Its always advisable to track down the noise on the frequency that you are receiving the noise on.
Noise is rarely correlated across a wide frequency range. Start and track the noise on the frequency with the highest noise level that annoys you. I have frequently tracked switched mode power supply noise like that from LED light power supplies that only exists on 1 or 2 HF bands and nowhere else on HF/VHF. Rarely does this interference extend into the AM broadcast band or into the VHF/UHF ranges. Noise heard on the broadcast band is rarely heard on the HF bands.
Arcing noise from power lines very rarely extends into the Lower HF ranges. It may exist on Airband, 2 meters, and 440 mhz and rarely be detected on HF. Its only under exceptional circumstances that VHF/UHF arcing noise is detected in the HF range in my experience.
The most frequently encountered broadband emitter these days is powerline ethernet adapters that can be heard right across the HF and VHF spectrum, the notches in the ham bands does help but there is still detectable levels of interference.
Likewise even monitoring high levels of arcing noise in the AM broadcast band rarely does this same noise even migrate to the 160 meter and 80 meter band. There are no hard rules for QRM/RFI and I am only speaking from my anecdotal experience of tracking down noise for a couple of years now. Its almost a second hobby that is required these days if you are a ham operating on HF such is the dismal failure of our self regulating EMC regulations.
A small portable shortwave receiver with a telescopic whip is going to make your life very difficult. Even a coat hanger bent into a 40 to 50cm loop plugged into the external antenna socket of your shortwave receiver will make nulling and finding the noise much easier. The best tool for the job is a tuned loop antenna from 40cm to 60cm in diameter.
In my car I have my QRM tracking receivers set up for spot frequencies where I can monitor them all simultaneously from LF through to the UHF band while monitoring in AM mode. Rarely is the noise correlated across the MF/LF/HF/VHF/UHF frequency range.
It seems that a 50HZ powerline frequency produces less wideband intense arcing that spreads noise across the HF spectrum. I routinely monitor on AM for arcing power line noise and I rarely find it. It maybe a combination of factors which includes no salt on the roads, less moisture, different mains frequency and different hardware designs on the power poles that makes the likelihood of arcing less apparent here in Australia. I rarely see the kind of HF frequency arcing that I see in the videos of people tracking powerline noise in the USA for example. The biggest trouble maker is switch mode power supplies in all the electronics gadgets and things such as battery chargers and LED light power supplies which cause bad and intense QRM from a very long distance away.
I also have an ultrasonic dish and must admit its the least useful of the tools required to track noise because arcing insulators and pole hardware is very rare down here in Australia and this may well be related to the dry hot climate. The other point is that heavy rainfall where I live is rare so arcing cant be only caused by things like dirty, dusty or faulty hardware.
I am not an expert in the field and all of the above is anecdotal observations rather than scientific expert opinion.
73
Craig
VK3OD