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160m Antenna Question




 
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WA2SQQ
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« on: October 09, 2019, 09:58:00 AM »

Time to get ready for another 160m season! I have a question that Id like to get some feedback on.

Due to a limited real-estate situation my antenna system is space compromised. I use a wave sloper, fed against by 50 ft tower. I use ~ 65 ft of wire with a loading coil at the feed point. It extends down at ~ a 45-degree angle the end about 5 ft above ground. The coaxs shield is directly connected to the tower, which is obviously grounded at the base. Despite its inefficiency, last season I worked HI to complete WAS on 160m. I got to thinking how it might work if instead of grounding the coax to the tower, I connected a 120ft counterpoise, let it hang from the tower and have it suspended a few feet above the ground?
Option #2 might be to add the 120 ft wire to the point where the coax is connected to the tower.

Suggestions?
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N1BCG
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« Reply #1 on: October 12, 2019, 10:33:02 AM »

You've picked a popular topic with winter band conditions approaching!

The tower is an odd kind of ground. True, it's a direct connection at D.C. but there's enough height at RF to raise the impedance somewhat. In other words, your feedpoint is roughly 1/8 wavelength away from the actual earth ground.

What kind of match do you get with your current arrangement without a tuner? It's hard to efficiently match an antenna through a coax without losses since the coax wants to "see" its characteristic impedance at the load end. The more "fixing" the tuner at the transmitter does, the greater the losses. I mention this because it applies to each of your configurations.

A 120' wire counterpoise would be great if it were stretched out in the clear since the voltage and impedance at the end will be very high. Suspending it a few feet above the ground will certainly couple it capacitively and you'll probably not need a full 1/4 wavelength in that case. Since it's so low to the ground, arranging it in a spiral or loop may yield the same results while taking up less space. Be mindful of the voltage at the end when transmitting.

Adding the 120' wire to the top of the tower at the feedpoint will put the wire and tower in competition for lowest impedance. Whichever wins will carry the majority of your RF and have the greatest effect.

Regardless of configuration, it's very important to match the antenna and coax at the feedpoint and it my take more than a series inductor.
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WA2SQQ
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« Reply #2 on: Yesterday at 11:03:06 AM »

So using the tower, 2:1 SWR points are at 1810 & 1915. Last night using FT8 I was able to work europeans and a station in Argentina. Not bad for 75w. Going up the tower today to try the counterpoise approach. As inefficient as this antenna is, I finished up my WAS last winter, and finished the DX season working a station in N Cook island.  My secret weapon is using a magnetic loop for receiving.
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K4EMF
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« Reply #3 on: Yesterday at 04:20:52 PM »

....My secret weapon is using a magnetic loop for receiving.

Interesting.

And it receives better than your transmitting antenna?  How large a loop are you using?
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WA2SQQ
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« Reply #4 on: Today at 08:40:01 AM »

I'm using the PIXEL loop which is now sold by DX Engineering. It's about 40" in diameter. Not cheap, but in my case it's a night and day difference. Noise mitigation is the real issue. I live in Northern NJ with the majority of the metro NYC AM radio transmitters located about 5 air miles away. WABC is a 50 KW station and its ~ 2miles away. The Flex's (6500) receiver is very tight so I'm not hearing any images, but they all contribute to increasing the noise floor. My average noise level last night was S6-S7. In the winter it drops about 1 S unit - all this on my sloper. When I use the PIXEL, my noise floor drops by ~ 3 S-units. When I switch over, it literally opens up a whole new group of stations. It's quite directional during the daytime, somewhat less at night with skywave propagation. It also performs very good down to about 75 khz, and remains usable down to 30 khz. Above 40m,  - meh ...

I'm also experimenting with this antenna, a "LOG" (loop on ground).
http://www.kk5jy.net/LoG/

Extremely easy to make and it is somewhat bi-directional. The psychological aspect which took some getting use to is when you see the S meter drop. Weaker signals (on the Smeter), - definitely - but most of the decrease is the noise. WAS on 160m was something I never imagined being able to do, especially due to my location and limited space. Granted, FT8 isn't the same as having a QSO but it still shows that it can be done! Last season I worked K9FD in Hawaii. I though that was the ultimate DX I could accomplish. Several weeks later at about 1 AM, I worked an "E51" from Cook Island, a few thousand miles further! This one was done with 300W using FT8, all the others about 80W.
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K4EMF
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« Reply #5 on: Today at 07:57:10 PM »

I'm using the PIXEL loop which is now sold by DX Engineering. It's about 40" in diameter. Not cheap, but in my case it's a night and day difference. Noise mitigation is the real issue. I live in Northern NJ with the majority of the metro NYC AM radio transmitters located about 5 air miles away. WABC is a 50 KW station and its ~ 2miles away. The Flex's (6500) receiver is very tight so I'm not hearing any images, but they all contribute to increasing the noise floor. My average noise level last night was S6-S7. In the winter it drops about 1 S unit - all this on my sloper. When I use the PIXEL, my noise floor drops by ~ 3 S-units. When I switch over, it literally opens up a whole new group of stations. It's quite directional during the daytime, somewhat less at night with skywave propagation. It also performs very good down to about 75 khz, and remains usable down to 30 khz. Above 40m,  - meh ...

I'm also experimenting with this antenna, a "LOG" (loop on ground).
http://www.kk5jy.net/LoG/

Extremely easy to make and it is somewhat bi-directional. The psychological aspect which took some getting use to is when you see the S meter drop. Weaker signals (on the Smeter), - definitely - but most of the decrease is the noise. WAS on 160m was something I never imagined being able to do, especially due to my location and limited space. Granted, FT8 isn't the same as having a QSO but it still shows that it can be done! Last season I worked K9FD in Hawaii. I though that was the ultimate DX I could accomplish. Several weeks later at about 1 AM, I worked an "E51" from Cook Island, a few thousand miles further! This one was done with 300W using FT8, all the others about 80W.

Thanks for the response. I have played around with a small loop antenna calculator.  But the calculated efficiencies were so low I never attempted to use one.

My (horizontal) 500' loop is relatively close to the ground, with a height ranging from 12' to maybe 24' or 20.   I do get a lot of noise though, particularly on the lower frequencies.   
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