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Seeking advice on a compromise 160 m antenna




 
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Author Topic: Seeking advice on a compromise 160 m antenna  (Read 1523 times)
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WO4K
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« on: February 15, 2017, 01:55:42 PM »

My XYL (N4YAK) and I recently moved into our retirement QTH on a relatively small urban lot in Dunedin, FL. The house, circular driveway and aluminum pool cage (12' up) take up most of the lot. No room or hope for radials. See photo. I have a 40' crank-up tower with a hex beam that will go in the front of the house. Location of the tower due to lack of space in the backyard or sideyards, and power lines on the back of the property... and negotiations with N4YAK. I do not have the radio room set up yet, but it will be in the SE corner of the house (lower left corner in the fuzzy photo). I have the ability to do an inverted V over the house to the back of the property. One leg would be 80', the other 90', plus or minus. I can do 15' poles in both corners of the back yard.

I researched 160 m antennas until the cows came home. Right now I am thinking a folded dipole. Either a tilted T2FD (home-brewed) on the 90' leg or something like the Cobra Ultra-Lite Senior set up as an inverted V. I know I will have transmission loss from the resistor on the T2FD but it is also supposed to be a quieter than normal antenna, and it appears we have moved into an RFI rich environment. Anything happening here on 160m is going to be a compromise and marginal at best. That don't skeer me none.

I know that a reasonable person would say forget 160m, but as we approach the minimum of the sunspot cycle, I want to focus more on 160 and 75. My AM rigs: DX-100B, DX-40 (with audio mod) driving an AL-811H, R-390A, and a pristine Nye-Viking MB-II tuner I just snagged at Hamcation. And a K-Line. Down the road I will be adding an RCA BTA 1MX, currently set up for 300w carrier at 1.885 mHz, which is another reason why I want to get on 160m and another reason I'm thinking a hefty, home-brewed T2FD.

Thoughts, ideas, and suggestions are welcomed. I would especially like to get input from anyone with T2FD or Cobra Senior AM experience.

Frank WO4K

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KD6VXI
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« Reply #1 on: February 15, 2017, 02:35:10 PM »

Frank,

Vertical for TX,  and a mag loop for rx?

Or,  a mag loop for both,  with a vac variable for tuning?

The mag loop is nice to be able to turn away from noise.



--Shane
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K0ARA
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The Bull


« Reply #2 on: February 15, 2017, 05:32:30 PM »

160 METER Reduced Half Sloper by HFWIREANTENNAS 160HS on E-bay
used to be W8AMZ.

Missouri to Maine over the Heavy Metal Rally with a BC-610I.

YMMV  Cheesy
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« Reply #3 on: February 15, 2017, 09:02:41 PM »

That aluminum pool cage could be part of a good counterpoise for a helically loaded antenna...
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KD6VXI
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« Reply #4 on: February 15, 2017, 09:46:41 PM »

Also,  for a radially compromised location,  check out the FCP,  Folded Counterpoise.

I've never used one,  but k2av is a pretty smart guy and a lot of people are successful on 80 and 160 with them.

--Shane
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W4DNR
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« Reply #5 on: February 17, 2017, 08:55:52 PM »

160 METER Reduced Half Sloper by HFWIREANTENNAS 160HS on E-bay
used to be W8AMZ.

Missouri to Maine over the Heavy Metal Rally with a BC-610I.

YMMV  Cheesy


Has anyone dissected the PVC feed point of one of these Half Slopers to
see what's inside ?     If it's  a one inch diameter wire coil, wouldn't it be better to wind one on a 4, 5, or 6 inch form with 1/4 inch copper coil rather than a 14 or 16 gauge wire ?

Just wondering.

