04 June 2008

Small Wonder Labs SW-30+ - tuning

Time to do the smoke test to my SW30+!

First I powered it up without ICs. At 12V it took 3.45mA. No short circuits, looks good.
I checked the 8V line on each IC socket, and it was there.

Switched it off, added all ICs,switched on. Current went up to 15.4mA, that should also be the SW30+ receive current, perhaps a bit more with an antenna and earphones connected.

Time to tune the VFO. Instead of keying the transmitter into a dummy load, I chose a different way: the local oscillator has to be 7.68 MHz below the 10 MHz band. With some easy math, the LO runs around 2.420-2.450 MHz, that's where I tuned the primary receiver. My VFO was quite high, I had to add C7=100pF and squeeze turns on the VFO coil to obtain a 2.426-2.46 MHz range.

This means ca. 10.106 to 10.140 MHz.

Every time I've tuned 30m here in Italy I've found a strong RTTY station on 10.100 MHz, so better stay away from the lower band limit. This 34 kHz coverage puts me also away from the DX window. Anyway, coil adjustment will allow me to change my mind without soldering.

Next step, once the 4m TX system is finished, will be to tune the transmitter.