BATC Forum

Has anybody home brewed a transistor based VFO to drive the digilite?
I have tried with a BFR106 without success.
Any comments welcome Mike G3TOI

Mike

There's no reason why a good vfo should not work. My article in CQ-TV 245 described the use of a COMTECH module, which is a transistor VFO with a bit too much phase noise (induced by the pll).

What frequency are you trying at?

Dave
G8GKQ

Hi

I am using 23 cms 1249 at the moment with an ultram with good results but the aim is to have all home brew

I can get a similar picture on an analyzer of the home brew vfo but with more close in noise and side bands.
This is both with and with out PLL control
The modulator I use is home brew but closely following the digilite, but with individual control on each of the four chanels to the mixer
I also matched each nyquist filter for phase shift
Regards G3TOI

OK Mike

I found Tutioune very useful for measuring and visualising (on the quadrature constellation plot) the effect of phase noise. Also, an RTL-SDR with SDR-sharp well zoomed in was good enough to see the phase noise difference between the Ultram and COMTECH-based LOs. The screenshots in the article show the difference.

Frequency accuracy did not seem to be too important. Some receivers will accept at least +/- 400 KHz.

Are the levels the same?

73

Dave

Hi Dave
I have a better wave form than the comtech as per your article in cqtv
The wave form I get from the Ultram is about the same as you show, so I am begining to think, what else.
I can not get a pic across the shack, however, I have not yet tried to raise the local repeater just in case my local oscillator is swamping the RX in the shack, a porty, that is the next move.
I have again checked the levels and using the ultram as a standard of 11 dbm mine is within the range of the AD 8346 mixer which I am using, in the range of just > 1 dbm
I have now got the analyzer in bits, chasing an intermittent fault

Thanks for info

Mike G3TOI