Hi, Yes, it's just another quick video on this Rubidium standard and frequency counter because Nitro 2001 on the A forum EV blog Forum A user on there asked what happens if we feed the Ridium reference external input up the frequency counter's own clacker. Well, that's exactly what I got. Would it read precisely 10? Well, TDA let's try it. Yes, it does.

All I'm doing is feeding the 10 MHz uh output of my Rubidium standard into the external input. You can see it says external reference there and I've set it to um 12-digit mode. and yes, it is absolutely bang on. And as I mentioned in the Uh Forum post, it doesn't have to be a Rubidium.

so let's try a few variations of this. It doesn't matter what frequency you put in there, it assumes in in the external reference, it assumes that it's precise l a 10 MHz reference. So that's why we're reading precisely 10 and um, he also wanted to know what happens if we add some extra coax on here. I don't have a huge amount of coax, but I'll add a little bit more just to add a little bit of Delay from the external input.

As you can see, I've got one here. It's maybe a meter long and it doesn't matter a rat's bum. And what I've done here is added another uh meter on there. so we got about 2 m of coax there and uh, because I've got it set to 12-digit The gate time is I don't exactly know how long it is I'm timing it now.

it's been uh 22 seconds already and uh, still hasn't done it. but we'll come back when it's uh done and see what we get. and I mentioned on the Forum that you could be possibly plus minus one uh, least significant digit out there depending on how the counter's designed, how all things are clocked, and uh, stuff like that I mean I won't go into Um architectures of various modes of how frequency counter works works right here, but come on. 50 seconds? Hey, there we go.

Bang on 10. MHz Not a problem. So instead of the uh, Rubidium standard What? I'm going to be a bit cheeky and I'm going to uh, feed the output of the internal oscillator in here that crappy 10 mahz Stock oscillator to the external reference input and to the input of this. So it really is feeding up its own clacker right about now.

So let me plug that in and uh, see what we get because we should read always precisely 10 Let's uh, wait for that to redo it. We'll just go back in there and we'll select the that and we'll go back in and it'll reset and we should find it'll still be 10 even though that frequency is not spot on. 10 MHz Because it just the counter is assumes it is precisely absolutely without question: 10. MHz And bang There It Is Folks, Spot on Precisely 10 even though it comes directly from the output here and from the internal counter itself.

so it's feeding itself and no, look, there's no. there's no funny business going on there, folks. It really is. uh, looping back and feeding itself.

There's the Uh output there, the 10 MHz crappy internal oscillator output going to the external reference in there, and uh, to the input. Not a problem. and while we're at it, just for a bit of fun I thought I'd Just uh, calibrate my old uh Phillips frequency counter here too. and uh, because it's got the oven oscillator.

You've seen this in the uh, tear down before. it's the PM 9690 um 01. It's an ovenized oscillator. It's uh, pretty.

Schmick and uh, as you can see, I'm not sure why the waveform out looks like uh, that out of this thing, but uh, it's not the greatest. um, but it does have the adjustment part on here, so let's it should be much finer adjustment of course than the other one. See if I turn it I'm turning multiple. This one looks like it has actually a proper Trim podt in it.

It feels like it has a a proper trim pod of course. I've let this, uh, warm up of course. very important when you're doing this sort of stuff. Although you know it is oven ovenized.

um, you still have to let it warm up. and if I keep dialing the other way it goes back. but yeah, much finer adjustment range than we were get in last time and it's really, you know, we practically bang on there. I Mean there's no movement in that waveform at all.

You know there's going to be some there going to be a little bit of drift in there, but uh, can't really see it so it's pretty darn spot on. And for you fans of the Lous pattern there it is. you can see some see a slight bit of movement on that. Of course you can see it closing in and if we switch back to uh, the um regular time mode probably be able to see that drif in there as well.

Yeah, very slight. I Can just see that tiny little drift in there. give it one last tweak taada. All right.

What I've got now is no Rubidium at all. just using the internal oscillator, not using it, not connected to the external. You see, there's no external uh signal there, so just the internal oscillator out the crappy one into up its own orifice. There it is.

and yeah, it's going to be almost spot on. 10. it's that plus minus one digit I was telling you about and of course we can go in there and um, increase uh, the digits on that. So let's H it's bloody weird operation this.

so let's give that say eight digits and go back there. We go bang on 10 so only at that lower one, uh, that lower count. is it actually problem? So I mean if we go right down to something like three, that's pretty silly. Ah, there we go.

10. So maybe like maybe that would had a sweet spot there that H Bloody hell, how do I do this again? Weird. So let's go up to four. Let's let's try them all.

Shall: We There We go bang on. Let's try it again. Five, We're bang on again again. Is it going to make a full full out of us? Let's uh, try that six digits and no, we're bang on.

So we were getting that one one least significant digit flip-flopping before I Think we were on seven weren't we? We were one more than that. So let's have a look at that. Let's try them all. no eight digits and uh, we're bang on again.

Not a problem. So we were getting the uh one bit. uh, flip-flopping before, but now we're not. It's bang on.

Gate time will take a few seconds for that. maybe 10 I don't know. Come on there. we go bang on.

So maybe if we actually put that back to auto for examp, hang on. How do we digits we want? Let's put it on auto Shall we? Let's try that? There we go and we get a bit of flip-flopping there on auto mode, but we don't get that on the um, fixed uh number of digits instead of the fixed art gate time. And let's actually set the gate time to some Oddball value I Don't know 914 seconds or something like that. Let's give that a go and see what happens.

No, we are bang on so thanks Nitro 2001 I Hope that answered your question of what happens when a frequency counter reads its own reference clock. Not a problem, it's bang on worst case. Plusus one least significant digit. If you want to discuss this, jump on over to the Eev blog Forum that's the place to do it.

I Won't promise there'll be no more videos on this, but you never know. Catch you next time. Oh, by the way I Found the schematics for this thing on the Agilant website. Yes, you can just download them so the link will be down below.

Check it out if you want to see the schematics for this puppy.