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Re: "spontaneous" LEILA activation << I hear the pulses here too>> ?? A radar or ranger?? Lband or U band???



The US Navy has had, for many years, ships with air search radars in the
420 to 450 Mhz frequency range which use pulse expansion/pulse
compression type of modulation.  The technique is somewhat like a cross
between spread spectrum and FM.  The pulse is generated by sending a
narrow pulse down an LC type delay line (at a lower IF frequency).  The
resultant pulse length is something on the order of 200 micro seconds
long and contains a more or less linear phase (freq) shift from start to
end.  On the receive end the process is reversed to recover the narrow
pulse for processing.  This is a very high (average) power radar with a
beam pattern looking up at the sky.  It could look somewhat like FM to a
narrow band receiver. There should be a slow antenna rotation rate
associated with this type of signal.  

There are also some airborne radars with actual swept frequency
modulation methods which I hear often here in the Norfolk, VA area. 
There is a Navy axillary landing field a couple of miles from my QTH and
when the AEW planes are flying there the interference on 435 is very
severe.  It is a wideband signal which covers all of my 432 to 437 Mhz
frequency range.  Fortunately the noise blanker takes them out almost
completely so they do not cause me a major problem.  These are equivalent
to the Air Force AWACS planes (the navy used to call them WF ("Willie
Fudd")  but I don't know what they are named now.  These signals have the
same type of slow rotation rate associated with them also.

Actually there are many swept frequency type radars in various frequency
bands in the military inventory that might cause interference on the
AO-40 uplinks.

73's de Jess - W4MVB
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