Collins Radio Company, Cedar Rapids, USA

651 S - 1

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überarbeitet am 31.12.2010

The 651S-1 communication receiver has been constructed by Collins in 1971/73, this modular constructed rugges and very reliable solid state receiver has been sold to many official services (as the U.S. Coast Gard, U.S. Air Force) in many different variants.

Triple conversion,

digital frequency display, 100 Hz

400 kHz - 30 MHz

AM, USB, LSB, CW, NBFM, optional ISB

SSB: 0,4-1,6 MHz 2 uV; 1,6-30 MHz 0,7 uV
AM: 0,4-1,6 MHz 10 uV; 1,6-30 MHz 3,5 uV

Selectivity -6 dB
AM 3 (opt) / 6 / 16 kHz; SSB 2,7 kHz;
CW 0,2 (opt) / 0,5 / 1,0 (opt) kHz, NBFM (opt) 6 / 16 kHz

RF gain, two AGC speeds, squelch, optional remote control

The Collins 651S-1 is a solid state communications receiver in modular construction, the triple conversion superhet with phase-locked lop synthesizer could be remote controlled and was available in several configurations, it was to replace the venerable hollow state 51S-1.

The receiver comes in a metal desktop cabinet, there was also a rack version used by several U.S. services. The desktop cabinet is33,3 x 15,9 x 38,7 cm wide and the receiver has a weight of 13,56 kg.
The receiver is usually powered from 115 or 230 V mains, there has been an optional 28 V DC power supply. There is no integrated antenna, You have to connect an external antenna at the N connector at the back of the receiver.

In the upper part of the front panel, you find at the left side the signal strength meter calibrated in dB and at the right the digital frequency display with an accuracy of 100 Hz, the nixie tubes in very early sets have been replaced be LEDs mounted on nixie tube sockets in later sets and fixed wired LEDs in the latest receivers.
In the bottom part of the front panel, you find at the left a row of switches, the main power switch, the switch for the variable BFO, the meter mode switch (to set the instrument to indicate signal strength or audio signal level), the AGC switch (FAST in the up position, SLOW in the down position, in the middle position, AGC is switched off and the gain is manually controlled) and a remote control switch which should be set to local for standalone use of the radio. Below, you find the BFO control, the RF and the AF gain control.
In the right half of the bottom part of the front panel, you find the main tuning knob to tune the receiver in 100 Hz steps, it will be muted for higher tuning speeds as you hear a clicking noise with each tuning step. The rotary switches at the left let you tune up or down in 100 kHz and 1 MHz steps, but the receiver is continuously tuned, so you could also use the main tuning knob.
Below, there are the audio squelch control and the modes / bandwidth selector; in the early 651S-1, the bandwith and reception modes are coupled, later variants habe separate bandwidth and reception mode switches, the squelch function has been omitted in these.

Operation of the receiver is fairly easy: connect a decent antenna to the antenna socket at the rear, an external speaker or some headphones and the mains cable and turn the set on with the POWER switch to OPER. The AGC switch should be set to FAST, RF Gain fully clockwise in the maximum position and the CONTROL switch in the LOCAL setting. You will hear the quite noisy cooling fan of the receiver, then use the rotary controls to select the MHz and 100 kHz digits of the desired frequency and use the main tuning knob to tune the radio, the annoying hiss when tuned to an empty frequency is witness of the very high receiver sensitivity, the receiver will be much more quiet when tuned to a station with a sufficient signal level.

The Collins 651S-1 is quite a rare bird, at least here in Europe: it's one of the last "real" solid state radios made by Collins and performs very well on the bands, the 2,7 kHz SSB and 3 kHZ AM filters are well suited for poor conditions on the tropical bands and the 6 kHz AM bandwidth is well suited for program listening. Well, there is no passband tuning, You might find an external audio notch filter as the ones from Dierking useful and the 651S-1 has no programmable frequency memories, but it's a great receiver for cruising the bands and a rock solid performer.

further literature:
d/e: Collins 651S-1 at www.radiomuseum.org

© Martin Boesch, 31.12.2010