[Test-Equipment] PTS250 - was General Radio module

[gandalfg8 at aol.com]

I'm still away from home and using an unfamiliar PC that's having some formatting problems with AOL mail so not sure how this might display, but I'm either missing something here or the "basic mathematical principle" suggested below is just not relevant in this instance.

Just as modern frequency counters certainly don't require anywhere near a 10 second gate time to measure to 0.1Hz accuracy, albeit for different reasons, a frequency synthesiser such as those in the PTS series does not require 10 seconds to generate a signal to 0.1s resolution.
I believe PTS quote something like 20microseconds for frequency changes to stabilise to within 0.1 radians, and although I can't confirm this I can be sure that to all intents and purposes it's nigh on instaneous.

Similarly, the HP 3336, to quote just one further example, offers frequency resolution into the microHertz region but again frequency changes settle very quickly.

So far I can see no obvious reason why one or more extra DM modules couldn't be inserted into the PTS synthesiser chain but if there is a limiting factor I expect it to be other than suggested below, as that would also limit the units as they stand.

regards

Nigel
GM8PZR




I just went to the office for a few minutes and checked. I have two PTS250 
anuals there (they belong to the NMR lab) and they are older ones using DM1000
odules. 
  The question gets down to a very basic mathematical principle. 
eltaF*DeltaT>1 .
or example to resolve 1 Hz you must count for 1 or more seconds. For .1Hz you 
ust count for 10 or more seconds.
nd you can say that the actual frequency resolution is limited by the time that 
he signal exist. That is a signal that 
xist for 1 second has a minimal bandwidth of 1 Hz. It can't have a bandwidth of 
ess than a Hertz.  Simply because it 
as not been around long enough to have enough zero crossings. A difficult thing 
o wrap your mind around at first but
fter studying it for a while you will understand. 
his relates to another one "HUP"  DeltaE*DeltaT>h
ou get the second from applying the first and  E=hF.
ither you will recoginize the relationships or not.