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Author Topic: Mag mounts  (Read 2827 times)

Posts: 4

« on: April 16, 2001, 09:12:31 PM »

How well does an HF mobile antenna work on a single mag mount?  Would using a 3 magnet mag mount work better due to the added coupling to the car body?  Thanks, Jerry  K8gww <

Posts: 21764

« Reply #1 on: April 17, 2001, 11:18:15 AM »

You've guessed correctly, for the most part.

You didn't mention which HF band(s) you're interested in working with the mag mount, but in general:

10m isn't too bad with mag mount...
80m is absolutely horrible...
And the bands in between fall in between, with regard to performance!  That is, 12m not quite as good as 10; 15m a bit worse; 17m a bit worse than that, etc.

In my experience, having tried almost everything imaginable for mobile HF operation, I'd probably only use a mag mount on 10 or 12 meters, and think of something else for the bands below 24 MHz.

However, I have also found, as you guessed, that the "large" mag mount bases that have multiple magnets (I've tried 3-mag and 4-mag versions) are not only a whole lot stronger (!!) but also do perform a bit better on the lower frequencies, obviously due to more effective coupling to the vehicle's sheet metal.

Since most effective HF mobile antennas are also fairly large and catch a lot of wind at 70mph, a single magnet base antenna probably isn't sufficient to hold one in place, anyway!  I currently use a Tenna Hitch product, which is a 3/8"-24 antenna mount that is installed in a very thick piece (about 1/4" thick) of aluminum stock that mounts between a trailer hitch and the hitch ball, forming an extremely strong base.  Although that system is quite well grounded by virtue of tightly clamped metal connections, and the hitch itself being welded to the frame of my car, I do use paralleled copper braid between the antenna base and the car frame, going to two additional locations, to promote an even better ground.

Using that simple mounting system (cheap and easy, if you happen to have a trailer hitch already), I've tried a wide variety of 3/8-24 base antennas, all of which seem to work quite well -- with results following the obvious rule, "the bigger, the better."  (That is to say, taller antennas with lower-loss loading coils do work better than shorter antennas using ordinary wire loading coils.) However, I don't notice the unbelievable 10-20 dB antenna variations that I hear some discuss.  It seems to be more like 3-6 dB variance from the best to the worst, as long as they're mounted on the hitch mount and tall enough to see over the car roof.

Have fun mobiling!

73 de Steve WB2WIK/6

Posts: 3

« Reply #2 on: June 08, 2001, 02:42:00 AM »

I haven't been on the site for a while, but about 8 years ago I built what might have been a one of a kind, and ordered 8 3" magnets, and mylar coverings from Hustler down in Texas, and built a crossbar network using 1" flat stock 1/4" thick aluminum; I run a Swan 45 in the middle, and 4 other smaller antennas off to the sides.......the only hf band that I operate on at night is 75 meters, and 40 in the daytime.

The best compliment I was ever paid was on 75 one night while a few miles south of the grapevine a friend of mine asked me what I was up to and I told him that I was going to a ham swap in Livermore, and he exclaimed "you mean that you're mobile, I thought you were at home on your base".  I run a single 4-1000 amp at home, and I was running 100 watts out of my Icom 706 at the time he said that.

One of the things that I did was that I didn't rely soley on the capacitive contact to the roof, I ran 4 1" flat silver braid strips from the mount to the inside the door posts of my 96 Impala, exactly the same way I did on my 89 Caprice; now the same setup is about to go up on the roof of my 2001 Suburban, and for the first time ever the Swan is going to get a kw run through it, which shouldn't be a problem its rated for 2kw pep.

So, the point of my response is don't believe people who say you can't work the lower bands mobile......I have a friend who's been working 160 mobile longer than the 21 years I've been a ham.

Another well kept secret to my setup is that I don't use a tuner or an inductor, but a single 500pf 15kv doorknob (lpn type)cap shunted at the gives me a 1.5 to 1 on 75, and a 1.2 to 1 on 40; if I worked higher freqs I'd have to unscrew it....that takes about 5 seconds.  I am a total believer in shunt grounding because it works extremely well, and even though lossy inductors are much more popular; I personally could care less what is popular.  73 and good luck on your mobiling endeavors.
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