Graham

I don't think impedance matching is as much of an issue as the level. From
what I can tell, Bill had it right. All it takes is a couple of resistors.
You got to reduce the level A BUNCH. I don't know if Bill's 100:1 is right,
I found the values for my Icom by experimentation, but it's pretty close.

Keep in mind that you want to run the computer's speaker volume pretty high
to reduce quantization error. If you adjust the resistance and mike gain so
that your power out is somewhat below max when you are generating SSTV, it
should be pretty close.

Digipan suggests a 100K in series and a 1K in parallel ... seems like I had
to get more extreme, but then I'm connecting up an Icom.

...

"G8YWL" wrote in message
...
Thanks Frank and Bill - I suspected that it was an impedance matching
problem but could not be sure - now I'll find someon's olf tranny

Graham

"Frank Dinger" wrote in message
...
Does anyone know how I can convert the output from a
speaker/headphones
jack
from a Laptop into a suitable input to the Mic socket of a TS430S?
It's
for
running SSTV

I have not been able to find anything on the net - probably 'cos I'm
asking
the wrong question.
===========================
The best way to roughly match the 2 impedances is to use any small
transformer which can pass SSTV audio tones.
It is not a critical matching

I don't know the microphone input circuit of the TS430S ,but you can
check
that by looking at the microphone itself.
Suppose that impedance is somewhere between 500 and 1000 Ohms and the
audio output of your Laptop 8 Ohms .

It means the impedance ratio is in the order of 800 to 8 is 100 ,so
the
winding ratio of the transformer should be in the order of sqrt 100 is
in
the order of 10 to 1. So you would have to find any (small )tansformer
with
that winding ratio ( meaning voltage ratio)

But again the ratio is NOT critical

If the TS430S would have a high impedance microphone in the order of 50
kOhms , assuming a low impedance output from the laptop of say 10 Ohms
the
transformer ratio would have to be in the order of sqrt 50000/10 =
sqrt
5000 = approx 70.

If you can't find an audio transformer for this application , just try
a
small power supply transformer ,since these will pass the low freq audio
sig
used for SSTV.

Good luck

Frank GM0CSZ / KN6WH