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STEALTHIER VERTICALS FOR 10, 12 and 17 METERS
USING MOBILE VERTICALS by John, HI3/KL7JR
(Updated 10-29-2012)

Having trouble getting on the air because of restrictions or just a small space? You could invest in expensive small antennas to try, or do what I do and modify ham and CB vertical mobile antennas to get on the air. Just about any brand of ham or CB vertical will work with a little bit of patience in adjusting!

Being retired allows me the time to pursue the aspects of Amateur Radio I like the most, DXing and antenna experimenting. They go hand-in-hand for me. This late September 2012 experiment is based upon what all started this a few years ago.

http://www.hamuniverse.com/kl7jr10meterstealth.html

I learned quite by accident that if I broadened the ground plane of the antenna mounted on my wine barrel, (see photo below), the ground radials were no longer required (see FGT-2 info below) therefore making the antenna stealthier! This experiment was made using a MFJ 20M mini-vertical mobile antenna and a Wilson FGT-2 CB mobile vertical. Note that I did not have a 17m vertical, just an extra 20m stick. Here's what I discovered:

I unscrewed the MFJ's 20m mini-vertical tip top connector (made the antenna about 1.5 inches shorter) and now the resonant frequency is 17.060 MHz (was 16.4 MHz with it on and no whip attached). SWR 1.1, R 44 and X 4 with 34 inch radials when used as a vertical monopole.

These numbers are better than the FGT-2 when used on 12m. Now I was faced with the decision of cutting the antenna more to get it closer to resonating on 17m and ruining it or leave as is. I decided to go for it.

I cut an inch off the metal connector, then another 1/4 inch which gave me 17.985 MHz (SWR 2.4, R 27 and X 26). My tuner again should give me a good match on 17m now so I then can compare my loop (another stealthy antenna!) with the 17m monopole...I guess it is still a monopole vs. a vertical (?). Mine was black, so I spray painted it white to match my patio walls. As modified, the antenna is 23 1/2 inches long.

Now back to the FGT-2 without a tip and using a pair of radials at various lengths from 38 inches long to no radials at all with some surprising numbers....they are were about the same! This tells me the 20 inch diameter tin pizza plate I added to my portable wine barrel mount is acting as the radials! Good to know I don't need the radials which makes it stealthier! Oh, I re-grounded (saltwater corrosion!) the antenna mount (8 inch long aluminum angle) and the pizza tin to the barrel staves which really broadened the ground plane. As modified, the antenna is 25 inches long. Here's how similar the readings were:

FGT-2 w/o tip but w/38" radials....SWR 1.2, R 58 and X 4

FGT-2 w/o tip and no radials........SWR 1.3, R 60 and X 14


1. FGT-2 without a tip


2. MFJ 20M on left - Wilson FGT-2 on right

When used last year with the tuned radials, the CB vertical was 2 "S" units stronger than my 3/4 WL 20m loop, and I worked over 40 countries on 12m and 60 some on 10m! See March 2012 QST page 20.

So, come on propagation.....I am ready for 10, 12 and 17m using these short verticals! Update to follow. kl7jr AT yahoo.com

Update 10-29-2012 - Map showing contacts in Sept, Oct 2012 from Cabarete Dom Rep 3rd floor condo on whisky garrel.....Pdf file download here (rotate view counterclockwise after download!)

73, John HI3/KL7JR








 



  

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