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 permissible in your locale.

Author Topic: Sky loop...height vs diameter  (Read 5425 times)

Offline IQ_imbalance

  • Sr. Member
  • ****
  • Posts: 345
  • 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/DJ-130/800Mhz Yagi
AFEDRI SDR-Net ICF-SC1 SDS-200 various RTL-SDR
Central MD

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 31396
  • 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
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline IQ_imbalance

  • Sr. Member
  • ****
  • Posts: 345
  • 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/DJ-130/800Mhz Yagi
AFEDRI SDR-Net ICF-SC1 SDS-200 various RTL-SDR
Central MD

Offline Pigmeat

  • Marconi Class DXer
  • ********
  • Posts: 6684
    • 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: 2122
    • 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

Offline N8BTR

  • Newbie
  • *
  • Posts: 4
    • View Profile
    • Email
Re: Sky loop...height vs diameter
« Reply #5 on: February 21, 2024, 1927 UTC »
10 years later....what's the thought on big loops, but low height?

I have a new KiwiSDR2. And I could put up a long loop this year, but it may only be 10-15 ft high for now..... My other likely option is an OCF 80m dipole at guessing 35-40 ft as an inverted V.
(The thought being probably next year I could get a higher 500 ft or 1100 ft loop in the air for transmitting as well, and use that.)

'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.

I found this article (here: https://ia904702.us.archive.org/35/items/73-magazine-1998-09/09_September_1998.pdf ) and read one from 1983: https://ia600602.us.archive.org/30/items/73-magazine-1983-05/05_May_1983.pdf

Which seems to make me think it's worth trying a 10 ft high big loop with a balun, but understanding it will be better when higher....
Any more insight on this since then?

I guess my question is: Horizontalish wire in the air 35-40 ft, or 10-15 ft high long (300-1000 ft) loop for 0-30 mhz receive?

-Nate
N8BTR

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1843
  • Tampa, FL USA
    • View Profile
Re: Sky loop...height vs diameter
« Reply #6 on: February 22, 2024, 0458 UTC »
Assuming a 300' loop, at low frequencies up to ~3-4MHz it will likely model as more of a blob shape with more "gain" (actually less loss) straight up than towards the horizon. It should be a decent NVIS antenna.

Around ~6-7MHz is going to shift the pattern more towards the horizon than straight up. Not exactly a big deal IMO, as NVIS tends to roll off above 7MHz, if even that most days, anyway.

As you go higher in frequencies the pattern towards starts breaking into multiple lobes, with the resulting gain and loses depending upon the distribution of those lobes.

Losses will increase as the loop approaches ground, especially as frequency drops. Works pretty much that way for most any horizontal antenna, be it a dipole, loop, etc. That said a low loop will likely have ground losses across pretty much the whole HF spectrum, thus the previous mention of "gain" in quotes.

Actually, lots of us have receiving loops placed directly on the ground. ;) Losses can be offset with a preamp if truly needed, though a preamp is often not a requirement at low frequencies, especially with large loop sizes. My 148' LoG typically suffices without a preamp from MW up to around mid-HF.

Summary? A large loop even at relatively low heights should suffice as a decent receiving antenna where losses at higher frequencies can be offset with a preamp if needed. Conversely, it not so much as a great transmitting antenna, though lots of people routinely work lots of contacts with horizontal antennas at low heights. YMMV.



Now as compared to an 80m dipole at 35'+ height? Ground losses still will be present at low frequencies, but that issue should improve around ~7MHz.

The dipole is still low enough to more favor NVIS at lower-HF frequencies. As frequency increases above ~7MHz the dipole should start having more gain at angles more towards the horizon than straight up.

As to pattern the dipole is going to become more bidirectional as frequencies increase, though opting for an inverted V deployment will somewhat improve an omnidirectional pattern at the sacrifice of some broadside directivity.

The dipole will start breaking into more lobes as frequency increases, too.



Personal thoughts? Given the feedpoint height differences present, I would likely favor the dipole with a feedpoint at 35'+..... though perhaps a different type of dipole with symmetrical balandce. An 90'+ doublet center fed at 35'+ as an inverted V should make for a decent HF antenna, especially from 80m to mid-HF. Coaxial feedline would suffice for receiving; just ignore the mismatches. If transmitting is desired, feeding a doublet with ladder line and using a tuner would be the (much!) better approach.

https://ftp.unpad.ac.id/orari/library/library-sw-hw/amateur-radio/ant/docs/Introducing%20the%20All-Band%20Doublet.htm
« Last Edit: February 22, 2024, 1301 UTC by RobRich »
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
148' + 60' Loops-on-Ground | 31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 31396
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: Sky loop...height vs diameter
« Reply #7 on: February 22, 2024, 1349 UTC »
My sky loop is currently around 900 feet in perimeter. It's been added to / re-routed / repaired more times than I can remember, so who knows exactly how much wire is there.

The height varies dramatically, perhaps 20 ft at the lowest, 60 or 70 ft (more?) at the highest.

It works extremely well from the upper half of the MW band right through 11 meters. It's deaf down on LW, as you would expect since it is "small" for those wavelengths, and is probably close to a short circuit.

I have tried modeling it, but as I have no idea what the actual antenna geometry is like, any detailed model output, especially the pattern, is likely random numbers.
 
My other antennas sometimes do better for specific applications (stations/bands) But overall it is my best performing antenna. "As much wire as you can get in the air, as high as practical" is not a bad philosophy when it comes to horizontal sky loops. If I could only have one antenna, this would be it.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 400 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1843
  • Tampa, FL USA
    • View Profile
Re: Sky loop...height vs diameter
« Reply #8 on: February 24, 2024, 0456 UTC »
Similar results with my current 148' LoG that has an 1:1 balun at the feedpoint. I could imagine low LF and especially VLF radiation resistance to be down into the low milliohms.

Interestingly my old 148' shielded LoG actually worked somehwat decently on longwave, though it was not using any balun or transformer at the feedpoint, so it might even have been common-mode on the feedline contributing to the low-frequency reception.
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
148' + 60' Loops-on-Ground | 31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline N8BTR

  • Newbie
  • *
  • Posts: 4
    • View Profile
    • Email
Re: Sky loop...height vs diameter
« Reply #9 on: July 10, 2024, 1245 UTC »
Follow up... I ended up putting up a 40m horizontal loop for now at 34 feet (10m) height, corner fed, 3 sides, with a 4:1 balun/1:1 balun combo. (Palomar Engineers)

http://21040.proxy.kiwisdr.com:8073/

I'll start with this, get some noise/RFI tackled, and eventually either add another antenna and a switch, or expand this to a larger loop.

-Nate
N8BTR



 

HFUnderground T-Shirt
HFUnderground Garden Flag
by MitchellTimeDesigns