So i heard about the diode/pot replacement, but I can¡¯t even find the dual diode on the board or where R105 used to be.
I am keying the transmitter into a dummy load and monitoring with a scope. ? I am also listening on a Collins receiver with its antenna disconnected. ?The carrier seems way to high but I didn¡¯t write down the exact voltage on the scope. ?The receiver across the room shows an S9 with no antenna, but the metal enclosure on the BiTX is open, so a lot of signal escaping. ?
Also, the audio sounds terrible from the little crystal mic. ?I injected a 20mV 400 cycle tone into the mic input just to see if it was the mic. ?The tone also sounds terrible. ?Sounds like the tone is modulated with another low frequency (I checked DC supply and its clean).
I was going to do some signal following with the scope, but I have a heck of a time trying to identify where the components are on the board. ?In another post I asked if anyone has a board layout drawing. There is one somewhere but not on Farhans site.
Thanks
KJ7UM Grayson
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On Oct 30, 2017, at 2:28 PM, Jerry Gaffke via Groups.Io <
jgaffke@...> wrote:
Most of these seem to have the carrier pretty well suppressed without adjustment.
The change to the dual-diode bat54s was made to avoid the need for such an adjustment,
since the two schottky diodes in that package are on the same die and at the same temperature,?
thus well matched. ?Unfortunately, the two diodes in the bat54s are joined where the bitx40 schematic?
shows the 100 ohm pot, so the pot won't work with the bat54s. ?There are other diode arrays
where they are on the same die but have the two diodes separated out.
Schottky or a standard 1n4148 silicon diode both seem to work fine.
Should be easy enough to remove the bat54s and add back in a couple diodes and a 100 ohm pot,
if that's what you want. ?Though my guess is that there may be something else wrong here.
Exactly how are you measuring the carrier level on your transmissions?
Yes, you will be able to hear it on a receiver in the same area, but it typically is not strong enough
to be of any concern.
Jerry
