Hi, In my opinion, a high selectivity device at the front end will help regarding noise and QRM only in case of relatively poor IM3 receiver.
73, Mirek SP5ENA -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Matt Murphy Sent: Thursday, December 22, 2016 11:19 PM To: k...@myfairpoint.net Cc: Topband <topband@contesting.com> Subject: Re: Topband: "Thinking out loud" This appears to be the 4O3A unit. I hadn't realized these existed, so I'm glad you posted the question: http://www.4o3a.com/index.php/products/ham-radio-gear/crystal-front-end-unit / On Thu, Dec 22, 2016 at 3:47 PM, K1FZ-Bruce <k...@myfairpoint.net> wrote: > > Thanks Mirko, > > > Very Good information. What is needed is to reduce noise more (lower) > than signals. > 73 > Bruce-k1fz > > > On Thu, 22 Dec 2016 22:36:30 +0100, S57AD wrote: > > 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 : > > > 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 > > > > ----- End forwarded message ----- > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband