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Causes of IF feedthru
On 11 Jun, 18:54, "Joel Koltner" wrote:
I've been playing around with some homebrew superhet radios, and I'm finding that a significant amount of energy ends up at my 1st IF frequency that seems to be coming from the LO. *While I expect to see energy from LO+/-IF end up at IF, of course, I've checked the LO+/-IF spurs (the LO is coming from a PLL-based synthesizer), and in general it seems that a lot more energy ends up at the IF than what the spurs alone would suggest. *I remember a talk I attended where the presenter mention that one of the biggest problems with building receivers was "the LO getting into the IF," so I'm thinking this is what he meant? *Are there other less obvious paths for the LO getting into the IF than just the LO+/-IF spurs? The signal right at the IF eventually gets turned into DC and hence filtered out, so in theory it doesn't really matter that much, but in practice with very weak signals eventually the IF feedthru is stronger than the weak signals, so it limits how much amplification I can provide and hence limits the ultimate sensitivity of the receiver. Thanks, ---Joel Koltner Screening is the best solution. Put the various stages in separate screened enclosures. Leon |
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