[Lowfer] Isolation transformer, Computer noise, etc.

[Andy - KU4XR]

--- On Thu, 1/21/10, Mike.WE0H <we0h at gmx.com> wrote:

> On those audio 1:1 isolation transformers, dig inside a old
> computer  power supply and find a 1:1 transformer with a whole 
> lot of inductance on each side. Use that. Problem solved. 
> My audio transformer is about 5 millihenry each side. 
> Been working great for 7 plus years.
> 
> Mike
> WE0H


Hey Mike:

I did the 600 Ohm - 1:1 transformer from Rat Shack in the audio
line going to the sound card. I put it on the sound card side of 
course, and It really did clean up the audio into the Computer.
My DSP software filter has a spectrum display, and I had lots of
little " Spikeies ", after inserting the transformer; No More
" Spikies " !! 

Thanks for your input :::

Andy - KU4XR - EM75xr - Friendsville, TN.
LOWfer Beacon " XR " @ 185.29866 KHz ( QRSS-60 )
Coordinates:  N:  35* 43' 54" - W:  84* 3' 16"
http://www.myspace.com/beaconxr
http://webpages.charter.net/ku4xr/


--- On Thu, 1/21/10, Mike.WE0H <we0h at gmx.com> wrote:

> From: Mike.WE0H <we0h at gmx.com>
> Subject: Re: [Lowfer] Isolation transformer, Computer noise, etc.
> To: "Discussion of the Lowfer (US, European, & UK) and MedFer bands" <lowfer at mailman.qth.net>
> Date: Thursday, January 21, 2010, 2:34 PM
> Hey Andy,
> 
> Turn the computer off and unplug the power supply. Is the
> noise gone 
> now? Build a 1:1 broadband transformer for your feedline.
> That will stop 
> the common mode noise you have. I did years ago, no noise
> now. I'd like 
> to say someone said years ago that you want 4x the feedline
> impedance 
> for the primary & secondary of the transformer.
> 
> How about this easy idea, wind 10 turns each side
> interweaving the turns 
> on a FT240-77 core. That should be enough inductance on
> each side to 
> work for your LF setup. You could use a much smaller core
> if you like 
> but use -77 material. On your HF antennas, use a -43 core.
> Stick with a 
> FT240-43 core for the typical 100-200w rig. It should work
> fine.
> 
> I found one other possible noise source hear many years ago
> and that was 
> the negative terminal on my bench power supply was tied to
> the A/C mains 
> ground. It isn't anymore.
> 
> On those audio 1:1 isolation transformers, dig inside a old
> computer 
> power supply and find a 1:1 transformer with a whole lot of
> inductance 
> on each side. Use that. Problem solved. My audio
> transformer is about 5 
> millihenry each side. Been working great for 7 plus years.
> 
> Mike
> WE0H
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