[aprssig] APRS-B?

John Wiseman john.wiseman at cantab.net
Mon Jun 24 16:31:06 CDT 2013

I posted a message about 6 months ago about experiments with the RFM22B (100
mW) and RFM23BP (1 Watt modules). I also obtained a couple of the RFM12B
(500 mw) units, but I found the interface much more difficult, and would
recommend the 22/23 modules. I made a board for the Raspberry PI, and it
seemed to work pretty well. and at $25 seems reasonable, but for a simple
dig function the code could probalby run on the PIC.

As I do a lot of sailing in the summer, the project has been put on hold
till the Autumn, but if anyone is interested in preogressing the ideas, I
can publish the board design and code.

To save you trawling throught the archive, I'vr repeated the message below.

73, John G8BPQ

A while ago (22 September) Bob posted a message about the RFM22 modules. I
was working on a TNC for the Raspberry PI at the time, so decided to try
building a TNC round these modules. There is a photo of the result here


The board is the same size as the PI (about the same as a credit card). This
one is fitted with the RFM22B module, with 100 mW output, but the board will
also take the 1 Watt RFM23BP. Although designed to work with the PI, it also
has a header for a serial to USB converter, so it can be used as a
standalone KISS TNC.

To test as a tracker I lashed up a board to connect the Adafruit Ultimate
GPS Breakout board. Photo here:


I've now got them running, and just completed my first tests. On the first
trial with the 100mW version I achieved a range of just under a mile, with a

5/8 over 5/8 70cms whip on the car, and a far from ideal Marine Band whip at
base (The 70 cms colinear I bought for the test turned out to have an
infinite SWR!).

Although very much a work in progress, I thought I'd share results so far -
if anyone else is working with these modules I'd be interested to hear from

BTW, the GPS module is pretty neat as well - it is about an inch square, and
includes a data logger -  <https://www.adafruit.com/products/746>

73, John G8BPQ



From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Robert Bruninga
Sent: 24 June 2013 13:55
To: aprssig at tapr.org
Subject: [aprssig] APRS-B?

I’m impressed with the 500 mw transceivers on 433 MHz costing $20 or so and
operating at 9600 baud.

Why don’t we call this APRS-B (plan B).  And start paralleling our network
with these devices.

Then instead of only 5% of hams having APRS capability, we could get more
people in the clubs to own a device and also to put one up at home so we
have a backup data channel as well?

Maybe lots of you are doing this alrady and I am the last one to the party.
But whatever we do, lets standardize on something so we are all headed in
the same direction.

These are wideband devices, so they are not compatible with any existing
APRS or other ham FM radios.  That is why it is a fresh start.  What is the
sync and key up time?

Sure the range of 500mw is small, but at only 10% of the cost of a digi we
can put them at more and closer places and even solar power them.


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