[aprssig] Why different freq in Europe vs US?
Stephen H. Smith
wa8lmf2 at aol.com
Mon Mar 26 13:49:05 CDT 2012
On 3/26/2012 12:52 PM, R. Rochte wrote:
> Why, though, are the different frequencies used? Why not standardize on one
> throughout the world? Is there some compelling reason for Europe to not use
> the U.S. frequency, or vice-versa?
> Robert KC8UCH
You are taking a very provincial US-only view of the issue.
1) In most of the world, the "two-meter band" is only 144-146 MHz. Long
before APRS, Europe channelized the LOWER half of two meters for repeaters, as
well as SSB/CW, at the same time North America was channelizing the upper half
(146-148 MHz) for FM.
The FM/repeater mode took off in the late 1960's due to the flood of obsolete
wide-band FM gear dumped on the second-hand market, due to FCC narrow-banding
mandates in the commercial land mobile services. At the time, the FCC only
allowed repeaters in the upper half of the two-meter band in the US. Further
the surplus commercial land mobile hardware was easier to tune down to the
upper part of the band from 150 MHz plus, than lower in the ham band.
FM/repeater operation overwhelmingly became the dominant mode of operation on
two meters by the early 1970s.
When the 146-148 range became saturated with repeaters in the early 1970s', the
FCC authorized a new segment for repeaters in the lightly-used lower half of
the North American band. This repeater "subband was shoehorned in to the
middle half of this segment (144.5 to 145.5 MHz) to protect classic weak-signal
CW/SSB/moonbounce activity at the very bottom of the band (144.00-144.3000 or
so) and the amateur space (satellite) segment at 145.800-146 Mhz . (By this
time, hams were mostly using purpose-built-for-amateur-radio solid state
Japanese boxes that could cover the entire 144-148 North American two-meter
band .) The subband then proceeded to fill up with more repeaters.
APRS was a late-comer to the two-meters party, and initially used a patchwork
of local simplex frequencies left-over from the repeater explosion. This
included the range from 145.5-145.80, and the "hole" between subband repeater
inputs and subband repeater outputs in the 144.9.-145.10 range, which was
already being used for classic connected packet operation. Indeed part of the
original APRS standard (destination addresses always starting with "APxxxx")
was defined to allow APRS and connected packet to co-exist on the 144.99,
145.01, .03, .05, .09 "packet channels". APRS apps would just ignore packets
with non APxxxx destinations.
[145.80 - 146.00 was off-limits since this is the internationally-recognized
satellite band on two meters -- i.e. located in the part of the 2M band common
to the whole world. ]
Since no single channel was used everywhere, the mobile user had to switch
channels as he traveled. In the late '70s-early '80s, a massive effort was made
to standardize APRS on a single national channel. 144.39 was chosen as being
high enough to not conflict with bottom-of-the-band weak signal SSB/CW and
just low enough to not cause problems with the sub-band repeater receivers
starting at 144.50. Even so, there were numerous disputes with groups with
"secret channels" at the bottom of the band, remote bases unknown to outsiders,
etc. It took the better part of 5 YEARS to move everyone off 145.01, 145.78
and several other local and regional frequencies to this new continent-wide
standard channel that was the most workable compromise IN NORTH AMERICA.
Usage in the already-far-MORE-crowded only-2MHz-wide two meter band
elsewhere in the world wound up with completely different frequencies being
More information about the aprssig