[OZAPRS] UHF APRS freqs in VK

Glen English VK1XX glenlist at pacificmedia.com.au
Mon Nov 13 10:49:57 AEDT 2017


Hi Matthew

Have you considered the issue and difficulty  of filtering the TX noise
of the repeater on the digipeater RX frequency maybe 500kHz away ?

IE the 90dB MINIMUM  you need say 500kHz away ?



On 13/11/2017 10:17 AM, Matthew Cook wrote:
> Unless you're repeater outputs are within 438.9 and 493.3 then
> filtering the 70cm APRS channel isn't difficult.   There are a heap of
> UHF services being pulled out of Victoria at the moment and very good
> cavities and isolators can be obtained for reasonable prices.
>
> Frequency allocation and band plans seem simple to do, but finding the
> right balance between all the different activities and requests for
> spectrum by the band police means administering this spectrum is
> harder than it looks.  I know what hoops had to be jumped through and
> buy whom for the current 70cm band plan, it's not perfect but when
> personalities get in the way it's difficult to get a "perfect" solution.  
>
> If you've got suggestions on how things can be improved then by all
> means fire them into the WIA TAC's in your separate states.
>
> 73
>
> Matthew
> VK5ZM
>
> On 12 November 2017 at 19:02, Glen English VK1XX
> <glenlist at pacificmedia.com.au <mailto:glenlist at pacificmedia.com.au>>
> wrote:
>
>     Hi Scott
>
>     yeah 439.1 which is USELESS DUMB IDEA I EVER HEARD OF , I see it
>     in the
>     bandplan.
>
>     why ? because it is too close to easily diplex into existing 70cm
>     repeater systems that it might have to share with. Whoever came up
>     with
>     439.1 had NFI.
>
>     Two problems
>
>     1) requires lots of filtering and or loss to combine with 438-440
>     transmitters
>
>     2) Because the digi would need to RECEIVE next door to the 70cm
>     repeater
>     transmitter, it will just get knocked over with TX noise unless you
>     throw something like 3 x 6" 3/4 wave cans at it.... like no way.
>
>     Canberra city is going on 442.975
>     Ginini will go on 442.775 , tentatively, barring staying out of
>     the way
>     of numerous UHF repeater links..
>     Maybe they should go on 12.5k offsets to stay clear. hmm.
>
>     200kHz apart in the same region is far enough that sidebands and spurs
>     from one TX (say on 442.775) will not get into the other receiver (say
>     on 442.975)
>
>     :-)
>     g
>
>
>
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