Tek 2465A Frequency readout


Nick
 

Hi
I fixed my 2465 over a number of years, replacing the ROMs etc and fighting my way through the CAL process despite not having the best kit.
My question relates to the frequency measurement readout. While I can get reasonably accurate 1/dt frequency readings with the cursors, the auto measurement function tops out around 10Mhz.
I cant find any useful info in the manual on what its capabilities are , so don't know for sure if its faulty and I've only ever had access to my own scope.
Should the frequency measurement work for the full bandwidth of the scope?
If so, is this likely to be connected to the final parts of the CAL which rely on the PG506, which I have never had access to, and which I had to "fudge " as best as I could with what I had.

If not, any tips on where to focus to clear up the problem.

Nick


Siggi
 

Hey Nick,

It's my understanding that the auto measurement functionality was
introduced with the 2465/2467B. Your 2465A and my 2467 should have all the
same features, aside from options (mine has opt 09, CTT - counter timer).
I think it might help if you describe the feature you're using to do this
measurement in more detail.
On my scope I can get a frequency reading with cursor measurements, with
single or dual delay, with or without B-trigger. These scopes pack a wallop
in features, so it helps to be specific.

Siggi

On Sun, May 15, 2022 at 4:26 PM <njkenworthy@...> wrote:

Hi
I fixed my 2465 over a number of years, replacing the ROMs etc and
fighting my way through the CAL process despite not having the best kit.
My question relates to the frequency measurement readout. While I can get
reasonably accurate 1/dt frequency readings with the cursors, the auto
measurement function tops out around 10Mhz.
I cant find any useful info in the manual on what its capabilities are ,
so don't know for sure if its faulty and I've only ever had access to my
own scope.
Should the frequency measurement work for the full bandwidth of the scope?
If so, is this likely to be connected to the final parts of the CAL which
rely on the PG506, which I have never had access to, and which I had to
"fudge " as best as I could with what I had.

If not, any tips on where to focus to clear up the problem.

Nick






 

Nick,

If you have option 06 (Counter/Timer/Trigger) then your scope can show you the frequency of a triggering input signal. If I am reading the manual correctly it looks like Option 06 is only good up to about 150 MHz. This coincides with my own experience using the counter/timer function on my 2465 DMS (Options 01, 06, 09, and 10: DMM, Counter/Timer, Word Recognizer, and GPIB) which seems to top out around 150 MHz.

If your scope's counter/timer function is topping out at only 10 MHz then either something is very wrong, or maybe you have the BW limit switch engaged? (that's a 20 MHz limit, but it's close enough to what you're seeing to be worth checking)

-- Jeff Dutky


Nick
 

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



Nick


Siggi
 

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.

Siggi

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



Nick











 

Nick,

I looked at the pictures in your album. I don't see the BW LIMIT indicator, so I think that's not the issue.

There are also two trigger modes that might be affecting this (if it is trigger related, which it may not be, if you don't have option 06. I don't have a B-model, so I can't say much about them). The HF and LF REJ trigger modes reject high and low frequency signals respectively. I'm not sure if the trigger mode is indicated on the CRT readout, as it has an LED on the front panel. Maybe you have HF REJ engaged?

You should be able to tell what options your scope has by checking the rear panel. There should be some markings indicating which options the scope has.

-- Jeff Dutky


Ozan
 

On Tue, May 17, 2022 at 05:39 AM, Nick wrote:

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.
In the first picture you are in 50-ohm mode but in later pictures you are in 1M-ohm DC mode. In 50-ohm mode I tested frequency measurement function up to 650MHz on a 2467B, which is very similar to 2465B.

Ozan


Dave Voorhis
 

As another data point (er, anecdote) I just tried my 2465B with my RF signal generator (a vintage National/Panasonic VP-8160A) tuned to 250mhz, which is close to its maximum of around 260mhz, and Measure Freq showed 250mhz in both 50-ohm and 1M-ohm input modes.

The feature did seem a bit unreliable just after I got the 'scope, which had apparently sat for a while. It usually worked, but sometimes seemed unable to measure -- complaining of noise or small signal -- what I thought should be relatively clean signals. I've not had any issues since.

Maybe it needed time and use for humidity to dry out?

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Ozan
Sent: 17 May 2022 16:29
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 2465A Frequency readout

On Tue, May 17, 2022 at 05:39 AM, Nick wrote:

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.
In the first picture you are in 50-ohm mode but in later pictures you are in 1M-ohm DC mode. In 50-ohm mode I tested frequency measurement function up to 650MHz on a 2467B, which is very similar to 2465B.

Ozan