EMRFD Message Archive 4846
Message Date From Subject 4846 2010-08-03 06:40:15 Tim Simultaneous T and R output VFO I think either here or on the R2Pro list I expressed my yearning for simultaneous T and R operation.
What I was yearning for, was the separate T and R CW operation that my HW-16 achieves, with the QSK so smooth it feels like I can hear the band even with my key down. But I wanted a single tuning control instead of separate T and R tuning knobs.
I think I have achieved this in real life with a R2Pro for the receiver and a VFO combination that hits a sweet spot. Let me describe it.
What I strung together over the weekend and had some good QSO's with, is a 30M scheme with a R2Pro for the receiver, a VFO with simultaneous T and R outputs in keydown, and a RIT shift of about 700Hz. The T output of the VFO goes to a logic-gate driver and a simple class E 30M IRF510 final.
How I achieve this in the VFO, is like this:
The variable part of the VFO, is tuned by a Russian surplus gear-drive no-backlash variable capacitor, and tunes from 1.908 MHz to 1.958 MHz.
For receive (always kept running) the 1.908 MHz to 1.958 MHz is mixed in a NE602 with a 8.192 MHz crystal to get a 10.10 to 10.15 MHz signal that is run through phase shift networks into the R2Pro. The output filtering is just a simple LC tank on the NE602 output.
On transmit, there is a keyed NE602 that has a 8.192 MHz rubbered about 700 Hz away via a trimmer capacitor in the oscillator. 700Hz shift in the crystal oscillator was achieved by trial and error. The oscillator in the NE602 is kept running all the time, and the keying is accomplished by turning the J310 buffer between the 1.908MHz VFO and the NE602 on and off and also keying the J310 buffer following the transmit NE602 on and off.
The result, I'm very happy with. There's a single tuning control, and there's a fixed 700 Hz offset, and the T VFO output is nicely keyed without any audible chirp. I dinked with the R2Pro muting just enough to allow me to hear my own transmit carrier in the receiver.
Somehow I gotta put all this together instead of having it strung across the bench. But I'm happy.
Translating this to other bands seems straightforward enough. I don't think the RIT range will ever go above a couple of kHz because I cannot reliably rubber the transmit mixer XO that much but I can count on maybe three or four hands the number of DXPeditions that operate at shifts more than a few kHz and I work each year. Putting the RIT shift on the front panel would be nice for the DXPeditions but for casual chatting up and down the CW bands it hardly seems necessary, the fixed 700 Hz shift seems ideal for 99% of operation.