Sunday, July 02, 2017

50 Mhz receiver with Bitx IF

As referenced on last post, I'm building a 50Mhz receiver, for now will leave the transmission capability out, in any case provision his there.

Basically this is a Bitx used as 28Mhz IF for a 50/28Mhz transverter kit.

I found it more convenient to buy the board from India instead of making it dead bug, still changed the first mixer to an SBL-1 and the crystal filter to the one available.
The IF is 9 MHz and the IF filter is one of the KVG type as on the Telrad board, look's like that my previous reference to 560 Ohm termination of the filter was incorrect, Pete N6QW, on his blog post has a reference of 1000 Ohm.
I made an impedance match transformer with 6 turns in, from the amplifier side, to 12 turns on the filter side, assuming 150 to 560 Ohm inpedance conversion (150 Ohm is the expected "normal" Bitx filter impedance), it works fine so not even will test with different impedance match.

Here's, first iteration of the audio output without BFO adjust:

VFO will be provided by an Si5351 controlled by and Arduino and custom code.
Initial tests of the Bitx board were made on 14Mhz, so the input filter is left in place:

..the final input filter for 28Mhz is the one on the green pcb

another detail of the 14Mhz inboard original filter

A note for the front end amplifier, I didn't had the recommended 2sc2570 so placed an 2N3904 temporarily and it still works acceptable.

This will be prey much the final result as soon as I place the power and antenna connections...

...and upside down:

Maybe latter will add the S-meter:

Have a nice week!