[Drake] Multimeter Suggestions for Drake Service

[Garey Barrell]

Jim -

The Calibrator is a useful, 'wide-range' signal generator for working on 
receivers.

Fortunately, we don't have to worry about mSec or uSec pulses!   :-)

A spectrum analyzer certainly IS 'handy'!!!  They have come down in 
price considerably, but since they started at $40-50k, even 10% is still 
a hefty price to work on a $200 receiver!  I too was spoiled at NASA and 
NRAO, we always had the latest and greatest, because we too were at the 
'margins'.  And of course being government financed,  _price was no 
object_. !

Certainly all of our equipment went in for routine calibration, 
typically every six months.  Keep in mind though, that we were 
designing, building and testing equipment where a failure could be a 
matter of life or death.  I had a good friend in our cal lab, and his 
opinion was that 95% of the time he spent 'calibrating' was simply 
verifying that operation was still in spec.  The Tek and HP stuff didn't 
'drift' much in my experience, most failures meant it quit working!

For our level of importance, calibrating a scope or a VTVM with a GOOD 
DMM puts it well within the accuracy range we NEED it to be.  A good 
scope, DC coupled, can be compared to the voltage measured and/or set by 
a DMM, and unless the attenuator is fried, will be fine on other ranges 
as well.  Of course there isn't anything preventing you from checking on 
several ranges if you're suspicious.  That 100 kHz calibrator signal 
also makes a pretty good 'time' reference, especially if it's been 
zeroed against a 10 or 15 MHz WWV.  Yeah, I know about phase shift, 
atmospherics, etc., etc., but again, we're not 'man critical' here.  We 
are far more interested in frequency than 'time' in what we do, so a 
modern transceiver is as good as any counter around, and a LOT more 
sensitive than most, so absolute accuracy in a scope time base isn't 
'life critical'.

Everywhere I've worked, the 'local knowledge' was that to find the new 
engineer or technician, just look for the guy with all the test 
equipment arrayed around his bench!!  The really GOOD engineers would 
have a Simpson 260 and make all the deviation compensations in his 
head!    :-)   Said another way, if you REALLY understood the equipment 
and measurements you were making, you could interpret what the '260 
showed and derive the 'real' answer.....    Perhaps a 'slight' 
exaggeration, but not a whole lot!

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>


Jim Lowman wrote:
> Good point about the RF signal generator, Garey.  I remember that, and a
> VTVM, was essential to aligning and troubleshooting Drake gear.
>
> In the years that I was in the Air Force and working on air traffic
> control radar systems, the first thing that I reached for was a scope.
> Of course, with radar, you're looking at waveforms in the millisecond
> and microsecond range that would never show up on a meter.
> The spectrum analyzer was handy.  Generally an unstable AFC (we called
> it "hunting") was a sign that the magnetron in the transmitter was
> double-moding, and the spectrum analyzer showed it as plain as day.
>
> I wish I still had access to all of that test equipment.  It was all
> top-of-the-line HP and Tektronix and the like.
>
> Can you really calibrate a scope with a DVM?  I always wondered, when
> guys would drag these monsters away from a swapmeet, if they would be
> accurate.
> Maybe if all one wants to do is look at waveforms they would be okay.
> But we had to rely not only on the accuracy of the time base, but also
> the ability to measure the amplitude of pulses.
> For this reason, all of our test equipment had to go in for calibration
> at regular intervals.
>
> 73 de Jim - AD6CW
>
>