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Author Topic: RF ground for antennas in high-rise condos  (Read 1092 times)
K4NNK
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Posts: 7




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« on: January 13, 2019, 06:33:51 PM »


I had a second home near Washington, DC, which is an apartment on the fourth floor.  I decided to move my FT-1000 transceiver from my primary residence in Atlanta to the apartment in Maryland. Like many others, I faced the problem of an antenna system with many restrictions on its size and location. I read several articles on how to solve the problem (example: Antennas and Grounds for Apartments, by Peter O’Dell, AE8Q, QST, Dec 1980), and learned several important lessons which I pass on in this letter. 

I put up a dipole for 20 meters by using very thin wire, fishing line and fishing weights which I tossed into the trees from my balcony.  It worked pretty well, but not impressive. Lots of noise, not many strong signals, and not many people heard me.  Next, I tried to load the 70-foot rain gutter downspout. I made a few contacts using that method also, but still not satisfying.

Then I found happiness.

First, I will disclose the secret grounding system:  I learned the value of using a good ground system.  It is comprised of two parts: one for DC ground, and one for an RF ground.  The DC ground I used is a wire braid connected to the grounding screw on the FT-1000 and connected to the ground screw on the water heater in my apartment.  The RF ground is the more interesting system.

Until this time, I never appreciated the value of an RF ground.  After doing some reading, and some thinking (guessing), I decided to try an antenna tuner with an artificial ground (MFJ Enterprises, Starkville, MS).

I tried three 33-ft lengths of wire lying on the floor of the apartment as the RF ground, connected to the tuner/artificial RF ground connection on the MFJ-934. That helped a lot, as determined by the signal reports that I received. 

Next, I disclose the secret radiating element: I used a 70-ft length of hood-up wire, end-fed; stapled to the ceiling, out the window, and hung in the trees near my balcony.  The far end of the wire is supported by fishing line and a lead fishing weight. The first antenna fell down because a squirrel chewed on the 2 oz fishing weight (I found teeth marks) and eventually broke the 6 lb-test fishing line. I moved up to a 4 oz weight, and 15-lb line, and thus deterred the squirrel(s). 

I tuned up and it worked well. However thanks to my knowledge of RF antenna theory, I made it better.
I made the RF ground wires fatter by replacing the hook-up wire with two 25-foot lengths of copper foil (Gordon West’s Foil from Ham Radio Outlet). SWR is less than 1.2:1 for the entire 40 M & 20 M bands without re-tuning. To compete for DX, I stay on 40M where there are fewer beams, and more wire antennas.

That did it.  Within 3 weeks, I worked VK3CWB, JW1CCA, 7X4AN, FK/KF4TUG, and EM1HO (Antarctica) all with less than 100 watts. I usually use CW because it is so aggravating and it makes life more interesting.

One final touch.  I connected 20 empty beer cans to a wire, and connected that wire to the copper foil (see photos). 
There are several benefits to this system: (1) It works well; (2) no one visits me because my apartment is cluttered with copper foil and beer cans, and (3) I have an excuse to generate more empty beer cans in an effort to increase the efficiency of the RF ground system.  I have calculated that I can increase my effective radiated power by 2% for every 45 beer cans. I now have 73 beer cans connected in AEGIS (Altman Effective Grounding Improvement System). Listen for me on 40 meters.

Best Regards,
Gary, K4NNK 
Excerped from my article in QST magazine, March 2005, page 53.
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W8LV
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Posts: 311


WWW

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« Reply #1 on: January 13, 2019, 06:53:23 PM »

Very interesting! I always wondered if the MFJ "Artificial Ground" was just an Antenna Tuner in Disguise...

73 DE W8LV BILL
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VA2DV
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Posts: 169




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« Reply #2 on: January 30, 2019, 08:24:54 AM »

Is light beer cans less effective on DX ?  Grin
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WW7KE
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Posts: 930




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« Reply #3 on: January 30, 2019, 06:17:00 PM »

Is light beer cans less effective on DX ?  Grin

I hear cans of IPA are preferred for working India.  I'll be more than happy to help anyone empty them -- you know, to prepare them for use as an antenna. Grin
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He speaks fluent PSK31, in FT8...  One QSO with him earns you 5BDXCC...  His Wouff Hong has two Wouffs... Hiram Percy Maxim called HIM "The Old Man..."  He is... The Most Interesting Ham In The World!
K4NNK
Member

Posts: 7




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« Reply #4 on: January 31, 2019, 03:06:42 PM »

Two excellent technical questions have been posted.  One from VA2DV and one from WW7KE.
1. Yes, it takes about 3.4159X more cans if the beer is light.
2. You are correct: IPA beer can could be an excellent antenna component for contacting India. What is the resonant frequency for one beer can? Is it about 5 gHz? Maybe moonbounce should be considered.
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