As far as I recall, Inrad sells front-end xtal filters. Some 25 years ago when I lived in Belgrade, at YU1EXY we had two six-pole filters for SSB part of 40M band but I can't recall and difference with or without those filters. Beside those two xtal filters we used 8 pole Cohn LC filter with 4-gang variable capacitor and with very step curve (I think it was 600 or 800 Hz at -6 dB), which drastically reduced noise and QRM. We could hear 3rd or even 4th layer of callers in 40m pile-ups.
As for xtal front end filters, I think 4O3A produces such a filters to be used at in-band stations, but didn't have chance to try & use them... 73, Mirko, S57AD 2016-12-22 21:57 GMT+01:00 K1FZ-Bruce <k...@myfairpoint.net>: > Tim, > > My single crystal was in the 1950's. > A crystal lattice could take in much of the 160 meter band and be > pratical. > Thanks for your input. > 73 > Bruce > > On Thu, 22 Dec 2016 15:49:12 -0500, Tim Shoppa wrote: > > Bruce - It has long been rumored that the big EU multi-multis have > a crystal filter at their run frequency receivers. e.g. if they are running > on 7003.4, they have a crystal filter in front of their receiver for > 7003.4. have never observed that in my visits but maybe in decades past, > when receivers had less damage range, it would've made sense. Also a good > reason to put up a fight for ownership of YOUR run frequency HI HI > > I believe EMRFD has a schematic for a single-frequency receiver, maybe > not exactly like you described but similar in principle. Let me see if I > can dig it up. > Tim N3QE > > > On Thu, Dec 22, 2016 at 3:41 PM, K1FZ-Bruce wrote: > > > We know that limiting the noise pick up from more directions of an antenna > we can usually hear better. We also know if we limit the noise from a > receiver IF we can hear less noise, and better yet, if we > have a roofing filter earlier in the receiver we can eliminate even more > noise in relationship to the wanted signals. > What if we take it a step further, could we limit the band-with of the > antenna signal with a crystal lattice for 160 meters before the receiver. > Years ago I played around with a single crystal at the input of an old > tube type receiver. It was remarkable what I could hear on 40 meters, > on what seemed to be one frequency. > 73 > Bruce-k1fz > http://www.qsl.net/k1fz/beverage_antenna.html > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > -- Mirko S57AD _________________ Topband Reflector Archives - http://www.contesting.com/_topband