[RTTY] RadioShack isolation transformer replacement

[Eric - VE3GSI]

Hi Don,

I have the R/S 270-054 isolation transformer and use it from time to time 
for testing on the bench. When ohmed out it has NO DC connection between any 
of the separate circuits, that  is left/right or in/out so it is total 
isolation.  Mine came with a RCA to 1/8" stereo adapter.

Another source of interface/isolation transformers. I went to one of the 
local Mom and Pop computer stores and asked for any old computer modems they 
were trashing.  Most (but not all) of these modem boards have a ~600/~600 
ohm isolation transformer that work fine for radio interfaces.  As for 
making the isolation cable with these PC mounted devices, I remove the 
transformer from the board, and simply solder a cable to each side, covered 
it with heat shrink and flooded it with RTV seal before hitting it with the 
heat gun.

Eric - VE3GSI


----- Original Message ----- 
From: "Don Hill AA5AU"

> Since I couldn't operate because of weather last night, I took time to 
> fabricate a RadioShack audio isolation transformer that I had
> in the junk drawer (was p/n 273-1374) into a small plastic project box 
> with two RCA jacks so I could use it on a 2nd radio for JT65
> AFSK transmission.
>
> Today I decided to check the local RadioShack store to see if they still 
> sold this transformer and I couldn't find it. I looked
> online on their website and that part number is no longer valid and I 
> could not find the transformer. Instead I found what they are
> calling a "Ground Loop Isolator". I have a strong suspicion that it's 
> basically the same thing built into an enclosure with leads
> coming out of it with RCA audio plugs. It's on their website as p/n 
> 270-054, shown here:
>
> http://www.radioshack.com/product/index.jsp?productId=2062214
>
> I wonder if anyone is using one of these to route audio to/from their PC 
> to their radio? Seems like a slick solution. I need to
> update my RTTY webpages if indeed this "Ground Loop Isolator" will replace 
> the old audio isolation transformer. I read through all
> the reviews. All but two were positive at getting rid of hum on audio but 
> all were from those using it with sound systems and none
> from hams. I see no reason why it wouldn't work for us hams.
>
> The only problem I see with it, is that you would have to use an RCA 
> female to 1/8" phono plug adapter in order to plug it into your
> PC sound card or else cut off the RCA plugs install your own 1/8" phono 
> plugs.
>
> Some of us still use homebrew interfaces and audio cables!
>
> Thanks!
>
> 73, Don AA5AU