[TowerTalk] Roof mounting 5BTV

[Alan C. Zack]

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:

> Tom,
> 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
> wall?
> 
> David VE3STT
> 
> 
>>----------------------------------------------------------------------
>>
>>Message: 1
>>Date: Sun, 7 Nov 2004 19:57:46 -0500
>>From: "Tom Rauch" <w8ji at contesting.com>
>>Subject: Re: [TowerTalk] Roof mounting 5BTV
>>To: "R. Kevin Stover" <rkstover at mchsi.com>, <towertalk at contesting.com>
>>Message-ID: <008801c4c52d$f61ccfa0$6501a8c0 at akorn.net>
>>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
>>
>>chokes.
>>
>>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.
>>
>>The
>>
>>>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
>>antenna.
>>
>>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
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