[Top] [All Lists]

Re: [TowerTalk] Physically Noisy mobile antenna

To: "K8RI" <>, <>
Subject: Re: [TowerTalk] Physically Noisy mobile antenna
From: Eric - VE3GSI <>
Date: Wed, 7 Dec 2011 20:46:33 -0500
List-post: <">>
Hi Roger,

I use a 'Super Gainer' and have not had a problem with the base fold-over 
joint.  But, I have had problems with noise which I traced to the joints 
where the rods go into the phasing components. So now, every spring I  take 
the antenna completely apart and clean each joint with emery paper and a 
wire wheel.  While at it I clean the fold-over joint as best I can and so 
far no problem there with mine.

Two words of caution, over time (mine is about 9 years old now) the top 
phase inductor is showing its age and has cracks in it. Liquid epoxy seems 
to have temporarily fixed the problem for now, and yes I know epoxy is not 
UV stable. Also a fellow Ham I know accidentally broke the bottom matching 
section. He was sure the fold-over joint was frozen and when trying to free 
it,  it broke.

As far as the specs, the max power is around 150 Watts. <grin>

Good Luck,
Eric - VE3GSI.

----- Original Message ----- 
From: "K8RI"
> There are several rather tall duo band (144/440) mobile antennas that
> work very well be they on a mag mount of more conventional, but the top
> of the line are rather tall and they have a "fold over" feature in the
> base for getting into "those parking ramps".  I have one of then, the
> Diamond "super gainer SG7900 in front of me.  It works great BUT with
> time they develop some play at the base where the fold over mechanism is
> located.  This almost has to be from the normal, day-to-day movement of
> the antenna wearing where to two pieces come together. The surfaces are
> tapered and make a good solid connection...for a while.  Eventually I
> start hearing a knocking sound whenever going over an uneven surface,
> particularly at low speeds  As the car rocks the knocking can get quite
> loud and annoying.  Uneven parking lots or speed bumps not crossed
> perpendicular are particularly annoying.
> Now I can take the base apart and lap the two surfaces into a very good
> fit and there is a fair amount of room to do this before I'd run out of
> material. I've also though of defeating the fold over feature with a bit
> small bit of epoxy, or even a sleeve of flooded heat shrink tubing over
> the junction. These would work but it would defeat the fold over and I
> just might need to pull it into the shop or garage to work on the car.
> Now this is a 5' antenna (155CM) on top of a 6-6 1/2foot tall SUV.  That
> means the thing sticks up about 11 feet and makes for a lot of places I
> can't go with the antenna up.  It also subjects the antennas to much
> more physical abuse than they'd see on a car at about half the height.
> When that SUV rocks the base of the antenna really whips it around. Once
> the base to antenna joint loosens to the point where the antenna rocks
> enough to hear it really starts to beat up that junction.   As it is a
> mag mount I can remove it if I eliminate the fold over feature, but that
> too is a royal PITA pulling the coax off the roof (it routes through the
> luggage rack and down the weather seal inside the door and involves a
> partial disassembling of that rack. It doesn't take long, but it's just
> one more thing that has to be done.
> I think the lapping is probably the most effective and useful of the
> methods, but it is also the most work AND requires careful cleaning of
> the parts to get all of the abrasive out to prevent accelerated wear. I
> basically have to disassemble the base to thoroughly clean out any left
> over particles and getting that threaded pin back in with that spring
> under tension is also a good way to lose parts. Fortunately I use a
> water based lapping compound so it's much easier to rinse out using hot,
> soapy water than an oil based compound would be.
> BTW Either the Comet or Diamond versions will allow me to run the 160 to
> 200 watt amp when out in the boonies.  I never tried to see just how
> much the antennas would take before smoking.
> Any one else ever run into this problem?
> Any opinions or suggestions?
> 73
> Roger (K8RI)


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>