K2 KIO2 Serial Data causes RX Interference

[Stephen Arnold]

Hi All,

I hope that someone out there might be able to help me with this one.

What I have is a basic K2 with KAT2 internal tuner (KSB2 and KBT2 are also
installed). Then I also have the KPA100 outboard in a EC2 with the
KAT100-2.

To say it another way (without all those K's ;-) what we have is the "K2
Twins".

All works very nicely (thankyou Elecraft!!) except that I am now starting
to play with digital modes.

I have the K2 connected to an Asus Eee PC running Linux (Mandriva 2008.1).
When I run the fldigi software and tell it to use hamlib to perform rig
control everything works perfectly BUT...

I now have RX audio interference. It sounds like a low volume puffing
steam train or a chuff-chuff type noise. It is pretty obvious what is
causing it. The constant serial data stream being sent by the fldigi
program.

The interference is all bands and all frequencies so far as I can tell. It
is very low level but quite audible and would drive you mad if you tried
to use the radio for any length without turning the volume down. Needless
to say it will no doubt play havoc with weak digital signals.

Questions is: Am I looking at a fault in my particular K2 set-up or just a
design limitation? (you would never notice the issue except for the
constant polling by fldigi). And how does one go about trying to fix the
problem?

Any ideas, anyone?

73, Steve
VK2SJA



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[Julian, G4ILO]

Stephen Arnold wrote

Hi All,

I hope that someone out there might be able to help me with this one.

What I have is a basic K2 with KAT2 internal tuner (KSB2 and KBT2 are also
installed). Then I also have the KPA100 outboard in a EC2 with the
KAT100-2.

To say it another way (without all those K's ;-) what we have is the "K2
Twins".

All works very nicely (thankyou Elecraft!!) except that I am now starting
to play with digital modes.

I have the K2 connected to an Asus Eee PC running Linux (Mandriva 2008.1).
When I run the fldigi software and tell it to use hamlib to perform rig
control everything works perfectly BUT...

I now have RX audio interference. It sounds like a low volume puffing
steam train or a chuff-chuff type noise. It is pretty obvious what is
causing it. The constant serial data stream being sent by the fldigi
program.

The interference is all bands and all frequencies so far as I can tell. It
is very low level but quite audible and would drive you mad if you tried
to use the radio for any length without turning the volume down. Needless
to say it will no doubt play havoc with weak digital signals.

Questions is: Am I looking at a fault in my particular K2 set-up or just a
design limitation? (you would never notice the issue except for the
constant polling by fldigi). And how does one go about trying to fix the
problem?

Any ideas, anyone?

I have used a K2 on data modes for years without observing anything like you describe. I doubt that it is anything in the K2 that is causing the problem.

My experience of USB devices is that some of these can cause low level wide band interference. I once had the bright idea of using a cheap USB soundcard as an extra audio input for a second receiver - the noise it generated more or less wiped out the signals I was trying to decode.

So my guess is that your USB to serial connector is the culprit.

[Vic K2VCO]

Stephen Arnold wrote:

> I now have RX audio interference. It sounds like a low volume puffing
> steam train or a chuff-chuff type noise. It is pretty obvious what is
> causing it. The constant serial data stream being sent by the fldigi
> program.
>
> The interference is all bands and all frequencies so far as I can tell. It
> is very low level but quite audible and would drive you mad if you tried
> to use the radio for any length without turning the volume down. Needless
> to say it will no doubt play havoc with weak digital signals.
>
> Questions is: Am I looking at a fault in my particular K2 set-up or just a
> design limitation? (you would never notice the issue except for the
> constant polling by fldigi). And how does one go about trying to fix the
> problem?

This is present with a non-split K2, although at a low-enough level that
it is masked by band noise. It is generated by the RS232 chip in the K2.
Apparently your setup is such that the noise is being radiated by the
control cables and somehow is getting into the antenna.

What might help is to wrap the control cable between the K2 and the
KPA/KAT in the EC2 around a chunk of ferrite. I am not sure what the
best location would be; try near the radio and near the EC2. You might
also do this to the cable that goes to the computer.

Clamp-on ferrite beads will probably not help unless you have one with a
hole big enough to wrap several turns of the cable through.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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