[amsat-bb] Re: FW: ARLB013 ARRL aiding effort to mitigate repeaterinterference to military radars

Tony Langdon vk3jed at gmail.com
Tue Apr 24 16:31:17 PDT 2007


At 03:20 AM 4/25/2007, Nate Duehr wrote:

>Proof positive that a reasonable solution can probably be found.
>
>The Amateur allocation in the UHF band is a Primary allocation of the
>US Military in the US, with the specific wording in the NTIA
>documentation stating the military is to "treat Amateurs as Primary".

Well, the military over here as well have certainly been more of a 
friend than a foe.  Our biggest dangers these days are not from the 
military, but from unlicensed gadgets, which have been approved for 
use in the 433 - 434 MHz band.  What made this a really nasty problem 
is that the authorities put few limits on the emission types, leading 
to cordless headphones, crane controllers (nasty potential for OHS 
implications here) and other high duty cycle devices on the 
band.  Wlesr, this happens to be about 80-90% of the available 
repeater inputs.  Because of the duty cycle, CTCSS is not a solution, 
all you end up is a bunch of "deaf" repeaters that takes a kW to 
open.  Had the devices been limited to low duty cycle applications, 
CTCSS would have been enough to prevent the occasional "blip" from 
someone's wireless doorbell opening up the repeater.

Oh, and as for satellites, well some of the cheap junk could drift 
into the 435 MHz region.  I already know of some cordless headphones 
that drift as high as 434.900, which is outside the allocated band 
for these devices.  These get into a repeater which was moved outside 
the affected band to get away from the problem.  Oh, and interference 
from these devices "does not exist", as far as the legislation 
goes.  It's actually written into the LCD (confirmed, I have read the 
clause myself).

The flip side of this madness is it is nigh on impossible to find a 
wireless doorbell or weather station that will work reliable in my 
environment.  They use SAW filters in their receivers, and these get 
severely desensed by ANY 70cm transmissions, even the repeater 
output, 5 MHz away.  The older 304 MHz stuff is much better for my uses. :)

Some new inputs (with an odd 5.4 MHz split) have been opened up to 
try and alleviate the problem with the repeaters, but it's a hack to 
work around the mess the authorities have given us.

Give me the military anytime to share the band with, they play ball 
much nicer than the rabble and the profiteers that feed them. :)

73 de VK3JED
http://vkradio.com



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