[amsat-bb] RS-13 Mode KA Primer

[K5OE@xxxxxxx]

A big THANK YOU to the RS-12/13 controllers for switching the bird into mode
KA!

Many of the new ops haven't had an opportunity to try this mode.  It's been
about 6 months since RS-12 was in this mode so I offer what I believe is the
basic information for operating this easiest of the easy-sats :

FREQUENCIES:
The RS-13 frequencies are just "above" the RS-12 ones:

Downlink:  29.460 - 29.500, beacon at about 29.504
Uplink:  21.260 - 21.300
Uplink:  145.960 - 146.000

The transponder is linear (non-inverting), and USB is the mode of choice.
Generally, the band plan is the bottom 20 kHz (29.460 -29.480) is for CW and
the upper 20 kHz (29.480 - 29.500) is for SSB.  RS-12 used to be so crowded at
night, the passband got unofficially "enlarged" to be the top 25 kHz, forcing
CW down a little.  The transponder is linear (non-inverting), and USB is the
SSB mode of choice for both uplink and downlink.  29.470 for CW and 29.480 -
.485 for SSB seem to be the prevelant calling frequencies.  The convention is
to fix your transmitting freq. and adjust the 10 m downlink for Doppler shift.

Note in the daytime you will get a lot of 15 m QRM, especially as the bird
comes up from the south over S.A. (multi-KW QRO stations)  More than once I
have had a QSO with somebody as they listen on 15 m (simplex) and I think they
are on the bird--hi hi.  Nightime passes are great w/o the 15 m QRM; s/n
ratios are great, making for extremely clear audio.

ANTENNAE:
Just about anything will work for the downlink.  Dipoles and inv-vee's are
very popular and work well--even in the attic.  If a single dipole is used, a
N-S orientation will work best for all passes over 15 degrees elevation.  My
experience with verticals on the downlink is they are 3-6 dB off from
horizontal antennas.  Of course, triband beams are FB, but not really
required.  Preamps are common for RS-15 but not really needed for RS-12/13.

Small beams, dipoles, or a 1/4 wavelength vertical will work well for both 15
m and 2 m uplinks.  I find about 50 Watts on 15 m is plenty into a vertical
and 10 Watts on 2 m into a 6 dBi antenna will give me an S5 signal.
Horizontal uplink antennas seem to perform better at the horizon, but I tend
to get receiver desense when both antennae are in the same polarization--hence
I favor a vetical uplink antenna.

OPTIONS:
Any 'ol receiver will work for the 10 m downlink.  I have spoken to quite a
few ops who use converted CBs and general coverage receivers.  I use an old
HTX-100 most of the time.

If you don't have a multi-mode 2 m rig (yet?), try hooking up a key to your 2
m FM rig you use for AO-27.  I bought a matching mic plug at Radio Shack and
wired it out to a straight key (my first AO-10 contact was made like this).
It won't sound pretty, but it will work to get you on.  I heard several
signals that sounded like FM this morning--the CW passband was really crowded
for SKN.  Another option is a 2 m transmitting converter or transverter; I use
a TenTec 2m transverter kit I built last summer (it also gets me on the mode J
analog birds).

73 es Happy New Year,
Jerry, K5OE
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