Collins Radio Group’s experience in the communications field, and more specifically in hf communication, dates as far back as 1933. Collins general purpose hf receiver products have set the pace for the industry throughout the years with the latest designs and highest performance. From the 51H Receiver series in the mid-1940’s, through the 51J series, R-390, and 51S-1 Receivers, Collins has designed and developed hf receivers that have attained universal acceptance. In the process, Collins has developed the expertise apparent in the current 651S-1 Receiver family. The 651S-1 Receiver has potential uses not possible for any receiver previously developed in the long line of Collins products. Handsomely styled, this unit is as suited for an executive’s office as it is for a remote, unattended communications site.

The 651S-1 Receiver series was developed and produced by Collins in late 1970 to meet the need for a remotely or locally controlled state-of-the-art general purpose hf receiver capable of reproducibility in high volume and at an economical cost. It was designed using modular, solid-state construction for ruggedness, reliability, maintainability, cost effectiveness. and flexibility of configuration for various functional applications. Optional functions, such as ISB, vlf, special if filter bandwidths, and various remote control interfaces were designed to be added by the simple insertion or substitution of plug-in modules. This flexible characteristic gives the 651S-1 the capability of being molded to meet specific customer requirements with minimum effort, minimum design changes, and minimum cost to the customer. The latest in the 651S-1 Receiver family is the 651S-1B configuration which incorporates a highly stable plug-in digital VBFO function, plug-in RS-232C/MIL-STD-188C computer interface, and a completely modular plug-in power supply. It can also be provided with a continuous 10-Hz tuning capability by combining the tuning functions of the digital VBFO and main receiver tuning.

Extensive domestic and international evaluations of various configurations have convinced many of our customers to classify this receiver family as standard. A typical example is the US Coast Guard, which has selected the 651S-1 as their standard general communications receiver. In addition, the Coast Guard is also using the 651S-1, with much success, in severe environment aboard patrol boats.

Another example is the US Air Force which has placed the 651S-1 in inventory under FSN 5820-141-8976. One application is the Tactical Weather System “C”, Module AN/TCC-77, which uses three 651S-1 Receivers per module. It was in this system that the 651S-1 was first placed in the Air Force inventory after passing severe environmental evaluations per MIL-STD-810B and MIL-S-52059B without experiencing a failure, while installed in the shelters.

A large number of 651S-1’s have also been procured by US Government organizations for numerous applications ranging from single-receiver installations to elaborate processor-controlled systems.

Response from all customers, in the US Government and internationally as well, has been extremely favorable, with good reports on the receiver design, performance, and reliability. Such acceptance fully demonstrates the quality of the 651S-1 Receiver family and Collins dedication to customer requirements, service, and support.

The typical systems described in this document have been designed for various customers using equipment from our proven product lines and from those of sub-contract firms from which we have satisfactorily acquired equipment over a number of years. Requirements for new equipment design and development for such systems are held to an absolute minimum. System engineering activities of this type are accomplished by the Telecommunications Equipment Division of Collins. This division, located in the largest engineering and manufacturing center of Collins, is devoted exclusively to the design, development, manufacture, and application of hf and uhf communications equipment and systems of the type described in this document.


The 651S-1/1A/1B is a triple-conversion superheterodyne receiver that provides continuous coverage of the 250-kHz to 29.9999-MHz frequency range. It is a completely solid-state desk-top or rack- mounted receiver and features direct-reading digital display of the operating frequency. The frequency range can be easily extended down to 12 kHz for vlf operation by the simple substitution of plug-in modules. Many other options are available, such as various remote control interfaces, narrow-band FM, independent sideband, and special filters; with each capable of being incorporated by the simple addition or substitution of plug-in modules. Information on these and other options is presented later in this document.

The 651S-1( ) provides reception of AM, ISB (independent sideband), USB, and LSB. The receiver is also compatible with RTTY and NBSV (narrow-band secure voice) modems. Designed for a variety of applications, this capability may be extended to meet specific requirements through the use of the many available options.

