EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: vinlove on July 28, 2019, 10:44:51 pm
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I have a FY6800, and was trying to use its Counter function to measure RF Frequency oscillated by an external signal generator (actually a Heathkit GD-1U Dip meter).
I connected a probe to Counter BNC connector of the FY6800, and the GD-1U was switched on with 1.7Mhz - 4Mhz coil plugged in.
I was under impression that when I rotate tuning dial of the GD-1U, FY6800 set to Freq. of the Counter mode would read out the frequency generated by the GD-1U. But there was no reading at all. Just 0.0Mhz.
Why could this be? Couldn't FY6800 counter BNC connector pickup the frequency generated by GD-1U by touching the coil of the GD-1U with the probe connected to the FY6800 BNC conector of the counter?
Does it need direct connection and fed with more voltages from the probe?
Loose coupling doesn't work? Or am I doing something wrong here?
The RIGOL DS1052E was reading the generated freq from the GD-1U by loose coupling no problem.
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Have you checked to see if the level is within the range of the FY6800? the manual says: "Amplitude of signal inputted should be bigger than 1.5V. Maximum safe voltage inputted from Input and Trig IN is 5V." Most dedicated counters can read signals down to the millivolt range.
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Have you checked to see if the level is within the range of the FY6800? the manual says: "Amplitude of signal inputted should be bigger than 1.5V. Maximum safe voltage inputted from Input and Trig IN is 5V." Most dedicated counters can read signals down to the millivolt range.
No, I have not read the manual. If its needing input voltage bigger than 1.5V, then it is natural that it doesn't read the freq from GD-1U. Because with loose coupling voltage read by the Rigol 1052E was about 10mV.
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Dear Customers,
The instrument counter function, in the DC-coupled state, the signal to be measured is input from the Trig IN terminal of the back panel. The signal to be measured is input from the INPUT terminal of the front panel in the AC-coupled state, and the measured signal amplitude needs to be greater than 1V.
FeelElec
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I measured signal generated from a DMM 1Khz and 1V, connected using a DSO probe to the DMM, and FY6800's Counter BNC connector. THe FY6800 was reading freq. 1Khz OK.
If the voltage is less than 1V, it will not read.
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I measured signal generated from a DMM 1Khz and 1V, connected using a DSO probe to the DMM, and FY6800's Counter BNC connector. THe FY6800 was reading freq. 1Khz OK.
If the voltage is less than 1V, it will not read.
Dear Customers,
If you want to measure the signal below 1V, it is recommended that the signal be amplified and then connected to the measuring terminal of the instrument.
FeelElec
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Dear Customers,
If you want to measure the signal below 1V, it is recommended that the signal be amplified and then connected to the measuring terminal of the instrument.
FeelElec
Can FY6800 read freq. from loosely coupled source? Without touching the probe, just by placing the oscillating source very close to the FY6800 counter probe?
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You can answer this question yourself by now, since you know that 1Vpp likely is required.
What you need is an analog frontend for the counter, based e.g. on a LT1016 with a hi-Z FET buffer on the input; like that you can get response down to a few mVpp.
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You can answer this question yourself by now, since you know that 1Vpp likely is required.
What you need is an analog frontend for the counter, based e.g. on a LT1016 with a hi-Z FET buffer on the input; like that you can get response down to a few mVpp.
I saw on youtube someone was reading freq. generated by GDO meter, and loose coupled (not touching the probe of the freq counter), but placing the GDO meter very close to the freq counter. The counter BNC input connector was inserted with some kind of small coil wound about 3-4 turns by the presenter, and it was working as an antenna.
Was wondering if FY6800 could do similar, although it needs over 1V to work. But I can see what you suggesting will be likely to work too.
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how should that work? inductive coupling can be used if the input of the counter is sensitive enough, but that's not the case in many of those function generators with frequency counter functionality - somewhere the manufacturer is going to save and that most likely on such addons. Also I doubt long- and shortterm stability of the reference clock of this device to be really usable for a counter.
for a test try such an inductive coupling and watch on a scope the signal level you achieve.
to implement a counter in a mcu is no big thing at all, but it's pretty useless if there isn't any analog frontend sensitive enough on the input and not delivering enough signal on the output - from all the counters I already built (one with a PIC, one with a ATmega and the newest one with a STM32F4) the frontend always needed much more engineering effort than the digital/counting part.
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Would DSOs be good tool to measure Freq. from RF sources such as HF transmitters?
My DSO is Rigol DS1052E.
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how should that work? inductive coupling can be used if the input of the counter is sensitive enough, but that's not the case in many of those function generators with frequency counter functionality - somewhere the manufacturer is going to save and that most likely on such addons. Also I doubt long- and short term stability of the reference clock of this device to be really usable for a counter.
Actually the stability and accuracy of the included 50Mhz oscillator is barely adequate for a function generator, let alone a frequency counter. That is why on my older FY6600 I not only replaced the crappy power supply with a high quality SMPS, I replaced the 50Mhz oscillator with a 5X PPL chip, and the oscillator with a high stability 10Mhz OCXO and included a switch to also use an external 10Mhz source like from one of my GPSDOs if I wanted even higher resolution and accuracy. The details for these changes are in the FY6600 thread if you're interested.
For a counter my modified FY6600 works quite well as you can see in the attached photo where the FY6600 is using the internal 10Mhz OXCO and counting one of my GPSDOs with a 10S sample time. It still has the limitation of needing a higher level to count but I have other high end counters for that purpose. When using the FY6600 as a function generator I can get about 12 digits of stable frequency.
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When my FY6800's probe was touching the signal source physically, it reads frequency accurately. I was comparing it with all other freq measuring devices from the same signal source.
It is just when I am trying to read freq by inductive way (not physically touching, but bringing the sig source very near to the input socket of FY6800, then it does not read.