- Amateur Radio (Ham Radio) Community

Call Search

New to Ham Radio?
My Profile

Friends Remembered
Survey Question

DX Cluster Spots

Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement

Reviews Categories | Receivers: General Coverage | Collins 651S-1 Help

Reviews Summary for Collins 651S-1
Collins 651S-1 Reviews: 2 Average rating: 5.0/5 MSRP: $9000.00
Description: 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.
Product is not in production.
More info: http://
Email Subscription
You are not subscribed to this review.

My Subscriptions
Subscriptions Help

You can write your own review of the Collins 651S-1.

HAMWITHOUTANTENNA Rating: 5/5 Jun 28, 2008 03:33 Send this review to a friend
Modern Classic  Time owned: 3 to 6 months
This receiver was conceived in the early 70s, when rapid advances in the field of semiconductors, mixers and synthesizers led to a radical change in shortwave receiver design. Mechanical tuning elements were eliminated, and a compact, lightweight, fully synthesized desktop HF receiver with superior performance became a reality.

The Collins 651S-1 incorporates all these technology changes. It's design was extremely advanced, while still economical. It is about the size and weight of it's predecessor, the 51S-1 tube receiver, but offers a markedly improved performance, reliability and flexibility.

The receiver front end uses an active FET mixer preceded by either a lowpass / highpass filter or sub-octave filters ( various RF front end modules were offered ). The first IF is at 109.35 MHz. This is downconverted to 10.35 MHz and finally to 450 kHz. Selectivity is provided either by crystal filters at the second IF or by mechanical filters at the third IF. The mechanical filters have the legendary Collins quality. Most 651S-1 in ham use seem to be equipped with 2.7 kHz USB/LSB filters, a 6 kHz AM and a 500 Hz CW filter. Additionally, a 16 kHz BW is available which is useful for narrowband FM or Hi-Fi broadcast reception.

Some variants of the 651S-1 are equipped with a squelch. The squelch circuit is unusual in that it does not simply operate on the signal level. Instead, it compares the energy in the lower and upper part of the audio spectrum, relying on the fact that the human voice has an energy peak at around 600 Hz.

The 651S-1 uses a two-loop PLL synthesizer ( described e.g. in the book "Single Sideband Systems & Circuits" by Sabin and Schoenike ), providing a 69 to 109 MHz LO signal for the first mixer with 100 Hz increments. The two PLLs use 10kHz and 9.9kHz reference frequencies, and the output frequency step is the difference of the the two PLL frequency steps. There are no significant spurious signals in the synthesizer output. Phase noise is in the order of -125 dBc/Hz 20 kHz from the carrier, dropping to -135 dBc/Hz at 100 kHz.

A weak point in the 651S-1 synthesizer is it's lock-in behaviour. The LO frequency tends to make a short 10-20 kHz excursion each time the frequency is changed. The receiver is muted during that time by a blanking pulse with the effect that whenever the tuning knob is turned at any reasonable speed ( say faster than 5 kHz / sec ), the receiver becomes completely silent. That blanking pulse can be disabled by a simple circuit modification. This makes the 651S-1 much better suited to ham or SWL use, but some strange effects during tuning do remain, of course.

The receiver is built on a lightweight aluminum chassis. About 10 to 12 PC boards ( depending on the variant) carrying the electronics are plugged into two electrically and magnetically screened compartments. Some of the boards use multilayer technology which is very remarkable for the time. The RF front-end board is completely screened by itself. A power supply assembly ( with cooling fan ) and the front panel assembly are bolted to the rear and front of the chassis. A certain degree of mechanical stability is provided by the die-cast front panel and the cabinet.

Aside from the synthesizer issue, the 651S-1 performance leaves not much to be desired. The receiver is very sensitive and does not have strong-signal overload problems. The IF filters provide extreme selectivity. The 651S-a provides outstanding AM reception, using the 6 kHz filter with its excellent selectivity and low distortion. The ALC has "hang" characteristic with selectable hang time, making listening to SSB signals extremely pleasant.

Possible problem zones with the 651S-1 are the front panel switches ( both toggle and rotary ) that may exhibit contact problems, and the audio amplifier, tending to produce distortion due to insufficient quiescent current in the output transistors ( a resistor may have to be changed to cure this ).

73, Martin
G4TCB Rating: 5/5 Nov 19, 2007 02:03 Send this review to a friend
Best of the bunch  Time owned: months
The 651s-1 performs with the best of the crop, even 30 years old it exceeds
My Icom R71e in sensitivity, far better audio quality and selectivity.
Higher up the dial , it is the equal of the R&S ESM500, and can pull signals
ďout of the mireĒ without DSP. The synthesiser takes more time to lock than
the modern gear, so spinning the dial wonít give that satisfying tuning noise
until the dial stops. The shining jewel under the 651s-1 crown is the filter bank.
For the CW man, itís ability to take out interference and leave only the signal
Shows what filtration is all about. For sheer quality of construction this set deserves
A five plus rating, add the military quality of performance and stability, and itís
Earned its place in the Collins stable. It has itís place as my main station receiver.
Pete Holland G4TCB.

If you have any questions, problems, or suggestions about Reviews, please email your Reviews Manager.