From: "Harold E. Johnson" on Wed, Feb 8 2006 1:31 am

"Henry" wrote in message

It would help more if you separated your MHz from KHz. Those are all WW2
tank transmitter frequencies and were for 54 X and 72 X multiplications so
that it could be FM'd.

Both Rx and Tx were crystal-controlled. Those were mostly MOBILE
radio sets (not restricted to armored vehicles or "tanks"). The
modulation was PM, not FM, using "reactance tube" modulators
prior to frequency multiplication; makes little difference to
receivers at the other end since FM and PM used the same limiters-
discriminators for demodulation.

Omitted from ham lore are some of the other radio sets of bygone
military days, those having "crystal boxes:" The AN/TRC-1, -3,
-4 VHF Radio Relay terminals and repeaters (70 to 90 MHz, design
beginning around 1941-1942)...lots made but sold to other militaries
after WW2, not many to surplus distributors; the original HF handie-
talkie and its companion, the ill-fated "Pogo Stick" HF transceiver
(both AM but the contract for the Pogo Stick was let AFTER the
Army disbanded horse-mounted cavalry). Motorola (then Galvin Mfg)
in Chicago made both of them.

The Army must have loved old Armstrong, they always
used FM even when the well understood capture effect kept killing off their
guys.

I disagree on the "killing off their guys." Both the handie-talkie
and early 1943 beginning walkie-talkie replaced an abominable three-
sack four-tube high-HF/low-VHF kluge used just prior to WW2. Those
two models were unsuited for ground military communications. Some
invited civilians from Motorola told the Army that in 1940. The
SCR-300 walkie-talkie, though cumbersome at roughly 40 pounds of
single backpack, used only one crystal and that one for tuning dial
calibration. The SCR-300's Tx and Rx were VFO-tuned! [marvelous
design job in my estimation considering the enormous range of
temperatures they underwent and the physical beating they took]

FM in mobile/portable radios was proven much more useable in 1939
to 1940 trials of police radios in various departments around the
USA, principally by those sets made by Link. Galvin (later re-
named Motorola after WW2) picked up on that to design the SCR-300
which was a communications success for ground-pounders. Since the
SCR-300 was tunable, and in the frequency range of those "tank"
radios, ground units could communicate together as the situation
demanded. The basic SCR-300 design was licensed out to several
foreign militaries right after WW2 and served past the 1950s even
after the replacement of the '300 by the AN/PRC-8, -9, -10 manpack
high-HF/low-VHF FM transceivers (I wore a -9 a few times in 1955).
It was half the weight of the older SCR-300.

In varying terrain over relatively short distances (under about 10
miles) and in the chaos of active combat, the constant-audio-level
of FM and reduction of electrical noise effects worked out better
than the AM radios of those days. The task was to coordinate and
communicate in combat situations, not to play with gain controls
or radio knobs. Consider that the "channelization" right up to the
push-button channel selection on the "tank" radios made it much
easier to USE in an extremely-busy-with-other-things combat
situation. Playing with radios was a no-no when there are bad
guys out there determined to snuff you out; attention can NOT
be disturbed in such conditions.

I'll disagree that the "capture effect" was either a buzzword at
the time or responsible for some alleged disturbance to vital
communications. Even with the crude AVC (what is now AGC) of AM
receivers back then, a stronger AM signal on the same frequency
could blot out a weaker AM signal every bit as much as any FM
limiter action doing the same. "Capture effect" buzzphrases
were popularized after WW2 and after the Korean War of '50-'53.

The migration to VHF for relatively short-distance comms had
begun DURING WW2. The "three-band" system of overlapping
frequency bands for infantry-artillery-armor in high-HF/low-VHF
was planned for post-WW2 military land forces use as a result of
lessons learned during WW2 by the USA and USMC. That plan was
in use for two decades, including the beginning of the Vietnam
War. The many-made AN/PRC-25 (later -77) of later Vietnam War
fame was VHF as a result of long experience in what worked and
what didn't.

Same reason the Air Force still can't talk to the ground pounder
unless they stick an AF guy with an AM rig with them on the ground. Sigh

Way untrue now. Airborne radios went VHF and AM for different
reasons beginning in later WW2 years. Airborne short-distance
(up to about 50 miles) can use relatively low-power Tx and with
tube architecture an AM Tx is less complex and weighed much
less. Weight in earlier aviation was still a driving factor in
what was bolted on an airframe. [still is, but a moot point
considering the marvels of solid-state miniaturization]

ICAO (International Civil Aviation Organization) rules specified
VHF AM at 108 to 137 MHz in 1955 on the basis of WW2 designs and
experience. Around the same time, the USAF (now a separate
U.S. military branch) standardized on 225-400 MHz UHF, AM, for
airborne communications. [see the ubiquitous old AN/ARC-27 for
a good example of airborne "push-button" channelization reducing
the need for playing with knobs in cockpits] None of those were
sharing any bands with folks on the ground. In actual use, it
was preferred to have air comms on DIFFERENT bands than surface
comms to avoid radio congestion.

A former neighbor was both a B-26 pilot and a Forward Air
Controller in Korea of the early 50s. Not the glamorous roles
shown in the movies but a decided advantage to have "an AF guy"
as the FAC because they KNEW how to talk to and direct the
flyboys whereas ground-pounders weren't familiar with their
needs, even to help out the guys on the ground needing support.

A lot of that began changing in the later 1960s with specific
ground equipment that could communicate with airborne radios
being procured. The SINCGARS family of VHF radios has four
specific models, 1 manpack, 2 vehicle/transportable, 1 airborne
to get everyone involved in coordination of nasty-business
action. [there's as much Army aviation used for land forces
support as there are USAF for the same role] A quarter-
million SINCGARS R/Ts have been produced and made operational
since 1989 and the successor is about to debut (see Harris
Corporation detailed PR). Frequency-synthesized as are all
military radios now, no boxes of crystals to lug around.

The new generations of military radios appearing now cover
frequencies from 30 MHz on up to the top of the airborne
military comm band...and any mode-modulation as needed,
the emphasis on digital (for encryption) and frequency-
hopping (to make RDF extremely hard for the "other side").

Nobody can hope for cheap, easy-to-convert for ham use
"surplus" radios now. :-( There haven't been any "surplus"
quartz crystals from the military for decades...although
there might be some from the 2nd and 3rd generation of VHF
"tank" radios when those are taken out of storage. During
the last three years of WW2, the USA produced an average of
a MILLION quartz crystal units a month! No wonder there
were surplus crystal units made available later.



ex-RA16408336