[Lowfer] Isolation Transformers

Tue, 20 Aug 2002 12:40:14 -0400

Hi Les,

I'd like to help out but it's difficult to suggest grounding and isolation 
schemes without really knowing all the details of what your system looks 
like. What works for my setup may be totally wrong for yours. Can put 
together a schematic diagram of your antenna/ground connections with MS word 
graphics or similar program and make it available on your Web site?

I should set up a Web site of my own, if for no other reason than explain 
solutions to similar problems, schematically. Seems to be an ever expanding 
problem here at work - too much discussion of electrical problems using 100s 
of words rather than a simple diagram. The younger guys, the ones with the 
most computer savvy, seem to have the most problem using simple pencil 
diagrams. I think we have forgotten that one picture is worth 1K words.

Bill

>From: "Les Rayburn" <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>Subject: Re: [Lowfer] Isolation Transformers
>Date: 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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