18 December 2012

Beach40 - oscillator waveforms

The Beach40 is a simple QRP DSB transceiver for 40m, designed by Peter VK3YE who released 4 youtube videos about it. In the first video Peter draws the schematic diagram, which has then been re-drawn in electronic form and shared through the Minimalist_QRP_Transceivers Yahoo group.

It is a simple circuit, whose development can be monitored with the 100 MHz equipment of my shack/lab (oscilloscope, frequency counter). So I dediced to give it a try.

After I built the oscillator, buffer and diode-ring mixer I checked waveforms on two "test points" as identified on this modified schematic diagram:

On TP1 the waveform is almost a sinewave. The small knee close to the top occurs both with a ceramic resonator and a quartz. It also gets worse when the resonator is pulled upwards: what is causing it? How to fix it?
Probe was 10x, so 2V/div, AC coupling

Then I measured voltage on TP2, with diode ring mixer installed but without the output transformer; the effect of diodes is evident:

Probe was 10x, so 2V/div, AC coupling

And finally a glimpse at my ugly Manhattan style (probe on TP1):