Madell Frequincy counter - Page 1
Forum section: electronics / repair

author: paronaram
author_rank: Regular Contributor
timestamp: May 21, 2021, 11:52:09 pm
content: Hello everybody.I purchased used Madell F1000-C frequency counter, and it was advertised as working.Counter arrived, and it does work, but it's not calibrated, it's off about 200kHzI borrowed another frequency counter from friend just to compare ... and actually that's how I find out that it's offWhat is involved in calibrating this device?Thank you.PS Display cable disconnected by me ...

author: xrunner
author_rank: Super Contributor
timestamp: May 22, 2021, 12:02:43 am
content: Probably the reference is in the metal box with the adjustment screw hole. Let it warm up for an hour or so. Turn the screw until you are as accurate as possible to the best reference you can compare to.

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 22, 2021, 01:07:15 am
content: How certain are we that the borrowed counter is calibrated?

author: coromonadalix
author_rank: Super Contributor
timestamp: May 22, 2021, 02:03:30 am
content: /as writen on earlier postsyep the metal box is the main time base oscillator, you need to compare it against another counter to adjust it, some counters have a 10Mhz timebaseThis one has an 10Mhz timebase indeed ...If you have access to a scope it could roughly help to readjust it, at least warm the counter for 1 hour before doing so

author: Miti
author_rank: Super Contributor
timestamp: May 22, 2021, 02:25:42 am
content: Quote from: paronaram on May 21, 2021, 11:52:09 pmFirst of all, did you let both counters warm up? What makes you think that your friend’s counter is perfectly calibrated? Does it have a GPSDO or at least an OCXO? If not, you have two watches and you don’t know which one shows the correct time.Your time base looks like a TCXO, don’t expect too much stability from it.

author: TimFox
author_rank: Super Contributor
timestamp: May 22, 2021, 02:36:32 am
content: An error of 200 kHz at what frequency? 200 kHz error at, for example, 10 MHz is not likely a crystal calibration error (2%), but could be a circuit failure.

author: floobydust
author_rank: Super Contributor
timestamp: May 22, 2021, 02:56:16 am
content: It also goes by ATTEN F1000C. Manual says 20 minute warmup, 13MHz ref osc. I'd make sure VDD is OK assuming 5VDC.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 22, 2021, 02:57:28 am
content: Seems a clone of Atten AT F1000-Chttps://www.eevblog.com/forum/repair/atten-f2700c-digitech-qt-2202-repair-review/LOLL got me while posting it loll

author: paronaram
author_rank: Regular Contributor
timestamp: May 22, 2021, 05:44:09 am
content: Thank you all for all recommendations.Counter that I borrowed is LEADERWill test this all tomorrow with 1kHZ calibration from my scopeThank you

author: Kleinstein
author_rank: Super Contributor
timestamp: May 22, 2021, 06:46:07 am
content: The 2 nd borrowed counter looks like about same quality grade. This is OK for a crude test, but not really for a calibration. For frequency there are good reference frequencies available as RF signal in many places.The difference of 200 kHz is huge ( still depends on the frequency, but even at 200 MHz, which would be close to the maximum of the slower of the 2 counters thus would be 1000 ppm and thus more than what a quartz crystal could sensible drift or be detuned. This looks more like a problem (e.g. quality of the test signal) or defect with the input stage (causing double triggering) or maybe just a very poor setting for one of the instruments (e.g. select external reference if not present).With such a large error it would at least be possible to see which reading / counter is off. Even the mains frequency is better with some patience or using info on the actual measured frequency from the web.

author: paronaram
author_rank: Regular Contributor
timestamp: May 23, 2021, 02:13:46 am
content: So I did more testing, and it looks like it's working, I mean it looks like calibrated , maybe type of signal? ...On the picture you can see it's connected to a scope calibration 1kHZ output.Before I was connecting to a Heathkit RF Generator SG-8Maybe signal is not stable from RF generator?http://pdf.textfiles.com/manuals/SCANNERS-F-R/Heathkit-SG-8.pdf

author: TimFox
author_rank: Super Contributor
timestamp: May 23, 2021, 02:25:44 am
content: On page 15 of the Heath manual, it states that frequency accuracy of 2 - 3 % is “expected”. Again, at what frequency did you see 200 kHz error?

author: xrunner
author_rank: Super Contributor
timestamp: May 23, 2021, 02:26:32 am
content: Quote from: paronaram on May 23, 2021, 02:13:46 amThat Heathkit RF signal gen starts at 160 kHz. Is the low pass filter button depressed on the counter (looks like it might be - also the attenuator)? It may be attenuating the signal you were trying to count but you didn't specify what freq. the Heathkit generator was set to. A 1 kHz square wave will pass OK if the low pass filter button is depressed but a much higher freq. will not.

author: paronaram
author_rank: Regular Contributor
timestamp: May 23, 2021, 09:21:04 pm
content: OK, did more testing this AM.It's all working, I can't replicate this issue... RF 455kHZ was showing 600kHz+ (I don't remember exact number) the day I was trying to do a RF alignment on tube radio. I was at my friends house, and the only difference from what I was doing that day and now, is BNC cables.I used his cables on the same equipment that have here... and counter was off ... today and yesterdays test was not showing any issues at all with my BNC cables.I set the Heathkit to 455kHz and both counters output 455 on the displayIt's just weird

author: TimFox
author_rank: Super Contributor
timestamp: May 23, 2021, 09:34:16 pm
content: Yes, 200 kHz error on 455 kHz is not a calibration problem. My guess is that the bad cables had an open circuit, so that the signal getting through was capacitively coupled and exaggerated noisy stuff on the 455 kHz sine wave. One would expect less than 20 kHz error with that generator at 455 kHz, even if it was not recently calibrated.

author: paronaram
author_rank: Regular Contributor
timestamp: May 24, 2021, 12:48:51 am
content: Thank you everybody for your help and support!