On Fri, 6 Feb 2015, FranK Turner-Smith G3VKI wrote:

"Ralph Mowery" wrote in message
...
"Michael Black" wrote in message
news:alpine.LNX.2.02.1502051950290.19867@darkstar. example.org...
On Thu, 5 Feb 2015, Ralph Mowery wrote:
I don't have any of the very old gear, but every so often I listen to the
hams around 3.85 MHz. that use the old military and AM gear. While I
don't think it is really legal (and don't really care) some of those AM
transmitters sound beter if I switch to FM on my Icom 746 pro. I think
when they were made they seem to put out about as much FM as AM.

That's weird. I thought those hardcore AMers wanted purity, and took
effort to ensure they were putting out a good signal. They sure aren't
using modulated oscillators, and I don't think anything where the
modulation would get back to the oscillator.

There may be two kinds of people using AM. One for 'good quality AM' ,but
the other is using mainly the military gear from around the WW2 era or so.
Maybe even before that if they can find it. That is the stuff that can
contain about as much FM as it does AM. The power supplies are often
feeding the oscillator as well as the final stages and not regulated very
well if at all. That probably helps modulate the transmitter to have a lot
of FM in the signal.

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.

But Ralph is complaining about a signal that is both AM and FM.

INtentional FM is different from incidental FM.

Certainly in the US (and I assume Canada), rules were in effect quite a
few decades ago about the stability of a signal. There was a point where
a signal had to be as stable as a crystal controlled signal on the HF
bands, which caused a shift to crystal control, I think that was even
before WWII. So incidental FM would seem to be out of the question after
that. It was only after WWII when things got crowded and better
techniques came along that VFOs made a comeback, obviously much better
built and stable than the variable oscillators of the old days. (And the
same sort of rule followed as the move up to higher frequencies.
Modulated oscillators would work the higher frequencies initially, then
the rule for better stability would come in, and the modulated oscillators
would move to the next higher band, and so forth).

If a signal is putting out both FM and AM, it is either doing it by
accident, and needs fixing, or is some weird form or modulation, that the
rules would either have a separate classification for, or a rule against
it.

Michael

"Michael Black" wrote in message
news:alpine.LNX.2.02.1502061353050.21109@darkstar. example.org...
But Ralph is complaining about a signal that is both AM and FM.

INtentional FM is different from incidental FM.

Certainly in the US (and I assume Canada), rules were in effect quite a
few decades ago about the stability of a signal. There was a point where
a signal had to be as stable as a crystal controlled signal on the HF
bands, which caused a shift to crystal control, I think that was even
before WWII. So incidental FM would seem to be out of the question after
that. It was only after WWII when things got crowded and better
techniques came along that VFOs made a comeback, obviously much better
built and stable than the variable oscillators of the old days. (And the
same sort of rule followed as the move up to higher frequencies. Modulated
oscillators would work the higher frequencies initially, then the rule for
better stability would come in, and the modulated oscillators would move
to the next higher band, and so forth).

If a signal is putting out both FM and AM, it is either doing it by
accident, and needs fixing, or is some weird form or modulation, that the
rules would either have a separate classification for, or a rule against
it.

I was not really complaining about the signal, just noting that it sounded
beter on FM than AM.

What might have been state of the art around 1930 or 1940 is probably not
legal now. Just as the old spark gap transmiters are not legal any more.
The station was suspose to be using AM, but probably the power supply was
not regulated enough that fed the audio amp and also the VFO so that the
changing of the VFO voltage was enough to FM the signal.

As you say Michael the design was for AM, but some of the old sets seem to
put out as much FM as they did AM. That was just the way it was 60 or 70
years ago. Especially some of the portable military gear.

Anyway I have no complaints about some guys having fun with the old gear as
long as they stay on or very near one frequency like they do.