开云体育

I was interested in Karl K0MWC's suggestion to use a PE digital attenuation chip to address the problem of variable power out on the ?BITx.? (Refer: /g/BITX20/message/42298).?? I was not so thrilled to note that this chip is only available as a "microscopic surface mount" package.

So, I did a bit of searching online and found an alternative device (less precision but we can live with 1dB steps) that is available as a pre-built module (using an HMC470 chip) for around US$13 ex China. This seems quite a nice little module that could be used as follows:

On TX:? control drive level to the pre-driver stage

On RX: as an RF gain control (selectable in the menu and using the encoder to control 32 steps from 0dB to 31dB of attenuation)?

AND

??? ??? ??? as part of an AGC circuit to reduce gain for strong signals.

I have summarized the discussion of all the options for addressing variable output power from the ?BITx in a news article on ubitx.net here:

I ordered a couple of the modules, and I will tell you the outcome of my experiments in 2-3 months time.? It takes a while for parcels to arrive from China down here.?? Somebody else might beat me to it hopefully (like they did with the little mic compressor/noise gate chip) and can let us know how this scheme works!

BTW - if you use two modules in series you can get 62dB of attenuation! That would be great for AGC control!

73?? Mike ZL1AXG