[OZAPRS] UHF APRS freqs in VK

[Matthew Cook]

Yes.   It helps if you start with commercial grade equipment and don't use
cheap notch based diplexers or broadband devices to achieve your
isolation.  There is no substitute for Q, so using decent tuned bandpass
(inc notch) with correctly phased jumpers and an isolator on the output
goes along way to achieving the > 100dB necessary.   We've had to do this
at all our sites here in VK5 to ensure we're good RF neighbours with the
co-located commercial services.

This UHF allocation problem is no different from co-locating a 145.175MHz
service with an analog voice repeater 800kHz up the band.   With the new
1.6MHz split it gets even more exciting.   There is argument for going back
up high to 147.575 but I'm going to keep quiet on that issue, the band
police will be out for my blood.

I agree the allocation doesn't make it easy, but it's not impossible either.

73

Matthew
VK5ZM


On 13 November 2017 at 10:19, Glen English VK1XX <
glenlist at pacificmedia.com.au> wrote:

> 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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