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Re: [TowerTalk] Roof mounting 5BTV

To: TowerTalk <>
Subject: Re: [TowerTalk] Roof mounting 5BTV
From: "Alan C. Zack" <>
Date: Mon, 08 Nov 2004 11:37:35 -0800
List-post: <>
May I suggest for a limited space antenna the MFJ-1786 loop. It covers all freqs between 10 and 30 mhz and is 3 ft (36 inches or 1 meter) in diameter.
I used one that I disguised as a T.V. antenna on my roof top in a HOA CC&R home and worked DXCC and all the contests. It out performed a R-7 that was later replaced by a R-7000 mounted on a 10 ft pole as recommend by Cushcraft.
I have attached a pic of the antenna to give you an idea of the installation. Those of you who are CC: should be able to see the pic although the list won't see it due to attachments being rejected.

I would also suggest the R-7 or R-7000 or their later versions over the 5BTV as they do not need the long radial wires at the base since they are 1/2 wave antennas vs 1/4 wave for the 5BTV.

My humble opinions only. Good luck.

David Jones wrote:

Great stuff as always.
Have a similar scenario about to happen here.  Just moved to a smaller lot
and for the next few years a tower is not part of the plan, so a vertical in
the backyard (with many radials) will have to do.

With respect to your question about the 5BTV and the manuals suggestion of
two coax chokes, assuming a vertical mid-backyard, about 20ft from the house
with coax going to a basement shack, and your suggestion of putting the
choke further from the base to avoid radial coupling...
a) Could you get by with simply one choke at the basement wall as the coax
enters the shack (given some of the radials will be that long and longer)?
b) Do what the manual says and put one at the base and one at the basement

David VE3STT


Message: 1
Date: Sun, 7 Nov 2004 19:57:46 -0500
From: "Tom Rauch" <>
Subject: Re: [TowerTalk] Roof mounting 5BTV
To: "R. Kevin Stover" <>, <>
Message-ID: <008801c4c52d$f61ccfa0$>
Content-Type: text/plain; charset="iso-8859-1"

The manual tells me that I should use 2 feed line chokes,

one at the

antenna and one at the radio. I'm planning on using a pair

of Radio

Works T-4 1:1 current "line isolators" instead of the


That'll work OK.  Those devices have an impedance between
500 and 2000 ohms over HF, so that'll be enough.  I would
NOT put one at the antenna and one at the radio, however.
I'd put one where the cable leaves the area of the radials
and one before it gets into the house, if you need it.

Here's the reasoning behind what I say...

You have a roof mount installation. If you put a choke right
at the antenna, the feedline will parallel the radials for
some distance.  That means the radials will couple to and
excite the feedline anyway. If you put that choke at a point
where the radials are at least a little distance from the
radials, that won't be as much of a problem.

The next choke would go outside the house. The reason for
this is simple, you don't want to bring common mode currents
and associated voltages into the house next to your radio.
Keep the unwanted voltages and currents outside.

One section of the manual has me a little confused though.


instructions say to RF isolate the antenna from the

mounting mast if the

mast is an appreciable fraction of a 1/4 wavelength in

frequency. The

tripod and mast will be 5ft tall. I've also noticed that

there is no

ground connection on this antenna. Is this correct?

Normally the base is grounded. Grounding the antenna to the tripod won't hurt a thing, as long as the tripod is not grounded. Even if it was 1/4 wl long, it would just act like another radial. I wouldn't worry about that at all. I assume you will have the radials attached to the antenna base as a common connection point??

This setup will be a temporary lash up to get me through

the winter when

I hope to be able to get a new tower and beam installed at

the new QTH.

If the vertical works well it will become my backup on the

higher bands.

We did that on a friend's house, and it became his permanent

73 Tom


Alan Zack
Amateur Radio Station K7ACZ
Las Vegas, Nevada, USA
Quality Engineer, The Boeing Company, Retired
Aviation Chief Warrant Officer, U.S. Coast Guard, Retired
U.S. Coast Guard, Always Ready, Always There
Every hour, Every day, Around the Clock and Around the World

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