[R-390] Mason Labs R-390A?

[John Vendely]

Howdy,

In the mid-1960s, Manson Laboratories had a contract with the Air Force 
to upgrade a number of AN/FRR-41 diversity receiving systems (two 
R-390As and two CV-157s) to frequency synthesis, by addition of what was 
referred to as "Stabilization Kit SBM-1102".  This receiver was from one 
of these systems.  These upgrades were done for the Air Force, not for 
NASA.  The Army also had a few.  The HF systems in the NASA ground 
network and on the tracking ships were all made by TMC: TSTE-10K and 
TSTE-40K transmitters, and DDR-506 receivers.

The R-390As and CV-157s of the FRR-41 upgrade were stock units modified 
by the addition of adaptors which plugged into the local oscillator tube 
sockets and contained control relays and coupling transformers which 
permitted switching out the internal oscillators and feeding in external 
synthesized L.O. injection frequencies to rear-panel connector 
brackets.  The external signals were provided by two associated 
frequency synthesizers produced by Manson.  One synthesizer (Manson 
Model 372) provided phase locked injection frequencies replacing the 
crystal L.O.s of the R-390As and a phase locked 555 kc and 100 kc for 
the two CV-157s.  The other synthesizer (Manson Model 299) provided the 
3.455-2.455 Mc injection, in 100 cps steps, for the two R-390s. The 
receivers and converters could thus be operated on their internal 
oscillators in the usual fashion (typically with pilot-carrier AFC to 
eliminate frequency drift), or from the synthesizers, with high 
frequency stability and accuracy.  The whole system was designed for 
easy installation.

Years ago, a fair number of these receivers were floating around, but 
hams simply yanked the adaptors and threw them out, returning the 
receivers to stock configuration.  I have one of these complete systems 
in operation, and it works well, though the Manson synthesizers are, 
like all frequency synthesizers of the era, rather cranky and require 
periodic TLC.

Manson Laboratories did a very similar system, AN/GRC-129, which was a 
frequency synthesized SSB upgrade for the Air Force's AN/GRC-26D RATT 
vans. In this case, however, the R-390As didn't have the plug-in 
adaptors, but were modified internally by Manson, and redesignated 
R-1247/GRC-129.  The T-368 transmitters were modified by removing the RF 
and modulator decks and replacing the RF deck with a 1 kW linear 
amplifier.  A Manson Laboratories sideband exciter and synthesizer was 
mounted on top of the transmitter.  The receive synthesizers in the 
GRC-129 were similar to those of the FRR-41 upgrade, but tuned in 1 kc 
steps.

Manson also did a synthesized SSB upgrade to the Air Force AN/FRT-24 
transmitters.

Regrettably, ham operators had no appreciation for any of this 
equipment, with the result than virtually all of it was hacked up and 
scrapped out over the years...

73,

John K9WT

On 1/30/2022 2:27 PM, W2HX wrote:
> Hi all,
>
> I came across a guys about 30 minutes from me who is selling an EAC R-390A radio. I haven't asked what he wants for it but I thought it was interesting. It has some mods by Mason Labs. He said when he bought it (ages ago) the seller told him it was used at NASA. Here are some pix of some of the mods.
> https://w2hx.com/?prefix=x/R-390A/Mason%20Labs/
>
> Is this a well-known set of mods or a rarity? Anything about them that improves the R-390A? Or are they just some specialized use case.
>
> 73 Eugene W2HX
> Subscribe to my Youtube Channel: https://www.youtube.com/c/w2hx-channel/videos
>
>
>
>
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