25 May 2009


Worked M0BXT tonight on 6m AM when Andrew was using a single transistor TX using a carbon mic to produce AM! His signal was RS58 with me at 2 miles range but modulation depth only about 5-10%. Still, it was a QSO.


Anonymous said...

I wish there was someone near me like Andrew M0BXT to conduct experiments with . What was the R.F output power of Andres Tx?
You have to shout to get any depth of modulation.
Try a 6v Mains transformer to step up the modulation.

73 Tony G4llw

Roger G3XBM said...

Hi Tony,

I am sure we will try things like the mains transformer to improve mod depth. The input on Andrew's TX was about 60mW so the output was most likely 10-20mW? All great fun.


Tony said...

Hi Roger

I like reading about your experiments with Andrew M0BX
it would great if there was someone like minded and local to me.
That's a good output for a one transistor transmitter.
Please post the circuit on your
I have got some 6 metre crystals
might give that a try.

Anonymous said...

Further to this I've done some measurements. As noted the DC input was about 60 mW but that includes power dissipated in the carbon granule microphone.

The RF output with this setup appears to be about 4 mW (+6dBm) as measured by a spectrum analyser and confirmed on a (200 MHz bandwidth) oscilloscope.

For next week perhaps we can try DSB using and SBL-1 mixer, my signal generator and the same carbon granule microphone (probably with a step down transformer).

I’ll see if I can hash something together in time!

Yes, I guess Roger and I are lucky to both enjoy very simple gear and live locally to each other but the GQRP club (and the corresponding Yahoo group) will be full of like minded individuals – hopefully all over the country.


… Andrew

Roger G3XBM said...

Yes,definitely game to try DSB next week Andrew.