Interesting 6m interference

[VK4WDM]

A couple of months ago I began experiencing some strange interference on 6m. Hard to describe the sound but it started with a sort "burrrrrr" then followed "yip yip yip yip" like a high pitched yelping dog (no I am NOT barking mad ) then another "burrrrrrr."

Whole sequence took about 10 seconds to complete. The interval varied but it usually went off every couple of minutes or so.

It was hard to get a frequency because it was so loud and broad, but my guess was arround 50.25MHZ.

My first instinct was to blame the military, who do use that part of the spectrum from time to time, but enquiries via my usual ADF sources drew a black.

A local club member said that he had experienced similar problems in another locality on 2m and the culprit turned out to be the transmissions used to change "electric bill-board" road works signs. It just so happened that major works were taking place just one street over from my QTH and there were several of these signs in use.

I don't have portable 6m receiver so I was unable to visibly check if the signal burst coincided with a sign change but soon as the work concluded and the signs removed the interference ceased.

I am not sure if 50MHZ was being used as the primary frequency to control the system or whether it was a result of product mixing but it sure was annoying.

I would be interested to hear if anyone else has encountered this.

73

Wayne VK4WDM

[VK2XQ]

Interesting Wayne, lucky you do not live in Sydney, all kinds of weird crud, noises and pulses across the band here, I gave up long ago to identify the sources. Part of living in a large city I guess. If it hard to pinpoint the exact frequency it could be a harmonic so you may need to look elsewhere too, industrial, commecial or domestic would be the source I expect. Good luck and if you find the source let the readership here know...Jack VK2XQ (QF-56ne).

[VK2CSW]

Hi Wayne,

The mob I am currently contracting at make, install, service all sorts of road safety electronics.

I it is unlikely that a VMS (Variable Message Sign) or CMS (Changeable Message Sign) was the culprit.

Put simply, the use of RF comms is simply not done. The only exception is the use of GSM modems where hardwired connections are just not available.

Now, having said all that, the portable traffic signal systems may have an RF link - I haven't actually had anything to do with them. My guess if they did they would be in the 433 MHz 'free' spectrum. The bean counters would prefer that...

[VK3RX]

Record it and post a .mp3 or .wav file and someone might recognise it.

Your description sounds like a pager, but you'd know what they sound like. With a site about 5km away, I've had mixing products from them down in the low 30MHz region.

[VK5LA]

Hi Wayne,
This sounds exactly like the interference we got up here several years ago. With some DFing we traced it to a set of portable traffic lights being used by a bitumen company. They finished and the noise went with them. The transmitter was all over the place including the input to our Repeater!!! I was supposed to be on 151Mhz or there abouts...

[VK4WDM]

Could be a complete coincidence of course, but the interference stopped as soon as the road repair gang moved away.

Wayne VK4WDM

[VK1VMA]

Now, having said all that, the portable traffic signal systems may have an RF link - I haven't actually had anything to do with them. My guess if they did they would be in the 433 MHz 'free' spectrum. The bean counters would prefer that...

The ones I've found have been running 151.3MHz at 100mW. Usually using Bell 202 tones, so it sounds just like 1200 baud AX.25 packet.

[VK4WDM]

The same crew are back in our area today so it will be interesting to see what pops up.

73

Wayne VK4WDM

[VK3BJM]

With fairy lights, perhaps, Wayne?

('tis the season - allegedly...)

73,

Barry
VK3BJM