I couldn't hear anything on 4625 kHz. I let my receiver scan and when it was done I checked out what it detected and found absolutely nothing interesting. The most powerful signals were Christian broadcasts that had a kind of doomsday feeling about them.
It seems like there's a lot of underutilized spectrum.
The shortwave frequencies still feel very underutilized. When I scan the FM (88 - 108 MHz) and AM (540-1600 kHz) radio frequencies, I pick up a lot of stuff. The shortwave band is relatively vast and feels very sparse. Considering how valuable spectrum is these days, it's hard to believe that we couldn't find a better use for it. Is it because it is so prone to noise that it's less valuable?
You can think of the trade off roughly as "frequency increases increase bandwidth and decrease penetration/range"
In amateur bands, symbol rate below 28 MHz is limited to 300 baud.
It's really frustrating if you want to do any development with digital modes.
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Looked it up, it's a 19.6k symbol rate limit(rather than leave it open and restrict bandwidth). You can carry a ton of data on 2M if you wanted but legally you can't exceed the speed of an old dial up modem.
Here in LA (Norway, for the ham prefix challenged), we can modulate in whatever way we feel like on 2M, as long as the signal bandwidth does not exceed 18kHz.
(So, using a clever modulation scheme, you could get very close to the Shannon limit for the given channel bandwidth and noise level - assuming a very healthy 30dB S/N, one should be able to wring approx. 180kbps from an 18kHz channel. (Granted, in the real world with filters without infinitely steep skirts we'd get nowhere near this - but, let's say you could get 1/3 or so without trying too hard.)
There are bandwidth restrictions on the 60m band, where amateur radio is secondary.
I love amateur radio but at least on the 2m bands it's mostly dominated by people just chatting on repeaters with others they already know or dead quiet. I monitor 146.52(our calling frequence) on my ~300mi weekly trip and I've made only one contact in 2 years.
APRS is pretty dead, there's a ton of interesting stuff that could be done on the ECC and symbol rate front but no one really seems interested. Not much has changed on the spec for a long time. Compared to some other countries where they have some very robust and flourishing 2m digital modes it's a shame.
But as others have said, in many parts of the world there aren't many shortwave stations left. Africa and parts of Asia still have quite a few however.
However, in general, I've noticed that there seems to be far fewer stations received on the shortwave band these days, compared to the 1980's when I listened to shortwave a lot as a kid. I think this is because I'm using a low-end receiver with its built-in telescopic antenna instead of a more sophisticated SWL setup with a proper antenna. Broadcasters such as the BBC World Service target specific geographies with their transmissions so they can be received on a low-end radio, and they no longer bother targeting developed regions such as North America with these transmissions. I'm guessing if I used the same radio somewhere like Africa, I'd be able to pick up a lot more stations.
There's some good reasons for this. HF is pretty challenging to fully utilize.
You have propagation that varies between "worldwide" (so it's difficult to assign new bands without ITU involvement), and "sunspot" (so you better have a plan B). And these variations aren't just over the duration of a sunspot cycle, but also over the day/night cycle.
eg, for maritime use, we have channel clusters at 2, 4, 6, 8, 12 and 16MHz. Which to use depends on the time of day the distance to the other station, and how much the sunspot cycle is messing with your first choice. Fun!
Then the physical challenges that arise from the ideal antenna length being proportional to the length of the wave. At 2.4GHz the challenge is precisely cutting your quarter-wave antenna to a fraction of a mm (31.25mm). At 2.4MHz same challenge becomes finding space for a 31.25m (~100feet) antenna.
Another big consideration is that these frequencies aren't particularly friendly to high-speed digital use. I suspect this is related to Nyquist theorem - the fewer waves you're receiving per second, the fewer symbols per second can be encoded into them.
And finally, some rather difficult legacy users. Aviation and Marine users who consider their usage life-or-death, radio amateurs that likely do too (heh), radio-navigation (I was reading about Loran making a comeback recently, to provide some backup when GPS is manipulated), over-the-horizon radar (which can be a lot like sharing a telephone call with a foghorn), etc.
All this taking up about as much bandwidth as one wifi channel ..
> The most powerful signals were Christian broadcasts that had a kind of doomsday feeling about them.
Here's the antenna:
https://www.google.com/maps/@40.4793923,-76.279183,3a,44y,28...
It could be off again, don't know.
I pick up a lot on the FM and AM bands. The shortwave bands feel comparatively empty.