[kefka]

400MHz/900MHz are not "slower", it's just that the band plans only allow less bandwidth usage. Because the 2.4GHz band is so high frequency, an individual channel can be bigger. For 802.11B, it's 22MHz channels.

But, it's easier to make a radio using lower frequencies. In the 70 cm band (400~MHz), you can get some ground-wave propagation. But the overall channel size is smaller. With 2.4, its Line of Sight only.

In all honesty, the ideal setup is a low frequency (144MHz or lower) for command and control, with a higher frequency video transmitter. No sense in sending every bit of data down the same pipe.

Source: Me, KC9JEF

[lutusp]

> 400MHz/900MHz are not "slower", it's just that the band plans only allow less bandwidth usage.

Yes, but bandwidth = speed, so all else equal, a wider allowed bandwidth produces greater speed.

> In all honesty, the ideal setup is a low frequency (144MHz or lower) for command and control ...

Maybe in a perfect world without anyone else competing for the frequencies. But even without competing uses, higher frequencies have reduced noise problems -- as you go up in frequency, thermal noise declines, so smaller transmitter powers become acceptable (or the same power produces more reliable communications).

But then there's the line-of sight problem, which gets worse at higher frequencies.

Note about radio control that, over decades of time, the command & control frequencies have been going up. There's a good reason -- the original 27 MHz scheme was unworkable for multiple reasons, but one of them was limited bandwidth.

[kefka]

> Yes, but bandwidth = speed, so all else equal, a wider allowed bandwidth produces greater speed.

That's not quite true. It's Bandwidth + encoding = speed . And there's tons of digital encoding schemes: ASK APSK CPM FSK MFSK MSK OOK PPM PSK QAM SC-FDE TCM for starters. And those would allow you to pick up and decode using any old computer running a HDTV usb capture card that can go into raw mode.

> Maybe in a perfect world without anyone else competing for the frequencies.

Nobody would bat an eye if I was to start doing UAV control over 145.50-145.80 with a 20KHz bandwidth . I'd just hop on the local repeater and announce that is what I was doing, and have a radio listening in priority mode to it. If I heard of any anomalies, I'd shut it down and investigate what's going on.

And I have no LoS issues and 2M usually has a nice noise floor. Obviously that doesn't quite apply at night, but just stay vigilant in not harming others.

> Note about radio control that, over decades of time, the command & control frequencies have been going up. There's a good reason -- the original 27 MHz scheme was unworkable for multiple reasons, but one of them was limited bandwidth.

Tubes and early silicon made access to the lower frequencies tenable. Of course the lower frequencies will fill up first. So, it does make great sense, for higher bandwidth using services, to use high frequencies. That's why I said the video could be on the 2.4 GHz spectrum, whereas the command can be on 144MHz.

I'd also consider going lower, making AM more usable. For command frequencies, NOT having capture* is a great deal. That's why control towers mainly use AM and digital modes/CSMA variant.

*Capture is an FM phenomenon, where the strongest FM signal that hits a receiver is the only signal the receiver can hear. The receiver is literally captured to that station. AM does not have that, and what you hear is the jumble of every station in range. Just tune at night on AM and you can hear this.

[sounds]

Good points, thanks. I know 400/900 are not "slower." But the radios designed for them generally are slower.