(c) 1999,2008 Peter McCollum
The RT-1-B and URT-11
Transmitters
The RT-1-B, and it’s 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.
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RT-1-B Transmitter Specifications |
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Transmitter RT-1-B |
Power Supply |
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Weight |
29 lbs |
58 lbs |
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Dimensions |
10"W X 9.5"H X 14"D |
10"W X 9.5"H X 14"D |
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Tube complement |
6AC7 osc./VFO buffer |
816 (two) |
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2E26 driver |
5R4 |
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4-65A final |
time-delay relay |
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VR 150/30 regulator |
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6Y6 clamper |
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Frequency Bands |
3-5, 5-8, 8-13, 13-21, 21-30 MC |
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Power Output |
about 100 watts |
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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.
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 power supply
schematic (138 KB)
URT-11 accessory unit
schematic (21 KB)
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 ¾” 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”.
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URT-11 Transmitter Specifications |
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Transmitter URT-11 |
Power Supply |
Accessory Unit |
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Weight |
36 lbs |
63-1/2 lbs |
40 lbs |
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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 |
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Tube complement |
6AG7 osc./VFO doubler |
816 (two) |
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2E26 driver |
5R4GY |
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4-65A final |
60 sec time-delay relay |
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0D3/VR-150 regulator |
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6AU5-GT clamper |
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Frequency Bands |
3-5, 5-8, 8-13, 13-21, 21-30 MC |
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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 |
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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 |
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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.