Some years ago NATO did a report about increasing noise in the HF spectrum because it was concerned that the reliability of its HF communications would be affected—the HF band being its ultimate fallback position for long distance communications.
If I recall correctly, the report said the noise floor had risen some 6 to 8dB in recent years (see the report for exact details).
About a decade later I was at a SMPTE broadcast equipment show and whilst discussing AM broadcast transmitters with the manufacture of said devices I mentioned the NATO figure for the HF spectrum. He retorted where had I been in recent years and said that the figure was over over 17dB.
Note: his company manufactured a range of transmitters and only some were in the normal AM broadcast band, other transmitters were for HF and FM broadcasting. There was no mistake that were were referring to the HF spectrum, i.e. 3 - 30MHz
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Edit: Just found the report on my PC, I've not had time to go through it so check my above figure. I'll try and see if it the links is still available, if so I'll add it as another edit:
HF Interference, Procedures and Tools
Final Report of NATO RTO Information Systems Technology (IST)
Panel Research Task Group IST-050/RTG-022 (or Research Task Group IST-050).
Published June 2007
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2nd Edit: Here's what I found, I haven't fully checked but I think they're all the same:
While NATO militaries still use HF radio systems, in the past 10-15 years increasingly anything that requires over the horizon comms has been built to use two way narrowband satellite instead. Iridium, or narrowband to a number of differnt types of geostationary DoD satellites (or geostationary capacity owned/controlled by UK or Australia), or things like this:
For something like Iridium you need an antenna with all of its gain aimed as much straight upwards as possible and tuned for the 1400 to 1700 MHz range.
Relying on the HF band to be clean and perform as needed at a randomly chosen location and point in time may be less likely than being able to move the same data by narrowband satellite. Particularly with advancements in ultra low bitrate voice codecs.
Right, I reckon that makes sense nowadays. I've had a little to do with spectrum management in the past, in fact I was once on several different committees making recommendations for WRC (aka WARC).
That said, I'm not currently fully up to date nor do
I have inside info on NATO's comms or spectrum use. Reading other info that initially led me to the report, I gathered that back then NATO's use of HF was already in decline and that HF was mainly a fallback option in the event of a calamity - a major failure, nuclear war etc.
In many ways that makes sense as it's a low tech option that needs few resources and usually works subject to ionospheric fluctuations.
Although I had expected the EMR/RFI noise floor to have increased on all bands from ELF through to at least UHF, I was very alarmed at the 17dB figure on HF when I heard about it (I'd not have anticipated that it would have been quite that high).
Even before I'd heard that figure I'd been watching the increase which I put down to the following reasons:
1. The obvious one is the large and increasing use of electrical and electronic technology.
2. A more significant reasons is that in the 1980s many countries downsized and or outsourced their spectrum management departments. Lisensing spectrum was often then separated from the engineering - i.e.: EMR noise suppression, reduced protection ratios in band planning, reduced physical separation for same-channel and adjacent-channel transmitters, etc. In essence, commercial pressures were deemed more important than engineering niceties such as ensuring all non-message producing equipment, motors etc. incorporated adequate RFI noise suppression.
(Previously, engineering often took precedence. Whilst it can be argued that in the past that this policy was too restrictive, there's little doubt that both deregulation and the economic imperative have driven down engineering standards too far - witness the evidence - increased interference and noise (especially so from digital switching).
3. With the enormous increase in digital electronics in recent decades there has been less emphasis on radio engineering in university electronics courses (50-plus years ago analog radio and television engineering almost dominated electronics). The outcome is that nowadays many electronic engineers no longer get the solid grounding in RFI and noise reduction techniques that they one did. (Remember Henry W. Ott's Noise Reduction Techniques in Electronic Systems.) Yes, I know that's a sweeping statement and there are many exceptions but in general it's true.
This has resulted in not only reduced RFI standards but also we've seen the introduction of some outrageously bad engeering. For example, BPL/PLT (Broadband over Power Lines/Power Line Transmission). Putting what is effectively broadband noise into the world's largest antenna - the power line grids - has to be as about as diabolical as it gets. Before deregulation, such outrageously bad engineering would have been unthinkable.
(Here's an example of the problem. I recall some years back a rather bright young engineer who was working with me coming to me wondering why he couldn't get a rather complicated circuit board full of CMOS and TTL logic working and that I may be able to help. He explained that he had double checked his circuit and board layout and could find no fault. With only a split second look at the board I saw the problem, I explained to him that he'd omitted to put 0.1 uF bypass capacitors across the IC's power supply rails. Little wonder the circuit didn't work.)
That all said, I don't expect the spectrum's noise floor to come down the foreseeable future.
>whilst discussing AM broadcast transmitters with the manufacture of said devices I mentioned the NATO figure for the HF spectrum. He retorted where had I been in recent years and said that the figure was over over 17dB.
I live in a semi-rural area and all but the most powerful nearby AM stations (Absolute Radio, 5 Live, and Talksport) are basically unlistenable because of the local noise. Can't imagine how bad it is in a city!
Since it's on its last legs for commercial broadcasting these days, I reckon the regulators should open the top 100 kHz or so of the AM band for low power hobby broadcasters. I know there's things like amateur radio for people who are interested in the technology alone but that's no good for people who are interested in the music or talk content too; I'd argue pirates are probably making the most efficient use of that spectrum as it stands anyway. You can often hear quite a few of them at weekends on the Dutch WebSDR.
"I live in a semi-rural area and all but the most powerful nearby AM stations (Absolute Radio, 5 Live, and Talksport) are basically unlistenable because of the local noise. Can't imagine how bad it is in a city!"
Yes, you're right. I don't have to imagine, I know.