Excellent frequency stability is obtained through the use of a frequency synthesizer that is phase locked to a temperature-compensated crystal oscillator. Two rotary switches provide coarse frequency adjustment in 1- and 0.1-MHz steps while a main tuning control varies frequency smoothly in 100-Hz increments with 10-kHz frequency change per revolution. Continuous coverage of the entire frequency range using only the main tuning control is possible without the need for band switching. For frequency interpolation between the 100-Hz steps, the VBFO may be used to adjust in 10-Hz steps over a 60-Hz range in SSB mode and in 150-Hz steps over a 900-Hz range in CW mode. A VBFO continuously tunable in 10-Hz steps over a +/-9990-Hz range with the VBFO frequency displayed on the front panel, is also available in the 651S-1B. In addition, a version of the 651S-1B can be provided with the digital VBFO and main tuning combined, thus giving tuning capability over the entire frequency range in 10-Hz steps. In this configuration the VBFO steps nine increments (or 90 Hz) after which it is reset to zero and the main tuning is stepped one increment (or 100 Hz). This sequence is then repeated as the sweep tuning knob is rotated.

Seven-bar indicators display selected frequency to six digits for rapid, accurate readout. All front panel controls except POWER, METER, AF GAIN, and DIAL LOCK can be remotely controlled when using the proper remote accessories.



250 kHz to 29.9999 MHz in 100-Hz increments (12 kHz to 29.9999 MHz optional).


Phase-locked to internal standard oscillator (phase-locked to an external standard, optional).

FREQUENCY STABILITY (with fixed bfo):

5 parts in 107 over any 30-day period if held within specified environmental limits. 1 part in
108 per week, typical, with constant temperature (drift rate). Stability of external standard
when used.


100-Hz steps by continuous tuning control or optional 10-Hz steps on 651S-1B by
continuous tuning control with VBFO and main tuning function combined. 1- and
0.1-MHz steps by rotary switches.


AM, SSB, and CW. ISB and NBFM provided as options.
RTTY and NBSV when using external modems.

BANDWIDTH (standard 651S-1):

AM: 16, 6 kHz, USB: 2.7 kHz (see optional configurations
description for additional bandwidths).


AM: 3, 6, 16 kHz, USB: 2.7 kHz, LSB: 2.7 kHz, CW: 370
Hz, 500 Hz, and 1.1 kHz. (Additional bandwidths are
available on request.)


AM: 16, 8, 4 kHz; USB: 2.7 kHz; LSB: 2.7 kHz; CW: 0.5,
1.0, 2.0 kHz. (Additional bandwidths are available.)


50 ohms, nominal, unbalanced (may be strapped to
1000 ohms on vlf option).

SENSITIVITY (for 10 dB (s+n)/n):

0.250 to 0.4 MHz:
SSB: 5 uV (2.7-kHz bw).
AM: 35 uV (6-kHz bw).

0.4 to 2.0 MHz:
SSB: 2.5 uV (2.7-kHz bw).
AM:  10  uV (6-kHz bw).

2.0 to 29.9999 MHz:
SSB: 0.7 uV (2.7-kHz bw).
AM:  3.5 uV (6.0-kHz bw).
NBFM (optional) 1.0 uV (12.0 dB SINAD).

12 to 559.9 kHz (50-ohm input with optional vlf converter):
SSB: 2.5 uV (2.7-kHz bw).
AM:  12  uV (6-kHz bw).

If feedthrough: -80 dB.
If image rejection: -80 dB.

Crossovers and noise modulation: -80 dB (interfering
signal at least 15 kHz removed).

CROSS MODULATION (-10 dB, 30-percent modulation with 50-uV desired signal):
+50 kHz from operating frequency: 0.35 V.
+10 percent from operating frequency: 0.50 V.


Not more than 2 ,uV equivalent except for four discrete
frequencies (0.9, 9.9, 19.8, and 20.7 MHz), which are
not more than 10 uV equivalent.

-40 dB, third order at 100 mV per tone.


Second order – Two equal signals +26 kHz or more removed from wanted signal shall be
at least 77 dB relative to one microvolt in order to produce equivalent input signal of one

Third order – Two equivalent signals +26 kHz or more removed from wanted signal shall
be at least 80 dB relative to one microvolt to produce equivalent input signal of one microvolt.

With optional half-octave filters–Second order product improved to 90 dB relative to
one microvolt to produce equivalent input signal of one microvolt. Third order product
remains unchanged except half-octave filters reduces receiver front-end exposure
to strong signals outside the filter bandpass.


