LO

[2e0phj]

Hi all board all most done, but i have to ask re the lo, whould it be posible to use the Comtech analog tx output with some mods?

Thanks

[G4EWJ]

I don't have any experience of the Comtech, but LO phase noise is important for DVB transmissions. This gives some idea of what the commercial spec is. Phase noise is apparently more important at the low symbol rates we use.

Brian

http://www.d-atv.nl/phasenoise.php

[g0uhy]

When I first started with the modulator I did try a Comtech as a VCO. As Brian says the phase noise was an important factor and the Comtech was quiet frankly awful!! This is why I hunted out the Ultram VCOs and their performance and phase noise are far superior.

73

Malc

G0UHY

[g4bbh]

Even if you disconnect the video input and both audio carriers at the module in a comtech the phase noise is still horrendous. I spent ages trying to improve it, even changing the crystal to no avail. The signal from my ageing HP signal generator (a klystron) is cleaner!
Dick G4BBH