28 Apr 2014

Super simple FM TX - try on 2m?

See http://makezine.com/projects/super-simple-fm-transmitter/ .

This is a super simple TX for Band II FM using readily available parts.  With a smaller coil (1 turn less) and C4 smaller (and made tunable) I think it could be used experimentally on 2m FM, but stability is likely to be poor, so really only of use for short range and short durations.  From here, I'd expect this to be detectable at least 3km away (next village) even if the power is at uW or low mW levels. A few uW go a LONG way if connected to a reasonable antenna like my V2000 or 3el beam. There is no harmonic filtering either: a small low pass filter is advisable really.

With lower modulation levels (adjust) it should be fine with NBFM. The 2N3904 is a ubiquitous transistor available for just a few pence from many sources. The other parts are just pence.
Image at http://makezineblog.files.wordpress.com/2013/10/kogawa_simplest_transmitter.png?w=620&h=354

My thanks to Southgate Amateur Radio News for finding this before me.


YO9IRF said...

Don't get your hopes ups, I used something like that before for a beacon, the modulation is both FM and AM and it's not linear. Stability is pretty bad and the antenna will change the oscillation frequency a great deal.

Roger G3XBM said...

YO9IRF thanks. I would not expect much, but it is so simple I must give it a try with G6ALB in the next village. We like doing this sort of "off-beat" test.