I had been looking for a portable antenna design for some time when I spotted an interesting article in the Nov 2002
issue of CQ magazine. My portable operating experiences to date convinced me that a short wire hanging down the side of a motel,
and a short counterpoise inside the room wasn't an effectve antenna system. What I really needed was a good balcony, picnic table, or mobile
K4VWK's article caught my attention because he mentioned a coax counterpoise. He expanded on a counterpoise concept
suggested by DL7PE in AntennaX Magazine. The counterpoise is made from a piece of coax in the feed line. The center
conductor conductor connects to the antenna and the shield is OPEN at the antenna end, only the center conductor
attaches to the antenna. The other end of the counterpoise is attached to the feed line. An RF choke is installed
in the feedline between the counterpoise and the rig. There is no radiation from the counterpoise so it can be
coiled up or strung any which way around the room , car, balcony, camper, picnic area, etc... This thing may answer
my needs for a portable antenna system.
I built the counterpoise by soldering the center conductor of a 1 foot piece of RG-58 to a PL-259 leaving
the shield 1" short and connected to nothing! A piece of heat shrinkable tubing provided a little stffness and
protection for the center conductor. This end is screwed onto the antenna mount. The other end has a coupler for
the rest of the counterpoise to mate with. Using the formula in Scott's article, L=190 / f (Mc). I made up a
jumper of RG-8X for 15M and 20M, subracting a foot for the antenna "pigtail". The feedline choke is my old standby,
10' of 8X coiled in a 7 turn coil.
Now for the antenna. I just had to homebrew something here so I made up a "take down" version of a Hustler mobile
mast. It's 54" of 1/2" copper pipe, with 3/8 x 24 bolts soldered into end caps. I put a coupler in the middle so it
could be broken down to enhance portability. Capping off the top of the mast is a Hustler 15M resonator and it's
screwed into a standard whip mount by Firestick (only $4.00). The mount is bolted to a 2" x 6" piece of 1/8"
aluminum for clamping to something.
Performance..... The whole shebang is clamped to the railing of the steps leading down to our llama barn, which makes
it about 3' off the ground, between a spruce tree and the house. My first contact was KØUSJ, Bob in Sun City AZ.
He could barely hear me and he was only about an S5 himself. The next contact was KAØZZO, Bill in Palm Springs, CA.
He was an S7 here and I was S6-7 on my 322' dipole, and S3-S6 on the short vertical.
The antenna performs a little better on 20m. Changing the resonator and counterpoise resulted in a very broad banded
20M short vertical. The swr is 1.2:1 at the top of the band, 1.0 in the middle and 1.1 att he bottom. Not bad for an 80" long antenna! W5KID in Baton Rouge reported S9+4 (not 40) with the big dipole and S9 with the SVCC (short vertical coax counterpoise, my term). W5KID is a WW2 destroyer museum ship. KL7/K1YS, North of Anchorage reported 1 S unit difference. Both were at 14.260 Mc. Remember it's clamped to a railing only 3' off the ground.
So give the SVCC a try if you like to experiment, I tried it out from the balcony of the Villa Mirage resort in
Scottsdale, AZ, in March 2003, and made 29 contacts in 2 nights of operating. States worked included HI, CA, IA, TN,
TX, WA, OH and others. For what it's worth, the signal reports I received averaged 5x5.6, the ones I sent averaged
5x7.3, 1.7 S unit difference. The highlight was working my fellow hams from Ottumwa, IA during OARC's regular monthly
meeting at NØSM's QTH, using the club's call, WAØDX! See the pictures at the right
I'll be doing more comparisons both on 15 and 20M. Stay tuned, I'll share my results if you're interested. This is
a promising portable antenna for camping, mobile, and motel operating. If you'd like more test info, email me - I 'll
send you an Excel spreadsheet with additional data including 2 & 3 wire counterpoise comparisons...
Thanks to Scott Harwood, K4VWK for publishing the CQ article. He also has some interesting ideas and results on
short CCD antennas. They have some real promise as portable antennas too
The pictures show the SVCC on the balcony in Scottsdale.
Revised 2 Dec 2012
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