Makes sense. Seems like good use for a 2N7000. 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? Dave On Fri, Jan 2, 2015 at 12:41 PM, allison <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> 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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