PRC-47
This unit is a PRC-47 transceiver built by Collins. It is full coverage synthesised from 2 to 12MHz. It emits 100W PEP, on either CW or USB. An FSK converter allows the use of RTTY. It is generally given the honour of being the first synthesized manpack.
COMMENTARY
The PRC-47 can be used in portable, vehicle and fixed station applications. It was used by the army and
marines. Original equipment cost was $6004. The entire station is contained in two waterproof aluminium cases. A frame allows the unit to be used in manpack configuration. The station uses standard GRC type audio
accessories. A built in tuner allows use of a 15ft whip antenna or wire antennas. A silver zinc battery provides 24volt for power, or alternately the unit can be operated from 115VAC 400Hz. The transmitter can accept signals from a microphone, key or fsk converter. A VOX circuit can be used to key
the transmitter. In CW mode an 800Hz oscillator is used in lieu of the audio input. After balanced modulation and mixing the USB signal is amplified by the final stage. Tuning is controlled by gearing directly from the front
panel. The PRC-47 has the massive gear train one would expect of a Collins radio. The antenna tuning unit tunes the radio set to the antenna being used.
The receiver uses many of the same circuits as the transmitter. Essentially signals travel through the signal processing stages in reverse to arrive with an audio signal.
The PRC-47 is a "spec" radio. In the early sixties Collins designed the radio without any orders from the military. Sure enough, Collins received orders and it became one of the more common military radios of its time.
The PRC-47 is quite a nice little radio, and is a good example of the progression from World War 2 type radios to the modern fully synthesized transceiver. The PRC-47 is not quite up to the standards of the GRC-106, but is
nonetheless an impressive design. The case is in theory semi-waterproof, however rather than securing the radio into the front of the case, the case has holes in the rear where screws screw into the rear of the radio. Thus when
the radio is placed on wet ground water had a tendency to seep into the radio. The set is quite powerful, however if used on high power with the silver zinc battery the battery does go flat
rather quickly. The final stage also generates quite a lot of heat, so if operating on high power it is necessary to use the blower/fsk unit for cooling. The blower sounds like a jet engine spooling up when it starts.
The front panel is quite simple. The operating frequency is selected using three rotary knobs on the front. These can be quite strenuous on the wrist due to the amount of gearing behind them. The current frequency is shown
on stencilled wheels which are part of the gear train. A meter is used to indicate transmitter power level. A meter sensitivity pot is used during tuning. A battery test button connects the 24Volts to the meter. The power knob is
also used to select the brightness of the red panel lighting. There is also a volume control. There is no RF-gain control. The CW/Voice switch selects mode. In CW mode the inverter operates all the time and the 800Hz
oscillator is enabled. In Voice mode the VOX switch is enabled. A tune and load control tune the antenna. There are two audio connectors.
The PRC-47 is a little inflexible for ham use. The set cover 2-12MHz, USB only although changing a mechanical filter in the translator stage converts the set to LSB operation. The receiver is inflexible. There is no frequency
vernier, thus operation is limited to 1kHz steps. The AGC is very fast, making CW operation difficult, although this should be adjustable. I have not been able to get consistent operation from the transmitter of my PRC-47.
The inverter seems to go into some sort of runaway mode.
The transceiver requires both 24VDC and 115VAC, however the unit is designed such that you provide one voltage and the power supply will make the other one. If you power the unit with 24VDC an inverter makes the
115VAC. If you power the unit with 115VAC this is rectified to 24VDC.
TECHNICAL SPECIFICATIONS
Power Source 24Volts or 115Volts AC 400Hz
Power Consumption Transmit 320W, Receive 21W
Duty Cycle (without blower) 1minute transmit, 9 minutes receive on high power
Mode USB, FSK, CW
Frequency Range 2-11.999MHz in 1kHz steps
Power Output 20W PEP or 100W PEP
Sensitivity 2uV
Stability +-25Hz
CONSTRUCTION
Below: Top view of the PRC-47. The modular nature of the construction is readily apparent. Below: PA cage. The roller inductors for the antenna tuning unit are at centre of picture. At right of shot is the antenna relay. Below: Bottom view. At left is the PA cage. At the right of the PA cage is the final tube.
OVERALL RATINGS
Engineering rating (taking into time of design).
The set is beautifully laid out, but could have used a little more thought in the design. 8/10
Fitness for purpose rating
Has a few weaknesses but a huge improvement over previous systems. 8.5/10
Usefulness as ham equipment rating
Limited frequency range and lack of receiver flexibility but good power output, 7.5/10