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I thougt the Rx low/Tx hi was because the mobile
commercial surplus equipment available for
low cost for ham use, also remember the Micor UHF
that use only one crystal for TX/RX....
maybe i was wrong????????????
Juan
----- Mensaje original -----
Enviado: Thursday, March 11, 2004 10:24
AM
Asunto: [Repeater-Builder] 440 - 450 Low
in High Out Repeaters
Skipp,
You made a comment about your local 440 Amateur
repeaters using the High
in and Low out plan and by doing this you suggest
that your area in
California is a "trend setter". I thought that I would
share some
information about the logic that went into our band planning and
actions
here in Utah.
In Utah and neighboring States, our 440-450
repeaters use low in and
high out. Most of our long standing repeaters
chose this plan because
they were co-located on mountain top radio
sites with commercial
equipment. The commercial repeaters transmitted
in the 450-455 Mhz band.
As an example, we did not want to have our
amateur 449.500 Mhz receiver
next to a 450.250 Mhz transmitter that
was used by the local TV
stations remote pickup broadcast repeater. Our our
antennas were
restricted to have only 40 ft or less horizontal separation
from each
other. The desense would have been difficult and expensive to
cure with
only 750 khz of frequency separation between the transmitter
and
receiver at 450 Mhz.
We chose to put our receiver inputs low in
and by using the 444.500 Mhz
frequency to receive, we gained 5 more
megahertz of frequency isolation
from the commercial transmitters. We still
have to use bandpass type
duplexers with band reject on our repeater to
co-exist with the
commercial transmitters. Yes, we do have a dual isolator
in our
transmitter output to the duplexer to keep the IM products down
to
acceptable levels..
This is only one of several examples I could
show you as to why Utah
chose the Low in and Hi Out Plan for our 440
Repeaters.
Maybe you do not have this kind of problem in your local
area. I'm sure
that's one of the reasons why the band plan is different in
other parts
of the country.
On our 420-435 Mhz band, we have links
that use a 10 Mhz or wider split.
Some links use the 5 Mhz split. We chose
this because this lowers the
cost of Duplexers and Cavity
filters.
We planned our 420-450 amateur band frequencies to work the
best in our
local RF environment without having costly
solutions.
John, K7JL
Utah VHF Society
http://www.ussc.com/~uvhfs/
http://www.ussc.com/~uvhfs/frqcoord.html
>Message:
6
> Date: Wed, 10 Mar 2004 22:09:11
-0000
> From: "skipp025" <[EMAIL PROTECTED]>
>
>Most
440 to 450MHz Amateur Repeaters in my
>area use 5MHz offsets, with the
transmitter
>on the lower frequency. I believe much of
>the
country uses the reverse. But we here in
>Northern California are always
the "trend setters".
>:-)
>
>Linking 420-425MHz range
amateur duplex links in
>Northern California use a 3MHz offset, as
does
>the 480-490 range "T Band"
repeaters.
>
>cheers
>skipp
>
>www.radiowrench.com
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