600 OHM ANTENNA

[W2PFY]

high-tensile fence construction here

I DIDN'T WANT TO HI JACK THE OTHER THREAD SO I'M ASKING THE QUESTIONS BELOW

Thanks for the lead on the hi tensile wire Don (KYV). I need to build cheap so I may try it.

A question, I was talking to HLR a while ago and he told me that if I put up an antenna 400 feet on a side it will tune 160 to 10 meters feed with open wire to directly hook up to my Westinghouse MW-2 which can be configured for 75 ohms or 600 ohms.

No antenna tuner needed?  

What kind of antenna is this? A loop? I think rhombic's are more in a diamond shape.

I'll need to make new feeder lines for it at 600 ohm.

What kind of pattern will it have.

Could a terminating resistor be used to make it directional and does it have any gain in any form?

[k4kyv]

high-tensile fence construction here

I DIDN'T WANT TO HI JACK THE OTHER THREAD SO I'M ASKING THE QUESTIONS BELOW

Thanks for the lead on the hi tensile wire Don (KYV). I need to build cheap so I may try it.

I didn't suggest using the high tensile galvanised fence wire for antennas. I would use copperweld.  I just suggested physically constructing the antenna in similar fashion using farm fence hardware and techniques to make it strong enough to withstand deer damage.

Maybe Timtron could answer your question about the antenna with 400' legs.

[Ed/KB1HYS]

Do you mean a square with 400 ft sides?  How High?  I can model it if you have the details...

[W2PFY]

I can probably get it up about 80 feet on all four sides. Thanks for your input and I look forward to see your results.

[KL7OF]

If I could get four 400ft legs up at 80 ft .........it would be a rhombic....

[W3SLK]

Terry,
I built a cloud burner that worked 160-10 with a tuner. It was 545' total wire but in a psuedo loop. The only reason I'm not using it now is because I don't have any supports for 2 sides. Hope this helps.

[KC4VWU]

What do you guys think about a NVIS for 75m? I know a couple of fellows who have one set up for 40m and they really love them. They say lower noise floor and improved close range transmitted sig. over a flat top dipole.

[k4kyv]

Isn't a NVIS antenna just something with predominately high angle radiation, like a low dipole?  I used to run a dipole about 25' in the air and got tremendous signal reports within a radius of a couple of hundred miles.  When I changed over to the dipole 110' high, the locals said my signal went way down, but I get much better coverage at longer distances, which is where most of the AM  signals are located that I now hear.

Tropical broadcasters sometimes use low dipoles to get local coverage on the 3 or 5 mc/s tropical bands, comparable to the ground wave signal one would get with a medium wave vertical.  They use short wave because tropical QRN makes the MW broadcast band almost useless.

[W2PFY]

Do you mean a square with 400 ft sides?  How High?  I can model it if you have the details...

Hello Ed, I await your findings

[Steve - WB3HUZ]

No need to wait. On 160 and 80 meters it will be a cloud warmer. It should be an excellent antenna for local/short-haul contacts.

[W2PFY]

No need to wait. On 160 and 80 meters it will be a cloud warmer. It should be an excellent antenna for local/short-haul contacts.

How do you think it will work on 20 meters and on ten meters. I'm excited about getting the generator repaired that powers it for the upcoming new sun spot cycle. I never operated the transmitter above or below 40 meters. I don't know which is up or down on HF

[flintstone mop]

No need to wait. On 160 and 80 meters it will be a cloud warmer. It should be an excellent antenna for local/short-haul contacts.

How do you think it will work on 20 meters and on ten meters. I'm excited about getting the generator repaired that powers it for the upcoming new sun spot cycle. I never operated the transmitter above or below 40 meters. I don't know which is up or down on HF

It might get a little complicated on the upper bands. Some modeling would be needed for those bands. Might be more lobes and nulls, pattern distortion, etc and might even be too high off the ground. 50 feet is usually optimum,,,, too high and it will be very low take off and skip the USA entirely.

FRED

[Steve - WB3HUZ]

I'd have to model it to tell you for sure. If you have room (remembering that 20-10 antennas are much smaller than 160-40 antennas), you could put up much superior antennas for these bands.

No need to wait. On 160 and 80 meters it will be a cloud warmer. It should be an excellent antenna for local/short-haul contacts.

How do you think it will work on 20 meters and on ten meters. I'm excited about getting the generator repaired that powers it for the upcoming new sun spot cycle. I never operated the transmitter above or below 40 meters. I don't know which is up or down on HF

[Steve - WB3HUZ]

I was thinking it was 80 feet on a side. But you are looking at 400 feet on a side at 80 feet above the ground. I modeled that with the feedpoint at one corner. It's not a cloud warmer on 160 meters. See the plots below. It appears to be bi-directional diagonally from the feedpoint to the opposite corner.