Don W4DNR
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W1ITT
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« Reply #6 on: February 17, 2017, 09:15:25 PM »

Forget the T2FD.  I don't have the figures in front of me but, at the lower end of the range, they dissipate most of the power into the resistor.  I recall the radiated power being something in the vicinity of 15 db down!  On the higher bands they are still lossy, but not nearly as much.  I'd go with something like K1JEK's 80m Cobra for 80m and above and then tie the feeder coax together and feed it with a matching network as a Marconi on 160m against whatever ground you can rustle up.  Any fences, that aluminum pool thing and whatever you can manage to stick into the ground.  Florida ground is much higher conductivity than much of the country, especially here in the granite foothills in Maine.  I recall seeing tower and guy foundations being poured near Orlando and the challenge was keeping brackish salty water out of the hole long enough to get forms in it.   The Folded Counterpoise FCP ground is a bit controversial, but fellows seem to do fairly well with it in limited-space circumstances.  If your neighbors are as close as it sounds, hearing signals over all their locally generated noise and buzzies may be a challenge, but well modulated 160m AM should sound very nice in their stereos.
Nothing ventured, nothing gained.
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« Reply #7 on: February 17, 2017, 09:30:09 PM »

http://www.eham.net/ehamforum/smf/index.php/topic,102323.0.html

Here's a thread where AC6LA did an eznec analysis of the T2FD.  He shows power into the termination load at various frequencies.  You can extrapolate this down to 160 with a bigger aerial but the sad story is the same.  You can extrapolate, but your signal won't strap.  The reason Uncle liked them is because he could QSY quickly, and the taxpayer was buying the transmitter and paying the electric bill.
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KD6VXI
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« Reply #8 on: February 17, 2017, 10:51:27 PM »

Hey Witt.....

You know a couple things about antennas....

What's your honest take on the FCP?

If you'd rather reply private,  that's fine.

I was getting ready to start a thread similar,  so this is somewhat timely.

--Shane
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« Reply #9 on: February 18, 2017, 10:08:48 AM »

Shane...
While I had learned a few things over the years installing MW and HF phased arrays worldwide, all I know about the FCP is what I have read.  K2AV has some informative articles, and there has been talk in the Topband Reflector.  Some anecdotal evidence indicates that fellows in antenna compromised locations have been happy with them.  There have been comments from guys who already have 120 radials and a clear near field who doubt their effectiveness.  One fellow has a working 4-square on 80m with FCP ground, so take your choice.
My 160m Tee is 85 feet tall and goes out about 30 feet either side. Mounted on the banks of a trout stream over ledge, I have some radials on this side and a buss crossing the brook to more radials and a 4x100 foot screen on the other side.  I work some good DX but there are stations that out-strap me.  Summer or fall plans include cobbling up an FCP.  It's just wire and a transformer, all easily buildable stuff.  A rigorous A-B comparison is not feasible, but I'll look at things with a network analyzer watching for changes in feed impedance that would indicate apparent efficiency changes, and I have some good RF ammeters to put into the system and look for more fire in the wire.  Probably a quick and dirty field strength meter could be set up as well, and I'll just try to get a feel for how competitive it is.  No doubt, the FCP will couple into the ground system that already exists, so it's not a fair comparison with someone starting out from a virgin location. 
For low band ground, I also like using two or three "radials" of galvanized fence laid on the ground, 3 or 4 feet wide and 50 to 100 feet long, bonded at the antenna feed, but that setup is not lawnmower friendly.
The short answer to your question is "I dunno" but I'm interested enough to give it a try.  My all time favorite 160 meter antenna would be one of the four-tower phased arrays I tuned in the Middle East in the AM broadcast band, using skirt fed grounded towers and switchable patterns within sight of the Gulf of Oman.  I think they ran 800 KW into them, but that ain't gonna work in my back yard in Maine.  There were 120 radials, set under fist sized crushed rock to slow down nocturnal copper theft. 
I think the FCP may be another tool in the lowband kit for those of us who can't put up a textbook system, and it's cheap enough to give it a try.
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WA2SQQ
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« Reply #10 on: February 18, 2017, 11:40:21 AM »

