[Milsurplus] WRA-3 and Mystery equipment NAVSHIPS manual

[John Vendely]

The 400 cycle power is indeed an odd choice, as the only thing in the 
O-1115 that actually runs on 400 cps is the blower.  The rest of the 
instrument is rated 50-400 cps.  If the synthesizer of the WRA-3 was a 
GFE item, and there were relatively few WRA-3s produced, perhaps it was 
simply a matter of availability.  Stranger decisions have been made in 
military procurement programs.

Since the WRA-3 features a mixer and tuneable bandpass amplifier, it 
must have been used (at least in some cases) in conjunction with some 
form of external modulator, perhaps a fixed-frequency sideband generator 
or some type of specialized data modulator. Though pictured with a 
telegraph key attached, I wonder if this was a bit of a ruse to conceal 
its true modulation source--the mysterious "auxiliary equipment".  It 
seems unlikely such an elaborate instrument would have been used very 
often for CW.

The seemingly overrated WRA-3 output stage may not be quite as absurd as 
it first appears.  The emphasis was probably on exceptional linearity 
for use as an RF driver, entirely unnecessary for CW-only service.  
We're all familiar with similar design practice in sideband exciters 
such as the TMC SBE/SBG series and MMX series.  In these exciters, 25W 
output devices running class A were used to produce a mere 100-200 mW of 
RF--a 6146 tube in the SBE and SBG exciters, and a 25 W planar RF 
transistor in the MMX exciters.  Third order intermod distortion on the 
order of -50 dB relative to either tone of a 2-tone signal were obtained 
this way, and the output devices lasted "forever". The Navy had a well 
known penchant for very high linearity SSB equipment, particularly for 
wideband ISB multichannel teletype and data transmission.  Handling 15 
kc worth of multitone intelligence requires transmitters with superb 
linearity.  Consider also the more recent Harris RF-110 amplifier which 
used two 4CX1500s to produce 1 kW PEP.  This amplifier ran nearly class 
A and here, too, the object was the highest possible linearity.  By 
contrast, virtually all modern amateur gear has rather poor transmitter 
linearity, vastly inferior to the performance of these old transmitters.

73,

John K9WT



On 7/16/2013 1:11 PM, Nick England wrote:
> Yep, the final is a 4CX250B running class A (200ma @ 950vdc) driven by a
> 6CL6.
> Output is 15W max or attenuated to 1.5W max when used as an exciter.
> I am NOT making this up - this is one strange transmitter/exciter. And it
> is 607 lbs with the shock mount base and stabilizer attached.....
> http://www.navy-radio.com/xmtrs/wra3/wra3-11.JPG
> http://www.navy-radio.com/xmtrs/wra3-spec.pdf
>
> Includes a 100 lb. freq synthesizer (O-1115/URC - 1 part in 100 million
> stability) feeding the RF deck. The 100 lb p/s includes a 115v 400 Hz
> output to drive the O-1115 (why did they choose a 400 Hz synthesizer?).
>
> Aside from the mysterious "auxiliary equipment" input, the only operation
> mentioned is CW with a key. No FSK, etc.
>
> Just plumb weird....
> Nick K4NYW
>
> On Tue, Jul 16, 2013 at 12:28 PM, Rob Flory <farmer.rob.flory at gmail.com>wrote:
>
>> Even at 150W output the 4CX250 would be loafing.    Did someone slip a
>> digit?
>>
>> RF
>>
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