[Elecraft] K2 SSB module help

[Don Wilhelm]

Bob,

You did not say what kind of interface you are using between the soundcard
and your mic input, so I will try to give a 'generic' response (that means
it may be right in some cases, but not for others).

That resistor puts +5v bias onto the mic AF pin - and is not an unusual
requirement for electret mics.
Your PSK31 interface must be isolated for DC to work properly in the
presence of this bias voltage or strange things will happen - many
interfaces are isolated for DC, but not all - if you are feeding bias
voltage back to your soundcard output, things may not work correctly at the
soundcard end either.

Some interfaces isolate the ground path with a transformer or opto-isolator,
but I have seen some implementations that could have trouble with a DC bias
applied.  Check the schematic of your interface to see if the +5 volts
(through the 5.6 k resistor) will cause any ill effects - or you could
simply put a capacitor in the PSK31 interface if there is not already one
there - a 10 uf 16 volt aluminum electrolytic should do the task, but
greater voltage or greater capacitance should work too - use what you have
in the junkbox.

If your interface is already DC isolated, you may have to increase the input
level a bit - for AC signals, that 5.6k resistor is electrically in parallel
with the microphone input - just the same as adding an additional resistor
to ground across the mic input of the K2.

73,
Don W3FPR

----- Original Message -----

> Eric,
> I am having trouble to get my K2 S/N 2062 to accept  PSK-31 modulation
> from my computer. It worked fine until I installed a MH2 Heil microphone.
> Your reply to Terry, W0FM of 11/23/03 about having to be sure that a
> 5.6K resistor was installed between pins 1 & 6 of the mic plug twigged
> as to possibly why my PSK-31 mode is no longer working. As indicated it
> worked just fine before adding this resistor to use the MH2 mic.
> To save me the trouble of tearing the rig apart and removing this
> resistor to try it, perhaps you could offer your opinion as to whether
> this is my problem.
>