I'm using a 1/4 wave slopes, fed from to top of my 48 ft tower. Wire is ant 85 ft long. Far from a dipole, but I can get out. I've worked into Europe using digital modes. Plan on starting to play with random wire, end fed. Look back in my logs, I've made some of my best contacts when the sunspots were killing the higher frequencies.
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K4RT
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« Reply #11 on: February 18, 2017, 02:24:08 PM »

I have been using a Cobra Sr deployed as an inverted-V on 160, 80, and 40 AM for over a year now. The center support broke, it was replaced with a new one from K1JEK, which broke a few days later, and was then replaced with a more robust support I made that has held up.
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Brad K4RT
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« Reply #12 on: February 18, 2017, 02:49:00 PM »

Brad,

How much power have you fed into the Cobra on AM on 160?

Frank WO4K
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Steve - K4HX
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« Reply #13 on: February 18, 2017, 02:58:17 PM »

Some ideas here.

http://amwindow.org/tech/htm/160smallants.htm
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KD6VXI
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« Reply #14 on: February 18, 2017, 08:38:57 PM »

Witt,

That's pretty much what I thought.....   Decent for compromise situations.

If I was able to stand on the top of the short tower here,  with binoculars,  I would be able to see VOA Delano.

Kills me I can't figure out a way to remote a station there.

--Shane
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« Reply #15 on: February 18, 2017, 10:03:30 PM »

Brad,

How much power have you fed into the Cobra on AM on 160?

Frank WO4K

Frank,

Up to 100W.  In the coming months, I will be upping the power when I get my Globe King on air. 

Presently, I'm using coax (RG-213) from tuner to a 5KW balun, and then 400 ohm ladder-line from balun to the Cobra.
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« Reply #16 on: February 18, 2017, 10:49:21 PM »

[...]
For low band ground, I also like using two or three "radials" of galvanized fence laid on the ground, 3 or 4 feet wide and 50 to 100 feet long, bonded at the antenna feed, but that setup is not lawnmower friendly.
[...]

I have found that just two radials, fifty feet long each, erected in exact 180 degree opposition, work amazingly well, on 160 through 20 meters, IF they are elevated seven to eight feet above the ground. At my location, they beat 8 radials on the ground by a noticeable degree.

73,

Kevin.
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« Reply #17 on: February 19, 2017, 09:48:19 AM »

My first house rental was in Ft. Lauderdale Florida and I had a nice canal out back and had big ideas about ground for my base loaded 80 Meter vertical.  I threw some thick wire into the canal and it was a great ground! Two weeks later I went out and checked the wire - it was pitted and was going away fast - Woops.

As Dr. Frankenstein said: ELEVATE ME!
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WB4AIO
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« Reply #18 on: February 19, 2017, 10:28:03 AM »

My XYL (N4YAK) and I recently moved into our retirement QTH on a relatively small urban lot in Dunedin, FL. The house, circular driveway and aluminum pool cage (12' up) take up most of the lot. No room or hope for radials. See photo. I have a 40' crank-up tower with a hex beam that will go in the front of the house. Location of the tower due to lack of space in the backyard or sideyards, and power lines on the back of the property... and negotiations with N4YAK. I do not have the radio room set up yet, but it will be in the SE corner of the house (lower left corner in the fuzzy photo). I have the ability to do an inverted V over the house to the back of the property. One leg would be 80', the other 90', plus or minus. I can do 15' poles in both corners of the back yard.

I researched 160 m antennas until the cows came home. Right now I am thinking a folded dipole. Either a tilted T2FD (home-brewed) on the 90' leg or something like the Cobra Ultra-Lite Senior set up as an inverted V. I know I will have transmission loss from the resistor on the T2FD but it is also supposed to be a quieter than normal antenna, and it appears we have moved into an RFI rich environment. Anything happening here on 160m is going to be a compromise and marginal at best. That don't skeer me none.

