Re: uBITX new build, quiet audio #ubitx
I have the same impression and experience like You!
I prodduced a so called level diagramme, see may attachment.
Interestingly thsi result was verified on my UBITX: at -107 dBm
(=1µV) at the antenna input I measured about 300 mVpp = 106 mVrms
at the louespeaker terminals; audio control potentiometer at full
gain. This level (into a 8 ohm impedance ludspeaker) gives about
1,4 mW of power.
Doing the samce lvel diagramme for the BITX40 gives 15 dB higher
gain: thre RF stages (but lower gain each stage), (two on the
UBITX) and a 6 dB higher audio gain (LM386). 10^(15/10) gives a
poer factor of 31.67, so the BITX40 would output 44.27 mW under
the same input conditions.
I also noticed a large amount of RF still at the loudspeaker terminals, about 100 mVpp. Using a frequency counter I observed 12 MHz, so this RF are leaks of the BFO.
One remedy coud be to palce a 100 pF cap across R50 (AF preamp).
Am 21.08.2018 um 12:38 schrieb jfein2000 via Groups.Io: