[amsat-bb] Re: Fw: Re: NASA's American Student Moon Orbiter...
Trevor
m5aka at yahoo.co.uk
Sun Jul 6 15:42:55 PDT 2008
The 420-450 MHz Military PRIMARY Allocation is an issue in a number of countries, in some of which Radio Amateurs do not have transmit access to 70cm at all.
The United Kingdom Regulator OFCOM has published on their website the following information on Fylingdales in the UK.
Interference to UHF Band 1 and GSM Radio Systems from Fylingdales Radar
http://www.ofcom.org.uk/radiocomms/spectrumawards/completedawards/award_412/documents/interference/
PDF Interference to UHF Band 1 and GSM Radio Systems from Fylingdales Radar
http://www.ofcom.org.uk/radiocomms/spectrumawards/completedawards/award_412/documents/interference/report.pdf
PDF Fylingdales co-ordination tool
http://www.ofcom.org.uk/radiocomms/spectrumawards/completedawards/award_412/documents/workshop/fylingdales.pdf
Fylingdales co-ordination tool workshops
http://www.ofcom.org.uk/radiocomms/spectrumawards/completedawards/award_412/documents/workshop/
Questions and Answers on the award of wireless telegraphy licences for use of the spectrum bands 412-414 MHz paired with 422-424 MHz
http://www.ofcom.org.uk/radiocomms/spectrumawards/completedawards/award_412/qas/
I recall that several years ago I think Peleg 4X1GP on this list, pointed out that 70cm isn't an Amateur band (apologies Peleg if I misquote you). The Amateur Primary allocations stop at 146 MHz and then there's nothing until 24 GHz.
73 Trevor M5AKA
--- On Sun, 6/7/08, John B. Stephensen <kd6ozh at comcast.net> wrote:
> UV is a problem as hams in much of the U.S. are limited to 1
> kW EIRP on 70
> cm. The military is the primary user of the band. Recently,
> some repeaters
> near PAVE PAWS sites have had to reduce power to 5 W due to
> interference
> with the return signal from the 4 GW EIRP RADAR.
>
> 73,
>
> John
> KD6OZH
>
> ----- Original Message -----
> From: "i8cvs" <domenico.i8cvs at tin.it>
> To: "AMSAT-BB" <amsat-bb at amsat.org>;
> <kl7uw at acsalaska.net>; "Joe"
> <nss at mwt.net>; "G0MRF David Bowman"
> <g0mrf at aol.com>
> Sent: Sunday, July 06, 2008 08:53 UTC
> Subject: [amsat-bb] Fw: Re: NASA's American Student
> Moon Orbiter...
>
>
> > ----- Original Message -----
> > From: G0MRF at aol.com
> > To: nss at mwt.net
> > Cc: domenico.i8cvs at tin.it ; kl7uw at acsalaska.net
> > Sent: Saturday, July 05, 2008 1:21 AM
> > Subject: Re: [amsat-bb] Re: NASA's American
> Student Moon Orbiter...
> >
> >
> > Hi Joe.
> >
> > Looking at 70cm up and 2m down, Dom has shown the 2m
> path can be achieved
> > with a 13dB gain antenna on the ground and 10 Watts on
> the satellite.
> > That's a very small bandwidth transponder
> >
> > For the uplink, it's not quite as easy.
> > I've just run a link budget calculator and it
> looks like you need about
> > 80 Watts and 20dB of antenna gain on 70cm. That
> produces around 5000 Watts
> > ERP (allowing for losses)
> >
> > As Dom pointed out, you dont just need a signal thats
> just above the
> > noise level at the satellite. Up there you need enough
> of a signal at the
> > receiver so that the satellites transmitter can
> generate a decent amount
> > of power on 2m.
> >
> > The 5kW ERP generates a signal around 16dB above
> noise at the satellite.
> > With luck, that will be sufficient to produce enough
> power on the 2m
> > downlink.
> >
> > Of course there are a lot of variables and
> 'detail' . but 5kW ERP up and
> > a 13dB gain antenna on the downlink are 'In the
> ballpark' for a minimal
> > working U/V system.
> >
> > Thanks
> >
> > David
> >
> > Hi David, G0MRF
> >
> > Looking at the specifications of AO40 I found that at
> 435 MHz the
> > equivalent noise temperature of the RX is
> > TN (k) = 500 kelvin
> > The Prx (23) i.e. the power needed by the receiver to
> develope a signal
> > of 23 dB over the noise is -145 dBW
> > The 435 MHz satellite antenna gain is 14 dBi
> > It is not specified the transponder output power with
> a S/N=23 dB because
> > it depends on what transponder is intended to be used
> for the downlink.
> > Probably -145 dBW at the RX input is the power needed
> to get a S/N = 23
> > dB at the IF input before to be switched by the matrix
> to different
> > transponders.
> >
> > By the way the attenuation earth to moon at 435 MHz
> for 400.000 km is 197
> > dB and going back to calculations
> > we get :
> >
> > TX power at 435 MHz on earth........................
> + 20 dBW (100 W)
> > 435 MHz antenna gain on earth .......................
> + 18 dB
> >
>
> > -----------------
> > EIRP of the ground
> station................................ + 38 dBW ( 6.3
> > kW)
> >
> > Attenuation 435 MHz for 400.000 km ..............
> -197 dB
> >
>
> > ------------------
> > Power received on a 435 MHz isotropic........... -
> 159 dBW
> > antenna at a distance of 400.000 km
> > Satellite antenna gain
> ......................................... + 14 dBi
> >
>
> > ------------------
> > Received power at RX input for S/N=23 dB.... - 145
> dBW
> >
> > It seems that both calculations match and 5 kW to 6
> kW EIRP up on 70 cm
> > and 13 dBi antenna gain on the 2 meters downlink are a
> minimum necessary
> > provided that the satellite antennas orbiting around
> the moon are
> > constantly directed toward the earth but this is a
> very difficult task.
> >
> > 73" de
> >
> > i8CVS Domenico
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. Opinions expressed are
> those of the author.
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>
> _______________________________________________
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