[amsat-bb] Re: D-STAR repeater problems in Copenhagen
m5aka at yahoo.co.uk
Sun Dec 7 15:52:29 PST 2008
D-STAR repeaters should theoretically be less of a problem on 145.7875 MHz than 2.5 kHz deviation FM repeaters as they have a slightly narrower bandwidth.
The use of 145.7875 assumes that people are using 2.5 kHz deviation FM radios fitted with filters with an 8 kHz bandwidth at -6db and max 16 kHz BW at -60 db, however, in practice most Amateur rigs don't meet that spec. Realistically anyone within 15 km of an FM or D-STAR repeater on 145.7885 is going to find the ISS downlink gets clobbered.
The IARU bandplan allocates 145.800-146.000 MHz to the Amateur Satellite service, doppler causes the 5 kHz deviation ISS signal to be below 145.8 thus there is a conflict with the IARU Region 1 2.5 kHz deviation FM repeater output channel on 145.7875.
Lets hope that eventually the ICOM and Kenwood NXDN™ 6.25 kHz channel spacing Digital Voice standard is adopted for 2 metre repeaters as a replacement for FM with an upper channel limit of 145.7875 MHz.
73 Trevor M5AKA
--- On Sun, 7/12/08, G0MRF at aol.com <G0MRF at aol.com> wrote:
> From: G0MRF at aol.com <G0MRF at aol.com>
> Subject: [amsat-bb] Re: D-STAR repeater problems in Copenhagen
> To: oz1my at privat.dk, amsat-bb at amsat.org
> Date: Sunday, 7 December, 2008, 11:28 PM
> Hello Ib.
> Interesting allocation for D-Star.
> -60dB at 145.800 may sound suitable, but in practice what
> matters is how
> many dB down it is at 145.800 minus one half of the
> bandwidth of your IF filter.
> Ball park.........
> So -4kHz of doppler and -7.5kHz for a narrow FM filter
> gives your receivers
> bandpass down to 145.7885 MHz just 10k above the D-Star
> Which means the two are probably going to overlap.
> In a message dated 07/12/2008 20:34:56 GMT Standard Time,
> oz1my at privat.dk
> The theoretic spectrum should be more than 60 dB down
> on 145.800 MHz,but that does not seem to be the case.
> Including doppler the downlink from ISS is 145.796 MHz,
> it is going away from us to the East, which is the
> of the repeater :-(
> Personally I am just 6 km away from the repeater with
> no obstructions on the pass from it.
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those
> of the author.
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