Re: D-STAR repeater problems in Copenhagen
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.
73
David
In a message dated 07/12/2008 20:34:56 GMT Standard Time, oz1my@privat.dk writes:
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, when it is going away from us to the East, which is the direction of the repeater :-(
Personally I am just 6 km away from the repeater with no obstructions on the pass from it.
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@aol.com G0MRF@aol.com wrote:
From: G0MRF@aol.com G0MRF@aol.com Subject: [amsat-bb] Re: D-STAR repeater problems in Copenhagen To: oz1my@privat.dk, amsat-bb@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.
73
David
In a message dated 07/12/2008 20:34:56 GMT Standard Time, oz1my@privat.dk writes:
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, when it is going away from us to the East, which is the direction 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@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Hi Graham, Trevor and David and the rest of the "listeners" on the amsat-bb Thanks for the answers. I may return to this subject later - but I found a very interesting homepage:
http://utahvhfs.org/dstar_testing.html
It looks like a very solid piece of work to me.
73 OZ1MY Ib ----- Original Message ----- From: "Trevor" m5aka@yahoo.co.uk To: amsat-bb@amsat.org Sent: Monday, December 08, 2008 12:52 AM Subject: [amsat-bb] Re: D-STAR repeater problems in Copenhagen
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@aol.com G0MRF@aol.com wrote:
From: G0MRF@aol.com G0MRF@aol.com Subject: [amsat-bb] Re: D-STAR repeater problems in Copenhagen To: oz1my@privat.dk, amsat-bb@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.
73
David
In a message dated 07/12/2008 20:34:56 GMT Standard Time, oz1my@privat.dk writes:
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, when it is going away from us to the East, which is the direction 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@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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