8-ohm speaker output; 600-ohm headphone output; 600 ohms, balanced, center tap
grounded or floating. Also, 600-ohm output for ISB channel.


In SSB, 3 uV produces 0.5 watt of audio into 8-ohm
load or 1 mW (0 dBm) into 600-ohm line output.


2-watt. 8,0-ohm output at not more than 3-percent
total distortion. 5-mW peak (+7 dBm), 600-ohm line
output, at not more than 1-percent total distortion.
6 mW at 600 ohms headphone output for not more than
3-percent distortion.

AUDIO RESPONSE (600-ohm line audio):

Within 1 dB from 100 Hz to 4 kHz. (If filter response
will further modify overall receiver response; example,
2.7-kHz SSB filter response is -3 dB at 350 and 3050 Hz.)

At least 40 dB below maximum output.

Audio rise: Not more than 6 dB from 3 uV to 0.3 V.
Attack time: 2 ms, nominal.
Release time: 100 ms (fast) or 1 s (slow), nominal.


50 mV at 450 kHz, 50-ohm load; same for the ISB channel.

BFO (fixed and variable):

Fixed: Bfo is phase-locked to internal standard oscillator
in the 651S-1/1A/1B.

Variable: In the 651S-1/1A, bfo in CW mode, tunable
+/-900 Hz in 150-Hz steps; in SSB mode, tunable +/-60
Hz in 10-Hz steps to interpolate between 100-Hz
positions. In the 651S-1B, bfo in all modes tunable
+/-9990 Hz in 10-Hz steps to interpolate between
100-Hz positions.

Overload diodes protect all circuits up to 10 Vrms.


Front panel meter indicates rf input signal level in
decibels above 1 volt or 600-ohm audio line level in dBm.


Predicted 7600-hour mean time between failures
(MTBF) in a fixed-station ground environment and with
temperature, shock, and vibration within environmental
limits specified.

An actual MTBF in excess of 80,000 hours was
demonstrated between July 1973 and January 1974 by
the US Coast Guard on 378 units, which they had
deployed in a controlled fixed-ground environment
having relatively controlled temperature and minimal
shock and vibration.


Temperature: 0 to +55 C for full performance.
Humidity: 90 percent.
Altitude: 10,000 feet.

Shock: Bench handling test per MIL-T-4807, method 4A.

A basic configuration of 651S-1 Receiver, hard-mounted
to an equipment rack in a US Air Force Tactical Weather
Shelter (“C” Module AN/TCC-77), has successfully passed
the temperature, humidity, and shock test specified in
MIL-STD-810B and MIL-S-52059B.

Operating power requirements for the 651S-1( ) are
115/230 volts +10 percent, 47 to 63 Hz, 70 watts. Up
to 40 watts additional power may be required when options
are implemented.

Under the hood…


Three types of the basic 651S-1 Receivers have been manufactured by Collins evolving to the current configuration now in production. In addition, two special receivers, the 651S-1A and 651S-1B, each of the more recent series, have been produced. For identification purposes, each of the three basic receivers has different last three digits (status) of the Collins part number, -002 series, -102 series,.and -152 series. In the process of the evolution, receiver module interchangeability has been a constant consideration. As a result, all the modules in the current -152 series and the 651S-1A are interchangeable with those of the older -102 series receiver. The same is true of the older -002 series receiver, with the exception of one module, the DCFE. Although it differs more functionally, many of the modules of the 651S-1B Receiver are also interchangeable with older receivers.

The 402 series was the first production 651S-1. The -002 status is the basic manual receiver. Status endings -002 through -019 are -002 derivatives, and are no longer in production. The -002 series receiver is documented in an earlier 651S-1 instruction book, Collins part number 523-0763090, dated 1 July 1971.

The-102 Series:

The -102 series was the second production series and had some minor configuration changes from the -002 series; the mode and bandwidth functions were separated, and audio squelch was deleted as a standard feature and made optional. The -102 status is the basic manual receiver and has an FM detector, a 500 Hz CW filter, rf input 1/2 octave filters, frequency memory keep alive circuit, and preselector control connector (J63). Statuses -102 through -136 are -102 derivatives and are no longer in production. The -102 series receiver is documented in the 651S-1/1A basic instruction book Collins part number 523-0764052.

