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Comment by squarefoot | Hacker News Reader

Night hours are best for shortwave reception. You could also need an external antenna depending on how far you are listening from. Another problem, probably the biggest one today, which affects reception on these frequencies (and generally on the HF bands) is the radio noise generated by many bad designed switching power supplies and appliances. Switching regulators (power supplies, converters, chargers etc.) for efficiency and size reasons have moved from the tens of KHz through the hundreds of KHz and recently they started working above 1 MHz which means having into our homes one or more transmitters with antennas (mains or output cable) that if not properly designed, filtered and shielded will render reception on HF bands next to impossible.

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Thanks for the information.

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?

Bandwidth is key. Transmitting digital signals at high rate would eat up most of the spectrum.

How were they able to pack so many digital radio stations on FM? Is it because it's higher frequency?

Yes, definitely.

You can think of the trade off roughly as "frequency increases increase bandwidth and decrease penetration/range"

Until you get to x-rays! I've always wondered why this is

If you are looking at xray penetration in the atmosphere, it is very opaque. Almost no xrays get through hence why space telescopes are needed to do xray astronomy.

The wavelength at these frequencies is very long, meaning antennas must be very large. In addition, the bandwidth is very small -- you can't exactly encode data on these frequencies for any practical purpose (some digital modes are popular on ham radio bands; e.g. PSK31, RTTY, etc.)

Yep, PSK31 has a baud rate of 31.25 - that's literally 31 bits per second. There's no practical use for that in modern commercial or consumer applications.

In amateur bands, symbol rate below 28 MHz is limited to 300 baud.

And anything in the 2M band is also symbol rate limited(I want to say it was 1200baud but I could be wrong).

It's really frustrating if you want to do any development with digital modes.

[edit]

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.

Are US ham bands really symbol rate (rather than bandwidth)limited?

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.)

Essentially, yes. My guess is that it's due to the fact that amateur radio for a long time has been CW and SSB, where there isn't much bandwidth issue. Digital modes are the new kid on the block (especially considering the average age of US hams is probably quite high), so rather than addressing the root issue, they decided just to target that new kid.

There are bandwidth restrictions on the 60m band, where amateur radio is secondary.

It's actually both, 20Khz bandwidth and the 19.6k symbol rate.

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.

There is more than one shortwave band, some are more useful than others and there are fairly large gaps between them, so it would feel sparse even if there were a lot of stations: https://en.wikipedia.org/wiki/Shortwave_bands

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.

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