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Re: Alinco $88 HT @ 9600 Baud

On Tue, 28 Sep 1999, Christopher Maness wrote:

> Bob, I would like to try this mod.  Is it the Alinco DJ41T?

ANS:  Yes.  After connecting an antenna, tho, I find the radio is about 6
dB worse than a really good radio.  Thus you will probably need a pre-amp.
ALso, the filter is only about 12 KHz and so more experimentation is
needed to see if this is sufficient..  One the one or two jurry rigged
passes I did with a preamp was not 100%, so maybe the filters are to
blame?  Please try it and let me know..

 > > 
> >From: Bob Bruninga <bruninga@nadn.navy.mil>
> >To: amsat-bb@AMSAT.Org
> >CC: TAPR APRS Special Interest Group <aprssig@tapr.org>
> >Subject: [amsat-bb] Alinco $88 HT @ 9600 Baud
> >Date: Wed, 8 Sep 1999 12:04:59 -0400 (EDT)
> >
> >Regarding using the $88 ALinco HT on 9600 Packet downlink:
> >
> >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.
> >
> >The Kenwood can get good data with a 3 element handheld beam.  The alinco
> >will need more elements or a preamp to get to the horizon.  But still good
> >for briefcase portable on the 9600 baud birds.  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 dont know how many packets I got.  Saw lots,
> >but doubt it was 100%...
> >
> >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.
> >
> >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
> >
> >
> >----
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