I built up Allison's (KB1GMX) anti-pop circuit on a small piece of single-sided copper-clad board, using Manhattan building techniques and MEPADS ()?
and I must say that it does an excellent job of suppressing the pops on both the RX to TX and the TX to RX transitions.
The idea of using the second diode connected to the Raduino T/R line is brilliant as it gives the circuit a head-start on muting the audio before the relays are engaged on TX.
Bravo !?
I ended up having to play with the value of the capacitor as I was still getting some noise on the TX to RX transition. For whatever reason I ended up with an extra
1uF paralleled with the specified 0.1 uF. I haven't really had a minute to go back and look in detail at why this was necessary, but the end result is that I can now use
headphones with my uBITX without hurting my ears so that is all that matters.?
I have attached a picture of my little board.?
BTW, since I do plan on using the rig for CW and thus did want to preserve sidetone, I replaced R70 (100 ohms located on the far right edge of the board about half way back) with a 1K resistor as Farhan has done on the V4 boards. ?
I connected the drain on the 2n7000 to the M2 end of R70 (the end furthest back).?
I connected a ground wire (twisted together with the above wire) to end of D8 closest to the right edge of the board (D8 is very close to R70).
The 5 v T/R input ?is connected via a single wire to the junction of C150 & R150 on the back left corned of the board (between relay K1 and P1 - the power connector).?
The TX input ?is connected to the end of C150 closest to D13 (this is 12v on TX).?
Cheers
Michael VE3WMB?
P.S. BTW the bulges in the wires are ferrite beads covered in heat shrink tubing.
Overkill, but I like to try to keep RF out of where it doesn't belong and I ended up with a life-time
supply of mix 43 beads as I needed one and had to order 100 so I figured that I might as well use them ;-)?
