[minima] Re: kerchucking noise in PTT
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Fri, 02 Jan 2015 21:41:53 -0500
On 01/02/2015 04:22 PM, David Fannin wrote:
> Makes sense. Seems like good use for a 2N7000.
>
Yes.
> Do I need any resistors between the Drain or Source and Ground, or can
> I just wire to provide a short to ground when switched on? Do I need
> R2 in the attached?
>
R2 no. Put the drain lead on the other side of R1. that will limit
peak current
and still pull it down hard. I usually put a resistor in series with
the 12V to the gate
anything in the 10-100K range is ok.
See if that helps.
Allison
> Dave
>
> On Fri, Jan 2, 2015 at 12:41 PM, allison <ajp166@xxxxxxxxxxx
> <mailto:ajp166@xxxxxxxxxxx>> wrote:
>
> On 01/02/2015 03:23 PM, David Fannin wrote:
>> On Fri, Jan 2, 2015 at 11:51 AM, allison <ajp166@xxxxxxxxxxx
>> <mailto: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.
>>
>
> Yes, the logic is if caps are allowed to discharge into the
> circuit they tend to take a while.
> So if you take R23 to ground on RX it may dump the remaining
> voltage in the circuit.
> A simple transistor switch using the RX+ Voltage to switch on a
> transistor on from R23
> to ground might be enough. Also the .1 caps at the input and
> output of the TX IFamp
> are likely larger than needed try .01.
>
>
> Allison/KB1GMX
>
>
>
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