Saturday, 26 September 2015

Chinese Airband Receiver Kit - Now with Digital readout!

Ok, so, its NOT a synthesiser, its not even a PLL, its still a free running LC VHF oscillator under varicap DC control. But, it is now much easier to put on frequency, or at least, close enough that the wide IF bandwidth means i'll hear the signal im listening for!

Chinese Airband Receiver with LCD Frequency Counter module

A couple of points here. First, the connections are only tag soldered onto the underside of the PCB at present, and the LCD is powered from the 8v regulator. I need to check that the additional current load isnt too much, although I doubt that the whole shebang takes the 100mA limit of the regulator. Second, the signal input to the counter is at present a single wire, eventually that will be replaced with a length of thin coax. Incidentally, the plugs and wires as supplied with the counter are such that the signal input is a black wire and its ground is a red one! Something to be wary of! I might modify the LCD module to allow the backlight brightness and the contrast to be adjusted.

On the back of the counter module are two push buttons. These allow the display to be changed between 1kHz or 100Hz resolution. Ive set it to 1kHz here, as the oscillators stability isnt up to 100Hz! The buttons also allow setting of an IF offset frequency and direction. By setting it to -10.7MHz, I have a readout of actual receive frequency, or as close as makes no odds.

If its of any interest, here its tuned to Leeds East Airport.

1 comment:

Unknown said...

Thanks for your blog. It offers a load of interesting info.
Could you post where are the LO signal tap points for the counter? The NE602 is usually very picky with stray capacitances...
Thanks for your help.
jon, ea2sn