[Lowfer] Isolation Transformers

Mon, 19 Aug 2002 10:15:55 -0500

>From: "Lyle Koehler" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: Re: [Lowfer] Isolation Transformers
>Date: Mon, 19 Aug 2002 09:11:15 -0500
>
>I'm not sure if isolation transformers alone will do a lot of good when you
>still have a DC path to the antenna via the power and tuning lines. With a
>good ground system at the antenna site, it's likely that a combination of
>isolation transformers on the coax, and chokes in both the power and ground
>lines would be effective in reducing the conducted noise from the shack. 
>The
>chokes could be something like 1 mH on MF; larger on LF if you can tolerate
>the DC resistance. It's important to stay below the self-resonant 
>frequency.
>There should also be isolation in the tuning line. Since the tuning circuit
>is usually high impedance, you can put a big resistor like 100k in series. 
>I
>haven't actually tried this kind of isolation, but theoretically it should
>work. Maybe others on the reflector have some practical experience with
>isolating remote-tuned preamps that are powered from the shack.
>
>Lyle, K0LR

Lyle,

Keep in mind, you're dealing with simple Simon here. Should
the chokes be in series (literally in line) with
the power leads? Do I need one on both the positive and
negative lead?

Do you know of a good source for these chokes? The only
one I know of is the 100uh that Radio Shack sells, though
I'm sure there are others out there.

Also, I have a rotor (three wire, tv type) mounted to
rotate the loop. Whenever I apply the power, it puts
out an awful hash on LF and MW. Is there anyway to
reduce or eliminate this?

Also, I'm powering all the remote amps via batteries to
reduce any coupling to the shack...

Thanks (as always)

73,

Les

Les Rayburn, director
High Noon Film & Interactive
100 Centerview Drive
Suite 111
Birmingham, AL 35080
(205) 824-8930
(205) 824-8960 FAX
(205) 253-4867 MOBILE
http://www.highnoonfilm.com

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