Hello,
I would like to get a stand alone frequency counter, to measure unknown frequencies without requiring my usb logic analyzer and a PC.
I've seen quite cheap 1,3GHz units, and also 2,4GHz which is far more than I'd need. But there are things I don't plenty understand.
All unit have 2 inputs. 1Mohm and 50 ohm input impedance.
Only the 50 ohm input is able to measure frequencies above 25-50 MHz. This means that most of signals can't just be coupled. For example the output of an IC. As soon as the output resistance of the source circuit is above 500 ohm, the voltage divider makes the voltage measured in the unit drop around 10 times (+/-). Most of these counter have a sensitivity of 50 mVrms. This makes it unusable for output resistance around 5 komh at 5V levels.
How could this be worked around?
The first thing that comes to mind is use an emitter follower to lower impedance seen by the load (in this case the counter), but is a bit annoying to have to do this all times. Sure I'm missing something out. I never used these equipments before. The freq counter I use is inside my logic analyzer and works with standard TTL and CMOS levels.
Thank you for helping me getting to know one more thing in this fascinating world of electronics ;-)
I would like to get a stand alone frequency counter, to measure unknown frequencies without requiring my usb logic analyzer and a PC.
I've seen quite cheap 1,3GHz units, and also 2,4GHz which is far more than I'd need. But there are things I don't plenty understand.
All unit have 2 inputs. 1Mohm and 50 ohm input impedance.
Only the 50 ohm input is able to measure frequencies above 25-50 MHz. This means that most of signals can't just be coupled. For example the output of an IC. As soon as the output resistance of the source circuit is above 500 ohm, the voltage divider makes the voltage measured in the unit drop around 10 times (+/-). Most of these counter have a sensitivity of 50 mVrms. This makes it unusable for output resistance around 5 komh at 5V levels.
How could this be worked around?
The first thing that comes to mind is use an emitter follower to lower impedance seen by the load (in this case the counter), but is a bit annoying to have to do this all times. Sure I'm missing something out. I never used these equipments before. The freq counter I use is inside my logic analyzer and works with standard TTL and CMOS levels.
Thank you for helping me getting to know one more thing in this fascinating world of electronics ;-)