[HIham] [Fwd: Re: [hamradiohawaii] ISS is in Cross-band mode until sometime Sunday]

Sat Jul 8 18:15:59 EDT 2006

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Ron H

-------- Original Message --------
Subject: 	Re: [hamradiohawaii] ISS is in Cross-band mode until sometime 
Sunday
Date: 	Sat, 08 Jul 2006 12:08:41 -1000
From: 	Ron Hashiro <rhashiro at hawaiiantel.net>
To: 	hamradiohawaii at yahoogroups.com
CC: 	Hawaii Ham <hiham at mailman.qth.net>
References: 	<20060708075048.83879.qmail at web38015.mail.mud.yahoo.com>

Dan, ever put together a two meter repeater?

You'll find that a piece of hardware known as a duplexor is needed to 
separate the received 2m signal from the transmit 2m signal and keep 
them from interfering.  It's essentially a very precise filter 
constructed from four or six large cylinders made of brass.  The size 
and weight of these duplexors are negative factors when attempting to 
launch a repeater into space.  (There is a rule of thumb known as the 
rocket principle that says that only one percent of a rocket's take-off 
weight makes it into orbit.  That's a lot of rocket needed to put 
payloads into orbit.)  For that reason, much of amateur radio repeater 
work (as well as many other radio services) in space is cross-band, 
eliminating the size, weight, durability and maintenance requirements 
for a duplexor.

The other part of a "satellite" radio is the ability to make fine 
changes in the transmit and receive frequencies.  That is due to the 
apparent shift in frequencies due to the effect of doppler shift (the 
same classical shift in audio frequency you here when a train whistle or 
car horn changes pitch as it approaches and recedes from you).  The 
effect of doppler is not too bad on 2 meters (about +/- 3 Khz) for an 
average ISS pass, but it is multiplied as the frequency increases.  The 
shift is three times as bad, or 9 Khz in the 430 Mhz range, an about 9 
times that amount, or 27 Khz in the 1.2 Ghz band.  That doppler is more 
than enough to "drift" outside the passband of the average 1.2 Ghz FM 
receiver without taking measures to compensate for that doppler shift.  
This becomes more of a requirement as one moves away from FM on 2 meters 
and into SSB on other bands for satellite work.

The proposed bandplan for the ISS is to have all voice uplinks on other 
frequencies, and the downlink on the 2m band.  The recent PCSAT2 module 
was constructed  and scheduled before that proposed bandplan went into 
effect.  When PCSAT2 is retired in about two months, all future modules 
will comply.

Note that when it goes into effect, you the user is required to 
compensate for doppler, not the satellite.  The onboard satelllite will 
gladly repeat any signal it finds when YOU (and others) compensate for 
the doppler shift.  That makes sense, because a satellite can typicall 
see say up to two thousand or more miles of land below it and at any 
given moment, half the potential signals are going up in frequency and 
the other half is going down in frequency.  It's not that bad in Hawaii 
when the majority of the land is really ocean and maybe two or four hams 
are on, but it's really bad over North America and Europe.

Incidentally, a recent poll of ISS users found that the majority use a 
VHF/UHF dual-band mobile radio and a vertical antenna to make contact 
with the space station.  So, the same dual-band mobile radio in your car 
or home is the favored rig for ISS work.  I used the Icom IC-208H 
dual-band single receive rig during Bill McArthur KC5ACR's flight with 
no problems.  I find the Kenwood TM-D700 to be ideal, as the built-in 
TNC decodes the APRS packet beacons whenever the ISS is in data mode 
above the horizon, giving confirmation whenever the ISS is around.

Good question.  Probably a longer primer on getting started on satellite 
work than you might have imagined, but it has quite a number of moving 
pieces that comes together for a quality, enjoyable QSO.  Parts of the 
material was covered at the EARC meeting in February 2006,which spured 
the recent interest and activity on space communications.

Ron H, AH6RH

Dan Buckheit wrote:

> Hi Ron. Thanks for the info.
>
> One question though.... many sattys have up links on 2 M and down 
> links on 70 cm. Why doesn't the ISS do this normally? Is this to make 
> it easier for Hams  to make contact on just one band ... eliminating 
> the need for two radios? or a Satl radio?
>
> Thanks 73
> Dan.
>
> Ron Hashiro <rhashiro at hawaiiantel.net> wrote:
>
>     Dear Hawaii Hams,
>
>     The ISS is now operating in a special QRP cross-band mode until
>     sometime
>     on Sunday.
>
>     You transmit on 437.800 Mhz
>     You receive on 145.800 Mhz
>
>     Passtimes for Honolulu can be gotten at
>     http://ronhashiro.htohananet.com/am-radio/fd.log
>     <http://ronhashiro.htohananet.com/am-radio/fd.log>
>
>     You should transmit no more than ten watts into a vertical antenna on
>     UHF to qualify for QRP operation.
>
>     Of special interest is Friday afternoon's 5:24 PM pass, which is a 54
>     degree pass over Honolulu, slightly east of directly overhead, and
>     the
>     ISS is heading towards the mainland. It might be possible to work
>     California on the last 30 seconds of the pass (you should be ready to
>     compensate for the doppler shift, which can be up to 9 Khz at the
>     ends
>     of the pass on UHF).
>
>     On Saturday, the 4:13 and 5:48 pm passes might be usable for Field
>     Day
>     space comm credit.
>
>     Also, the Sunday morning 1:53 am and 3:28 am passes are of
>     interest for
>     Field Day space comm credit. There is a possibility that the
>     astronauts
>     might be on for these passes..
>
>     For real-time news, see:
>
>
>
>     http://www.issfanclub.com <http://www.issfanclub.com>
>
>
>
>     Ron Hashiro, AH6RH
>
>
> __,_._,___ 