[minima] Re: kerchucking noise in PTT
- From: David Fannin <dfannin@xxxxxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Fri, 2 Jan 2015 11:38:22 -0800
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
2) disconnected the mic pre-amp and cw oscillator from the audio pre-amp
input - no change.
3) replaced the relay - no change
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> 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
> >
> >
>
>
>
Other related posts:
