[OZAPRS] Stray Interference

[G T & C A Beagley]

About 4 weeks back I found that our local ROT digipeater (or Node as it 
was then) was suffering some interference which was holding the squelch 
open for extended periods on 144.575mhz. Using a handheld I went hunting 
and traced the source to our Photocopier on the floor above. I turned it 
off and the problem disappeared.
However, I have since found - Beware of what havoc this sort of 
interference can create with APRS positions. After driving to Tauranga 
and back last week I found some very strange position reports on 
findu.com when I got home. I had appeared as ZL1GTB-8, ZL0GTB and a 
couple of others as well.
On Sat I saw ZL1UKC-9 mobile along Fairy Springs Rd doing 768 Knots (not 
bad in a 60kph area for a four cylinder car) and also at various places 
round town as ZL1UIC-9,ZL1TKC-9 and ZL1QKC-9. One of my own positions 
fronted up as ZL0GDB in the middle of the Atlantic as an Earthquake and 
my positions (which had been digipeated by ROT) kept regularly greying 
out and disappearing after 5mins and fronting up in the station list 
with weird results.
When I got to work yesterday I checked and sure enough someone had been 
using the photocopier several days ago and left it turned on. I turned 
it off, left a note to leave it off pending repairs and have had no more 
problems since.
As Murphy would have it the interference is widespread across the VHF 
spectrum but the only affected frequency of the several in use at work 
was our APRS digipeater 144.575mhz. All the others were unaffected which 
probably explains also why we didn't know there was any interference 
until quite by chance I saw the squelch light hanging on with no signals 
present.
So if you find your APRS transmissions produce some weird callsigns or 
positions at findu.com it may be time to have a look for local
interference.

Graham

ZL1GTB

-- 
G T & C A Beagley
24 Blomfield St
Rotorua 3201
New Zealand

Ph 07 3460677
(64 7 3460677)
Mob 025 531584

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