[Premium-Rx] Watkins Johnson DMS-107 Demodulator

Sun May 10 03:15:51 EDT 2015

Hi Bob,

Thanks for your comments, and I must admit it was a "lucky" antenna  
scenario, at least in part, that allowed my original DMS-105 to shine as  much as 
it did.

I was living in an electrically very quiet location,  with virtually zero 
internally generated interference, and could  use a desktop amplified Palomar 
tuned ferrite rod system to very  good effect.

Having said that, I can't recall anything else with quite the same range of 
 built in crystal filters and still think of the DMS-105 as  a beautiful 
example of WJ engineering at its best.

Some eight years on, and in a more remote spot on the west coast of  
Scotland, I'm yet another victim of "progress" and swamped by the  noise of 
switch-mode PSUs and electronic ballasts.

The Palomar has long been retired, and although  outdoor antennas can 
reduce the noise to something approaching a  more acceptable level this is an 
ideal spot to funnel the full  force of the west coast gales, which of course 
does tend to bring  its own problems:-)

All good fun.......

Regards

Nigel
GM8PZR

In a message dated 10/05/2015 00:49:36 GMT Daylight Time,  
rwbetts at sbcglobal.net writes:

Nigel:I  can confirm the sensitivity specs that Terry quoted.On the bench 
both of my  DMS105 (A and A2) show a similar sensitivity. Typically they are 
close to 40dB  down from my 8718 and MFP receivers, close to 100:1. Those 
figure are from  memory, but I think I remember correctly. 
Since one of my relaxation  passtimes is DXing the AM b'cast band, I had to 
give the DMS a shot at it. I  finally decided to use a preselector with a 
20dB preamp. That worked out very  well, but with necessary input filtering. 
sys1

Obviously, AM DXing with  W-J stuff is more about testing my antennas than 
evaluating the  radios.
Good signals to all,
Bob, N1KPR
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Engineering: Where Enigma meets  Paradox
From: GandalfG8--- via Premium-Rx  <premium-rx at mailman.qth.net>
To: premium-rx at mailman.qth.net 
Sent:  Saturday, May 9, 2015 6:04 PM
Subject: Re: [Premium-Rx] Watkins Johnson  DMS-107 Demodulator

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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