[amsat-bb] Re: Eagle U/V modes

Paul Williamson kb5mu at amsat.org
Sun Oct 8 09:39:56 PDT 2006

At 10:23 AM -0400 10/8/06, McGrane wrote:
>Could someone please explain further the capabilities of the U/V text
>messaging mode. Would this incude the use of typical packet equipment?

No. In order to transfer information (even at low data rates) with 
very small antennas and low power, it's necessary to use every trick 
in the digital optimization book, so it won't be compatible with 
existing packet equipment.

By very small, it's meant that the radio might clip onto the back of 
a handheld PDA, with an antenna system small enough to be manageable 
handheld. Probably not as small as a rubber duckie, but something 
that doesn't need pointing. Exact details are still to be designed.

There's not a lot of detail yet about how the system will work from a 
user standpoint. The work so far has been on making the links work 
and determining the spacecraft requirements. For higher level 
architecture, one idea is to use Jabber, which is an open protocol 
for instant messaging (keyboard chat) used on the internet. It's 
thought that many of the applications that work on APRS would work 
great on this system (not just positioning).

Now would be a good time to throw out your ideas for applications for 
a service like this, so the system designers can try to accommodate 

(The above info is based on what I heard at the Space Symposium and 
not to be considered official in any way.)

>Could some old timers describe a typical AO-13 or AO-40 mode U/V station
>for my education and to help me build a station.

The baseline AO-13 Mode B station was a 20-foot-long circularly 
polarized cross-yagi for 2m, plus a 14-to-20-foot circularly 
polarized cross-yagi for 70cm, mounted for azimuth and elevation 
rotation. Rather short low-loss coax feed (e.g., Belden 9913) or a 
mast-mounted low-noise preamp on the downlink. On the uplink, 
operators who wanted to work under all conditions had about 100 watts 
available, but under good conditions much less power was needed. 
Continuously variable uplink power was considered mandatory since 
being too loud is bad practice and being too weak meant marginal 
stations couldn't hear you. SSB and/or CW capability on the radios. 
Most conveniently, a single-box "satellite" rig would allow the use 
of a single knob to tune around the transponder, but separate 
transmit and receive rigs were also common.

Seriously hard-core stations who wanted to hear down to the 
transponder noise floor even when conditions were poor would phase 
two or more of the 20-foot cross-yagis. It was good to have a few of 
those stations around to pick out the very weak uplinks, but it 
wasn't really necessary for most users to have that much gain.

Computer control of the rotators was convenient but not necessary, 
since the satellite moves slowly across the sky. Likewise computer 
control of radio frequency was generally not required, since the 
Doppler shift changed rather slowly.

73  -Paul
kb5mu at amsat.org

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