EMRFD Message Archive 12909

Message Date From Subject
12909 2016-06-04 18:22:01 gamma_function Which probes for frequency counter?
Hi all-

I've just acquired an HP 53131a counter and would like to know what kind of probes would work best for building and testing VFOs in the HF range and for exploring chapter 4 in general. On my device the inputs can be set to 50 ohms or 1M ohm.


12910 2016-06-04 19:25:27 Jim Leslie Re: Which probes for frequency counter?
For most projects, my scope probes work well on my 5334A. I also have a simple cable with alligator clips on the end but rarely use that.

12911 2016-06-04 19:39:05 vasilyivanenko Re: Which probes for frequency counter?
See  http://lea.hamradio.si/~s53mv/counter/probes.html

I've got that counter.

For AF - HF and even lower VHF  -- whatever works to a point. You just need enough signal to trigger the counter's front end which for a sinusoid is ~ 20 mV rms up to 100 MHz and about double that to trigger as you move closer to the maximum 225 MHz bandwidth in Channel 1.

For VFO measures, you want to avoid disturbing the tank circuitry and changing its frequency, so build the buffer and measure at the buffer's output.

I often connect a (temporary) BNC connector to my 50 ohm output Z circuits and run a 50 ohm coaxial cable with BNC ends directly to the counter with it set it 50 ohm input mode.   Further, you can use the same 50 ohm output with any 50 ohm detector to measure voltage, or power, etc.

Many of my [homebrew] signal generators feature a dedicated counter BNC output that runs a separate buffer
consisting of a common base amp driving an emitter follower with low Z output for patching with a coax cable to the counter set in 50 ohm input Z mode.

For higher impedance, measures from AF to HF,  I'll often just Use a 10x 'scope probe with the counter input set for 1M input Z.  Need enough signal since the 'scope probe will attenuate per usual.