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It's my understanding that FM is used for UHF, VHF, and SSB is generally reserved for other bands.
From my understanding,

FM

  • better audio quality when reception is good

SSB:

  • more efficient (can transmit farther with the same amount of power as fm or the same distance as fm with less power)\
  • more understandable when the quality is low

Are there other, more efficient audio modes other than the most common two?

If my above understanding is correct, why aren't there any SSB HT's that operate in the UHF or VHF range, especially considering that efficiency is so important for battery life?

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  • $\begingroup$ I'm really not sure your first SSB point is true: SSB uses less bandwidth, for sure, thus increasing SNR if noise power density is constant. What you claim is "for the same perceived quality, an SSB transmitter at the same distance needs less power", and I think that's false. The quality-over-SNR curves simply look different. They might cross in multiple points. $\endgroup$ – Marcus Müller Jan 11 at 22:39
  • $\begingroup$ I'm not sure about it. Just what I've heard. But I really do mean at poor qualities. As if our brains are better at distinguishing words and phrases of am better then FM when both signals are terrible. I'd that just mumbo jumbo? $\endgroup$ – begs-the-hessian Jan 11 at 22:46
  • $\begingroup$ that sounds really reasonable; at low SNRs, our hearing does the error correction because it kind of hears the original signal superimposed with the noise; in FM demodulation, additive noise really has a very non-linear effect, hence you're absolutely right: there's simply a threshold below which FM reception becomes impossible, and that's higher than the same threshold for SSB. The question is just for "how far up" in SNR the "intelligibility vs SNR" curve of SSB is above that of FM. I bet there's some 1940's and 50's extensive research on that, but any publications elude me. $\endgroup$ – Marcus Müller Jan 11 at 22:49
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SSB phone requires good frequency stability to be intelligible. Anything over 10Hz of frequency difference between transmitter and receiver and the signal starts to sound funny; beyond 50-70 Hz of error, intelligibility starts to drop. Hitting that target is more difficult at higher frequencies than at low frequencies. In the HF bands, getting within 10Hz requires 1 part per million (order of magnitude) relative frequency accuracy. For VHF it's more like 0.1 ppm, UHF is 0.01 ppm, and microwave we start thinking about GPS-locked oscillators.

FM, on the other hand, is pretty insensitive to frequency errors. For an FM signal with a deviation of 5kHz, a frequency offset of 1kHz between transmitter and receiver is almost unnoticeable, and even 2 kHz doesn't impair communications too much. So for practical purposes, let's say FM is 50 times as forgiving.

Even base station and mobile VHF/UHF rigs are much more likely to have FM than SSB for this reason — it's simply much easier to get acceptable FM at those frequencies than acceptable SSB. "All-mode" rigs are usually (though not always) the more expensive ones.

HTs have the same problems to contend with plus they're generally lower-cost, need to be smaller and lighter, and generally use unregulated battery power that tends to droop over the course of a transmission. All of those negatively impact frequency regulation, and keeping a signal accurate to within a few tens of Hz under those conditions is simply impractical.

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Commercially, the distribution of the two modes is pretty much as you say,but in Amateur Radio, SSB is used in all bands.

Generally, FM is also usable in all bands, but usually, only very small frequency deviations are allowable below the Ham "10 metre band".(about 28 MHz to 29.9MHz)

In Commercial "two way radio", FM is preferred over SSB, because, in use, the probable necessity of adjusting a "clarifier" control wastes time.

To hams, neither careful tuning nor using the clarifier to resolve an SSB signal are particularly onerous tasks, so commercially produced Amateur Radio transceivers for VHF/UHF can be either "FM only" for the least expensive, or "multimode" for the more costly ones.

Older VHF or UHF SSB radios are often used with "transverters" to produce output in that mode on microwave frequencies.

There have been handheld SSB radios, but they were mainly on the 10m band.

Not quite "HTs", were the single mode Icom IC 202 & IC502 "handbag" sized SSB/CW radios on 2m & 6m back in the 1970s.

The Yaesu FT290/490/690 of the 1980s/90s were nearly small enough to be handheld, & were multimode radios on 2m, 6m, & 70cm, respectively.

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