The Transmitter Set



Shown here is the entire suite of 8 MF and HF transmitters in the ARC-5 set. Frequency ranges, along with the most common calibration crystal frequencies, are shown below. (Be aware that the SCR-274N and Navy ATA sets had different "standard" crystal frequencies.)

T-15 500-800 kHz (Calibration crystal 800 kHz)
T-16 800-1,300 kHz (Calibration crystal 1,300 kHz)
T-17 1,300-2,100 kHz (Calibration crystal 2,100 kHz)
T-18 2.1-3.0 MHz (Calibration crystal 2,601 kHz)
T-19 3.0-4.0 MHz (Calibration crystal 3,265 kHz)
T-20 4.0-5.3 MHz (Calibration crystal 4,435 kHz)
T-21 5.3-7.0 MHz (Calibration crystal 5,505 kHz)
T-22 7.0-9.1 MHz (Calibration crystal 8,870 kHz)
Starting at upper left in the photo above is the O-4/ARC-5 crystal oscillator that was used for setting the later "lock tuned" ARC-5 receivers to a predetermined mission frequency. A close-up of this unit and more about its purpose is on the ARC-5 receiver page. To its left is a box of six crystals that was packaged for its specific use. Behind it is an MD-7/ARC-5 modulator, used with all of the ARC-5 transmitters to provide power and modulation. To the O-4's right is a TN-6/ARC-5 MF antenna tuner, used with the T-15 and T-16 transmitters to its right. It reflects the considerable reuse of older components that was ARC's SOP - the small grille guard for the neon lamp is from an earlier GF-* transmitter control box. The T-17 finishes off the top row.


TN-6/ARC-5 antenna loading coil

There is some degree of controversy over the employment of these three MF sets. The most credible explanation to date in my mind is that they were used with the float planes stationed for reconnaisance on the tails of the battleships - this from two veterans who were there. The use of MF (500-2100kHz) was apparently geared toward the numerous available receivers covering this range on board in the various radio rooms within the ship. Other theories include air to ground applications and small ship comms. There are probably more ideas kicking around out there, but no definitive documentation as yet.

The second row contains the RE-2 antenna relay on the far left, the five common HF ARC-5 transmitters, and on the far right, the problematical !@%#/ARC-5 modulation monitor oscilloscope. An MFP flavored lollipop is offered to anyone who can identify its antecedents. See photo below for this mysterious concoction. The braided cable leads to a power supply and audio from the modulator to obtain the classic trapezoid image shape.



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