On 2/7/2015 8:07 AM, Ian Jackson wrote:
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.



Actually not. Aircraft worldwide were using AM radios before FM became
popular. To change would require every radio-equipped airplane in the
world, from Cessna 150's to Antonov An-225's, change at the same time,
as well as all land-based stations including ATC, Flight Service
Stations, Unicoms, and even handhelds on the tarmac.

Plus, with the 8.33Khz channel spacing, deviation would be limited to
about +/- about 3Khz. Even with the old 25Khz channel spacing (allowing
about +/- 10Khz deviation), there is no clear advantage to FM over AM.
Fidelity is not a concern for the aircraft band.

It isn't going to happen It's going to take least 13 years just to
get new NextGen navigation system installed in aircraft in the United
States.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================