[aprssig] RFM22B UHF Transceiver Module

John Wiseman john.wiseman at cantab.net
Tue Dec 11 12:57:50 EST 2012

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 desined to work with the PI, it aslo
has a header for a serial to USN 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

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