Quote:
Originally Posted by G6Tanuki
Regarding the WWII-and-immediately-following-years US adoption of FM for tank and manpack comms - it's interesting to note that "Squelch" was pretty much universal on US FM gear but absent from the likes of the UK WS88 and similar.
Indeed, I believe that at one time "Squelch" was actually *removed* from certain US-designed FM radios when these were subsequently manufactured in the UK.
Which seems deeply odd: the nerve-shattering effects on a wireless-operator of FM-detector "white noise" in the absence of a signal must surely have been considered? Likewise, I'd rather not have wanted to be an infantry-signaller hiding in a bush or other cover and trying not to be noticed by an enemy patrol if the handset of my radio was emitting the typical "sharsh". It's not as if the likes of the WS88 had a volume-control you could turn down....
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Well, that's partly accurate. The WS88 never had squelch at any time. Its as simple as its possible to be with just two switches: on/off and channel select (only 4!)
But the WS31, which was the first of the UK copies of an American set (the BC-1000) started life with squelch fitted - in what later became the WS31 Mk.1 It then went through an update programme to become the WS31 Mk.1/1 which included the removal of the entire squelch system (which saved 3 valves in total), plus various other mods to the aerial etc. That version was finally updated to the Mk.2, which also had no squelch.
And others pointed out the WS31 replacement, the A41 started out with no squelch, but then had it put back in the Mk.2 version.
I have never seen a document detailing the thinking behind all this apparent nonsense. The only sense I can make of it is that the average squaddie couldn't cope with something as complicated as a squelch control and tended to wind it up far too high (to shut the noise off), and then missed critical messages. Clearly someone much later then realised that operator fatigue - from listening to incessant white noise - could have exactly the same effect. And no doubt they then spent some money training operators in how to use a squelch control properly!
Another factor to bear in mind in these early VHF/FM sets is that they were very wideband by modern standards. No crystal filters in these sets, and VFOs only kept vaguely on frequency by an AFC loop. So the deviation was typically +-15kHz, and the IF bandwidth could be around 50kHz. This was mainly to cope with drift of oscillators of course. The result of all this rather basic performance was that the receivers were insensitive - at best around 1uV, which should be compared with modern sets doing around 0.1 to 0.15uV. What that mean operationally was that the range was poor because the link budget was limited by the insensitive receivers. Low transmit power also came into it, with a WS31 managing around 0.3W typically. When you add that into the mix, dodgy operators winding squelch controls up a bit high is not good.....
Richard