Chapters this page:-
Another source of interference is from power line type noise. This is considered serious, as it prevents, or blocks out all amateur DX signals on the HF bands. Knowing that power line noise is a possible sources of blocking I began to investigate the causes. In my attempt to clean the station of power line QRM, I spent almost one year searching and analyzing the situation. The list of procedures I undertook are covered in the appendix at the bottom of this page.
Having satisfied myself that the station was clear of transmit TVi and locally generated QRM , I began to monitor condition on a daily basis. This involves noting date time frequency and prorogation condition. It became apparent that apart from the unlicensed intruders there was a far greater underling sources of interference.
The Real Culprits
I reported these observation to a RAST committee member who suggested that I join the IARU monitoring services as the coordinator for Thailand. I accepted this position in June of 2003 and have continued as much a circumstances permit. The duty consists of submitting monthly reports to the regional three coordinators in India. Who in turn sends collected reports to the region three directors. These reports are then posted onto the IARU wed site.
Whilst intruders of the type described above can be classified as amateurs, I don't consider them to be a serious long term threat to our allotted armature bands. Local rules and regulation and policing of this type of interference will eventually prevail.
My main concern are the professional intruders who have a commercial interest in making QRM. These include atmospheric sounder, over the horizon radar (OTHR), weather radars, coastal intruder radars, sea state transmitters, fishing markers buoys, official jamming station, and military traffic encrypted signals, just to name a few.
The antenna systems and rig hears very well, and picks up motor bike ignition on the main road some 300 meters away when the antenna is point in that direction, on ten meters. The other antennas normally lift the S meter several point when pointing to the daylight zones.
My interest in monitoring strange noises was increased by the ability to actually see the interference, which is in most cases sounds just like white noise. There are many spectrum scopes programs available for free downloading. All utilize the computer sound card and connected to the rigs audio output source. The pictures produced are stunning in showing the audio spectrum and can be saved to any JPG file for reference, as well as the sound tracks, in MP3 format.
IARU Monitoring Network
I have also included spectrograms and sound files recently recorded at this QTH. It is interesting to note that these pictures closely agree with similar pictures appearing world wide, not just from monitoring stations, but by amateurs interested and very well qualified to name the type of transmission, modulation mode, and most likely countries.
I hope that this page has been informative and I encourage you search the WWW for further details about this subject.
IARU Reports and Log Samples.
Pictures files of QRM:-
Display groups ( 1 to 3 ) ( 4 to 6 ) ( 7 to 9 ) ( 10 to 12 ) ( 13 to 15 )
TVi Interference - Basic.