I know that a reasonable person would say forget 160m, but as we approach the minimum of the sunspot cycle, I want to focus more on 160 and 75. My AM rigs: DX-100B, DX-40 (with audio mod) driving an AL-811H, R-390A, and a pristine Nye-Viking MB-II tuner I just snagged at Hamcation. And a K-Line. Down the road I will be adding an RCA BTA 1MX, currently set up for 300w carrier at 1.885 mHz, which is another reason why I want to get on 160m and another reason I'm thinking a hefty, home-brewed T2FD.

Thoughts, ideas, and suggestions are welcomed. I would especially like to get input from anyone with T2FD or Cobra Senior AM experience.

Frank WO4K



Forget the T2FD. Its losses on 80 are the equivalent of running 5 Watts with 100 Watts input to the antenna. It would be much worse on 160.

Your best bet in your location, I think, is probably an inverted L. (A 120-foot vertical with 90 120-foot ground radials -- or a 240-foot dipole at 150 feet in the air -- would probably be a little better, though!)

One way to get up an L would be to shunt feed the tower (plenty of info in the _Antenna Handbook_ on doing that) and use a 90' extension wire from the top of the tower into the back yard's trees. Hide some wires  just barely in or on the ground (the grass covers them in a few months), as many as you can, for a ground system. (Using the shunt-fed, grounded tower precludes the use of elevated radials, which help efficiency.)

Even better, though, would be to use wire for the vertical part of the L, and space the vertical run of the L off the tower, using the same basic layout as described above -- _except_ elevate the feedpoint and the radials seven or eight feet off the ground. Then a couple radials, 50 to 100 feet long each, will be enough. You can even bend them around the house, but try to make them symmetrical if you can -- but they'll work at a slight loss of efficiency and a slight increase in noise even if they're not.

This would actually be a good, effective transmitting antenna for 160, 75, and 40 -- not really a compromise. (Noise on receive, and the possible need for a low-noise receiving antenna, will depend on your local RFI environment.)

With elevated radials, you will want the entire antenna isolated from the Earth, so a current balun at the feedpoint is a must. There are various ways to match the antenna (series capacitor if the antenna is long enough, tuner at the base, tuner at the shack if you use open wire feedline and two current baluns, one at each end).

Have fun!

Kevin, WB4AIO.
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« Reply #19 on: March 07, 2017, 06:01:25 AM »

Yes, the best solution is to fold.
Make a full size 160 m dipole and fold it the way you prefer, just keep few inches between wires if you turn back 360 degrees...    No need to be symmetric in shape, just be symmetric in length. The less you fold the better it is. Just use all your space. You will need to trim it for precise tuning, anyway this is the best we can do.

G.


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WO4K
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« Reply #20 on: March 07, 2017, 07:34:55 AM »

Thank you, everyone, for the responses. So the T2FD is off the list, but I now have a lot more options to consider...and with which I can experiment. I will start with a full size 160m dipole in an inverted V, each side looking like a sideways V, like this:  >  .
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« Reply #21 on: March 07, 2017, 10:36:28 AM »

160 METER Reduced Half Sloper by HFWIREANTENNAS 160HS on E-bay
used to be W8AMZ.

Missouri to Maine over the Heavy Metal Rally with a BC-610I.

YMMV  Cheesy


That antenna is a horrible waste of time and money!!!!!!!!!!
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« Reply #22 on: March 11, 2017, 01:20:35 PM »

Some more possibilities:

http://amfone.net/Amforum/index.php?topic=33230.msg257078#msg257078
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« Reply #23 on: March 12, 2017, 03:24:00 PM »

Frank,

I would put up a 160 foot dipole, if you can.  Put loading coils in the center of each leg to keep losses down, and feed it with number 12 wire spaced 4 inches, to a low loss transmatch.  It would be efficient on all bands, and might outperform the hex beam.
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