I have a couple of HTs with channel scanning features. I imagine setting the radio to scan mode takes more power than just listening to a single channel, but what rough order of magnitude? Will I lose 1%, 10% or 50% of my battery life? Are some brands or models notably better than others for power efficiency while scanning?
There are a few states of listening that you should think about:
listening with the squelch closed, the receiver is probably off for 95% of the time, turned on a couple of times a second to check for a signal. This is the lowest power state.
receiving a signal, squelch open, the receiver is fully on.
Also the loudspeaker takes some power, not much if it's soft, but more than the receiver if the volume is loud.
scanning at full speed, the receiver is on all the time. Re-tuning won't increase its power consumption significantly (there is some time wasted while the tuner settles, but this is just part of scanning).
So I estimate that scanning, with the squelch closed, takes the same or less power than listening to a busy channel at low volume, but many times more than monitoring an empty channel.
Why not do an experiment? Disconnect the battery, power the HT from an external source, and monitor the current that it draws. You might have to do some work to smooth out the pulses of current in monitoring mode, something like this:
simulate this circuit – Schematic created using CircuitLab
$\begingroup$ I'd assume the first point doesn't actually work that way: How would the receiver know to release the squelch if it wasn't already receiving? So, barring something like squelch being low-power analog and the rest of the receiver being digital, I'd even assume that the receiver part as is uses more power in squelched mode than in unsquelched, because you'd typically increase analog gain and look for signal statistics indicating channel usage in the digitized signal. $\endgroup$ May 24, 2019 at 9:49
$\begingroup$ however, the measuring approach is absolute cool :) $\endgroup$ May 24, 2019 at 10:52
$\begingroup$ @MarcusMüller I think Tom is right. I thought the same thing even before he posted this answer. However, the way to tell is by measuring. I remember a manual even listing the battery drain in different RX modes. Whatever it was, scanning drew more current than listening to a quiet channel with squelch. But not all HTs might be that way. $\endgroup$– Mike Waters ♦May 24, 2019 at 16:16
$\begingroup$ Thanks for suggesting the ammeter, I hadn't thought of it. My method of measurement was going to be to run the battery dry both ways, but that's much less accurate, informative or convenient. $\endgroup$– K0SWEMay 24, 2019 at 19:37
$\begingroup$ @MarcusMüller > How would the receiver know to release the squelch if it wasn't already receiving? A: It doesn't need to receive all the time just to detect the channel in use. The receiver - RF amplifiers and LO synthesizer - can be turned on and off very quickly, perhaps < 1 ms. To save power it can be off most of the time when monitoring. 5 times per second it's turned on for long enough to stabilise and compare the level to the squelch setting. If it's below the threshold then it sleeps again. You can hear the small delay in the squelch opening on a handheld radio because of this. $\endgroup$– tomnexusMay 25, 2019 at 9:00
I would not be surprised if the audio amp used more power than the rf front, tuner osc, and signal detect combined. Thus listening at some reasonable speaker volume, and using energy to vibrate a physical mass, might consume more power than just retuning and monitoring some level.
But measuring your particular radio is much better than guessing.