[aprssig] D7 digipeating success!

Dave Baxter dave at emv.co.uk
Mon Jun 4 04:51:37 EDT 2007

Well done that man!....

Yes, the D7's do not handle low battery conditions well at all, even
when used in your fist for voice comms, they can misbehave.  Often the
only way out is to remove the battery!

For the sort of thing you are doing, best feed the radio (and
calculator) with power externaly, then you know you have enough.  Well,
you know how much you have at the start!

RF:  Yes, again it is known that high levels of RF will screw with the
serial link.  Ferrites may help in some circumstances, but an isolated
adapter is best (there are several designs about if you search)
However, the best way by far, is to not use the rig's own antenna, as
that is using the body of the radio (and any other attached devices) as
the ground plane for the antenna, result...  RF in everything!

If you use an external antenna, a J pole or similar etc, you will have
(a) much better TX/RX coverage, and (b) much less RF in the
interconnecting leads.

For true portable use though, backpack etc, try running a 1/4 wave
length of wire as a couterpoise from the antenna jack body, and dangle
it out of the back pack.  That and ferries on the serial and power
cables should increase relaibility no end.

The D7 not receiveing packets from the other radio, the Icom T7H.  Check
the deviation settings on each radio.  The D7's have direct connections
between the discriminator and the TNC (no de-emphasis afik) where as the
other radio most certainly has some pre-emphasis in it's TX audio.
It's been much debated here and in other places in the past, but with
care it can work OK.  Often reducing the deviation of the "other" radio
will make a D7 much happier with it's signal, as well as not bouncing
off the limiter and the resulting distortion caused..

Again, nice work sir, well done.


Dave G0WBX.

> -----Original Message-----
> From: gerheim at cox.net
> Sent: Saturday, June 02, 2007 2:53 AM
> Subject: [aprssig] D7 digipeating success!
> See attachment.  The "D7 DIGIPEAT" was appended within the 
> calculator program, so it actually went from K1QN-3, in the 
> basement at one frequency, to K1QN-2 upstairs (a D7) , and 
> from there to the APRS net on another frequency.  It was the 
> only way I could insure the packets weren't going directly 
> from K1QN-3 to the net.  
> There are still some bugs to iron out.  The most pernicious 
> one has to do with the cable.  When the batteries get low 
> and/or if there's too much RF, the serial port may transfer 
> commands OK, but foul up when an incoming packet arrives.  
> Can't quite diagnose or cure this one yet.  Very hard to 
> reset once the cable goes down the drain.  
> It woiks!
> --
> -Al Gerheim
> HP-49G+ Software Page:
> http://members.cox.net/above
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