Airband receiver

[Wendymott]

Further update of development "finds".
A few weeks ago I decided to make a smaller version, with a PLL Module and Combined RF ,IF,VFO and audio module. The electrical design was very similar but various problems came to light.

Unusual PLL Operation, while locking at 128 Mhz and 148 Mhz, in the centre approx. 143 Mhz the PLL output reduced to near zero. After changing all the components I used the dentist burr and removed copper ground near the printed inductor - this cured the fault.

Low RF Sensitivity. Again as the RF front end was almost identical to the modular design, I was at least 40 db down. After much head scratching, it was nothing to do with the RF front end, by chance I found the PLL was injecting the VFO at - 12.5Khz. Even though the display was showing correctly, the PLL loop was locking low.
Checking the reference crystal at 6.4Mhz with a good frequency counter, using a X10 probe, the sensitivity bounced up to correct levels. As I had no buffer between the CXO and the PLL chip, I was loading the CXO with the scope probe capacity, and giving a good reading of 6.4 Mhz. Removing the probe the CXO was shifting high. The cure was to add 6.8PF to the source of the XCO fet - voila - PLL locking on the correct IF offset.

This has taught me well; don't assume, just because you want it to be.

I can now concentrate on making a box to fit the receiver into.

[Radio Wrangler]

And then an aeroplane to fit the box into?

David

[Wendymott]

Why not David. There's a huge lot parked up in Arizona I understand.

[Herald1360]

That's probably the only sort you could fit it to. Without all sorts of approvals it could probably only go as hold luggage in a flyable plane.......