Re: Tinny sounding electric miss on uBitx

Jerry Gaffke
 

Transmit and receive are symetrical on the uBitx and Bitx40, uses the same bfo and IF filter.
Should have about the same audio characteristics on transmit as receive.

Assume the crystal filter has a passband from 11.998 to 11.996, the BFO is at 11.9955mhz
When transmitting, audio from the mike amp of 0 hz is at 11.9955mhz, audio that was 500hz is now 11.996mhz
and audio that was at 2500hz is now mixed with the BFO to create a signal at 11.998mhz.
Only stuff between 11.996 and 11.998 mhz will make it through the crystal filter.
So any audio from the mike between 500 and 2500 hz goes into the IF amp at frequencies between 11.996 and 11.998mhz.

On receive, the math is exactly the same.  The crystal filter only accepts incoming RF between 11.996 and 11.998,
when that RF is combined with our 11.9955mhz BFO we wind up with audio between 500 and 2500 hz.

Now if the BFO was at 11.9950 mhz but everything else was the same, the audio on transmit and receive
would be between 100 and 3000 hz, and perhaps sound a bit tinny.

Jerry, KE7ER


On Sun, Feb 11, 2018 at 02:49 pm, John Backo wrote:
Oops -- I noticed you said "tinny when
monitoring in another receiver..."

That would rule out the BFO in YOUR receiver.

It could be the voice quality of your mic amplifier.
There have been various solutions posited for
that, including Kang's replacing resistors in
the amp. He also noticed a similar thing and
posited a larger solution. See his website
Small Wonder QRP for clues.

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