EMRFD Message Archive 6292

Message	Date	From	Subject
6292	2011-05-15 09:10:56	pauldebono@rocket...	AM detection in DC receivers
Despite the theory, that switching and diode ring mixers cure AM breaktrough in DC receivers, my experiments, are showing a different story. I have tried both front ends, and both suffer from AM breaktrough on both 40 and 20 meters. Is a rejector tuned circuit at the antenna input a cure ? Has anyone tried it ? Any web resources please !
6293	2011-05-15 09:45:30	Leon Heller	Re: AM detection in DC receivers
6295	2011-05-15 10:46:39	kb1gmx	Re: AM detection in DC receivers
6306	2011-05-16 07:36:03	Tim	Re: AM detection in DC receivers
6307	2011-05-16 08:02:05	Chris Trask	Re: AM detection in DC receivers
> > If the AM carrier gets large enough to be similar in voltage > to the switching threshold of the mixer diodes then all hell > breaks loose. Is your problem, the SW broadcasters near 40M? > To be fair those of us in the US do not suffer from them > nearly as badly as those closer to Europe. > That poses an interesting problem, one that will require some form of signal nulling antenna array rather than sharp pre-mixer filtering. Even a simple 2-antenna canceling array would be effective here. I have a design for such an antenna that I've never formalized. I'll put what I have into the files section shortly. I do have a PCB designed for this, but cannot get anyone to make me one or two to verify the design. Every time I touch the prototype I end up having to repair it. Chris Trask N7ZWY / WDX3HLB Senior Member IEEE http://www.home.earthlink.net/~christrask/
6309	2011-05-16 11:49:04	Tim	Re: AM detection in DC receivers
6310	2011-05-16 11:58:23	Pawlu	Re: AM detection in DC receivers
I have to check the lo injection level. I am pumping 2.40 volts to the Tayloe switching mixers. I want to remedy the situation at the rx end, and not at the antenna, or tuner. AM should not enter in SSB/CW mode. Paul
6311	2011-05-16 12:05:07	Chris Trask	Re: AM detection in DC receivers
> > I have to check the lo injection level. I am pumping 2.40 volts to the > Tayloe switching mixers. > > I want to remedy the situation at the rx end, and not at the antenna, or > tuner. > AM should not enter in SSB/CW mode. > You might want to consider using a bandpass type matching/preselector unit such as the one I added to the group files section a week or two ago: http://groups.yahoo.com/group/emrfd/files/Charlie%20the%20Tuner%20Rev%200.pd f Chris Trask N7ZWY / WDX3HLB Senior Member IEEE http://www.home.earthlink.net/~christrask/
6312	2011-05-16 23:47:15	davidpnewkirk	Re: AM detection in DC receivers
6313	2011-05-17 04:05:05	Pawlu	Re: AM detection in DC receivers
Dave , Thanks for your comments. I am suspecting either the LO injection voltage, or harmonics from the SI570, or even unbalancing in the 4 trifiliar turns on a BN43 2402 feeding the switching mixer input preceeding the passive low pass filter. I need to know the exact LO injection to the FST switches. I am at present feeding some 20 db's (in 50 ohms) or 2.40 volts. But this is probably standard from the 74ac74 flip flops. Same thing with the other experiment. I am using an R2pro frond end with a TUF-3 diode balanced mixer, feeding some 13 db's LO injection. Probably the theoretical +7bd's should do and eliminate the BC breaktrough Paul 9H1FQ