[Elecraft] OT: Aircraft radio FM

[Hop - AC8NS]

Hmm. I noticed but it doesn't bother me. Presumably all who post here are 
either Elecraft owners or wannabees. I enjoy reading stuff from all those 
old hams who are "been there, done that, wore out a dozen tee-shirts" types. 
I am gonna join the Quarter Century Wireless Association (QWCA) this month, 
Chapter 9 (Southwestern Ohio), just to be around some of those guys who meet 
for lunch once a month. Many were born shortly after the turn of the 
previous century and have plenty of history to share.

As for FM... gee, we are well into the 21st Century. If there was some 
overwhelming demand for aeronautical FM I am sure someone could engineer a 
chip that would eliminate the "capture effect" which, if I recall correctly, 
is an artifact of discriminator and ratio detector design, not a given 
because of the modulation mode. Maybe some sort of delayed auto-correlation 
algorithm applied prior to the limiter or in lieu of it would allow weak 
signals to be selected in preference to nearby strong signals, thereby 
preventing the "capture effect." Ask Wayne. I don't see a limiter or a 
discriminator or a ratio detector in my KX3 schematic, yet it does FM. You 
can do almost anything with an SDR, except maybe brew coffee.

End thread?

74 de AC8NS
Hop


----- Original Message ----- 
From: "Rich" <r.bro84 at googlemail.com>
To: <elecraft at mailman.qth.net>
Sent: Tuesday, July 16, 2013 6:11 PM
Subject: Re: [Elecraft] OT: Aircraft radio FM


Am I the only one wondering what has any of this got to do with Elecraft??

Can the moderators put an end to all of these OT posts and return it to a 
reflector for its purpose please?? Yes I know where the delete button is but 
the threads get longer and longer.

Nothing personal Mike, just picked your post to reply to.
Sent from my BlackBerry® wireless device

-----Original Message-----
From: Mike Morrow <kk5f at earthlink.net>
Sender: elecraft-bounces at mailman.qth.net
Date: Tue, 16 Jul 2013 18:02:36
To: <elecraft at mailman.qth.net>; <KX3 at yahoogroups.com>
Reply-To: Mike Morrow <kk5f at arrl.net>
Subject: Re: [Elecraft] OT: Aircraft radio FM

Ken wrote:

> AM aircraft radio has been around since the end of spark and
> steadily growing world-wide since that time.  It was solidly in
> place -long- before FM was a gleam in Armstrong's eye.

Er...I'm not sure how that supports an argument that transition
to FM was *at any point and time* considered *by any responsible
party* to have characteristics that were more desirable than AM
for aircraft communications.

The characterization that AM was "solidly in place -long- before FM
was a gleam in Armstrong's eye" refers accurately only to the era
when aircraft communications were only on medium and high frequencies...
an era when long-range aircraft communications often still made use
of Morse CW (hence the FCC Element 7 exam for Aircraft Radiotelegraph
Endorsement, now discontinued).

The transition from MF/HF to VHF for aircraft communications received
its greatest push with the UK's pioneering use after 1940 of aircraft
AM command sets operating in the range of 100 to 156 MHz.  This sparked
the allied US military's transition from MF/HF command sets to VHF
command sets, one of the earliest being the Western Electric 233A set.
At this point, VHF FM could have been *very easily* adopted, had it not
been for its undesirable capture effect.

Aircraft VHF-AM was chosen long after FM had been developed.  The
decision to use AM was purposely made.  The adoption of aircraft VHF-AM
was NOT the result of constraints from earlier legacy technology.
All civil aviation eventually adopted the military standard of VHF-AM,
although up to the mid-1950s many private aircraft continued to use
MF/HF sets with receivers in the 200 to 400 kHz range and a transmitter
on 3105 (later 3023.5) kHz...still far from a universal commitment
to VHF-AM at that late date, had VHF-FM been a better choice.

Further, by 1945, the US military began exploring UHF for aircraft
comms.  These new sets had no reason to stick with AM, if FM were
superior.  But FM was not superior...or as good.  AM was chosen for
use in the military UHF aircraft band as well.

> It remains that the staggering cost of conversion to FM is the
> real reason it continues today.

That is a gratuitous assertion for which my decades of study in this
area finds no substantiation.

73,
Mike / KK5F
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