Re: uBITX new build, quiet audio #ubitx

Henning Weddig
 

Jeff,

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).

Henning Weddig

DK5LV


 

Am 21.08.2018 um 12:38 schrieb jfein2000 via Groups.Io:

I have a current version of the BITX which I just finished assembling in the case.  It works after some debugging....replacing the code in the Arduino due to a cw fault per another discussion.  It is now working on ssb and cw although power output should be higher on 80 and 40 meters. BUT, I also feel the audio is too low.  I don't have a hum issue but at full volume I can hear stations but even with an amplified speaker it is just not up to snuff.  I saw Arv's suggestion for wiring an amplified speaker to the volume control and will try that to see if it helps. I am responding to this post as the cw issue seems to be  general fault and with two of us with recent bitx builds having audio issues I felt it would be good to get this on the radar in case it is a trend building.   Any other suggestions to remedy would be appreciated.  
cheers

Jeff 

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