[Test-Equipment] PTS250 - was General Radio module

[GandalfG8 at aol.com]

In a message dated 29/12/2011 22:34:38 GMT Standard Time,  
pete at petelancashire.com writes:

Finally  got it powered up.

As the option plate says, it does not have an  internal osc, could
really care less about that.

The problem so far  is the 10 HZ DM module is jumping around 1 or 2
units. For example  if
the 250 is set at 100,000 KHz, the output jumps exactly 10 or 20  Hz.
Does not seem to care
what the 10 Hz is set to, if 5 the jump is  still +10 or 20 Hz Rate is
variable for a few per second
to every 2  seconds.
---------------
Hi Pete
 
Next test I would suggest is to swap out the 10Hz DM1000 module for  one of 
the others, doesn't really matter which one, 1Hz or 100Hz would seem like  
a good option, just to see if the instability moves with the module.
 
If it does then you have a couple of options.
One is to just leave out that module and move the 1Hz module along and live 
 with 10 Hz resolution, the other is to attempt a fix or try to find a  
replacement module.
Oh, ok, so that might be three options:-)
 
I have repaired PTS units, things like solder blobs moving in transit and  
shorting out a module or fairly obvious faulty components, but must admit 
I've  not attempted any realignment of the modules and wouldn't really want to 
if I  could avoid it.
 
Remembering that resolution is not the same as accuracy I find that I don't 
 really need 0.1 or 1 Hz resolution all that often. What I do need is to 
know  that my set frequency is accurate, which is where my external references 
come  in, and absolute resolution is often secondary.
 
If the instability doesn't move with the module then you need to look at  
the associated switch and attached diodes etc, but I suspect that might be 
quite  unlikely.
---------------------------------

The other issue is the  output drops off very quickly below about 500 KHz
 
--------------------------------
 
The PTS250 is specified from 1MHz to 250Mhz, so if your bottom limit  is 
500KHz I would say that isn't too bad:-)
 
regards
 
Nigel
GM8PZR