Fluke PM6690 12 digit/s frequency counter

[Jörg]

Now I have finished changing the standard time base of my Tek FCA 3000.
The free space on the board is now equipped with a compatible OCXO. I only desoldered the connections of the standard crystal and left the crystal in the device.
For the correct function, the Fluke PM 6690 utility is required. With the software, the CPU is given the instruction to switch from the standard TCXO to the OCXO.
The selected Timebase option 30 or 40 is then shown in the information display.
Next, with a suitable 10 MHz source you can make a factory calibration. The date is also shown in the information display.
However, the following must be considered for the owners of the Pendulum CNT or Tektronix FCA equivalent.  The Fluke utility renames each device as Fluke PM 6690!!
This name is displayed on the information display and also on a PC when connected to a USB cable.
Next, i exchange the cheap case fan and implement the prescaler PM 9624 clones from China.

Jörg

[jpb]

Now I have finished changing the standard time base of my Tek FCA 3000.
The free space on the board is now equipped with a compatible OCXO. I only desoldered the connections of the standard crystal and left the crystal in the device.
For the correct function, the Fluke PM 6690 utility is required. With the software, the CPU is given the instruction to switch from the standard TCXO to the OCXO.
The selected Timebase option 30 or 40 is then shown in the information display.
Next, with a suitable 10 MHz source you can make a factory calibration. The date is also shown in the information display.
However, the following must be considered for the owners of the Pendulum CNT or Tektronix FCA equivalent.  The Fluke utility renames each device as Fluke PM 6690!!
This name is displayed on the information display and also on a PC when connected to a USB cable.
Next, i exchange the cheap case fan and implement the prescaler PM 9624 clones from China.

Jörg

Interesting. My counter is out-of-warranty now so I may think about doing some improvements. I intend using an external reference (GPSDO or possibly Rubidium) so I'm not sure how much I'd gain from an OCXO except that the crystals in OCXOs tend to be higher quality.
The prescaler may be useful, at present I use my TTi counter for anything over 300MHz and below 3GHz.

[Jörg]

Hi jpb. Of course, if you always use your counter with a good GPSDO as an external reference,
you don't need to worry about the internal timebase.
I can also use a GPSDO. But I also need to be able to use the counter in other places.
For this purpose, I consider the default TCXO to be inappropriate in a device with this resolution.
In a more serious scenario, this can only be appreciated.
The OCXO has the short-term stability at least a factor of 100 better than the TCXO.
Also provides a more predictable temperature stability. I like that.
Everyone needs to assess the benefits of this upgrade. 
Homemade is the upgrade in any case cheaper than the original options from the manufacturer.


Meanwhile, the 2.7 GHz Prescaler has arrived from China. I tested it quickly. The Prescaler works in FCA 3000, but is shown as option 13 in the display.

[Jörg]

I quickly built an em-shield for the prescaler.
In the background you can also see the replacement for the simple fan.

[Jörg]

I have noticed a weakness of the China prescaler.
The circuit in the area of the FET 1-4 behind the signal input, is sensitive when metal comes close.
My EMF Shield unfortunately has no benefit. The right side of the counter housing is also slightly too close to the circuit. Without input signal, the display for input c shows alternating, random readings.
Without housing near the Prescaler, the frequency display is blank.
However, this behavior has no negative effect on the accuracy of the measurement.
At the moment, I can test the measurement only up to 78 MHz.

[DaJMasta]

I wonder if that's an interference thing or if that's a nearfield coupling thing.  If you have any RF absorber material, it could be worth testing with it next to the location in question.


Actually, it may be worth checking the grounding of the chassis.  It could be that the chassis ground isn't great, and it's picking up some ambient RF field that's influencing the gain stages early on in the circuit.  Could be tricky to troubleshoot, though.

[Jörg]

That's a good question.
> The behavior is also shown when the SMB to N connector cable is not plugged into the prescaler.
> The data on the display is similar if you connect an unshielded cable to input A or B.
> If you are very close to the area with your finger or metal (1-2 mm), data up to 230 MHz will be displayed.
   If you are farther away (10-15 mm), the display shows about 30-80 Hz.
> The shield I built is made of copper-coated PCB material with good contact to the equipment ground.
   I just didn't have a better material.

It could be that the original prescaler has a slightly different design.

[little.tesla]

Hello,

regarding the Fluke Utility which renames the counter to FLUKE / PM6690, there is an easy way to rename it back.
Use this commands with a generic GPIB Utility or even using the FLUKE Utility (Manual Command) did work for me:

SYST:INST:TYPE:HEMLIGKO 'CNT-90'
SYST:INST:MAN:HEMLIGKO 'PENDULUM'
(was already correct on my device): SYST:MOD:HEMLIGKO CNT90

Bonus commands (not tested):

Change SN to 123456: SYST:SNUM:HEMLIGKO 123456
Change Timebase to Standard: :SYST:INST:TBAS:HEMLIGKO STANDARD
Change Timebase to OPT30: :SYST:INST:TBAS:HEMLIGKO OCXO30
Change Timebase to OPT30: :SYST:INST:TBAS:HEMLIGKO OCXO40

Regards,
 Dimce

PS. The 8GHz option from https://cojotech.com/ works very well with the CNT-90.

[Micke]

I wonder, can it be a coincidence, or a software engineer had some fun...
Since the counter is made in Sweden and HEMLIGKO (if you divide it to HEMLIG KO) means "Secret Cow" in Swedish  

[DaJMasta]

Has got to be, the secret cow level unlock code! 

[Jörg]

Hi little.tesla. Thank you for your help.
I did this with my FCA 3000 today and it worked fine.
Best regards.

[MegaVolt]

The Spectracom CNT-9X v1.28 update worked just fine on my PM6690.

Please post a firmware update file. It is no longer available on the website.

I found an update on the tektronics website: https://uk.tek.com/frequency-counter-supplies/mca3027-software/firmware-update-loader-and-fca3000-fca3100-and-mca3000-0

But the description does not mention the Fluke 6690

The model number is a PM6690/AN, which isn't listed as an official spec in Fluke's datasheet... it's supposed to have a three digit code not a two letter one.

The three numbers you need are hidden at the end of the code:

[MegaVolt]

Please post a firmware update file. It is no longer available on the website.

I found it myself )) The firmware files are identical. Loaders are different. Just in case, I post it here.

[rockwell]

I'm trying to update the firmware from my Pendulum PM6690.
Installed on the counter is firmware v1.08 and I would like to update to v1.28
I have the NI-Visa drivers installed on a windows 10 computer and connected the counter to it via USB.

Now when I start the CNT9xLoader program I get the error message:

"can't open the counter with the following Visa symbolic address:
 USB::0x14EB::0x0090::88884::INSTR"

Has someone a idea what I'm doing wrong?