[OZAPRS] UHF APRS freqs in VK

[Glen English VK1XX]

I'll write a tech paper and send it to NTAC.

plenty of spectrum even with the repeater links

analog ATVers on 444.25  would still produce a bit of rubbish on the
bottom of their VSB into the top end of 442. how much I dunno. a problem
, dont think so.

DTVers  carrier on 446.5 with 7 MHz nominal BW is actually ahh 6.65 MHz
BW or extending to 443.175

but in practice due to non linearities, it will spill over another half
MHz at -40dB. probably 442.675 is most likely the highest you might want
to use where there is 446.5 ADTV in use like cap cities....






On 15/11/2017 2:24 PM, Matthew Cook wrote:
> As I mentioned not easy, but not impossible either :)
>
> In liu of going around in circles then the question is where to move
> it that will gain the support of the WIA TAC.
>
> 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....
>
> Suggestions ?
>
> Matthew
> VK5ZM
>
> On 15 November 2017 at 11:18, Glen English VK1XX
> <glenlist at pacificmedia.com.au <mailto:glenlist at pacificmedia.com.au>>
> wrote:
>
>     Hi Matthew
>
>     You are right about TX combining, but your argument does not correctly
>     consider TX noise. You will need a cubic meter of filters to do it
>     with
>     a reasonable loss of  < 3dB....
>
>     You have to look at the percentages...
>
>     800kHz on 2m (your 145.175 with 1,6meg 2m repester offsets )  is OK.
>
>     But  800kHz on 2m is NOT 800kHz on UHF, it is 2.4 MHz on UHF.
>
>     300kHz on UHF  (what you proposed) is  100kHz on 2m.
>
>     anyone care to build a 100kHz offset 2m duplexor ?
>
>     at 300kHz away on UHF, most radios will be ~ 80dB down in a 16kHz
>     bandwidth .
>     so if we have +43dBm TX, noise is -37dBm.
>
>     if we are on the same coax ,  we need the difference of  -127 -
>     -37 = 90dB
>
>     if we are on a split antenna system (all TX in ANT1, all RX in antenna
>     2) then the isolation between the two antennas subtracts from the
>     filter
>     requirement call it 40dB on 70cm, so now you require 50dB .
>
>     300kHz at UHF  is 0.06% frequency spacing. This wont be practically
>     realisable with a bandpass-notch configuration because the return loss
>     will suffer. Back to a bandpass configuration, 10dB isolation is about
>     all you'll get so you'll need 5 x 6" 3/4 wave filters for about 7 dB
>     loss.  and god awful return loss
>
>     For fixing the return loss you could use a balanced hybrid
>     combiner, and
>     2x the filters, so 10 x 6"  filters and 2 hybrids will yield good
>     return
>     loss and perhaps 6-7dB loss for your 50dB....
>
>     It's clearly not too easy.
>
>     -glen
>
>
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