[Premium-Rx] Watkins Johnson DMS-107 Demodulator

Sat May 9 18:04:45 EDT 2015

Hi Terry

Many thanks for the information, I must have been looking in the wrong  
place as the only catalogs I've found it in, 1970 and 71, don't seem  to show a 
sensitivity figure, but at least I know now that mine does  seems to be 
living up to expectations.

Something else I've learned too, I always thought DMS stood for  
"demodulator selective" as they were tunable, probably just assumed that from  SLM for 
"selective level meter".

The DMS-105 was a beautiful receiver, I couldn't believe it when I  tried 
my first one on the broadcast band as I only did that by way of  experiment 
and I didn't really expect it to have that sort of sensitivity. I've  had 
both the DMS-105A and 105R but both have gone now as will all my  rackmount and 
desktop kit eventually.

I knew the DMS-107 didn't have the same bandwidths as the DMS-105  but had 
assumed the sensitivity would be similar....that'll teach  me:-)

I might try it with a pre-amp anyway, and just for fun again, after  all I 
have nothing to lose:-)

Regards

Nigel

In a message dated 09/05/2015 22:26:23 GMT Daylight Time,  
watkins-johnson at terryo.org writes:

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-72157603308200
517/  
with a closeup of the DMS-105 here:  
https://www.flickr.com/photos/9716802@N02/1393513204/in/album-72157603308200
517/  
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
>
>

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