pretty good frequency counter

This looks OK.

The B+K stuff is usually pretty good.

I have one I'm not using at the moment. Want me to ship it to you? I expect I can go to a shipper when I go out for groceries tomorrow or the next day. HP 5314-A

I got one last year with the intention of building a usable counter by adding input stages, power supply, etc., but so far have never got around to playing with it.

Get a frequency counter with an external 10MHz reference clock input and use a GPSDO with 10MHz output which you can get for less than $100.

The GPSDO takes a while to stabilise, I just leave it on.

At PPoE we ditched a (cheaper) B&K counter. The problem for us was that it didn't actually give the number of pulses, (or rising edges) in the time window. But it did some sort of unknown averaging, so that though the average number was correct, there was not enough scatter in the count number. (This was for a random source... counting pmt pulses.)

For what you want it may be fine.

George H.

I use an HP 5316 for lower frequency and an EIP 578 for up to 18 GHz. Both cheap on eBay, but don't come with Prime shipping. ;)

Cheers

Phil Hobbs

I bought two on Ebay a while back, but I haven't used them yet. I need to pick up some scrap square tubing the frame screen rooms with for cases.

John, I have bought a couple HP HP 5334B counters with the optional 1.3 GHz inputs for under $100.

The most common options:

Most selers don't know what they have and miss that the units have these op tions installed. They have a 10 MHz input, if you have an in house frequenc y standard. I am working on a GPS derived standard, and some Distribution A mplifiers. They were originally 350 MHz Video DAs that are being converted to 50 Ohms.

We have a high-end GPS source in-house, but it's not run into my office.

In measuring LC oscillator tempco, something stable to 1 PPM for an hour would be plenty good. Any counter with a crystal timebase can do that.

I want to tweak the LC to be +-100 PPM maybe from 0 to 60C, something like that. It will have a varicap pull range of maybe +-1000. It will power up at some frequency, doesn't matter much what, and I don't want it to ever drift out of lock range.

I found a B+K 1823A on Amazon

so I ordered one of them. It has ac/dc input coupling and an adjustable trigger level, so it should be good counting pulses too.

They say they'll deliver to my house on Saturday.

"Frequency" counters are often AC-coupled with a zero-volts trigger threshold. They count sine waves fine but are terrible with pulses. For pulses, you need DC coupling and a settable trigger level.

Yeah. For pulses it's really nice to have a discriminator where you can see the input and output to set the threshold.

George H.

I investigated the input stages of a good HP frequency counter, because the cheap one I have is not very reliable, and was quite surprised what I saw.

There is a huge amount of attenuation first (presumably mostly for protection) followed by lots of amplification - three stages of differential ECL or something, I think.

I guess the attenuation ensures that the first amplification stage stays linear, and the amp provides progressive compression ala a log-amp, which (it seems to me) should be much better than just zero-crossing detection. I couldn't see any sign of AGC leading up to the (clamped) output.

Does that make sense?

Clifford Heath.

Yes, I have two, one mounted in a little case with a USB power pack. The module is a clone (from multiple suppliers) of a *hobbyist* project, and it shows.

The inputs are not very sensitive, and the zero-crossing detector is not very reliable. If you have a clean signal with adequate and fairly constant strength you can get a stable reading, but otherwise the readout will wander around or just lie to you.

The 2.4GHz and 60MHz inputs are both wired to the same input. They work better if you separate the two inputs. That's a little awkward, because you have to cut and paste a PCB trace that's sandwiched (near the edge) under the LED.

They would be just fine with a better input circuit. Buy one with a TCXO.

Clifford Heath.

Makes perfect sense. The log amp approach prevents the threshold from changing on the scale of the AGC bandwidth--it responds cycle-by-cycle.

The attenuation of course introduces jitter, but you usually don't care much in a counter.

Cheers

Phil Hobbs

Does your oscilloscope have a counter? I do not hink I have actually ever used a frequency counter. Between having a spectrum analyzer and O-scopes that can measure frequency I have never needed one.

Am 01.04.20 um 18:35 schrieb Phil Hobbs:

I have just sold this one, never used in > 4 years:

It can do a lot of stunts that normal counters cannot.

But I will never ever let the Timepod go or the Stanford SR620.

I still have a HP5473, but it is just an array of intermittent contacts. Takes up valuable rack space. I have already removed its 10811A time base oscillator.

cheers, Gerhard

Yeah, I have a 5372A with the jitter FFT option. A great instrument for looking at PLL settling and so on, but a big pain to set up, so I don't use it much either.

Tally-ho

Phil Hobbs

Oooh, way to go, I understood something tricky, the first time, without bumping my head on it :)

The guy who designed these counter modules went through lots of iterations to come up with his dual-gate MOSFET setup that still doesn't work very well. I found the Chinese forum where he posted (and got feedback on) his earlier versions, and read much of it using Google Translate.

Someone should clone the design but replace the input with a log-amp... What's the best chip for that these days?

Clifford Heath.

Am 02.04.20 um 04:08 schrieb Clifford Heath:

Get the service manual of the Stanford SR620 or HP 5473. (not log)

cheers, Gerhard