Horizontal "Sky Loop" Antenna

[RufusDawes]

Going to put up a Horizontal “Sky Loop” antenna for HF and BCB receiving, it will be 4 sided approximate perimeter length of 200 ft, about 15 ft off the ground…

Looking for some insight on how best to maximize the antenna. Using 16awg stranded copper wire with poly insulation, black with the hope that it conceals well against the sky. Not sure if a balun is needed, have seen some use a 4:1 and happy with the results. From my understanding no ground wire is needed with this type of antenna… please advise!

 

[EAFrizzle]

I use elevated and Loop on Ground antennas for HF and MF. I use a nooelec 9:1 balun(good and cheap) to transition to co-ax for the receivers. They work well, and you're correct, no ground wire is needed for the antenna.

You're going to enjoy it. Much quieter than dipoles and ground planes, they make a perfect antenna for an LNA to help bring in the weakest signals.

 

[WB5UOM]

I have about 350 feet in a quasi somewhat maybe diamond shape..fed direct with Rg8.
Have had it for years

 

[Yagi]

For several years I had about 260 feet of wire up in a somewhat 5 sided horizontal loop. I used the trees that I had for the supports so it wasn't a perfect box shape. The length was based on what I had room for. It was limited to about 25 - 30 feet high.

The feed line down to my house was 300 ohm (Radio Shack foam lead). From there I had a 4:1 balun and coax to an Alpha Delta coaxial surge protector that was connected to a ground rod.

I was able to use it on 15, 20, 40 & 80. Because of the limited height 80m didn't work that great But I felt like the loop worked reasonably well on 20m and 40m. The loop was quieter then a vertical I put up a few years later.

 

[prcguy]

A horizontal loop at 15ft is going to be a cloud burner over most of the HF band and won't have a very good low angle for DX.

 

[RufusDawes]

A horizontal loop at 15ft is going to be a cloud burner over most of the HF band and won't have a very good low angle for DX.

Yep, it's the best I can do where I live... rn my 120' random wire is pretty decent and at the same height, so the loop should at least be as good as that while lowering the noise floor a few S levels, that is my hope

 

[db_gain]

It'll be fine, I have a single element Wullenweber (GAP Titan DX) vertical and a 120ft horiz loop and There really hasn't been a case where one heard something the other didn't. That said, when working nvis stations they won't hear me on the vert but will on the loop.

 

[RufusDawes]

Finally got the sky loop done and decided to start with a Delta loop to see how it would perform. Easily gave me a 2 to 4 S-meter stronger signal over a 120 ft random wire and the 1M Wellbrook. Ran it through a 4:1 balun. Some frequencies noise was reduced, on some it was slightly more. The noise was a little more on 14 MHz and higher frequencies, but still very "listenable" and doesn't diminish the signal strength. I think the noise issue is related to the loop not being perfectly flat, one corner is 20ft high while the other corners are 13ft, so perhaps that slight vertical lift is adding neighborhood RFI, but not sure. Not as good on AM BCB as the Wellbrook, but not far behind, but the sky loop was for SWL anyway so doesn't really matter to me. For AM BCB Dxing nothing beats the 8" Ferrite Sleeve Antenna I built. Took 4 weekends to install the sky loop but, IMO worth the effort. I now going make it a squre loop and add 50 ft, and try to lower that one corner so the loop is flatter, should only make it better. So, overall, it's a pretty good project, takes some time and cost maybe $150 but a good investment.

 

[pjxii]

Finally got the sky loop done and decided to start with a Delta loop to see how it would perform. Easily gave me a 2 to 4 S-meter stronger signal over a 120 ft random wire and the 1M Wellbrook. Ran it through a 4:1 balun. Some frequencies noise was reduced, on some it was slightly more. The noise was a little more on 14 MHz and higher frequencies, but still very "listenable" and doesn't diminish the signal strength. I think the noise issue is related to the loop not being perfectly flat, one corner is 20ft high while the other corners are 13ft, so perhaps that slight vertical lift is adding neighborhood RFI, but not sure. Not as good on AM BCB as the Wellbrook, but not far behind, but the sky loop was for SWL anyway so doesn't really matter to me. For AM BCB Dxing nothing beats the 8" Ferrite Sleeve Antenna I built. Took 4 weekends to install the sky loop but, IMO worth the effort. I now going make it a squre loop and add 50 ft, and try to lower that one corner so the loop is flatter, should only make it better. So, overall, it's a pretty good project, takes some time and cost maybe $150 but a good investment.

Ferrite Sleeves are awesome. It's great to experiment with wire antennas if you can. Ironically I am looking to put up about 120' of wire here for a starter then see where to go from there, so your comparison is very helpful.

 

[RufusDawes]

The solar storms over the last week or two aren't the best environment to test this right now LOL, hopefully better conditions this weekend.

 

[RufusDawes]

Ferrite Sleeves are awesome. It's great to experiment with wire antennas if you can. Ironically I am looking to put up about 120' of wire here for a starter then see where to go from there, so your comparison is very helpful.

I'm researching a common mode choke for the RFI... problem I run in to is that most of these are for hams transmitting and not just for SWL, they typically don't go low enough to filter the AM BCB... so looking at a two stage choke that uses 43 mix torroid for 10MHZ-30MHZ, and 75 mix for 0.5MHZ-10MHZ.

