In message , FranK Turner-Smith G3VKI
writes
"Spike" wrote in message
...
On 06/02/15 12:39, Jeff wrote:
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

There was an adaptation of the WS19 (I think it was the WS32) that
used FM instead of AM, to test the use of FM on the battlefield. I
guess it was unsuccessful or other considerations mitigated against
it, because it wasn't adopted in that form, but some manpack sets and
WS19 candidate replacements were FM. I think that only about 100 WS32
were made.

To ensure compatibility it would have been necessary to swap all the
military AM radios to FM at the same time.

The middle of a global war is not the time to make changes on that
scale, especially as the advantages of doing so seem minimal.

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some used
FM?

IIRC, most WW2 gear used simple 'Lo-Fi' forms of AM modulation (grid or
screen-grid), and not hi-level plate and screen (which requires more
valves, more current drain, a heavy mod transformer etc). As such, the
component count would be similar to FM equipment.

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


--
Ian