K3 twin & audio noise

[N5NYM]

We have successfully set up a K3 Twin remote installation and CW is working well, as well as a remote interface to the SteppIR via RC-1216H.

Unfortunately we have a bad noise problem with SSB audio- it is much noisier than the modulated voice on xmit... And there seems to be a distinct hum in the receive audio as well.

We are using a Kenwood mic in lieu of the Elecraft unit; but, have tried JMP1 both open and closed (per the docs) to no discernible difference.  As there is a hum in the receive audio I don't think the mic setting is necessarily to blame.  Suspecting power supply issues both RRC's are connected to the switching power supplies powering the rigs so I don't think power is a problem either.  We are acquiring an Elecraft mic; but, I am not confident that will solve the problem.  All of our jumper settings have been double checked. All cabling is new and was supplied with the new RemoteRig gear. Strapping is via the K3 Twin PCB's.

I expect the solution will be a simple one; but, we are at a loss at what to try next.

Any thoughts or suggestions are welcome...

Thanks & 73 de N5NYM

[dj0qn]

There are only two areas I am aware of that can cause that type of problem and you may have
already addressed them.

Since the microphone audio is only done in hardware, there are no RRC settings as such that can
affect this. The two possibilities would be the power supply and the red straps (not jumpers).

My hunch is that one of your strapping PCB's is not making contact in at least one hole. I would use
an ohmmeter to check all the connections to verify.

73,
Mitch DJ0QN / K7DX

[NA6O]

It's pretty unusual to have hum with your kind of setup...

On the Control side, the CODEC gain settings need to be appropriate to the mic you are using: higher gain for a dynamic mic, lower for an electret. And on the radio side the same is true, but usually it's more a problem of avoiding overload (excessive gain) rather than not having enough gain and ending up down in the hum/noise world. Also set the CODEC HPF to something like 163 or 204 Hz. Might be worth a few tests.

As Mitch said, solid connections everywhere are always important. A bad shield connection would certainly be bad news.

I assume you're using only the shortest possible audio cable connections, i.e., no extensions.

One other thing comes to mind and that is proximity of the RRC to something containing a large power transformer, which can magnetically couple hum into audio equipment.

73
Gary NA6O

[N5NYM]

We had presumed that since the mic worked fine with the K3, that it would also work fine with K3 default settings on the RRC.  No extension cables are in use anywhere... 
We will verify the pcb strapping with a multimeter and try varying the codec settings and report back.  Hopefully, that will put us on the right track.
Thanks & 73- N5NYM

[N5NYM]

We received the Elecraft mic and still have excessive broadcast audio noise. The recommended K3 twin settings are all in use and we did verify the pcb strapping as correct and ok.  We have physically relocated the control RRC away from the power supply as well as tried it via an alternate power supply.  None of this has been successful at eliminating the noise... 

Perhaps toroids are the next thing to try?

We have been working under the assumption that the noise originates at the control end; and, while I still think that is likely, is there a quick way to insure that our assumption is correct?  Remote power source has been isolated, cabling, settings, strapping and jumpers have all been verified at the remote RRC as well...

Thanks & 73 de N5NYM

[dj0qn]

You can let someone else try it out.

If you want me to try it out, contact me directly at dj0qn (at) darc (dot) de and I will try it from
my QTH. Otherwise, you may know someone already who has a K3/0 and can try it out.

BTW, I use the Elecraft microphone.

73,
Mitch DJ0QN / K7DX