22 Jun 2009

A very basic 4m AM transceiver

In the coming days I am planning to modify my SixBox 6m AM QRP breadboard to 4m so that I can have a first 4m QSO using my own callsign. As I don't have suitable crystals I was planning to use (very temporarily) a free running oscillator at half frequency, even though I might have to re-net to 35.13MHz (half 70.26MHz) quite often. Today, someone pointed out that the 14.060 crystals sold by GQRP club multiply x5 to 70.3MHz, which would easily pull down to 70.26MHz. Although a x5 multiplier won't be efficient, it is worth a go don't you think?

If things go to plan, I should have a very basic 30-50mW AM transceiver working on 4m by the weekend. It will be a rats nest on a piece of copper clad board, but it should allow me that first 4m QSO. Whether it gets put into a neat box remains to be seen.

[See later blog post on improvements to the TX lineup]

1 comment:

Andrew VK6JBL said...

Get a square wave (using a logic chip) and you'll have plenty of strong odd harmonics. EMRFD has an example of this dividing a 14.318 crystal by 2 with a 74HC74 and extracting the 7th harmonic around 50.110.

A neat trick which I'm tempted to use one day for a 6m dsb receiver. The divide by 2 doesn't help you for 4m though.