[minima] Re: kerchucking noise in PTT
- From: David Fannin <dfannin@xxxxxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Fri, 2 Jan 2015 12:23:01 -0800
On Fri, Jan 2, 2015 at 11:51 AM, allison <ajp166@xxxxxxxxxxx> wrote:
> On 01/02/2015 02:38 PM, David Fannin wrote:
>
> Ok, an update , but no solution yet.
>
> Here's what I've done so far:
>
> 1) changed the mic preamp C3 cap from 10uf to 1uf. (from my schematic,
> I'm using a NE5534 op amp mic preamp) - no change
>
> Does not match any schematic I have. You need to put up a AS BUILT
> schematic.
>
Schematic for my mic preamp was posted earlier in this thread.
>
> What I'd asked was to disable the output of the mic preamp and see if the
> TX/RX pop remained.
> That was what I'd meant by pulling C48 (V2 schematic).
>
I disconnected both mic pre-amp and cw oscillator , so I cut the leads of
C48 and C47. That was #2.
>
>
> 2) disconnected the mic pre-amp and cw oscillator from the audio pre-amp
> input - no change.
>
> 3) replaced the relay - no change
>
> I cannot imagine how the relay could be at fault.
>
Someone suggested this, and I had used a socket for the relay and had an
extra one, so it was about 15 seconds of work to rule this out.
>
> However when I do a DC switched TR circuit I usually return the alternate
> lead to ground so that
> when I go TX all the RX+ points are forced to ground and same from going
> to RX wher all the
> TX+ points are grounded. It can be done with realy or my preference a few
> transistors.
>
Some progress based on this idea. On the BiDi amplifier, I disconnected the
12v power input to the TX side of the BiDi amplifer (R23) , but left the
12v input to the RX side (R65) . Both sides are switched by the relay.
The popping sound went away ( the sound is only going from TX to RX, not
RX to TX.). So with the current V2 circuit, when +12v/Xmit/R23 is
deactivated, that point is isolated, not grounded.
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