There are two problems here although many will disagree. The first is that AM radio is on its last legs and it should not be so. As I grew up with AM radio some would say it's just nostalgia (and you cannot build a crystal set radio for digital radio). Partially true, but it's irrelevant. I'd argue that AM radio - like the point I made in my second post about NATO's HF fallback strategy - is of strategic importance. First, because both its transmitting and receiving technology are simple and can be cobbled together with minimum resources and cost. Thus, in emergencies, natural disasters, nuclear war or even a backup when fiber optic cables or satellite comms fail, it serves a useful purpose.
The key advantage of AM broadcasting is that its service area range is much larger than say FM broadcasting - especially so its secondary (and even its tertiary service) areas - even in daytime when ionospheric skip is absent. Of course, at night time when the skip kicks in that distance is
extended substantially - that is if there is no interference.
Let me give you an example. I'm in Australia and years ago I could drive from Sydney to Adelaide some 840 miles and listen to the national broadcaster the Australian Broadcasting Commission (ABC) - sort of equivalent to NPR - all the way without interruption or significant interference except for switching frequencies, three in total.
The three transmitters were located in Sydney, Melbourne an Adelaide and Melbourne was not on the way but hundreds of miles tangential to the cross country route. Moreover, this was daytime reception without the aid of ionospheric skip. There is absolutely no way this could be accomplished with 88-108 MHz FM transmiiers, it would take many dozens of them to service the route (and even now it's sparsely populated - mainly hundreds of miles of semi arid desert, thus there's no way one could justify the cost of FM coverage).
Unfortunately, nowadays that is no longer possible due to the increased noise floor within the AM band and the fact that more adjacent and co-channel services have been added.
AM broadcasting is especially useful (or it ought be) in rural or sparsely populated areas especially in large countries such as the US, Australia, Canada, Russia, etc. It's madness to close these services down - and it's also the reason why we need to protect such services from increasing noise and interference.
BTW, I say this as a person (one of a half dozen or more) who was instrumental in getting FM broadcasting services established here. No, I'm not a traitor to the FM cause. What I'm saying just makes strategic and pragmatic sense - it's a shame governments have lost the plot on this. It'll likely be too late when the need arises and all services have been shut down.
A final point, I've always believed that AM radio is one of the greatest and most significant engineering developments of the 20th Century. After the telegraph, it was the next 'quantum' leap in communications and an essential stepping stone to latter services - FM and TV broadcasting, satellite communications - even the internet. Unfortunately, its gloss has rubbed off and it no longer gets the recognition it deserves.
Noise is a fascinating topic. It seems a nuisance but if you investigate it you’re bound to find interesting phenomena. “Radio astronomy” is, at heart, a science of understanding and managing noise.
* Even if you can get an instrument far away from other noise sources, there is significant noise from physical processes inside the detector (thermal noise) and even statistical fluctuations owning to the discrete nature of photons themselves (shot noise)
One of my favourite things about the Schumann resonances is how humanity effectively did an experiment on them: the Starfish Prime nuclear test several hundred km above Hawaii dumped a load of charged particles into the ionosphere, destroying several satellites in space at the time, and, yes, changing the spectrum of the Schumann resonances.
>Even if you can get an instrument far away from other noise sources, there is significant noise from physical processes inside the detector
There's disorders which can make the brain's own noise consciously perceptible, even if you do away with the instruments there's still noise to contend with! Interestingly the visual aspects are very similar to old-fashioned analogue TV noise which gives the disorder its name, Visual Snow. Usually this noise is automatically filtered out but (at least according to the current theory) defects in the metabolism of certain parts of the brain prevent this, allowing it to become visible.
If you really want to see terrible noise in a big metro area, look at a spectrum analyzer and the 900 MHz band noise floor in a major metro area from things like intercoms, baby monitors, smart grid power meter systems, etc.
Best seen if you have something like a fairly "high" gain 3 to 4 foot length single polarity yagi tuned for 890-920 MHz and can connect it so a spectrum analyzer, and sweep it around.
It's a minor miracle that something like low bitrate LoRA in 915 MHz works at all in a major US city.
I'm honestly surprised it's not higher than an overall average below -100, though if one looks at a narrower range and those spikes that bring the local noise floor to -80 in a few specific frequencies, it's definitely noisy.
Related: The DARC (German Amateur Radio club) is conducting a long term study on local HF noise by deploying 50 wide-band SDR receivers at various locations all over the country:
If I recall correctly, the report said the noise floor had risen some 6 to 8dB in recent years (see the report for exact details).
About a decade later I was at a SMPTE broadcast equipment show and whilst discussing AM broadcast transmitters with the manufacture of said devices I mentioned the NATO figure for the HF spectrum. He retorted where had I been in recent years and said that the figure was over over 17dB.
Note: his company manufactured a range of transmitters and only some were in the normal AM broadcast band, other transmitters were for HF and FM broadcasting. There was no mistake that were were referring to the HF spectrum, i.e. 3 - 30MHz
____________
Edit: Just found the report on my PC, I've not had time to go through it so check my above figure. I'll try and see if it the links is still available, if so I'll add it as another edit:
HF Interference, Procedures and Tools
Final Report of NATO RTO Information Systems Technology (IST)
Panel Research Task Group IST-050/RTG-022 (or Research Task Group IST-050).
Published June 2007
___________
2nd Edit: Here's what I found, I haven't fully checked but I think they're all the same:
https://manualzz.com/doc/18577111/hf-interference--procedure......
Panel Research Task Group IST-050/RTG-022 (or Research Task Group IST-050).
Download: http://www.darc-c12.de/system/files/%24%24TR-IST-050-ALL.pdf
Internet Archive: https://archive.org/details/DTIC_ADA473220