QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/files/infodata/ham_sat.txt

Text File | 1994-11-27 | 11KB | 260 lines

>Newsgroups: rec.radio.amateur.misc
>Path: news.unomaha.edu!unlinfo.unl.edu!wupost!cs.utexas.edu!uunet!psinntp!digex!sgreene
>From: [e-mail] (Stephan Greene)
>Subject: Summary - Getting onto the Hamsats
>Message-ID: <[e-mail]>
>Keywords:  Satellites, OSCAR, AMSAT
>Organization: Express Access Public Access UNIX, Greenbelt, Maryland USA
>Date: Fri, 20 Mar 1992 16:57:07 GMT
>Lines: 249

On Wednesday, 11 March 1992, I posted a message to rec.radio.amateur.misc asking for suggestions and advice on
equipment for using the amateur satellites.  This article is a
summary of the responses I received, as well as some related
e-mail and news articles.

A big thank-you to those who responded directly to my
posting or posted a related article:

    [e-mail]  or [e-mail] (Mike Butts), KC7IT
    [e-mail] (Presley Smith), N5VGC
    [e-mail] (Ross Alexander), VE6PDQ
    [e-mail] (Gary Coffman), KE4ZV
    Andy MacAllister, WA5ZIB (via CompuServe's Internet gateway)
    [e-mail], WB6LFC

Here's the consensus opinions (any misrepresentations or
misquotes are my own - so flame me, not the nice folks who contributed!)


Antennas:
------------

For AO-13, the consensus is get to get KLMs, Telex/Hy-Gains, or
roll-your own,  Nobody liked the Cushcraft satellite antennas -
they appear to have problems in wet weather.  Bigger is also
better, if you have the space.  Several people mentioned the
KLM  22C and 40CX pair as excellent performers (again - you
need the room for those long booms!)  KE4ZV stated his pair of
KLMs (the big ones!) lets him work AO-13 with 3 to 30 watts
(hardline feed and rigorous attention to routing the feedlines a
nd cables properly to maintain the antenna patterns helps, too.).
Others mentioned the KLM 14C/18C pair as good performers -
but you need more power on the uplink.

Telex/Hy-Gain antennas were recommended by several people
as a less expensive alternative to KLMs that work almost as
well.  There's also M2 (started by an engineer from KLM).
While no one who responded uses them, the information I
received from a call to their factory in California suggests
they are comparable to slightly better than the KLMs in
performance, and about the same in cost.  Dave, WB6LFC, said homebrewing antennas is also feasible - it takes work,
but attention to detail results in top-notch performance
for very little money.  Finally, Ross, VE6PDQ, reported good
results using a pair of Cushcraft 215WBs on receive.

Problems encountered with AO-13 antennas include routing
cables and feedlines off the back of the antennas
(to preserve antenna patterns), use of fiberglass cross
booms, mounting preamps as close to the feedpoint as
possible, and long antenna booms drooping.  (Gary, KE4ZV,
recommends using a rope to brace the boom or stiffening
booms and fiberglass masts internally with foam-in-a-can
insulation.)

On antenna rotators, it appears the Alliance UD-100 is no
longer made, though it should still show up at hamfests.
People with long-boom antennas report the Alliance
rotator is too weak to move a big array anyway, and
recommended Yaesu's elevation-only rotator or their
Model 5400 azimuth-elevation unit.

Antennas for the low-altitude satellites appear to be much
less critical.  J-poles were most frequently mentioned
(the design from the AMSAT Journal?), but dipoles, ground-
planes, and yagis are also in use.  Several people work
RS-10 quite well with antennas in the attic.  Best results
are with steerable antennas, but the high operator
workload during a pass (unless the satellite is just
grazing your access circle) almost demands computer
control of the rotators.


Preamps:
-----------

You need a preamp for AO-13.  (I can hear the downlink
after a fashion on a Ringo fed with cheap coax and a
10 dB preamp in the shack, but it's not communications
quality reception!)  Only two people mentioned a specific
brand name (Advanced Receiver Research and the unit
included with the Ten-Tec 2510), so I assume almost
any GAsFET preamp in the 20dB gain class is adequate.
THE PREAMP MUST (almost always) BE MOUNTED AT THE
ANTENNA (check the discussion in Chapter 9 of the
Satellite Experimenter's Handbook and you'll see why!).
KE4ZV recommends mounting the preamp AT the antenna
feedpoint, if your elevation rotator can handle the
unbalanced load.

While no one mentioned it (maybe it's obvious), if the
antenna is used to transmit (say Mode J) as well as
receive (on Mode B, for example), the preamp MUST
either include RF-sensed switching, or be switched
out of the line before you transmit.  TRANSMITTING
INTO AN UNPROTECTED PREAMP WILL DESTROY IT INSTANTLY!

Preamps also seem to help on RS-10 (especially with
older HF rigs) and on the Pacsats.  It seems to be a
case of "try it, and get a preamp if it looks like it
would help").


Rigs:
------

Three radios were mentioned by name - Yaesu FT736
(and it's predecessor, the 726 with satellite module),
Kenwood TR751 (a mobile-capable 2 meter multimode),
and Ten-Tec's 2510.  The Ten-Tec unit is out of production.
The few units left are selling for about $300-350.  I'm
sure other multi-mode radios, and setups with converters
and transverters work well, too - it's just that no one
mentioned any by name.

