Re: Carrier Null revisited
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?e are duiscuissing around BFO carrier leak. As has been explained well that a chip dual diodes are internally balancedenough. Even if suppose one uses discrete diodes,one could minimize but not eliminate carrier leak. It is analogeous to? non exuixtance of 0 and Infinity.
The nulled carrier to one's expectation gets amplified at PA as correctly suggested by Asher Farhan.? but I suppose that we need to make relative measurements. ? sarma
?vu3zmv
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On Tue, Oct 31, 2017 at 8:27 AM, Raj vu2zap <rajendrakumargg@...> wrote: Grayson,
Measure the DC voltage in both RX and TX modes across C107. It should be zeroif not you will have a carrier
leak.
You complaint that external modulation sounds bad could be something related to the above or simply that
in close proximity you will hear mains hum modulating a carrier. Try a QSO with some near by ham and see.
Raj
At 31/10/2017, you wrote:
>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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