One must remember that the purpose of these filters is to reduce the total
energy presented to circuitry that would otherwise be overloaded by it, or
create crud at any level because of the poor IMD characteristics of the
radio circuits.
I did something of the sort at W4BVV in the 1960's with tuned circuits in
front of the 40 meter RX to get rid of all the carrier energy at 7100 and
up.
These days with a K3 I can tune right under a 30 over 9 BC carrier and
listen to the way-down 60 Hz energy in their audio.
Are we back with these filters being used to provide a crutch for inferior
RX? Isn't a roofing filter the same thing, but effectively tuneable, except
for the first conversion stage. Isn't this high level bleed measured in the
standard tests you find on the Sherwood Engineering site?
The advantages being touted for the filters seem to be the same thing I
finally got when I bought a K3.
Limiting on frequency noise coming from the antenna with RX antenna pattern
is another thing altogether.
73, Guy K2AV
On Thu, Dec 22, 2016 at 8:51 PM, GALE STEWARD via Topband <
topband@contesting.com> wrote:
> Years ago at the W3GM M/M station, Gerry had several crystal filters (50
> ohm Z input & output) in the 40M RX path. As I recall, these were about
> 20-30 khz wide (each) and were of slightly different center frequencies so
> that most of the 40M CW band could be covered.
> I DO remember that they worked very well. I never saw one for 160.
> 73, Stew K3ND
>
> From: K1FZ-Bruce <k1fz@myfairpoint.net>
> To: Topband <topband@contesting.com>
> Sent: Thursday, December 22, 2016 3:41 PM
> Subject: Topband: "Thinking out loud"
>
>
>
> 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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