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Comment by psim1 | Hacker News Reader

I remember an old TV set that had UHF channels from 14 to 83. How is the exclusion of a single channel, 37, a problem for TV broadcasters?

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Overlapping broadcast areas. It's one less channel to use for deconflicting the need for broadcast spectrum and the desire to have a broadcast channel while avoiding interference from neighbors.

They get at this with the New Jersey case, where in order for the station to get a channel it had to be 37. Presumably this was because of there being too many other broadcasters in the area. It's been a long time since I studied radio so I can't recall the specifics, but if there are 70 channels available (total) in a specific area perhaps only half or a quarter of them might be usable without producing interference with others.

EDIT: You also see this play out with conventional AM/FM broadcasting. You typically won't find adjacent stations, like 91.3 and 91.5, in the same area and when it happens (perhaps you're on the edge between the two broadcast areas) you'll hear one station bleeding into the other.

same principle applies to WiFi routers. That's why you look at other channels being used in your aread, and then pick a channel that has the least overlap with your neighbors.

The concept of a "channel" on WiFi bands (particularly 2.4GHz) is pretty much done. 802.11ac can use 80MHz of spectrum on the 2.4 band, which is pretty much the entire set of available channels all at once.

Not everyone has an ac chipset.

True, but if you live in a congested area, chances are good that one of your neighbors does. I have a house in a new community of "smart homes" where each home has two AC WAPs. Every single 2.4GHz channel has several users. MIMO helps, but 5GHz (or the new 6e band) are much more preferable.

Not everyone but it's been out for 8 years.

If you're worried about congestion, you're probably going to see ac.

Wow 8 years. Are there any ac chipsets with open source firmware yet? Has the nut been cracked?

Unless you are in a rural area, trying to use an 80 MHz channel in 2.4 GHz almost guarantees your radio is going to spend far more time waiting to transmit because of interference than doing anything useful. Finding the least congested 20 MHz channel is likely to give higher overall throughput.

[0] claims 802.11ac explicitly does not support 2.4 GHz. Further search did not reveal any strong evidence for any VHT support on 2.4 GHz. What do you base your claim on? Can you share the source?

[0]: https://www.cisco.com/c/dam/en/us/products/collateral/wirele...

Isn't being on the same channel as another network actually OK-ish with newer standards? The worst is when you partially overlap another channel.

FM has a property known as "capture effect". The result is that the stronger station will usually "capture" the PLL (back when they used PLLs instead of SDRs for FM demod) and you will not hear the adjacent station. It can become a problem in a mobile environment (car stereo) when the signal levels are constantly changing, but "bleeding" is a problem usually associated with other modulation types (typically AM and SSB).

Supposedly this is one of the reasons aircraft radios are AM instead of FM. If two stations transmit at the same time, you want to recipients to hear the interference so they can ask for a retransmission instead of one hearing a clear message and the other having no idea that someone tried to transmit to them.

This.

Plus the fact that AM is actually capable of better sensitivity than FM, especially in the narrow bandwidths necessary for aircraft VHF communications.

Capture effect has nothing to do with the operation of PLL's.

Most FM radios have a Limiter stage which strips of all Amplitude variations. This means that any strong signal in the passband will completely suppress a weaker signal.

https://en.wikipedia.org/wiki/Capture_effect

You typically won't find adjacent stations, like 91.3 and 91.5, in the same area and when it happens (perhaps you're on the edge between the two broadcast areas) you'll hear one station bleeding into the other.

Back when I used to listen to terrestrial radio, I noticed that "bleeding" was much more common with "Christian" radio stations. I could be trying to listen to NPR broadcast from 30 miles away, and it would be totally drowned out by a Christian station an entire channel away (e.g. 92.3 - 91.3) broadcast from a different state.

A lot of religious radio types tend to play fast and loose with transmit regulations, or even quality of hw to prevent randomly sprouting harmonics few channels away (a certain somewhat "loud" case in Poland was illegal rebroadcast that managed to spill over to airport frequency...)

In Spain there was the infamous case of "Radio Maria" (no explanation needed, UltraCatholic band) on being tunable everywhere even if you were in the remotest farm ever with no traces of civilization 100 kms around that point.

They look that the had illegal repeaters/relays.

hahahahaha...

To explain, that's essentially the same name as the one ultra-religious radio in Poland, that was also known for abusing RDS system to force-switch everyone's car radios to their channel :)

https://en.m.wikipedia.org/wiki/Radio_Maria

It’s not a coincidence.

It would seem there is some suggestion of independence between the Polish station and those linked:

> Not to be confused with Italy-based international Catholic radio broadcasting service Radio Maria.

https://en.wikipedia.org/wiki/Radio_Maryja

In Spain it happened with a local radio station with 91.3-91.5 and 94.5-94.7

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