[Premium-Rx] Watkins Johnson DMS-107 Demodulator

[Terry O']

Nigel,
The catalog says the DMS-107 has a input sensitivity of 30 mV (to 1 V 
maximum).  The designation DMS is DeModulator Special.   At 30 mV 
sensitivity connecting it to an antenna just demonstrates it is a brick.

The DMS-105 was designed as an enhanced 357 receiver and is an excellent 
BCB and Lowfer receiver.  The original production order lists it as the 
358, but to my knowledge none were produced with that number.   It is an 
oddball among the older DMS.

In the field it was primarily used for getting subcarriers. There's one 
on display in the National Cryptological Museum at Fort Meade as part of 
the Rissman Telemetry Processing System.  A former WJ employee posted 
some pictures of that system here: 
https://www.flickr.com/photos/9716802@N02/1393497950/in/album-72157603308200517/ 
with a closeup of the DMS-105 here: 
https://www.flickr.com/photos/9716802@N02/1393513204/in/album-72157603308200517/ 
The Microdyne 1100 below the DMS-105 is probably the main receiver in 
this system.

Some of the later FDM demods are sensitive enough to be used as 
receivers.  I've seen the WJ-9548 used for SSB aviation on frequencies 
like 5550, 6604, 10051...  It works very well.  These units are 
effectively 6, 12 and up to 24 HF DSP SSB receivers in one box.  A WJ 
engineer told me this capability of the 9548 was used to convince 
management to invest development dollars in what came to market as the 
WJ-8711.

Terry O'
http://Watkins-Johnson.terryo.org
http://BlackRadios.terryo.org


On 5/9/2015 9:37 AM, GandalfG8--- via Premium-Rx wrote:
> Hi All,
>   
> I know this isn't exactly a premium receiver but I'm hoping someone here
> might be able to offer some assistance.
>   
> I've read online of the DMS-107 being used as a broadcast  receiver but my
> attempts with this one have revealed very low  sensitivity, a couple of
> strong local stations and that's it, and a bench  test at 1.5MHz shows it needs
> approx 7.5mV to reach the "set" position  on the signal strength meter.
> I'm more used to the DMS-105A, where the manual specifies sensitivity as
> 30uV but in practice they always seem to be much better than that, but I
> don't  have a sensitivity spec for the DMS-107.
>   
> The only information I have been able to find is an entry in the 1970
> Receiving Systems catalogue that shows the intended use for this was  for
> spectrum analysis of complex signals from wideband tape recorders.
> Presumably microvolt sensitivity wouldn't have been necessary for that  but
> if anyone could offer confirmation of the specified or actual to be
> expected sensitivity, or even a copy of the specification or manual, that would
> be much appreciated.
>   
> If I know there's something wrong then I'm happy to fault find it but all
> the original WJ calibration seals on the modules are still intact so I'm
> reluctant to break these until I'm sure it's not operating as it  should be.
>   
> Regards
>   
> Nigel
> GM8PZR
>
>