LAZY wrote:Turns out I don't know how to use my power meter. I had it set to 75 ohms not 50. Now the readings are more to be what's expected, with 12v in I get 7w in the middle of the band and 5w at the ends.
This is quite strange. It should read higher when set to 50 Ohms, than when set to 75 Ohms. I'm fairly sure the Zetagi is taking a direct sample of the RF voltage on the stripline transmission line (not via the pickup lines it uses for Forward and Reflected power in SWR mode). As an example, 10V into a 50 Ohm load = 2 Watts. Into a 75 Ohm load, it would be 1 and 1/3 Watts.
LAZY wrote:I do have a little problem with the audio though. It may be related to me fitting the 10K pot for volume where I should have fitted the 5K one? When the audio is low it crackles, it sounds fine when louder. Could this also have something to do with the coils not being canned as in Mauri's picture by the output, or that i've fitted a phono socket and not used a piece of coax to pass through the can again like Mauri's picture.
From the diagram, I can see that the audio input is DC coupled to the deviation pot, and the other end of the pot is DC coupled to a grounded resistor (R22). If the crackling is the kind of crackling you get from a noisy pot, it could be that the output of your source device is also DC coupled, with the result that the DC offset is passing through the pot and R22. It might be worth experimenting with putting a cap in series with the audio in (eg between the centre of the phono socket, and the audio in pin on the PCB). The audio in - at least at the highest deviation settings, will present a low impedance, due to the low value of R22, so the capacitor value should be relatively large. It should really be in the region of 100uF, but you could probably go down to 47uF without noticing any difference. Lower if you're not using anywhere near the "full" setting on the deviation pot. In theory, it should really be a non-polarised type (or two electrolytics, double the value, connected back to back; eg +ve to +ve, in series, with DC bias via a high value resistor at the centre point), but a normal electrolytic will be fine for experimentation. It's unlikely the DC offset will be high enough to matter much which way round the electrolytic is connected, but probably best to check your source first anyway. If the DC offset is measurable, use the polarity of the offset, to decide which way round the electrolytic should go.