Navy Model MAB Radio Telephone Transmitting and Receiving Equipment
The MAB was one of a series of relatively small portable HF Voice radio sets designed for tactical Naval communications early in WWII.
This 1942 Instruction Book includes photos of the nascent US Marine Corps paratroopers wearing their chutes along with the MAB set.
As described, the Navy Model MAB operates AM voice on a single channel in the frequency range of 2.3 – 4.6 mc with a power output of 200 milliwatts. The transmitter and receiver are both crystal controlled. Planning range was approximately 1 mile depending upon terrain; more to an aircraft or ship over sea water.
Catalog image from Reference (82).
Above: Overall equipment. I bought this one from Fair Radio Sales in the 1980’s for $7.95 in their catalog. I thought it was a bargain for all the tubes. Later I captured the detachable headset and antenna. Grenade optional for scale.
This set is a 7-tube circuit and was quite compact for the technology available at the time. By contrast, the earlier SCR-536 (BC-611) Handy Talkie utilizes a 5 tube circuit, one of which doubles as a receiver RF amplifier which the MAB lacks.
The SCR-536 has about 80% more transmitter power but a shorter (39 inch versus 70 inch in the MAB), much less efficient antenna, a significant difference in favor of the MAB.
The data tag indicates it is crystalled for operation on 4435 kc. They were interoperable with the SCR-536 (aka BC-611), the SCR-284, SCR-694 and of course various Navy shipboard sets and many others of the time. I don’t know what the “-1” variant signifies.
Above: The phenolic “plastic” case material is interesting. Seems to be molded with a bunch of string or twine mixed with some kind of resin. Look closely.
The headphones slipped into a cotton cap to keep them in place against your ears while wearing the M-1 steel helmet. I have yet to find that cotton cap or carrying bag.
These sets came from Fair Radio with no antennas or headsets; the carbon microphones were cut off. This presumably while Fair decided the hard-wired microphones could be sold for more that the radio itself. The CTE-51042 mic was similar to the RS-38 shown above. The mic cable had an intergral ON/OFF power switch, the PTT switch is on the microphone. There are no other controls.
The telescoping 7 section, 70″ whip antenna collapses into that assembly that slid into the carrying bag. The antenna base included an adjustable tuning coil to better match it to the selected frequency in use.
The radio included a dry cell battery installed inside the overall phenolic case. Those 5 pins connected to the battery or vibrator supply. There is an opening in the sheet metal shield so the frequency of the two installed R/T FT-243 crystals could be seen easily.
Battery voltages were A: 1.5 volts, B: 135 volts tapped at 67.5 volts, C: 6 Volts. The battery was considered to be for emergency use. The primary option was a vibrator type powered by a non-spillable lead acid battery, all enclosed within the case.
The environmental protection of the radio itself is good with its gasketed case and wiring seals. However the headset and microphone might be problematic if wet, especially in sea water.
A former OSS Officer veteran told his neighbor (my Ham buddy) that the MAB was designed for the Office of Strategic Services use. Easy to imagine but I kind of question that since the requirements development, design and subsequent contract for the MAB pre-dated the formation of the OSS (at least the Maritime Unit) by nearly a year.
It was actually contracted for (contract number NXss-14439) by the US Navy Bureau of Ships, presumably for USMC use; the OSS was an Army unit. But who knows?
I can easily understand that the USMC needed something better (and especially more rugged and easily operated) than the 1930’s pre-war TBY which they had at the time.
I think it is unlikely that the “Big Army” (which had little use for the OSS) would have the Navy provide radios for them. Not to mention the rampant inter-service rivalry in early WWII. The Army had the well established Signal Corps to provide its communications equipment. A Navy “false flag” operation to confuse the enemy? Naw…
However, it is known from an OSS wartime training video made in Florida that the OSS Maritime Unit at least trained with the MAB. There is also a photo of one being carried by a US Army Ranger in Normandy and another photo of a probable one being carried by a Marine at Tarawa.
There seems to be very limited information available on the operational use or deployment of the MAB in WWII. The hunt continues.
We did some operational field evaluations of the MAB in a Ham radio net that included a BC-611, GRC-9, SCR-511 “Pogo Stick” and a TCS set. This was conducted at both the Military Radio Collectors Group at Camp San Luis Obispo, a nearby Pacific beach, as well as in mountainous terrain near Coalinga CA. The MAB performed admirably, sounded very good with its Heising AM modulation and I concluded that it was more effective than the otherwise comparable BC-611 in intelligibility and range.