The Navy "Miniatures"

The 1930s represented a time of rapid communications systems development for the Navy, led primarily by efforts at the Naval Research Laboratory, but also by various manufacturers like Bendix and Westinghouse. Naval nomenclature for the sets of the time generally followed a variation of today's software release philosophy, with an original set having only the code letters of its type assignment like GO or GP, and subsequent improvements reflected with -1, -2, and so forth. The GO-9 100 watt HF/MF transmitter at the top of this photo is the last in the GO line, just as the GP-7 transmitter beneath it is the last of the GP line. This naming convention began being corrupted with the introduction of three letter designators. For example, the RAT receivers seen elsewhere on this website were also issued in a RAT-1 configuration, the -1 signifying a 28v power variant of the basic set. At the same time, the ARD countermeasures receiver mentioned in the Old Crow's Corner saw ARD, ARD-1, and ARD-2 designations successively issued with the same 28v power requirements, but with improvements at each step.

The GO-9 is by far the physically largest HF and MF transmitter set designed for aircraft, and competes for the heaviest based on documented weights - this despite both it and the GP-7 below it requiring 800Hz power in an attempt to reduce avionics weight. It is all the more surprising when you consider it lacks a modulator of any sort - only the TBW version intended for ground use had an AM capability. No remote control was available - without the ability to switch channels in a discrete jump, a radio operator was necessary anyway. These sets were primarily used on long range Navy patrol aircraft, and were still being carried around in those planes as late as the 1950s.

The GP-7 transmitter below it was somewhat of an improvement over the GO. It was certainly lighter, though with six plug-in tuning units it takes up about the same volume. It also had the capability for an AM mode, through grid modulation of its 803 final amplifier. Frequency coverage was 350kHz to 9,050kHz with the tuning units. A distant third in the competition to the Collins ATC (ART-13) after the ATD, the GP-7 shared the 800~ power requirement beloved of the Navy during the last half of the 1930s and early 1940s, including the rather complex set of switches to equalize power factor with other varying loads in the aircraft at that high supply frequency. The need to set PA filament voltage was a fairly standard feature in the higher powered 1930s sets - the GO-9 and Signal Corps BC-191/375 share it. (The ATC and ATD do not, but then they were fresh designs in 1940, not retreads.) A schematic with parts values is located here.

The LM-** frequency meter to the right of the GP-7 was essential for accurate frequency setting of transmitters of the period, and there are "CFI" terminals on all of them to permit connection of this signal generator (CFI = Crystal Frequency Indicator...a Navy-unique term for their LM, the Army preferring the term "frequency meter" for their BC-221 equivalent). The LM power supply is to the rear. Directly beneath the LM is the radio operator's control box for the GP-7. Unseen is a pilot's control box for the GP-7, a smaller control with fewer functions.

GP-7 front panel

The mounts for the GP-7 are, like all the WWII mounts prior to adoption of the ARINC standard, unique to the transmitter. They resemble the configuration adopted for the original ATC and ATD trasnmitters, which required holding the transmitter "just right" to engage the ends of two supports in the mounts and sliding the whole assembly backwards into final position.

GP-7 mounting rails

Here are the two available control heads for the GP-7. Interestingly enough, the pilot's control box on the bottom is a rare example of a short period of time where Westinghouse was given permission to make paper copies of the nomenclature tag and glue it to the control box with a thin celluloid cover, apparently due to production problems and the need to get tarnsmitters out to the fleet.

GP-7 CAY-23220 operator's control box

GP-7 CAY-23219 pilot's control box

Below the GP-7 is an AN/ARC-27, set sideways to fit into the rack. The September 1945 cutoff date for inclusion in the flight deck actually included equipment whose nomenclature went through AN/ARC-28, despite delays in actual production which may have subsequently occured. The ARC-21 and ARC-27 were good examples of that delay. To its right is the primary receiver used with the GO-9 and GP-7, an RU employing a 1930s TRF design. These were used throughout the war, even when more modern receivers were available.

Top view of GO-9, showing "Rajah" spark plug antenna terminals and unique anti-sway shocks

Closeup of top shock mount

Closeup of bottom shock and mounting rail

View of 800-1 rotary inverter used for Navy 800~ equipment

The difficulty in using this equipment on the radio amateur bands is compounded by the power requirements for 115 volts AC at 800Hz, used to decrease the weight of transformers. The Navy pioneered that frequency for aircraft before operational difficulties showed the wisdom of the compromise 400Hz power that the airlines and Signal Corps were using. The 28 volt inverter for this equipment is shown here. For more on this rotary inverter, see 800-1 Inverter. You can be sure that the disturbing similarity of the fan exhaust to a siren isn't lost on the user, and it's probably a good thing that the GO-9 is CW/MCW only and used with headphones...

Kellogg Type A Condenser box

There are a number of precautions that must be taken when using the 800-1 inverter with loads above 500 watts, the most important of which is the use of a compensating capacitor shown in the above link. This is in addition to the switchable compensating capacitors in each of the transmitters of the era. Kellogg produced this neat little junction box to provide protection from accidental contact with the terminals, and consolidate 28 volt DC and 115 volt AC cabling for the F-8/AR noise filter below.

F-8/AR 115 volt 800~ line filter for the GO-9 (F-5/AR 28 volt filter for the ARC-5 is shown above it for size comparison)

Finally, above is the power line RF filter designed for the GO-9, similar to the F-5/AR shown above it for the AN/ARC-5. It goes into the 115 volt power line between the Kellogg capacitor and the transmitter, but also filters the 28 volt DC bus.

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