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<p><font face="Arial">And how does that solve the basic RF problems
of tx noise and rx overload for a shared site? </font><br>
</p>
Ray vk2tv<br>
<br>
<div class="moz-cite-prefix">On 15/11/17 14:29, Andrew Rich wrote:<br>
</div>
<blockquote type="cite"
cite="mid:27880FBC-1F6E-4ED2-BB1F-5D8F332FAEF4@tech-software.net">
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Go 19k2 <br>
<br>
<div id="AppleMailSignature">Sent from my iPhone</div>
<div><br>
On 15 Nov 2017, at 1:24 pm, Matthew Cook <<a
href="mailto:vk5zm@bistre.net" moz-do-not-send="true">vk5zm@bistre.net</a>>
wrote:<br>
<br>
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<blockquote type="cite">
<div>
<div dir="ltr">As I mentioned not easy, but not impossible
either :)
<div><br>
</div>
<div>In liu of going around in circles then the question is
where to move it that will gain the support of the WIA
TAC.</div>
<div><br>
</div>
<div>There is no where that I can see within 430-440MHz
where this could go and co-site happily it's just too
crowded.... so really the only logical place is where
you've already suggested between 441.000 & 442.975 in
the ALL MODE section... The complication here being it
won't work well co-sited with a DATV TX and at the other
end you're up against the top of the repeater links....</div>
<div><br>
</div>
<div>Suggestions ?</div>
<div><br>
</div>
<div>Matthew</div>
<div>VK5ZM</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On 15 November 2017 at 11:18, Glen
English VK1XX <span dir="ltr"><<a
href="mailto:glenlist@pacificmedia.com.au"
target="_blank" moz-do-not-send="true">glenlist@pacificmedia.com.au</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi
Matthew<br>
<br>
You are right about TX combining, but your argument does
not correctly<br>
consider TX noise. You will need a cubic meter of
filters to do it with<br>
a reasonable loss of < 3dB....<br>
<br>
You have to look at the percentages...<br>
<br>
800kHz on 2m (your 145.175 with 1,6meg 2m repester
offsets ) is OK.<br>
<br>
But 800kHz on 2m is NOT 800kHz on UHF, it is 2.4 MHz on
UHF.<br>
<br>
300kHz on UHF (what you proposed) is 100kHz on 2m.<br>
<br>
anyone care to build a 100kHz offset 2m duplexor ?<br>
<br>
at 300kHz away on UHF, most radios will be ~ 80dB down
in a 16kHz<br>
bandwidth .<br>
so if we have +43dBm TX, noise is -37dBm.<br>
<br>
if we are on the same coax , we need the difference of
-127 - -37 = 90dB<br>
<br>
if we are on a split antenna system (all TX in ANT1, all
RX in antenna<br>
2) then the isolation between the two antennas subtracts
from the filter<br>
requirement call it 40dB on 70cm, so now you require
50dB .<br>
<br>
300kHz at UHF is 0.06% frequency spacing. This wont be
practically<br>
realisable with a bandpass-notch configuration because
the return loss<br>
will suffer. Back to a bandpass configuration, 10dB
isolation is about<br>
all you'll get so you'll need 5 x 6" 3/4 wave filters
for about 7 dB<br>
loss. and god awful return loss<br>
<br>
For fixing the return loss you could use a balanced
hybrid combiner, and<br>
2x the filters, so 10 x 6" filters and 2 hybrids will
yield good return<br>
loss and perhaps 6-7dB loss for your 50dB....<br>
<br>
It's clearly not too easy.<br>
<span class="HOEnZb"><font color="#888888"><br>
-glen<br>
</font></span>
<div class="HOEnZb">
<div class="h5"><br>
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