Actually, there is an easier test - just put a temporary jumper between the connector and emitter of Q7. Do not expect it to receive with that jumper in place, but observe what happens to the sidebands when you transmit. If it cleans things up with the jumper in place, replace Q7 and make certain R28 is well soldered.
Stan reported a negative voltage on the base of Q7 - I trust that was while transmitting, and if that assumption is true, I suspect R28 has a problem. One end of R28 should be near 6 volts when transmitting and the other end should be near 0.6 volts. 73, Don W3FPR On 5/8/2012 7:39 PM, Geoffrey Mackenzie-Kennedy wrote: > Hello Stan, > > If Q7 is not conducting and is not in effect grounding one side of CA, then > a loop is created between the input (Q1 Gate) and output stage of the > transmitter. Part of this loop contains the Rx RF Gain pot R1, the Rx's > input tuned circuit, and the coupling between pins 1 and 6 of U6 be it > inside or external to the chip. > > To eliminate (or not) the possibility that on 20m transmitter is unstable > because Q7 is not removing this loop, I suggest that while transmitting you > wind down the Rx RF Gain pot R1 to see if the spectrum improves. > > I am curious as to why the sidebands on 20m are spaced at 60 Hz intervals. > > 73, > > Geoff > LX2AO > > > > On May 08, 2012 at 18:07 +0200, Stan Gibbs wrote: > > >> As I said in my original post, Q7 is the place where my DC troubleshooting >> measurements differed from specs. The base of Q7, which is supposed to be >> 0.7V, is -0.895V on 40 and -0.195 on 20. The voltage on Q7 should >> definitely be positive in order for it to ground capacitor CA, so >> something >> is screwy. >> >> Someone suggested that either C45 or C32 were possibly bad, allowing RF on >> to the base of Q7, which might cause the bogus voltages. I tried adding >> additional capacitance in parallel with C45/C32, but that had no effect. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
