Frequency Counter  and probes !!   - Page 1
Forum section: electronics / projects

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: May 29, 2011, 10:46:12 am
content: I have one Leader LDC-831 Frequency Counter, that got it as used before long long time.Even so I have the box of it, but no users manual, or the original probe ( lead ).And so I have to ask .Does the Frequency Counters use any specific type of probes ?( Theoretically it depends on the Frequency ,and so for the "150Mhz Max limit of the device" ,I had build my own probe with BNC + RG-58 that splits in two crock clips )If you have a picture of something more special , just post it. ( 400X400 Max size )

author: tekfan
author_rank: Frequent Contributor
timestamp: May 29, 2011, 11:11:46 am
content: For higher frequencies >20MHz you can use a standard 10x oscilloscope probe to reduce loading capacitive effects on the circuit. For lower frequencies your BNC + RG-58 setup should work fine.

author: Unknown
author_rank: Unknown
timestamp: May 29, 2011, 01:42:42 pm
content: Depending on frequencies, amplitudes and tolerated loading, either a simple coax lead, 1x scope probe or 10x scope probe should be fine. You might even want to use a 100x or 1000x probes if the voltages involved are very high. Note that unless terminated into their characteristic impedance (eg. 50 ohms), a standard coax cable represents a huge capacitive load, like 100pF/m (Xc = 1/(2*pi*f*C)). A 1x scope probe is better, and a 10x one much better. This limits the performance at high frequencies. For example, a 2m 1x scope probe may have a capacitance of 100pF, which at 100MHz will represent a load of 16 ohms. You will need a pretty beefy source to overcome that.Not sure how to handle low-frequency compensation of 10x probes on a counter, you can't check for clean edge on a square wave, although I guess it's less important than for scopes.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 29, 2011, 02:01:10 pm
content: if you need detail info start from basic my how do and dont on high frequency signal you can check here,How to Better Wire the BNC Connector and GHz issuethe question is, what are you trying to do? my quick answer, you can mod your bnc cable and good up to few GHz, just cut out the crock clips, thats no good for high freq signal.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: May 29, 2011, 03:33:37 pm
content: Quote from: Mechatrommer on May 29, 2011, 02:01:10 pm1) I wish that I could see what the manufacturer of it, had in mind as probe for it.2) The input voltage goes up to 20-20 P-P .( but I solved this, by never have an direct connection with anything powerful above the 20Mhz )3) At the range of the acoustic frequencies , the crocks works nicely.4) When I was fine-tune FM PLL synthesizers, it was sensitive enough with out direct connection.But mostly I care to see , how the original probe was look like.

author: Unknown
author_rank: Unknown
timestamp: May 29, 2011, 04:28:56 pm
content: No idea about the original probe for the Leader counter (the manual may be helpful, if available), butthis probewas used with some Tektronix counters.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: May 29, 2011, 06:20:03 pm
content: Nice find , Thanks..

author: vk6zgo
author_rank: Super Contributor
timestamp: May 30, 2011, 12:49:10 am
content: The downside of using X10 Oscilloscope probes with a frequency counter is reduced signal level into the counter,so that if youare looking at a fairly low level originally,it will be below the sensitivity of the device,& you will get false readings.One answer to this,if you have an analog Oscilloscope which gives you access to the output of one of the vertical amplifiers,isto use the 'scope as an adjustable buffer/preamp.This has the advantage that you can examine the signal waveshape at thesame time.Of course not all Oscilloscopes have this capability,& I have often thought that a good project would be a "stand alone"preamp/buffer for frequency counters.This could be done either by building it up from scratch,or modifying a vertical plugin from a Tektronix or similar Oscilloscope.VK6ZGO