[CW] another earhart blurb

[David J. Ring, Jr.]

One thing should be noted though, that the radio WAS operating on the 2nd
harmonic.

In ships and aircraft the working frequencies were harmonically related.

2090 4180 8360 12540 16720 were examples of ship frequencies.  Each of the
frequencies is harmonically related to the earlier frequency.  Thus a ship
transmitter could cover many bands by simply having one crystal.

Ships used crystal control for transmitting until the 1970s when frequency
synthesizers started to be introduced and it was only by the early 1980s
that synthesizers were mandatory to be carried in the radio installation.

If a radio station was meant for a radio officer, the frequencies were not
pre-set, but they were set up on a tuning card allowing the radio officer to
quickly set up the various knobs (oscillator, buffer, multiplier, final
tuning, antenna coupling/rough, antenna coupling/fine.)  There also was a
knob to set the filament voltage of the tubes.

The frequencies used by Airhart were harmonically related:  3505 and 6210.
The transmitter had to be set up to be used on the second harmonic.  The
frequencies used for direction finder were also harmonically related 500 and
7500.  I would sincerely hope that the design engineer used a separate
crystal for 7500 as it is bothersome to make sure you haven't peaked for
7,000 or 8,000 kc/s.

73

DR
----- Original Message ----- >
> This is the text he's talking about:
>
> }}}  Think we should give a bit more credit to American aircraft radio
> engineers of the mid to late 1930s.
> The ARC-5 transmitters are of that era, and there is no way they could be
> tuned up on second and third harmonics without extensive electrical and
> mechanical modifications.
> The crystal controlled transmitters of the day used in civil aircraft were
> channelised and fixed tuned with usually only antenna loading adjustable
> within the aircraft.
> They were set up before flight and operated by the pilot via a control
box.
> As you say, one can visualise scenarios whereby the radio was damaged in a
> forced landing and somehow came to put out signals on a harmonic but this
is
> stretching the bounds of plausibility.