Thursday, 27 June 2013

4m Transverter - Receiver success

After a bit of lack-of-sleep brain addled cocking up, I have managed to get the coils for the receive side of the transverter wound properly. A quick, but not exactly accurate, test was set up, using the Marconi 2955 test set as signal generator on 70.4MHz, and the MVT-7100 scanner as the receiver, tuned 28.4MHz. With a source signal with 1kHz 45% AM, this little circuit worked nicely, giving a 12dB SINAD (roughly, by ear) of about -87dBm. With the modulation off, and the scanner in USB mode, a tone could be detected by ear with a signal of about -102dB. The set up was far from ideal, the input from the signal generator was connected with a croc-clip lead, and the scanner connected with an array of various adapters to connect to the TNC connector used to wire up the converter output. The scanner didnt even need tuning a couple of kHz away, as being a scanner its frequency resolution isnt great to start with. It was also a bit intermittent, did some odd changes when I touched the case. I suspect a proper test set up will be much better. I did notice that the trimmer capacitor in the receive circuit was best set at max, I may try a bigger value in here to see what effect it has, or maybe widen out the turns of the coil.

Onto the antenna and power switching arrangements now, which I want to have done before starting on the transmit side.

Before however, im going to pinch yet another of G3XBMs designs, and make a start on the 10m WSPR transceiver. I have the necessary toroids and crystals now, so first job is to make a rough draft layout, and then build and test the oscillator and doubler.

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