Geographical (magnetic) limitation of Hi Frequency communcation? - Page 1
Forum section: electronics / general

author: Rick Law
author_rank: Super Contributor
timestamp: April 25, 2020, 12:28:25 am
content: Question to those with the knowledge: To what extend will earth's magnetic field and Solar Min interfere High Frequency Communication?Context of the question: I was watching some WW2 documentary in the South Pacific theater just north of Australia. The narrator proposed that (not verbatim quote) "Due to Solar Min and the earth's magnetic field in the Guadalcanal area, the radios were practically useless, so the Japanese Navy ignore the existence of the radio (on the plane) and the Japanese Army pull the radios from the planes." (The planes they were referring to was the A6M -- ie: the Zeros)I can understand interference being worst in Solar Max, but Solar Min? As for geographical location, I can understand interference near the pole, but I would imagine as far north (from the south pole) as the northern shores of Australia, there should not be much interference.Before I put this documentary's opinion in the "full of sh*t" bin, I better seek expert opinion. What are your views?

author: daqq
author_rank: Super Contributor
timestamp: April 25, 2020, 06:29:34 am
content: Sounds wrong. The Earth's magnetic field is practically stationary, practically DC, so it shouldn't affect high frequency stuff at all. Maybe it could affect the propagation of the waves due to atmosphere bounce? Dunno.

author: Ian.M
author_rank: Super Contributor
timestamp: April 25, 2020, 08:18:31 am
content: GoogleMaunder minimum radio propagationand you'll find out why over-the-horizon HF propagation is highly dependent on sunspot activity. Also, the maximum usable frequency drops dramatically when there is little activity, which has severe implications for radios with antennae dimensions limited by the aircraft wing and fuselage lengths.

author: M0HZH
author_rank: Regular Contributor
timestamp: April 25, 2020, 08:23:44 am
content: HF (3-30MHz) radios use ionospheric reflection to reach distances way beyond the line of sight. Radio waves in this segment typically "bounce" on a region of the atmosphere, back on the Earth's surface then back on the atmosphere a couple of times. If the conditions are right they can reach almost any area of the globe, independently of any infrastructure. This is why the military, the aeronautic industry, any sea-going ship and most critical emergency services have at least one HF radio as a backup. Back in WW II there were no satellites so HF propagation was the only way to communicate over long distances from a boat or an airplane.The atmosphere has different layers and they have different properties when it comes to HF radio waves: some are transparent, some absorb, some reflect and these properties constantly change with the level of ionization, frequency, time of day and even weather patterns (mostly relevant to VHF and up). A low-medium level (this happens all the time to a certain degreee) of solar wind will ionize the F layer (the outermost layer that is relevant for radio propagation), which in turn becomes a "mirror" at HF frequencies and starts reflecting radio waves back to Earth. A medium-high level (typically during solar maximum) will result in very good ionization of the F layer and will also break through to the next next layer (E): this is what some of us hope for, as at this point F-layer reflection propagation mode is quite reliable on HF and you also get patches of ionized E layer that reflect VHF signals to really long distances. A high & very high level of solar ionizing radiation (like during a solar storm) will make its way down to the D layer, which is the atmoshperic layer that absorbs radio waves; this is what we don't want and sometimes it gets so bad that makes it in the mainstream news.As for the geographic location, Guadalcanal is in theEquatorial anomaly.TL;DR: Solar Minimum = no HF propagation because the atmosphere isn't ionized so it doesn't reflect radio waves, Solar Storm (more frequent around Solar Maximum) = no HF propagation because ionization is so bad that radio waves are absorbed.By the way, we are currently at the lowest Solar Minimum in modern history.

author: Rick Law
author_rank: Super Contributor
timestamp: April 25, 2020, 07:33:22 pm
content: Quote from: Ian.M on April 25, 2020, 08:18:31 amYour bold text is the secret key I was missing - I kept search combination of Radio and HF, and I got lots of Hi Fi stuff in return... Thanks---------- ---------- ---------- ----------Quote from: M0HZH on April 25, 2020, 08:23:44 amThanks! Great explanation. Your reply (in it's entirety) was just the spark needed to remind me of some of the Physics that I've forgot - Ionization layer needed for the bounce, and I even forgot the bounce altogether. I was fixated on magnetic field which the narrator was commenting on and I totally missed the Short Wave bounce.Looks like in the WW2 era, the Japanese pick the wrong time for their expansion. Their Zeros were basically small groups of loners without proper communication and missed the bigger picture. Midway could have turned out rather different had they not been lacking reliable radio communication.Good that I seek expert advice. I was ready to chuck that HF communication issue due to Solar Min and Magnetic field as BS excuses...