The-152 Series:

The -152 series is the latest version of the 651S-1 Receiver. The keep-alive circuit. preselector control connector (J63), FM detector, 500-Hz bandwidth if filter, and 1/2-octave filters are deleted, but can be added back as options. All statuses above -152 are derived from the basic -152. The various configuration options of the 651S-1 Receiver (-152 series) are shown in table 1. Configuration of special purpose receivers 651S-1A and 651S-1B are shown in table 2. To determine what configuration options are installed in a specific 651S-1 Receiver, locate the Collins part number in the 651S-1 part number column of table 1: Columns to the right indicate which chassis and plug-in circuit cards/modules are installed in that particular status of receiver: columns to the left show what options are incorporated in that particular receiver. For added information on the basic 651S-1 Receiver and all available plug-in modules refer to the 651S-1/1A Instruction Book Collins part number 523-0764052.

The 651S-1 configuration options currently available are briefly described in the following paragraphs.


Provides low-frequency reception by extending the lower frequency limit to 12 kHz. Two subassemblies are replaced to obtain vlf coverage, rf module A6 and synthesizer divider card A10. Refer to the configuration chart for the status numbers of receivers that already have the option installed and for part numbers of the vlf subassemblies.


Permits independent reception of upper and lower SSB signals; and contains if amplifier, detector, and line audio amplifier. Independent sideband operation is obtained by the addition of an ISB plug-in circuit card (A3).


Provides audio frequency squelch that is adjustable on a signal-to-noise basis. To obtain this option the AF GAIN control on the front panel is replaced with a combination gain/squelch control; in addition, the plug-in audio card (A2) is replaced with an audio card with squelch circuits. Refer to the configuration chart for the status numbers of the receivers that have the squelch option already installed and the part number of the audio card that has the optional squelch circuits.


Permits reception of narrow-band FM signals. To obtain this option, the standard if amplifier card A4 is replaced with an if amplifier card containing the FM detector. Refer to the configuration chart (table 1 for the status numbers of receivers that have the NBFM option installed and the part number of the if amplifier card that has the FM limiter/detector circuits.


Provides an automatic sweep of frequencies in 100-Hz increments to a maximum range of 100 kHz with dwell time (period in which the receiver remains on a discrete frequency) variable from 100 to 600 milliseconds. Sweep range and dwell time are selected internally by strapping the frequency scan card or externally with the use of an associated 775L-1 Local Scan Control Unit. To obtain this option a frequency scan card is added.


Allows the use of an external 100-kHz, 1-MHz, or 5-MHz frequency standard. This option is obtained by replacing the normal synthesizer frequency reference card (A11) with a new card. Refer to the configuration chart for part number of the new card. This option can be added to any 651S-1 Receiver.


Used to maintain storage of frequency information during power interruptions. An external 6- to 8-volt battery supplies the necessary power for the circuit. This option is implemented by wiring the special keep-alive assembly into the chassis subassembly. Refer to the configuration chart for status numbers of receivers that include this option and for the part number of the chassis subassembly that includes the special keep-alive power assembly.


Some of the if filters available as options are listed below. Installation consists of placing the appropriate filter on the optional if filter piggy-back card. Additional filter options are available upon request. Refer to the configuration chart for status numbers of receivers that include available filter options and for the part numbers of the various filter cards.


0.2         CW
0.370      RTTY
1.0         CW
3.0         AM
1.1         RTTY
0.5         CW


Provides the proper interface between the 651S-1 and a 514S-1 Remote Control Unit. The control interface between the 514S-1 and the 651S-1 is a 20-mA neutral TTY loop, using ASCII coded characters. A printer control unit (TCU) plug-in card and a device control functional element (DCFE) plug-in card are added to implement this option. Refer to the configuration chart (table 1) for status numbers of receivers that include this option and for part numbers of the plug-in cards.


Provides control interface for processor control of the 651S-1 Receiver. Several different processor control interfaces can be implemented in the receiver by the addition of the appropriate device control unit (DCU) and device control functional element (DCFE) plug-in cards. Interfaces available include the serial CCCS 4800-bit and 76.8-kb configurations for use with the Collins processors, and a 75 to 19,200 baud RS-232C/MIL-STD-188C configuration for use with commercial processors. Refer to the configuration chart for status numbers of receivers that include this option and for part numbers of the plug-in cards.