Exactly my feeling. We've got low-band fire here with channels close-spaced and
high power TX and desense on an adjacent channel is rarely an issue. Usually
you've got to be within one or two blocks from the 1/4K before it gets noticed.
Chuck
----- Original Message -----
From: Doug Bade
To: Repeater-Builder@yahoogroups.com
Sent: Friday, January 22, 2010 9:24 AM
Subject: Re: [Repeater-Builder] 6 Meter Repeater spacing (no duplexers)
I had a quite much longer reply in the buffer and decided to shorten
it.. .. but 19 miles for any tx to rx coupling would seem to make the band
unusable in a metro area.. due to every radio would swamp every receiver in the
market...This is just not the case..
The only influence the tx could have on the rx (500khz spacing) at over maybe
a mile or two would be white noise.. as the carrier would be well below desense
levels itself at that range.... The implication is every white noise generator
within 19 miles would disrupt the rx site.... aka every mobile in the band.....
or base or other repeater......
I can say I am aware of a system that a group here operated a 6m repeater
site to site at .5 miles at 300khz with modest filters on the TX end.. The RX
site actually had 3 repeater receivers for 3 different clubs...
Proper engineering would put at least a single bandpass can and maybe an
isolator if possible on the TX site.. to minimize white noise to other
users...and by itself should make the system useable within a mile let alone
8...or 19...
Doug
KD8B
At 08:59 AM 1/22/2010, you wrote:
Boy, that seems excessive to me, even at 500 kHz. My hunch is that you'll
have acceptable performance much closer in distance. 1 MHz spacing was
mentioned which would obviously be even better.
Chuck
WB2EDV
----- Original Message -----
From: "Eric Lemmon" <wb6...@verizon.net>
To: < Repeater-Builder@yahoogroups.com>
Sent: Friday, January 22, 2010 12:19 AM
Subject: RE: [Repeater-Builder] 6 Meter Repeater spacing (no duplexers)
> Tim,
>
> I use CommShop for Windows, a handy package that does much more than
> duplexer isolation calculations. Go here for more info:
> < www.dcico.com/dcilmr.htm>
>
> It calculates that you'll need about 93 dB of isolation, which requires
> more
> than 19 miles of horizontal separation. This can be reduced by using
> lower
> power output, a better receiver and PA, and perhaps directional antennas.
> Bear in mind that CommShop and similar programs make many assumptions to
> come up with these estimates, and some or all of those assumption might be
> invalid. YMMV...
>
> 73, Eric Lemmon WB6FLY
>
>
>
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [ mailto:repeater-buil...@yahoogroups.com] On Behalf Of Tim Ahrens
> Sent: Thursday, January 21, 2010 7:21 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] 6 Meter Repeater spacing (no duplexers)
>
>
>
> Hi Eric/all,
>
> Since this is just a curiosity at this time, let's figure 50 watts,
> 0.25uV, & 500khz split.
>
> I figured that was the case about the vertical separation, but
> threw it in anyway.
>
> One site would be a solar site, so it would make sense to
> make it the RX. Guess it might require a notch can at
> the rx site, based on what Chris said.
>
> BTW, what software package are you using?
>
> I've been using Radio Mobile for coverage, & it works
> pretty good.
>
> Thanks,
>
> Tim W5FN
>
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