Wednesday, March 2, 2011

2m QRSS

Something I was thinking of occasionally, QRSS on VHF, UHF, SHF and EHF bands.

Lets first start with a band that is accessible to all of us, the 2m band.

A short chat with Dave (G7UVW) brought up two frequencies of interest.
  • 144.070 MHz
  • 144.4905 MHz (WSPR)

Both QRGs can be reached with CB-TX-crystals on their fundamental frequency and doubling the signals a couple of times. 9.x MHz will have to be multiplied by a factor of 16. With a little pull and the right oscillator circuit, this all should be fairely easy.

144.070 MHz
Channel 5T (27.015MHz) will be, very obviously, be 9.005MHz on the fundamental frequency. The resulting frequency on the 2m would be 144.080MHz. A little harmless down pull to 9.004375MHz on the fundamental will get us to 144.070MHz.

144.4905 MHz (WSPR-QRG)
We got two options here,  channels 11T (27.085MHz) and 12T (27.105MHz).
11T would require a Pierce oscillator which oscillates above the series frequency of the crystal. The fundamental of 11T is 9.028333MHz, while the required frequency for the target-frequency would be 9.03065625MHz. The difference of 2.323kHz is not problem to a Pierce oscillator at all.
12T will provide a 9.035MHz signal. The pull of 4.344kHz to 9.03065625MHz is doable, could however result in a less stable oscillator.

Put the design into practice seem not to be a great deal, however, frequency stability is a great deal here. So, I figure, good temperature stabilization is in order. The rest is in fact pretty straight forward. I do have to admit that the first ever ham-radio transmitter I built (age 15, just licensed) was a 144MHz A1A TX, based on a CB crystal and BF199 transistors.

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