[Lowfer] Operating from 12VDC battery full time.

[Rye Gewalt]

Les:

I experienced the same thing with my AR3030 receiver which can run off of a 12
volt battery quite easily.  I think what you are experiencing is the dreaded and
much talked about ground loop(!!).  I spent quite a bit of time messing with my
setup in a similar noise situation with the receiver and preamp running off of
separate batteries -- one at the receiver and one at the antenna.  The ultimate
solution was isolation transformers -- cheaper and easier too.

I now have a 1:1 wideband isolation transformer in the antenna coax line between
the preamp and the receiver  and I also have a 600 ohm 1:1 modem transformer
(radio shack) in the audio line to the computer.  My current wideband isolation
transformer is a  10Hz - 5Mhz North Hills 0017CC (big bux) that runs with 50 ohm
cable -- insertion loss is really unnoticeable and not a problem since it is after
the preamp.

I wound a similar wideband transformer on a 1.25" diameter 43 material toroidal
core (not critical size) and got very similar results -- I just have not had time
to package it a nicely as the North Hills.  I wound two windings of about 30 turns
of convenient wire (#24) on each side of the toroid -- don't wind bifilar since
the objective is to  minimize interwinding capacitance.  My measured insertion
loss was nearly zero at 180KHz but I don't know if it's flat across the spectrum
like the North Hills unit, but it's surely OK for the 160-180 band.   A good trick
is to stick the transformers noted above in the RF and Audio lines and then switch
from AC to battery to see if there is any difference.  After a few permutations of
removing transformers and measuring, you will get the idea of what works and what
doesn't.   It's well worth the exercise and you can probably forget about the
battery lash-up.

The idea is to keep ground currents (noise) from flowing in the shields or returns
of the low level lines and coupling into the desired signal.  It's part art and
part science.....

There is an incantation that you have to mutter while looking for ground loops,
but I can not repeat in this public forum.  If the transformers don't work, I can
recite it to you over the phone on the next night of a full moon.  You will of
course have to have a special hat too......

Regards
Rye K9LCJ
Springfield, VA

Les Rayburn wrote:

> Tonight I was testing my new set up for emergency operation preparing for
> an upcoming
> MARS net. I've just purchased a large, deep cycle marine battery for
> powering the
> shack. Made up some cables with quick disconnect fuses, etc.
>
> When I switched from the power supply to the battery the noise floor on 518khz
> the noise floor dropped quite a bit! Tuning around a bit, I was really
> surprised, considering
> that I use a very large, (non-switching) type power supply, with lots of
> filtering...the
> AC is filter and conditioned, etc. But there was the proof, a much quieter
> receiver.
>
> Now my mind is racing at the possibilities for improved weak signal
> reception. I have
> also purchased a plastic marine box and automatic charger, which I had planned
> to install just outside the shack window so that the battery could be kept in
> a fully charged condition.
>
> My question now is, is it possible to operate the station from the battery
> full time,
> with the charger connected and protected, perhaps by diodes or something?
> Have others tried this!!!??
>
> 73,
>
> Les Rayburn, N1LF
>
> Les Rayburn, director
> High Noon Film & Interactive
> 100 Centerview Drive
> Suite 111
> Birmingham, AL 35216
> (205) 824-8930
> (205) 824-8960 FAX
> (205) 253-4867 CELL
> http://www.highnoonfilm.com
>
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