Re: Tek 2465A Frequency readout


Hey Nick,

Nice pics. I don't have a -B scope, so I've never seen the measurement
features firsthand. I did take a peek at the service manual, which states
that the measurements all use the trigger hybrids, and the timing
measurements also use the A/B sweep hybrids. For the timing measurements
there's a PAL or CPLD U975 that's mentioned briefly as responsible for the
timing measurements. It does take the 10MHz clock, so I guess it contains a
timer/counter of some description.
There doesn't seem to be anything wrong with your A-trigger and sweep, but
have you tested your B trigger and sweep? From the theory of operation, it
looks like you might need accurate level and delay timing control on both
sweeps for this to work right.

I have to say the voltage measurement feature in these scopes can be
described either as "hokey" or "resourceful", as it basically uses the
analog controls to sweep the trigger level around the peak levels of the
signal. The voltage displayed is then inferred from the cut off trigger
levels. The AUTO-LVL trigger mode works the same way, if the signal drops
out of trigger range, the MCU sweeps the trigger level to detect the P2P
level of the signal and sets the trigger in the middle. This differs from
the analog method that does continuous positive/negative peak detection and
averages those levels for the trigger.


On Tue, May 17, 2022 at 8:39 AM Nick <njkenworthy@...> wrote:

Hi gents

My mistake, my 2465 is a "B" model, I just haven't had chance to play with
it for a while and forgot.

Using the “Measure-Freq” sequence I get a decent readout up to 10Mhz,
after that I note that the trace doesn't trigger and the display reads
something like 36khz. The Width measurement also fails but in a slightly
different way, the signal is triggered and locked even at a >10Mhz but the
readout doesn’t make much sense.

I note that amplitude measurement pk-pk does cause a trigger and a decent
measurement . It's the time based auto measurements causing grief.
Triggers and cursor measurements are good to 500+ Mhz.

There is no CTT module on this one, not sure if it has any options at all.
Mention of the need to trigger to get a successful measurement has got me
thinking...I note that above 10Mhz it didn't trigger.

As I said, I cant find much in the manual about how the unit is making
these measurements.

I’ve put some photos in an Album “ 2465B frequency measurements” so you
can see the displays.

Thanks for the responses chaps and open to any help offered


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