The feedpoint is not 600 Ohms but you would have an SWR of a little more the 4.5 with 600 Ohm open-wire line: 175 - j326 Ohms. The take-off angle is 54 degrees at an azimuth angle of about 45 degrees. Even on this band, the thing is pretty directional, so point it accordingly. You can see how signals off this side could be down substantially.

[Steve - WB3HUZ]

On 80 meters, more lobes begin to appear in the pattern, as expected. The take-off angle is now down to 24 degrees on the main lobe. In the direction of this lobe, it would be a good DX antenna. A dipole at the same height would be much better for local stuff (note there is very little high-angle radiation in the pattern of the loop). Notice the big nulls between the lobes. If someone is in one of these nulls, you'll be PW and vice-versa.

The feedpoint impedance is 296 + j561. This would yield an SWR of about 4 on a 600 Ohm line.

[Steve - WB3HUZ]

On 40 meters it gets even crazier - tons of lobes. The take-off angle is now down to 24 degrees and the lobe is VERY narrow. Lots of nulls too, so the PW thing is true twice as often as on 80 meters.

The feedpoint impedance is 933 - j1087. This would be an SWR of about 4 on a 600 Ohm line.

I didn't even bother to model this thing on 20 meters. Once again, the number of lobes would double. You would have some gain in the main lobe(s) but they would be so narrow you would be strapping to one or two countries!

So, although feeding this thing with a 600 Ohm line would result in reasonable SWRs and attendant low loss, I wouldn't bother with it. Other than on 160 meters, it has too many lobes and nulls and the pattern has minimal radiation at the higher angles (good for local, and medium haul contacts). If you do want low angles on the higher bands for DX, there are other (and better IMO) options that you could fit in the amount of real estate required for this loop.

Hope  this helps.

[W2PFY]

Thanks Steve, that plotting sure does help. I was surprised about the gain it would have in some of the lobes. I guess I'll stick to the simple dipole for 160-40 meters. I cannot put up towers but what I do have is about 50ea 115-125 foot pine trees behind the cabin to the west and more on the north side. I can hit any broadside direction with the trees available. Is there a wire antenna that will do 20 through 10 that exhibits gain. I'll have to dial in the directions but I know I want Alaska, AU and Japan. I can almost work just about all Europe up there on some band but rarely the above.   

[Steve - WB3HUZ]

If you are up for open-wire feed, consider a Lazy-H. Feed it in the center of the line connecting the upper and lower elements and it will work 20-10 meters with a tuner. It will have gain on 20 meters and the gain will be even higher on 15 and 10 meters.

Since it's bi-directional, you could put two up at right angles and have coverage in all directions. Just make sure the lower element is at least 0.5 WL high on 20 meters.

[Steve - WB3HUZ]

I tried a 20 meter Lazy H. It works well on 20 meters but had too many lobes on the higher bands for me. So I tried stacked 20 meter dipoles. The top dipole was at 66 feet and the lower one at 33 feet and fed in-phase. This is half a Lazy H.

The pattern is nice and broad with no nulls, other than off the ends. In the elevation plot below, the red line is the phased dipole array. The dotted line is a single dipole at 66 feet for comparison. As you can see, the phased dipoles beat the single dipole by about 3 dB. Also there is no high-angle radiation, which should make the phased dipoles a little quieter on receive.

Let's see what happens on 15 meters next....

[Steve - WB3HUZ]

On 15 meters some higher angle radiation does begin to appear. This is because the lower dipole in the phased array is now 0.7 WL above ground. And the spacing is now not a perfect 0.5 WL as it was on 20 meters. Still, the gain of the systems is about 5 dB over a 15 meter dipole in the main lobe. Yes, there are some lobes in the elevation pattern and the are small compared to the main lobe. Also look at the 3D plot. The main low-angle lobe is still pretty broad and smooth - no nulls. This will give you good coverage.

So, what happens on 10 meters?

[Steve - WB3HUZ]

On 10 meters, we get more lobes in the elevation pattern. Unfortunately, some are pretty large. There is no free lunch. However, the main low-angle lobe is still the largest and it beats a 10 meter dipole by 3 dB. Once again, in the 3D plot you can see this low-angle lobe is still fairly broad and smooth.

If this pattern degradation is unacceptable, I would put up this antenna for 20 and 15 meters and another system geared for 10 meters. The dimensions are small on 10 and you could put one or more almost anywhere. Even at only 30 feet above the ground, the antenna is up nearly one-wavelength yielding good low-angle radiation.

[W2PFY]

So I tried stacked 20 meter dipoles

Thanks Steve, Great information. Most of this work will take place next spring, maybe some this year depending on snow. It's the depth of the snow that is the problem at camp. I once put up a 75 meter antenna 80 feet into the trees when it was only 8 degrees out. Forget it when it two feet deep in the woods. I don't want to become Coyote bait! We have hundreds of those in our woods up there.