[Milsurplus] Collins automatic antenna coupler / tuner

[David Ross]

Jim and the gang -

   The SRA-22 antenna coupler runs off 60~ power and the coupler 
assembly uses 60~ motors -  no 400~ parts here at all.  Yes there is a 
fan inside the pressurized SRA-22 housing and it circulates air through 
the double-walled housing.  The CU-714 has extra ducting to move that 
air through the coupler itself.  The CU-714 does not have a 
forward/reflected power discriminator on it's front panel -  the 
forward/reflected power sensor is on the rear of the SRA-22 control panel.

   You may see beryllium oxide warning tags on the SRA-22 housing and on 
the CU-714 itself.  The CU-714 has a ferrite slug inside the main 
inductor, and that core has problems with local overheating in spots.  A 
later mod put a beryllium oxide sleeve over the ferrite slug to better 
distribute heat throughout the slug.

   There are no servoamps in the SRA-22 -  that is the operator's 
function.  The control panel has two five position lever switches, one 
switch moves the coil and the other switch moves the tap along the 
coil.  The switch center position is 'off', the far left position is 
'run left' and the far right position is 'run right'.  The mid-left 
position is 'jog left' and the mid-right position is 'jog right'.  A 
simple rotary switch controls the position of the vacuum variable cap in 
the CU-714, allowing for ten or twelve discrete cap positions.

   There are follow-up potentiometers on both the coil and the tap 
geartrains in the CU-714 and these pots drive the two zero-center meters 
on the SRA-22 front panel.  The multiturn pots on the SRA-22 front panel 
are used to null out the meters -  the reading on the multiturn pots 
then provides a record of coil and tap settings for later use.

   I have used an SRA-22 with my URC-32B and it does a good job, with a 
little fussing you can get the reflected power down to where it will not 
even make the reflected power meter deflect with a forward power of 500 
Watts.  With practice you can get tune time down to a minute or so, with 
most of that being time spent waiting for the motors to move.



   The 490B-1 uses a 180R-6C antenna coupler, which is an 
automatically-tuned unit with 400~ servomotors.  There is no 
'coupler-controller' package inside the 490B-1, just discrete modules 
attached to the 490B-1 chassis.  I think that the servo amps and 
sequencer modules are straight out of the 309A-2E coupler controller.

   The CU-749/TRC-75 coupler looks similar to the 180R-6C but I do not 
think they are interchangeable.  I'd have to do a lot of studying 
schematics before I would swap one with the other.

73
Dave Ross    N7EPI



On 4/12/2011 7:58 AM, Jim Whartenby wrote:
> The 1965 Collins 618T catalog adds:
> HF-101 = 618T-1
> HF-102 = 618T-2
> HF-103 = 618T-3
> no mention here of the HF-104
>
> By observation, the 180R-6 antenna tuner / coupler appears to be the same as:
> 490B-1
> CU-714/SRA-22
> CU-749/TRC-75
> They all have the same form, fit and function.  The addition of the
> Discriminator module to the front panel and the axillary control module makes
> this tuner automatic, without these, the tuner can be controlled manually by
> wire cable as is the case for the URC-32 which uses the C-2698/SRA-22.  Having
> never seen one, I assume the SRA-22 has an internal 60 to 400 cycle converter
> inside that big box and perhaps a fan.  Has anyone ever worked on one?
>
> I am amazed that the 18Z-3 (ARC-58) and the 618T-2 are both in the 1959 Collins
> Aviation catalog.  This is only a few short years after the development of the
> silicon transistor by TI.  Fast moving times in the early days of the Cold War.
> Jim
>