[aprssig] Re: Does anyone have a fix for the 70cm tone encoder problem on the TH-7ag?

Thomas t hamaddict2001 at yahoo.com
Mon Mar 19 13:38:22 EDT 2007

Well I was thinking about it last night, and I remember at the time I was convinced that the problem was in part rf feedback, so I experimented with shielding different parts of the rig. 
  To see if the mic wires or mic itself were picking up rf before I spent a lot of time shielding them, I remember disconnecting the wires from the mic and I'm not sure about this, but I think I remember that the problem remained.  I guess this would leave microphonics of the circuit and physical disturbance of the unit?

"Stephen H. Smith" <wa8lmf2 at aol.com> wrote:
  hamaddict2001 at yahoo.com wrote:
> Al,
> Thanks for the response...that sounds feasible to me. Also if this is 
> the problem I think it will not be too hard to correct.
> But why would the problem only manifest itself on 70cm and not 2m as 
> well? 
> Thanks again,
> Tom-N2YTF
> *//*

At UHF, the transmitter synthesizer VCO (Voltage Controlled Oscillator) 
is either running at the VHF frequency and then tripled, or the VCO is 
running directly at three times the frequency that it is on VHF. 

In either case, any kind of electrical or mechanical disturbance 
(possibly the VCO tuned circuit is microphonic; i.e. sensitive to 
vibration or mechanical shock) is going to be three times as pronounced 
on UHF as it would be on VHF. 


Stephen H. Smith wa8lmf (at) aol.com
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