We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Sky loop...height vs diameter  (Read 2597 times)

Offline IQ_imbalance

  • Full Member
  • ***
  • Posts: 226
  • Central MD
    • View Profile
Sky loop...height vs diameter
« on: August 02, 2014, 1435 UTC »
This may have already been discussed but for some reason tapatalk doesn't want to let me search through posts....so here goes.

For a sky loop antenna, which variable has the largest effect on reception...height above ground or diameter?  It's a practical question since I could put a loop around the top story of my house (guessing a 28 m loop....maybe 60m if I shoot a line to the backyard trees) without much effort, but while a loop around the entire house would be twice the diameter (up to 120m perhaps, again including a treetop run) the loop would only be ~3 meters above the ground on the front .  The house is on the side of a hill so the front is much closer to the ground than the back.

I -might- be able to rig up a valley span longwire, but it would be in the bottom of the valley (running SW to NE) and probably only 10m or so high so it might not be worth the trouble.  That's also assuming I can get enough tension on it, otherwise I might close line folks passing by in their kayaks :)
LOG/NE-SW unterminated BOG
AFEDRI SDR-Net
Central MD

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23608
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: Sky loop...height vs diameter
« Reply #1 on: August 02, 2014, 1524 UTC »
Here's my experience, YMMV:

The perimeter (length) of the loop sets the lowest frequency where it will operate well. My loop is 670 ft  (206 meters) and works down to the upper end of MW, just around one wavelength, which makes some sense. It doesn't do too bad into the middle of the MW band, but signal are quite weak in the lower end of MW. And nonexistent on LW.

As for height, mine varies a lot, from probably 20 ft on the low run s, to maybe 50/60 ft at the highest. My goal was to get as much wire in the air as possible. From theory I'd guess that higher height will favor low angle (DX) radiation. So I would not worry too much if parts of your sky loop are lower than others.

I feed mine with a 9:1 balun and 75 ohm RG6 coax.  I've tried a 4:1 and 16:1 balun, they work about the same. The impedance of the sky loop various by insane amounts over all of HF, attempting to match impedance is an exercise in futility, and not critical for receiving anyway. But I strongly recommend a balun. I use RG6 because 1) it is cheap 2) you can buy long runs with weatherproof F connectors already installed and 3) life is too short to mess around with soldering PL-259 connectors. Throw an F to PL-259 on each end, with some coax seal, and you are done.


Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline IQ_imbalance

  • Full Member
  • ***
  • Posts: 226
  • Central MD
    • View Profile
Re: Sky loop...height vs diameter
« Reply #2 on: August 02, 2014, 1901 UTC »
After I get my ground rods pounded in and my bulkhead box mounted I'll dig out the fishing bow and see what I can get into the trees....
LOG/NE-SW unterminated BOG
AFEDRI SDR-Net
Central MD

Offline Pigmeat

  • DX Legend
  • ******
  • Posts: 4233
    • View Profile
Re: Sky loop...height vs diameter
« Reply #3 on: August 03, 2014, 0626 UTC »
'73 Magazine ran an in depth article in the late 90's called , "What's The Scoop on The Lazy Loop?" on full wavelength horizontal NVIS loops. As Chris said, the bottom frequency seems to be the key with the things. According to the author, if you could get up to about 1/8 of a wavelength for the bottom frequency the thing was an exceptional performer for receiving and transmitting up to about 15 meters.

Seems to me the guy used a tuner, as he was testing it for ham work.

Offline Token

  • Global Moderator
  • DX Legend
  • *****
  • Posts: 1798
    • View Profile
Re: Sky loop...height vs diameter
« Reply #4 on: August 07, 2014, 2158 UTC »
My Skyloop is a full wavelength on 80 meters, at 35 feet height.  I would prefer to have it a little higher but winds here  and where I want to put it prevent that and it seems to work acceptably well there.  I have tried heights from 20 to 60 feet with the same size loop and did not see a great deal of performance change with those heights.  I do have to use a tuner if I am going to transmit on any band except 80 meters, but it does work well up to about 20 meters or slightly above, falling off after that.

I have three other antennas that are “sort of” Skyloops also.  I have three Rhombic antennas, each on a different bearing.  Two are 450 feet apex to apex and one is 320 feet apex to apex.  At the far end of each of these I have a three position pneumatic switch.  The switch defaults to the “terminated” condition, this terminates the Rhombic with an 800 Ohm load, making the Rhombic directional.  The next condition of the switch is “open”, or unterminated, this makes the Rhombic bidirectional.  The last switch position is “shorted”, this makes the Rhombic now a big, slightly squashed, loop.  The two 450 foot Rhombics each make a loop of about 1100 feet of wire, the 320 foot Rhombic makes a loop of slightly over 700 feet (guessing on both lengths, I have never actually calculated the total wire length).  They work pretty well down into MW, but seem to fall on their faces (as loops) a bit under 20 meters.

T!
T!
Mojave Desert, California USA