Wednesday 9 July 2014

Wireless Headphone Hell

For the past several years I have been aware of a very loud wideband FM signal just below the 6m band....about 49.8 MHz. Any time I listened to it, it seemed to be rebroadcasting TV audio so I assumed that it was a set of wireless headphones somewhere in the neighbourhood. I was thankful that it did not cause any problems to my 6m reception, being far enough down the band.
About two weeks ago, during my normal early-morning band check, I noticed that the FM signal had suddenly shifted much higher and was now approaching the bottom edge of 6m. As the day got longer and the temperature climbed, so did the FM signal! Soon it was inside the band, but right at the bottom end. Within two days, its morning 'start' frequency climbed higher and higher and eventually the signal lodged itself smack dab into the working portion of the band, centering itself at around 50.090, depending on the temperature. Being such a wideband signal, it effectively wiped-out 6m operation for me when its wide raspy carrier was modulated....which was most of the time. Thankfully it would usually be just below the beacon portion of the band until the morning 'European window' time had past.

Two days ago I decided that it was not drifting any higher and had happily entrenched itself on 50.090. It needed to be eliminated.

I constructed a 6m dipole (106") from some scrap aluminum tubing and dug out my Icom IC-R20 handheld scanner.

The next day I set about walking around the neighbourhood, taking bearings at various locations, as the signal was easily heard with the dipole. I had earlier determined the rough direction of the signal using my main 6m antenna, a 4 element homebrew Yagi at 55'.

Courtesy: Google Maps
It didn't take long to triangulate the suspected residence as the dipole kept pointing to one particular house as I walked past it. Luckily it was someone I knew and it seemed that they did indeed have a wireless headset that had been plugged-in for several years but never used! They were more than happy to remove it as we both expressed how surprised we were to see how far the signal was radiating. The home in question is about a quarter-mile away.

The band is wonderfully peaceful once again (except when the power lines start arcing at about noon) and within minutes of the headphone system shut down I was able to work a loud BV2DQ in Taiwan and several JA's, shortly before dinner time.

These amazing early July conditions continue on the magicband.

No comments: