block, up to 900 feet.  Dunno what effect that would have, if any.

At first I only had one side connected to the fence, and it was extremely noisy.  Made a huge difference when I closed the loop.


Loose connections could be part of the noise problem, especially if there is a wind of any kind. Add a little rust and corrosion on those unknown sections, and it could turn into noise generator.

With antennas like that, a good gain control on the receiver is a big help. Start at the low setting on a strong station then start tuning around, adjusting the gain as you go. You'll reach a point where the S/N ratio peaks out.

I went to the set-up in the of '02, static was fierce that summer. It was tough to listen to KIPM that summer and Max was running power out the wazoo. The noise levels went to dead of winter levels when I hooked into that fence.

Part of the idea came from Bob Crane. He recommended a yard loop made of whatever wire you had laying around. You strung it up high enough not to strangle the kids and neighbors along the edge of the yard.

The fence idea came from when I was a kid. I lived with my grandparents far out in the country. (We were at the end of the power line.) I used to hook my Uncle's old Hallicrafters receiver to a barbed wire fence around the kitchen garden with a chunk of house wire. You couldn't overload the thing on SW, but MW was a mess until the 10 pm. and midnight stations in my timezone shut down. The lead in wire got unhooked and chucked out the window when I went to sleep or bad weather was expected.

In the summer you could listen to minor league and American Legion baseball from all across the Great Plains and Rockies as the locals shut down with that set-up.

In '02 I got so fed up with the noise I combined the ideas.

You might find that stations well to your east start coming in about 45 minutes earlier than they would with other types of antennas. That's been my experience with these antennas over the years.
Title: Re: Cyclone fence antenna?
Post by: John Poet on October 30, 2015, 1839 UTC
Quote
How are you feeding the antenna?

Just what is already hooked up now, heavy 300 ohm twinlead into an MFJ-948 tuner.  The 300 ohm was meant for transmitting purposes; always suspected it picked up extra noise on the receiver.

I may rig up a dual coax for a feed, and just use the center-conductors, maybe ground the shield; I have a reel of RG-58 with extra shielding. 

So far, I like this.
Title: Re: Cyclone fence antenna?
Post by: ChrisSmolinski on October 30, 2015, 1915 UTC
I'm wondering if you can treat it like a sky loop. Feed with a 4:1 balun and coax?
Title: Re: Cyclone fence antenna?
Post by: John Poet on November 01, 2015, 1923 UTC
A normal loop at resonance at half-wave off the ground is supposed to be 100 ohms or so impedance.  Because of the low or very low height of this thing, it may well be only 50 ohms or perhaps even quite a bit less at resonance, or 100 ohms or less at the second harmonic.  Using a 4:1 in this case would probably put it further from a match between feed and antenna than just plain coax.  A dual-coax balanced line (using only the 2 center conductors) would be about 100 ohms, a near perfect match to the 2nd harmonic (pirate band) of this particular "antenna", and have no need for a balun... speaking roughly and theorectically, as I haven't actually measured the exact length of the thing.

On the transmitting side, I never worried about trying to match impedances between my 300 ohm feeds and antennas, because the calculations were only correct for a narrow range of frequencies, and I tended to move around so much-- and using the balanced line eliminated the need for any balun, and reduced line losses vs. coax from the use of non-resonant frequencies. Any signal loss from mismatch was probably more or less cancelled out by the lower loss of the balanced lines vs. coax. (I actually researched those at length at one time via your 'RF Toolbox' !)

Just out of curiosity, and leaving impedance matching out of the question-- is there any other particular reason to use a balun on a receive-only loop, even if fed with coax?  I mean, you aren't worried about feedline radiation...  or is that a question I should not ask?  ;-)

Title: Re: Cyclone fence (sort of - loop) antenna?
Post by: Lex on November 02, 2015, 0421 UTC
I had better results using the chain link fence in our yard as a ground rather than antenna.  Even with the portables on a whip it made a big difference, reducing noise to nil.

But as an antenna it didn't do much.  Maybe it was the galvanized coating, or the grounding from the metal fence posts.

Best results I've had combining fences and antennas was a cheap and dirty stealth loop mounted on the wooden fence near my window.  Unfortunately the maintenance crew cut my coax feedline a few weeks ago and I haven't had a chance to replace it.  But they didn't even notice the antenna itself, which is just magnet wire strung along the fence, with an ordinary TV balun.
Title: Re: Cyclone fence antenna?
Post by: ChrisSmolinski on November 02, 2015, 1128 UTC
Just out of curiosity, and leaving impedance matching out of the question-- is there any other particular reason to use a balun on a receive-only loop, even if fed with coax?  I mean, you aren't worried about feedline radiation...  or is that a question I should not ask?  ;-)

You may have issues with your feed line picking up unwanted signals/RFI, sometimes a balun can reduce that.
Title: Re: Cyclone fence (sort of - loop) antenna?
Post by: John Poet on November 03, 2015, 1530 UTC
OK... thanks.

Title: Re: Cyclone fence (sort of - loop) antenna?
Post by: RobRich on November 04, 2015, 1801 UTC
Curious, are you not experiencing static issue when the metal links slide across one another, likely when windy enough to slightly move the fencing? It can be a common problem with chain-link fences used as antennas.

Likewise, rusted fencing components can act as diodes, thus potentially increasing noise. If it is an older fence, a quick cleanup of any rusted spots and hardware with sandpaper and dielectric protectant might further mitigate noise or at least prolong the viability of the fence as an antenna.
Title: Re: Cyclone fence (sort of - loop) antenna?
Post by: John Poet on November 06, 2015, 0028 UTC
It's all fairly new and clean fence, no rust that I've seen.

All I know is the static and noise are lower now than they were on the doublet/dipole.