Some really good info here:

Limitations of Coaxial Air-Cored Balun Chokes – Q82.uk – Antenna Resources by Steve G0UIH – ex Vortex Antenna Systems

and here:

Common-mode chokes

Photographs of a copy of the Ten Tec Argosy transceiver

www.karinya.net

 

[RufusDawes]

Update on this project... I added another 50 ft and made it a rectangle with a total length of 250ft... it slopes up from 13ft to 20ft on the short sides... really satisfied with the performance, it gives equal or better signal than the 100ft random wire on all bands except AM BCB but approximately S2 less noise... I have a 3 way antenna switch in the shack that is fed with the Horizontal Loop, Random Wire, and a 1M Wellbrook vertical loop. The Horizontal Loop can dig out stations that can't be heard over the noise with the other two. The random wire and Wellbrook do much better on the AM BCB.

Also, I was getting some "motor boating" noise on frequencies > 15 MHZ, it was found on the horizontal loop and random wire, it has been less intense the last month or so. The Noise Blanker on the R5000 takes it out, some kind of noise on the neighborhood, maybe and air conditioner compressor.

 

[philipus]

Really interesting Rufus, thank you for posting about it.

I was wondering about the 4:1 balun. Would there be any difference in performance with for instance a 9:1 or even higher?

I'm only a newbie but assuming your receiver has 50 Ohms going in, wouldn't the impedance of the wire be more than 200 Ohms? Then again perhaps it makes little difference for receiving to pull down the impedance.

I'm toying around with write antennas too trying to learn as I go along.

Best
Philip

 

[RufusDawes]

Hey Philip... the two antenna designs are fundamentally different:

Horizontal Loop: fed in the middle where there is high current and low voltage, which creates lower impedance (100-300 ohms), since the antenna is balanced a smaller 4:1 balun is all that is needed, in fact I have experimented using no balun at all and it doesn't seem to make any difference! The loop is balanced and it is being tied into coax which is unbalanced (BAL-UN)... balanced means that the currents in loop are the same. The loop is balanced and needs no grounding system for it work work. The currents on each side of the loop flow in opposite directions creating a noise cancelling effect for any RFI that gets picked up

Random Wire: end fed where there is low current and high voltage, which creates much higher impedance (1000-9000 ohms), since the antenna is unbalanced a 9:1 unun is needed to reduce the higher impedance to feed to the receiver. The wire is unbalanced and is being fed into coax which is also unbalanced (UN-UN).. the random wire is considered unbalanced since the currents in the random wire and the grounded side are not the same, which is why a good grounding system is needed/desired. Since current in the wire flows in one direction it offers no noise cancelling of RFI and chokes/filters are needed to reduce/eliminate them.

That is my understanding anyway, I'm sure someone will correct my errors.

 

[Token]

Hey Philip... the two antenna designs are fundamentally different:

Horizontal Loop: fed in the middle where there is high current and low voltage, which creates lower impedance (100-300 ohms), since the antenna is balanced a smaller 4:1 balun is all that is needed, in fact I have experimented using no balun at all and it doesn't seem to make any difference!

The bit about the balun is kind of what I have found also.

My SkyLoop is square, 517 feet total wire, and up 30 feet. For receive applications I find little difference, balun or no. In fact, I would say it is a bit broader banded without a balun, direct fed from coax. It has good performance from a bit below the MW BCB up to about 9 or 10 MHz, and decent performance from there up to about 18 MHz. Above about 18 MHz it seems to fall a bit flat, and I assume that is a combination of take-off angle and the fact it is ~10 wavelengths long by then. It works, kind of, up to 10 meters, but I find a basic dipole works better from ~10 MHz up.

(edit) I have a second antenna that can be kind of a SkyLoop. One of my Rhombics has a vacuum operated shorting switch at the 800 Ohm load end (I have three options with that antenna, terminated, open, and shorted, default is terminated). When I short that switch the Rhombic turns into a skewed shape Loop of about 1100 feet of wire.

T!

 

[philipus]

Hey Philip... the two antenna designs are fundamentally different:

Horizontal Loop: fed in the middle where there is high current and low voltage, which creates lower impedance (100-300 ohms), since the antenna is balanced a smaller 4:1 balun is all that is needed, in fact I have experimented using no balun at all and it doesn't seem to make any difference! The loop is balanced and it is being tied into coax which is unbalanced (BAL-UN)... balanced means that the currents in loop are the same. The loop is balanced and needs no grounding system for it work work. The currents on each side of the loop flow in opposite directions creating a noise cancelling effect for any RFI that gets picked up

Random Wire: end fed where there is low current and high voltage, which creates much higher impedance (1000-9000 ohms), since the antenna is unbalanced a 9:1 unun is needed to reduce the higher impedance to feed to the receiver. The wire is unbalanced and is being fed into coax which is also unbalanced (UN-UN).. the random wire is considered unbalanced since the currents in the random wire and the grounded side are not the same, which is why a good grounding system is needed/desired. Since current in the wire flows in one direction it offers no noise cancelling of RFI and chokes/filters are needed to reduce/eliminate them.

That is my understanding anyway, I'm sure someone will correct my errors.

Ah of course, that makes perfect sense. I find loops intriguing and will probably play around with them but on a smaller scale as I'm a bit space-constrained.
cheers
philip