[minima] Re: kerchucking noise in PTT
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Fri, 02 Jan 2015 14:51:48 -0500
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.
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).
> 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.
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.
Allison/KB1GMX
> 4) separated the PTT and TX_RX circuits, and updated the code to use a
> separate PTT line to trigger the TX_RX relay. The TX_RX line is now
> output only, so no input/output switching. The PTT line is now a
> simple input line that triggers on going to ground. - No change.
> I wanted to make this change, anyway, as I wanted to be able to
> trigger TX via the arduino (for digital modes, possibly).
>
> So next I'm going to try to disconnect the cw oscillator output to the
> relay (the V2 design uses separate outputs for audio and transmit
> paths, using the collector and emitter outputs, respectively. ) -
> I'll see if that can isolate where the bias point change is occurring.
>
> Dave
>
> On Wed, Dec 31, 2014 at 6:29 PM, allison <ajp166@xxxxxxxxxxx
> <mailto:ajp166@xxxxxxxxxxx>> wrote:
>
> I've looked at the circuit and assuming there is no wiring error or
> layout error
> the likely source is the DC switching to the MIC preamp going from
> TX to RX.
>
> The test for that is to remove C48 from the mic preamp to the
> modulator. If it stops
> you know the cause.
>
> Allison/KB1GMX
>
>
> On 12/28/2014 11:25 PM, David Fannin wrote:
> >
> > I'm having an issue with a loud kerchunk when going from TX to RX
> > state, and wanted to get some ideas from the mail list on how to
> solve
> > it. Going from RX to TX works fine.
> >
> > When press the PTT button, the radio goes from RX to TX mode - no
> > issue there. However, when I release the button, I get an immediate
> > loud kerchunk in the speaker/headphone output. The issue is
> the same
> > in CW mode, as soon the radio transitions back to RX mode.
> >
> > I tried putting in a delay in the "changeToReceive" function,
> where I
> > delay the relay transition from TX to RX. Specially, I delayed the
> > resetting of the TX_RX pin from output to input by 2 seconds. It
> > turns out that its not the relay switching, but something else that
> > causing the noise. It appears to be the release of the PTT button
> > that triggers something that causes the noise.
> >
> > The PTT button is a spst momentary button mounted on the front panel
> > of the Minima radio. The leads from the board to the switch are
> about
> > 6 inches long. The relay is a DPDT relay (Omron G5V-2). I'm
> using
> > the V2 schematic and I using a modified version of the radiono_erb
> > firmware (the modifications are for a different rotary encoder, and
> > button array)
> >
> > Any ideas on things I can check? The rest of the radio appear to be
> > working quite well - the receiver is very clear, and although it
> only
> > has 25 mW or so (I don't have the PA built yet), I'm getting a good
> > transmit signal as well.
> >
> > thanks,
> >
> > Dave KK6DF
> >
> >
>
>
>
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