From the AMSAT-BB mailing list, 31 July 1997:
Here is the correct information on AO-27 about packet vs. voice operation.
What is the satellite called?
------------------------------------------
Object 22825 is called AO-27 by the Amateur and Eyesat-1 by the commercial
interests.
When can AO-27 operate?
-----------------------
The Satellite contains batteries and solar panels and is could run the
transmitters during ANY portion of a pass. Due to power budget limits, the
AO-27 Transmitter can not run all the time. If it did, the batteries would
run down in a week's time. Therefore the AO-27 TX is on only for 17 Minutes
a pass. This is a difference in the Amateur and Commercial sides. The
Eyesat-1 commercial Transmitter could be left on all the time at different
power levels.
What Hardware is on-board?
------------------------------------------
The Satellite contains 3 Transmitters and 7 Receivers. It also has 5 FSK
demodulators, 2 GMSK demodulators, 2 GMSK modulators,1 G3RUH modulator, 1
AFSK modulator and 3 analog modulators for sending received analog to any of
the 3 transmitters. There is NO DSP on-board.
What are the differences between the Amateur and Commercial sides of the
satellite?
------------------------------------------------------------------------
For all practical purposes any RX can be switched to and demodulator and
any TX can be switched to any modulator. AO-27 and Eyesat-1 can both be used
to send Packet (any of the modulations the modems support) and Voice. There
is no real difference from the Amateur AO-27 side and the Commercial Eyesat-1
side as far as modems are concerned. Both AO-27 and Eyesat-1 can run the
AO-16 microsat style software and can be used as a digital-store-and-Forward
satellite. The Commercial TXs have 16 power levels and the Amateur TX has
only 4 levels.
What can the Analog mode do?
----------------------------
The Analog mode simply hooks the discriminator of the Receiver to the
varactor of the Transmitter. Tests before launch showed about 30KHz can be
passed through in this mode. If you can fit it into 30KHz (well almost) you
can send it through AO-27.
Slow-Scan TV, 1200 baud GMSK, 1200 AFSK, Lets not forget Voice,
DOVE (DO-17) Telemetry and a host of other modes have been sent through
AO-27 in Analog mode.
What should we be sending through AO-27?
----------------------------------------
AO-27 in Analog mode is not a very good way to send Packet. There are
enough packet satellites out there that do a better job. Voice is the
preferred use as it reaches the most people. But from time to time, other
modes should not be ruled out. The slow-scan TV worked very well, and I for
one like to see new ways to use the satellite that we did not think of when
we built it.
So if we should not use packet, WHO is sending packet to AO-27?
---------------------------------------------------------------
1) The uplink 145.850 is very close to other satellite uplinks. LO-19 has
Uplinks at 840 and 860 that pass through the Analog passband. When LO-19 is
in the sky at the same time AO-27 is, you can hear uplinks from ground
stations.
2) There is ground based packet station that don't pay attention to band
plans, it comes up on the Analog passband. (you can decode some packets with
a TNC to see who).
What can we do?
---------------
Just enjoy the satellite when you can. Most people enjoy making contacts
and don't worry about the interference picked up by the receivers. If we
had built deaf receivers so only 5 KW EIRP could make it into the satellite,
there would be far less contacts from low power stations and many of you
would never have known that AO-27 was available.
If you do happen to decode a packet callsign, just drop them a nice note.
I have called several stations that were using packet and some that were
using simplex voice that never knew they were operating on a satellite
frequency. If you demand they move, you might be surprised just how strong
their signal becomes in the following weeks.
Final Note.
-----------
Please LISTEN before you transmit. If you can't hear the satellite, you
can't make a contact and you will keep everyone else from making one.
- - Michael
(**************************************************************************)
(* Michael Wyrick *)
(* N4USI *)
(* AO-27 Control Operator *)
(* *)
(* PGP-public key can be found at www.umbra.com *)
(**************************************************************************)