USING THE ALINCO DJ-S41 $88 Handi Talkie as a 9600 Baud UHF Receiver:
Bob Bruninga, WB4APR


Good news:  The Disc output is easy to get to, and looks linear.
            Its easy to mount a SIP header pair through the side
            of the case for easy interfacing.

Good news:  The sensitivity is *as* good at 436 for satellites as 446 MHz

Bad news:   After adding an external Antenna connection, I measured the
            receive sensitivity at -116 dBm.  That's 6 dB worse than my
            Kenwood THD7 (with built in 9600 baud TNC) but still usable
            *with* a preamp.

Just news:  Of course, there is no provision for automatically tuning the
            radio by PC, so this simple mod will be best used for manned ops.
            for tuning the 5 Khz steps needed to track doppler.

The Kenwood can get good data with a whip overhead or a 3 element handheld beam.
The Alinco will need a preamp.  But for home stations with anything more than
a 10 foot cable run, a preamp will be needed anyway for best performance.

The 5 Khz steps seemed adequate to keep the pattern on a scope  clean.

I am not configured for PACSAT Protocol and was only viewing packets on
a dumb terminal screen.  So I do not know how many packets I got.  Saw lots,
but doubt it was 100%... So overall QUALITY of this system is un-tested...

DISC OUTPUT:  THe DISC output is easy to find.  Open up the back and right
in the center, just above the VCO metal box is printed "SQ" and "RT3".
The chip capacitor to the left of the "RT3" is a blocking capacitor
between the discriminator output and the Squlech POT just above it.  The
end closest to the "RT3" is the DISC side.   I broke off two pins of a SIP
header socket and melted it slightly into the lower case just above the
VCO can.

The lower pin goes to the DISC, and the upper is soldered to the VCO can
as ground.  This also provides solid mounting for the plastic header.
Then I cut out a matching slot in the back cover so that it fits back on.

The result is a flush mounted barely noticible 2 pin SIP socket into which
you can plug your 9600 baud TNC.

I visually observed DISC noise components no shorter than  80 us which
sure enough equates to 12.5 KHz.  So this is a narrow receiver... and
others may be able to draw conclusions as to the overall viability of this
radio for 9600 baud use.   This narrow IF will probably loose some data
between the 5 Khz shifts, but we dont know yet.

For an external antenna, there is a SIP header on the board with 2 pins
just for this purpose.  I soldered a short 3 foot pigtail with a BNC on
the end to this point, just long enough to reach a handheld antenna.
Sorry, I dont have any more time for further testing, but it appears as a
low cost entry into the 9600 baud downlinks.. (How many are there now? 5?)

I'll bring it to the AMSAT COnference

de Bob, WB4APR