rt-1 transmitter

The RT-1-B and URT-11 Transmitters

The RT-1-B, and its successor, the URT-11, is a transmitter/power supply combination that is portable, but considerably heavier than an "agent radio" such as the SSTR-1. Judging by the nomenclature and the technology used, the RT-1 may be the first transmitter developed by the CIA. It was used in largely fixed installations such as embassies.

The RT-1-B is a CW transmitter that covers 3 to 30 MC in five bands, and operates from 115 VAC 50-400 cycle power. Frequency control is via a single crystal, or an external VFO through an SO-239 connector. There are crystal sockets for both FT-243 type crystals, or the larger type with 3/4" spacing. The front panel includes a meter numbered 0-5, plus a switch to select 6 different measurements (the first is Line Volts, the other five are for transmitter tune-up). The final plate voltage is 1350, and is controlled by a 1-minute delay relay in the power supply. There is a terminal strip on the side with connections marked "KEY GND MUTE". Antenna connections are via four banana jacks marked "GND ANT LINK LINK" (antenna output is a PI network, but also has an untuned link on each band). Cabinet paint is a fine-grained gray wrinkle finish.

A third unit in the set (described in the URT-11 manual) was called the "Accessory Unit", and contained a 2000 watt variac and storage for spare parts. The variac allowed operation from AC lines in the 90-140 or 180-280 volt ranges. If operation from only 115 VAC was required, then the accessory unit would not have been needed.

The RT-1 is documented as part of a “Net Central Station” in Germany in late 1951 [ref 129]; and on a boat used for propaganda broadcasts into Albania that same year [ref 138]; and as part of the PASTIME project in late 1952 [ref 144].

The manufacturer of the RT-1 and RT-1-B was apparently Pioneer Electric & Research Corp. The RT-1 variant has an ID plate naming Pioneer, and the RT-1-B front panel is nearly identical, suggesting that they made those units as well. Pioneer Electric was one of the contractors for the wartime SSTR-1, and their name is mentioned in communications projects until at least the mid-50’s. See the RT-1 pictures below.

RT-1-B Transmitter Specifications
	Transmitter RT-1-B	Power Supply
Weight	29 lbs	58 lbs
Dimensions	10"W X 9.5"H X 14"D	10"W X 9.5"H X 14"D
Tube complement	6AC7 osc./VFO buffer	816 (two)
	2E26 driver	5R4
	4-65A final	time-delay relay
	VR 150/30 regulator
	6Y6 clamper
Frequency Bands	3-5, 5-8, 8-13, 13-21, 21-30 MC
Power Output	about 100 watts

An RT-1-B transmitter with power supply. Photo courtesy of Roy Morgan.

The RT-1-B transmitter. Author's collection.

Right side of RT-1-B. Photo courtesy of Roy Morgan.

Left side of RT-1-B. Photo courtesy of Roy Morgan.

An RT-1 transmitter, serial #163. Note the marking that identifies Pioneer Electric & Research Corp. The RT-1 apparently lacks the time-delay relay found in the RT-1-B, as noted by the warning to warm up the filaments before applying plate voltage. Image courtesy of Jeremy Frost.

RT-1 rear panel.

RT-1-B notes from a user:

The RT-1-B came out in about 1950. I never loaded this up to more than 100 watts. A better version known as the URT-11 [not the same as the military URT-11] came out shortly thereafter. This unit was used in a great number of embassies when CW was king. The RT-1-B had some keying problems due primarily to the keying relay. I changed this on mine to grid block keying which was clean and could also be used with a 300 wpm keyer. The old relay limited you to 60 wpm but was sluggish at 25 wpm. The URT-11 also had this problem in the beginning. The URT-11 was used to drive a 400 watt unit which we called the RT-4.

[In some embassy installations] we had old military hand-me downs... transmitters were WILCOX 96-C and a BC-339, and receivers were Hammarlund super-pro (military BC-779 I believe). Everything was CW so we really didn't need the power for the field stations. Since this time period was before the RS-1, we usually used the Collins 32-RA which was a 100 watt rig (rugged and had 3 each 807 in parallel in the final). It was 4 channel xtal control but had a slug tuned VFO, and pi coupler and would tune to anything. The RT-1-B and later URT-ll was good to have around for field expedient stations as we were always prepared to push off at a moments notice and activate a station during times of crisis (and there were plenty of these).

RT-1-B notes from another user, "kwcactus":

I used an RT-1 frequently. We had a club station that had a Collins 75S1 and an RT-1. We had no voice capability, and were not permitted to use voice even if it were available. We were told to always say "transmitter is a homebrew, at 100 watts." (on CW, of course). Later we had a complete S-line, 32S3, 75S3C, 30-S1, and still weren't permitted to use voice. Several years later, an RT-1 was given to me. Markings were removed, of course, and a lot of the panels were scratched but the rig worked quite well.

RT-1-B schematic

RT-1-B power supply schematic

URT-11 accessory unit schematic

As mentioned above, the URT-11 was a replacement for the RT-1-B. The basic features and specifications appear to be the same. Some differences noted are as follows:

· The XTAL/VFO switch is on the side panel, instead of the front.

· There is only a single crystal socket (no socket for 3/4" pin spacing).

· The crystal oscillator circuit is not a Pierce design, and uses a 6AG7 instead of a 6AC7.

· The P.A. screen clamper tube is a 6AU5 instead of a 6Y6.

The URT-11 was introduced in the very early 50's, but is known to have been used in the field in the early 60's, in such places as the Belgian Congo and Managua. The set was used in radio operator training until at least 1964.

The "URT" nomenclature stands for "Universal Radio Transmitter".

URT-11 Transmitter Specifications
	Transmitter URT-11	Power Supply	Accessory Unit
Weight	36 lbs	63-1/2 lbs	40 lbs
Dimensions	10-3/8"W X 9-9/16"H X 14"D	10-3/8"W X 9-9/16"H X 14-1/4"D	10-3/8"W X 9-5/8"H X 14"D
Tube complement	6AG7 osc./VFO doubler	816 (two)
	2E26 driver	5R4GY
	4-65A final	60 sec time-delay relay
	0D3/VR-150 regulator
	6AU5-GT clamper
Frequency Bands	3-5, 5-8, 8-13, 13-21, 21-30 MC
Power Requirements	1350 V @ 200 mA, 500 V @ 100 mA, 115 VAC 50-400 cycles	115 VAC, 50-400 cycles, 430 watts	90-140 VAC or 180-280 VAC, 50-400 cycles
Power Output	100 watts, 3-21 MC; 75 watts, 21-30 MC	1350 V @ 200 mA, 500 V @ 100 mA, 115 VAC 50-400 cycles

A URT-11 transmitter, serial # 40.

The "Accessory Unit" for the URT-11, which consists of nothing more than a large (2000 watt) Variac to adjust for different line voltages. Image courtesy of Nathan Eubank.