OBSERVATIONS FROM SCOTLAND                            28 May 2008                                GM1SXX

Today's experiment was simple enough.  Tie the RA1772 receiver and MA1720 Transmit Driver together to tune as a single unit.  At least, it seemed a simple idea.

I unsoldered the centre coax conductor from Pin 8 of the PM342 board  and checked that it was indeed feeding RF out.  It was. Pin 8 is the local oscillator input to the transmit mixer board.

I then made up an RG58 cable with a  BNC on one end and a pair of croc clips on the other.  This I plugged in to the local oscillator output of the RA1772 receiver. The other end went to the chassis and to pin 8 of the mixer board as in the photo below.

Switch on, quick 'smoke check' and then measure the output of the TX strip on my pocket DFM.

MA 1720 mixer board LO input (fed from the RA1772 LO Output)

The RX display said 14.01990 while the TX trip measured 14.019752Mhz This was with the TX strip set to CW mode, a 148Hz error.  My experiment was a grand success.  In addition, I didn't end up having to make an attenuator to connect the RX and TX together. The drive level just happened to be close enough not to matter when loaded by the mixer circuit. I now have the makings of a pair of RACAL 'Twins', a single tuning knob Racal transceiver, built from an RA1772 and MA1720. Now I only need to sort out some TX/RX sequencing.

73 Al.
GM1SXX
 

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