[WriteLog] PC / WriteLog audio setup

[Dave Hachadorian]

On Thu, 9 Oct 2003 08:14:56 -0400 "Bob McCormick W1QA"
<writelog at W1QA.com> writes:

> We get audio through to the rig ... but as one may expect,
> with all the levels cranked up its pretty crappy quality.
> 
> My observation is that the problem lies with the input;
> in using the Windows Sound Recorder applet ... do not
> get much amplititude deviation in the graphic window.

The Heil mic has a relatively low output, but sound cards
with a 20dB boost are usually good enough. Try listening
to the sound card output on a set of walkman-type headphones.
That's a good way to see if the distortion is in the sound
card or the rig interface.

You can also use a cheap computer mic to do the recordings.
They usually sound pretty good on the air, and have plenty
of output.



> 
> Is a simple pre-amp like what's referred to on the 
> epanorama.net web site all that's needed?

I would try the two methods above first. I'd be worried
about rfi problems during the contest with a preamp.

> 
> Additionally, I found a reference that suggested 
> the following circuit as input to the rig's audio:
> 
>     <--)(----+
> L o    )(    R1
> i u    )(    +---R3--->
> n t    )(    R2         FT1000MP
> e   <--)(----+-------->
> 
> R1=470 ohms  R2=100 ohms  R3=2.2k ohms
> 600 ohm 1:1 Radio Shack transformer

That looks pretty good to me. You do need some sort of attenuator,
isolation, and impedance transformation at the mic input. This ckt
should do it.

Dave Hachadorian, K6LL
Yuma, AZ