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-bounces@contesting.com] On Behalf Of Matt
Murphy
Sent: Thursday, December 22, 2016 11:19 PM
To: k1fz@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 <k1fz@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
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