Contents :

A collection of thoughts, and my notes about experiments and ideas, technical or otherwise, connected to Amateur Radio, Satellite working and monitoring and other electronics.

Monday, January 25, 2010

Rock-Mite 80 update

A new crystal in the oscillator brought the lower frequency down to 3579.350. That is quite acceptable for a grabber, the audio range for the 3579.500 - 3580 will end up at 150 - 650Hz. Not ideal, but workable.

Here is what it looks like with a few minutes of low - high - low frequency :

Still, with the 5V shift the TX frequency only went up to 3579.500, the shift is just too low at 150 Hz.

Enter the Q2 switch transistor and the 12V pull-up resistor. Voila, the upper frequency is now 3579.850, a 500 Hz difference, bringing the TX frequency just inside the 3579.800 - 3580.000 band.

It looks like it will be a good idea to have more than 2 crystals on 3579 for this construction, so a selection of the most suitable frequency can be made, alternatively find a better suitable varactor diode with more capacitance variation at 0 - 5 V.

The other point, with the current (original) "firmware", the RM starts up at the higher frequency rx local oscillator and will have to be switched manually to the lower lo frequency.

Later the test of the receiver as such, enough done for today.

I am optimistic that this will work as a MEPT tx and Grabber rx, but the rx test will show.

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