Power output required is a function of the satellite,
your antennas, and how badly you want to communicate.
[QRP on the satellites is just like QRP on HF - you need
good antennas and feedline, you have to pick optimal
passes, and skilled operators at both ends are needed.
Given the apparent "calmer" operating style on AO-13,
QRP is probably easier there than on 20 meters!]

Anyway -about power for AO-13.  3-30 watts will
work if you have top-notch antennas (KE4ZV).
KC7IT uses 50-100 watts (Ten Tec 2510, Mirage D1010
amplifier, KLM 14C/18C fed with 50 feet of 9913).
Both KE4ZV and KC7IT use Mirage D1010 amplifiers
on 70 cm when they need a little extra power.
For an "optimum station", WA5ZIB recommends
60 watts on 70 cm and 80 watts on 2 meters for
AO-13, assuming good antennas (Telex/Hy-Gain or
better) and feedlines, and 20 watts to a 5' dish for Mode L.
Andy emphasized that you can get by and have lots
of fun with much less!

For Mode A, WA5ZIB said 6 watts to the AO-13 2 meter
antenna will work well.  People using omnis report
success with the Pacsats running 50-70 watts to a
J-Pole (N5VGC).  Several people said they (or someone
they know) have no trouble using RS-10 at lower
power (10-25 watts) with simple, omnidirectional
antennas.  Again, it's a case of "try it and see if it works."

There was unanimous consensus that the receiving
quipment (antenna, preamp, feedline, and receiver)
is more important than the transmit equipment.
Running more power "to hear yourself" is frowned
upon, to say the least!  It's also important to be able
to vary uplink power to adjust to specific conditions.
Both the Ten Tec 2510 and the Yaesu 736 have
continuously variable power output  (I guess the
rest of us just have to fiddle with the drive controls
on our rigs!).


Accessories and Other Stuff:
----------------------------------

You need a PSK modem to use the Pacsats.  PacCom
makes fully assembled units, either already integrated
with their own TNC, or as a board you install in your
TNC-2 clone.  They make similar 9600 bps units for
accessing UO-22.  The downlink receiver (on 70 cm)
should be capable of being tuned by the PSK modem's
AFC lines.  Newer radios can use the up/down lines from
the microphone jack or an accessory connection on the
rear panel.  Older radios must be modified, or be tuned
manually.  N5VGC told me he sees about 20KHz of doppler
on an AO-16 pass, and that without automatic tuning,
operator workload is too high to do much else besides
tune the receiver!

Just about any radio suitable for packet on 2 meters
will work for  AO-16, WO18, and LU-19.  To run 9600
bps on UO-22, modifications to bypass the microphone
and speaker's audio processing circuits are required.
I've seen some reports on rec.radio.packet and in the
various Hamsat columns that differences between
UO14 and UO-22's transmitters make UO-22 more
difficult to copy.  (I'll worry about that problem
later - I'll start with AO-16 and LU-19 first!)

No one mentioned computers - again, it must be
obvious (also, we're "talking" using computers!).
They're handy, and you need one IN THE SHACK when
working the Pacsats or for automated, real-time
control of antenna rotators (useful for low altitude satellites).

Other operator aids mentioned, or I thought of on my
own:  If your radio can't slave uplink and downlink
tuning (Ten Tec 2510 and Yaesu 736 can), you need
something to help convert between uplink and downlink
frequencies (and account for doppler shift and calibration
errors on the radios' frequency readouts).  A cardboard
slide scale or dial will work.  I'm thinking of programming
my HP48 to do the conversion for me.  You need something
like this to know where to tune on the uplink to hear
a given downlink frequency.

Software to track satellites and predict passes.  There
are many programs that work.  Price ranges from free
to $70 for state-of-the-art QuickTrack or InstantTrack
(available from AMSAT).  Special software is also needed
to use the Pacsats, and to interpret telemetry data.  This
software is also available from the usual ham sources, and
from AMSAT (BTW, software sales support the
amateur satellite program!)

Polarity switchers optimize antenna performance by
allowing switching antenna feeds from RHCP to LHCP as
the need arises.  They are a very useful add-on, but
don't appear essential.

Equipment to measure power output, SWR, transmit
 frequency - all useful (see - satellites are not that
different from HF!).


Conclusion:
---------------

Finally, there's AMSAT!  They're the people who build
and run several of the satellites (AO-10, AO-13, AO-16),
and have a hand in many of the others!  They're also
beginning development of the replacement for
Oscar 13 (known as Phase 3-D).  ANYONE INTERESTED IN THE
AMATEUR SATELLITES SHOULD BECOME AN AMSAT MEMBER.
Its' the closest place I've found to one-stop-shopping
for information on the satellites (this newsgroup is number
two, at least until I get onto the satellites myself!).
You can reach AMSAT at:

    AMSAT
    PO Box 27
    Washington, DC  20044
    [phone]

I know there are several AMSAT members in this
newsgroup (who even have satellite experience.  I'm
still working on it!) - so you can always ask here!


Again, thanks to everyone who answered my query!
You've helped a great deal.   I'll look for you on the birds!

73, Steve          (AMSAT Member 21876)

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