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R-1051B Front View (1639155 bytes)

R-1051H (101471 bytes)

Thumbnail of front of R-1051H

I have two R-1051 HF receivers, an R-1051B and an R-1051H. The "B" model was taken out of service some years back, but the Navy only started phasing out the "H" model about 2000; it still is in service in some surface ships and submarines.


FIrst is my R-1051B, which I bought from Gary Gleicher. It works just as advertised.


It's not the most sensitive radio in the world, but it's not the least sensitive, either. It is about equal to my Stewart-Warner R-390A,which really needs to be tweaked and peaked, in sensitivity. Neither does it have variable bandwidth, being designed for ISB RTTY. It makes up for it in rock-solid stability, with an internal standard good for 10-8 parts per day. Though the rest of the radio is solid-state, the front end uses two vacuum tubes -- possibly for "hardening" against EMP, possibly just to provide a front end that won't be damaged by static. It should be noted that the venerable R-390A came into use again during the first Gulf War, after several otherwise very fine receivers had their front-end transistors destroyed by static charges. Desert sand blowing past the antenna can build up enough charge to render a receiver useless.


It does have some interesting features, including the following reception modes:

  • LSB - Lower SideBand
  • FSK - Frequency Shift Keying.
  • AM - Amplitude Modulation
  • CW - Continuous Wave (Morse)
  • USB - Upper SideBand
  • ISB - Independent Sideband (Upper And Lower sidebands, each carrying its own datastream.



It also uses roller chains to couple the three KHz tuning knobs to the parts that need to move, and motors to move the parts related to MHz tuning. The motors and tuning detents make a very distinctive "whirr" and "clunk" when they're turned. Imagine the MHz tuning knob on a brand-new R-390. That's what all five of these knobs feel like, except with a stiffer detent. It is _not_ for bandscanning and/or variable frequency intercepts.

It is fairly obvious that this is a "set-and-forget" receiver, probably intended for Fleet Broadcast reception and similar usually-on HF circuits. I have mental images of walls of these receivers, with their output being fed to bank upon bank of crypto gear and order-wires.


The R-1051B controls are, from left to right, and top to bottom,

  1. LSB Phone Level (potentiometer)
  2. Mode (rotary switch): OFF, STD BY, LSB, FSK, AM, CW, USB,
    and ISB.
  3. USB Phone Level (potentiometer)
  4. 100Hz tuning increments ring (switch) around continuous
    tuning knob (potentiometer).
    The switch has eleven positions: V (variable) and 100 through
    1000 HZ in 100 Hz steps.
  5. LSB Meter Level (switch): in 0 dB, it sets the meter to show
    the actual line level in dB referred to something; in 20dB, it drops
    the levels by that much to allow them to be displayed without pegging
    the meter. This knob has a lock ring to keep it in position.
  6. RF Gain (potentiometer)
  7. BFO Freq. (potentiometer) adjusts BFO frequency in CW mode.
  8. USB Meter Level (switch): in 0 dB, it sets the meter to show
    the actual line level in dB referred to something; in 20dB, it
    drops the levels by that much to allow them to be displayed without
    pegging the meter. This knob has a lock ring to keep it in position.
  9. Tuning knob, for units of 10MHz.
  10. Tuning knob, for units of 1MHz.
  11. Tuning knob, for units of 100KHz.
  12. Tuning knob, for units of 10KHz.
  13. Tuning knob, for units of 1KHz


All models of R-1051 receivers come in a diecast or welded aluminum(?) case with no openings, and all the controls feel as though they have O-ring seals on them. To open it up, one unscrews the six captive screws that hold the control panel to the front of the case, makes sure that the case is anchored so that it won't tip and fall, andthen pulls straight out. The chassis comes out on very nice ball-bearing slides with a 90-degree pivot at the end, so that one can work on the top or the underside without having to pull the chassis out and take it to the bench. It is all modular, and field maintenance is pretty much a matter of swapping modules along the failing chain until things work again. Real repairs are done at the depot level.


The chassis has a microswitch to remove power when the case is opened. I strongly suspect that this, together with the extreme signal suppression provided by the case, is so that the ship carrying the receiver can't be located by listening for the local oscillators of superheterodyne receivers and other undesired emissions.



R-1051B Front View (1639155 bytes)





What this R-1051B looks like underneath.


Everybody talks about all the chains and motors on the R-1051, but nobody shows pictures.

Here is the underside of my R-1051B:






Note the teensy-tiny roller chain to drive the 1KHz, 10KHz, and 100KHz (right, middle, and left chains, respectively).

The "B" model uses stainless steel roller chains, also 0.1475" pitch, from Sterling Instrument, and were available from their Stock Drive Products website at http://sdp-si.com/estore as part numbers numbers A 6Y 7-M140 ($53.52), A 6Y 7-M160 ($60.13), and A 6Y 7-M210 ($76.21), and the blanks in the part numbers are significant.

That's pricy; I think I understand why they went to the Posi-Drive Belt in the later models, but it just doesn't hold up to long use.


It is interesting that some of the coax cables on the underside appear to have been cut off short. Perhaps they were used only when the receiver was being tested in the factory.


A view of the top of my R-1051B.






Everything's modularized and pluggable except the power supply transformer and chokes. It makes things really easy to fix out on the water where all you have to do is pull the suspected module and stuff in a replacement, but a bit more difficult if you don't have replacements or extenders.



Another view of the underside of my R-1051B.






Note, again, the roller chain to drive the 1KHz, 10KHz, and 100KHz (right, middle, and left chains, respectively).


Here is the front of my R-1051H:




Thumbnail of front of R-1051H

It's not a lot different from the R-1051B, but there are a few things changed. Some of it's just for better ergonomics and labeling, but the "H" model also has selectable AGC as well as manual gain control, and there's only one meter, with a switch to select what the meter measures.The line level controls now require a screwdriver to adjust them, and a wrench to loosen the locknuts first, which reduces the probability that someone will turn the wrong knob by mistake. It appears that the designers read the gripe sheets about ease of use and about operator errors induced by the layout of earlier models.




A view of the rear part of the underside of my R-1051H.







A view of the front part of the underside of my R-1051H.






The "H" model uses twin-core Posi-Drive Belt, 0.1475" pitch, to drive the 1KHz, 10KHz, and 100KHz (right, middle, and left chains, respectively). These are made by Sterling Instrument, and were available from their Stock Drive Products website at http://sdp-si.com/estore as part numbers S7915Y-CPSST140 ($16.58), S7915Y-CPSST160 (18.49), and S7915Y-CPSST210 ($22.91).

The last time I looked (24 Sep 2004), these were (predictably) Out Of Stock.

These belts are made of molded polyurethane, with a core of stainless steel on each side, and polyurethane bits between the sides like the steps on a ladder. They don't hold up to heavy use: the very strong spring detents on the tuning mechanisms for the 100, 10, and 1 KHz knobs require that the belt pull *hard* to overcome them, and this puts enough force on the belts to wear them out eventually: the sprocket on the 1 KHz tuning mechanism has ripped through the middle of its belt on my R-1051H. I'll be replacing all three with the considerably pricier stainless steel roller chains documented earlier on this page.