Feeltech FY6800 60Mhz Function Generator frequency calibration - Page 1
Forum section: electronics / testgear

author: cemelec
author_rank: Contributor
timestamp: June 27, 2018, 07:03:00 am
content: Hi, has anyone managed to calibrate the new fy6800 frequency?I have one of these and also the older FY6600 - I successfully calibrated the 6600 using the method outlined by Val - « Reply #805 on: February 23, 2018, 08:38:20 am »but it does not seem to work with the FY6800The procedure works, the frequency is corrected, but on power down then reboot the new settings are lost and the old frequency is outputOddly if I repeat the procedure the modified frequency shows under "SYS", "More" but the actual output remains uncalibrated.Anyone had any luck?Thanks, Charles

author: Mozee
author_rank: Contributor
timestamp: June 28, 2018, 10:05:52 pm
content: I've got one as well and I see that the frequency is a little bit off .. also the amplitude voltage as well as the offset is not as shown on the display!how did you calibrate yours?

author: cemelec
author_rank: Contributor
timestamp: June 30, 2018, 04:48:37 am
content: That's the point - I can't calibrate the FY6800. I can calibrate the FY6600 frequency but using the same procedure doesn't seem to work

author: Mozee
author_rank: Contributor
timestamp: July 02, 2018, 03:08:24 pm
content: ahha ok. but could you please direct me to the method cant seem to find it

author: Mozee
author_rank: Contributor
timestamp: July 02, 2018, 04:23:15 pm
content: Ok I found it but I don't seem to understand what frequency is to be set.when I enter the calibration mode and the oscillator indicates 10MHZ I connected my ch1 to the oscilloscope and using the counter function it indicated about 60MHZ (60000025 Hz ) so should I set the 10MHz in the FY6800 to the exact frequency measure by the counter?thank you

author: Miti
author_rank: Super Contributor
timestamp: July 03, 2018, 11:31:51 pm
content: Quote from: Mozee on July 02, 2018, 04:23:15 pmI have an FY6600 Ver 3.3 and this is the procedure that worked for me:1. Enter the calibration mode by pressing and holding STBY button and CH1 at power up2. Set CH1 frequency to 10MHz3. Go to the adjustment menu (SYSTEM, MORE, OSC)3. Move the cursor to the right to reduce the frequency step4. Adjust the frequency until your frequency counter reading is 10MHz5. Long press the encoder to save the new setting. In your case is probably the OK buttonI bet you know already, the oscilloscope is not an accurate frequency counter by any mean, not enough to do frequency calibration anyway.

author: ArthurDent
author_rank: Super Contributor
timestamp: July 20, 2018, 11:12:51 pm
content: On my FY6600 I replaced the not so great 50Mhz oscillator with a x5 PLL chip and added a OCXO and switch so I can use either the internal high accuracy 10Mhz OCXO or feed an external 10Mhz in from my GPS standard.To check the output frequency I feed the signal from the FY6600 to my scope that is triggered from my GPS standard and watch for drift at 2ns/div.

author: cemelec
author_rank: Contributor
timestamp: August 19, 2018, 10:22:09 am
content: For anyone still interested in this thread, the latest FY6800 firmware - version 1.7 - seems to fix my original problem. On power down the FY6800 remembers the new calibration value, at least for now, havn't tried long term.

author: janjor
author_rank: Newbie
timestamp: September 06, 2020, 06:57:58 pm
content: Dear Mr. DenT, although I reaLISE THAT YOUR POST CONCERNING THE REPLACEMENT OF THE fy6800 OSCILLATOR BY AN ocxo IS TWO YEARS OLD BY NOW, I ONLY RECENTLY CAME ACROSS THE PROBLEM OF THE RELATIVELY INSTABLE OSCILLATOR IN THE fy6800, SINCE I BOUGHT ONE ONLY TWO MONTHS AGO. COULD YOU PLEASE INFORM ME HOW YOU MANAGED TO DO THIS REPLACEMENT? ALSO, WOULDN'T IT BE EASIER TO REPLACE THE OSCILLATOR BY A 50 MhZ OCXO INSTEAD OF ADDING A 5X PLL? THANK YOU FOR YOUR HELP IN THIS MATTER,JAN JOR

author: ArthurDent
author_rank: Super Contributor
timestamp: September 06, 2020, 07:30:25 pm
content: Jan Jor - There aren't a lot of good 50Mhz oscillators out there and you will have a much harder time calibrating them. 10Mhz is a universal standard frequency and you can get that from a GPSDO with great accuracy. I felt that if I'm going to make the time base in the FY6600 more accurate I might as well use an inexpensive high stability 10Mhz OCXO and also have it set up so I could use an external 10Mhz from a GPSDO if I didn't want to wait for internal OCXO to warm up. This modification took care of stabilizing the time base and the simple 5X PLL converted this 10Mhz standard frequency to the 50Mhz the FY6600 needed. If you are just using the function generator for audio work or other non critical applications then the standard oscillator is more than adequate but if you want to make use of the setability of the frequency displayed then a more accurate time base is needed.

author: Labrat101
author_rank: Unknown
timestamp: September 06, 2020, 08:03:02 pm
content: Quote from: cemelec on June 27, 2018, 07:03:00 amHiI also have one of these FY68.. I also tried all the mods which help some what withaccurate . including OCXO and PLL .And after many hours I ran a full test on the Cyclone chip which is a FAKE ...so the chances are that you will have this 4 / 6ns phase Offset error that is a faultwith the Cyclone.No on the FY6800 its NOT Jitter its a phasing error with the cyclone itself .The external DAC's are low quality . There is also the Z miss matchbut that's just the icing on the cake .

author: mawyatt
author_rank: Super Contributor
timestamp: September 06, 2020, 10:00:27 pm
content: I don't have a FY68 but thought have you tried "Injection Locking" the 50MHz oscillator to the 10MHz reference source? If the 10MHz source is somewhat square-wave it will have significant odd harmonics and thus a strong 5th will be present, and a simple light coupling between the oscillators might be all that's required. Maybe try a 10~100pf capacitor in series with a 100~1K resistor connecting the outputs.You can tell if they lock together by the monitoring each oscillator and see if they drift with respect to each other. Of course the 10MHz oscillator may end up getting locked to the 50MHz, which is what you don't want. If this happens then you will need a buffer on the 10MHz reference oscillator, a simple CMOS inverter (74AC04) should work.Another way is to inject the reference oscillator signal thru a series RC as mentioned into the Ground or Vcc pin on the 50MHz oscillator. This usually will couple enough energy into the oscillator to cause it to injection lock. The Vcc pin may be more successful if the decoupling capacitors have a high ESR, which may be true on a cheap instrument where cost corners are cut.Hope this helps,Best,Mike