Satgen 162  Radar QRM of Amsats - Summary       by GM4IHJ       3rd May 92

My thanks to all who sent me data in regard to this 70cm radar
interference. It is clear that Amateur Radio has been dealt a double blow,
with operations of both up and downlinks to satellites being disrupted
over the whole of Europe, all Africa North of the Equator, the North
Atlantic, Greenland and the north east of the American continent. Noting
that effects are occuring out to 4000kms radius on low orbit sats from at
least two widely separated sources, and high orbit sats are being affected
worldwide. The most powerful signals occur right on top of the main
cluster of amateur satellites around 435 MHz, the sources are very wide
band ( > 300 Khz ), and are repeating down as low as 427MHz.
This has a number of effects on satellite operations :-
UPLINKS on Oscar 10. Oscar 13 and RM1 using frequencies near 435 MHz are
compromised in two ways. Firstly low power uplinks by amateurs are totally
defeated by the enormous power of these radars, and worse still the radar
and any legitimate satellite uplink which gets through , are then mixed up
, often non linearly, and retransmitted on the satellite downlink as a
total mess.
Secondly , these satellites are sophisticated devices which Amateur Radio
Controllers must position to maximise Solar insolation, and antenna
pointing. Unfortunately the regular uplinking of control software for
these purposes is being hopelessly jammed by the radar interference. Ten
attempts being necessary to get up one short message block.
DOWNLINKS on amateur satellites which use frequencies near 435 MHz Eg
Uosat Oscar 11, Uosat Oscar 22 , Fuji Oscar 20 and Oscar 13 are all
received ( even at 300 kms terrestrially, and two ranges of hills more
than half a mile high ,from the nearest radar) against a very loud
spasmodic background of burst of radar. Indeed, because of the radars
extremly wide bandwidth ,high power ,frequency modulation, and
frequency agility, it simply penetrates and destroys any consistent
attempts to monitor data signals from space. This is particularly savage
now that amateur radio has built its own worldwide satellite linked ,store
and forward high speed data capability.

It is imperative that something is done to reduce this apparently mindless
destruction of both the hardwork of so many dedicated people, and the
enjoyment and self education of so many others. Equally important it has
to be clearly understood that we as radio amateurs must get a positive
understanding that this kind of thoughtless " bulldozer type" antisocial
behaviour is not repeated or extended. Please talk or write to your RSGB
reps and tell them to get something done. If they do not move, try telling
your MP what is going on. Many years ago when radars around 200 Mhz
interfered with TV reception , the military was ordered to keep them off
during TV hours and/or anywhere in range of land. This present situation
is quite different. For no obvious reason the radars seem to have been
specifically tuned to a narrow part of the 70cm spectrum where they can be
guaranteed to cause maximum trouble . This need not be the case. We cannot
climb up long poles and shift the frequencies of our satellites, but there
are lots of other slots on 70cms, the radar could use, where far less
interference would result. 73 de GM4IHJ @ GB7SAN