Noise on TX with Anan 7000

[N8MW]

I have a constant digital type buzzing noise on TX when using the 1258 with directly connected ethernet cables to the routers.  This noise is loud enough to cause full rf power output when the mic gain on the radio is turned up enough to hear the audio from the mic at the control end.  This noise doesn't occur when the tx is keyed locally, even with the 1258 connected.  But as soon as the PTT is pushed at the control end and the radio goes into TX, the noise appears.  I have tried two completely different 1258's on both radio and control ends, and both sets of 1258's have the same behavior. I've tried different codec gains on the control unit and the same noise occurs.  I've tried different mics and connection cables with the same result. No noise problem with a mic connected directly to the same mic input on the radio(no 1258).  Only the PTT and Mic are connected at the control and radio units, and both grounds are connected. No noise on the receive audio at the control end.   I've seen many posts on the forum describing a similar problem, but no posted solution.    Please help.

[sm2o]

I guess it's related to the mic input of the Anan. The mic output of the Radio-RRC is a trafo, so the mic output is balanced. One end of the trafo is mic audio and the other is mic ground this works perfect in most radio which have a separate mic gnd input. I have no idea how the Anan is designed. The Radio RRC Mic output schematic is shown in the manual

73 de mike

[N8MW]

Yes, the Anan 7000 mic and PTT have a common ground.  If I disconnect the RRC PTT wire from the Anan, there is no more noise.  How can I work around this with the RRC?  Would an isolation transformer for the Mic help? What is a trafo?

[N8MW]

I am thinking of an isolation relay for the PTT.  How much current can the PTT sink?  What is the value of R115?  Can it handle 12VDC?

[sm2o]

Trafo is shortform for transformer. Yes you can use a small relay or even better a opto coupler for the ptt. You can use 12v relay. The FDV301 can sink 200 mA

Mike

[N8MW]

OK great.  Can you explain how a common ground can cause the noise in the mic circuit? Can the mic output circuit in the RRC be modified to prevent this?

[sm2o]

It's a Anan problem, nothing can be better than using a isolation transformer for the audio output. Probably som kind of ground loop is created when connecting the RRC which never happen when connecting a isolated mic, If you try to connect the mic input direct to a PC probably the same problem will show

73 de mike

[N8MW]

OK, i understand.  But the noise is somehow related to the PTT hot, because without the PTT hot connected to the Anan, there is no noise, even with the Mic hot connected, and the Mic ground, and the PTT ground both connected to the common ground in the Anan. So somehow the PTT circuit in the RRC interacts with the Anan PTT circuit. Hard for me to figure out.

[N8MW]

Turns out the fix is not so simple, because there is some current leakage between the PLL ground and the MIC ground internal to the RRC. Had to design the isolation relay circuit to accommodate for this.  Anyone interested contact me for details.