That's one of my EPROMs. I bet it's just got some oxidation on it. The sockets never go bad, but do come unsoldered due to board flexing over time, as they are surface mount. I'd reflow it. Also discord noises in the background, kek. It's IRC for people to dumb to figure out IRC.
Nice video, but I have couple of notes. 1. You really should have a proper heatsink on the RbO base plate. The base plate temperature should be somewhere around 30-38 deg. C (mine is currently operating at 33 deg. C with passive heatsink). 2. Personally, I am not sure that the idea to put RbO inside the GPS loop is a good idea. I am certainly no time/frequency professional or academic, but I had a rather long e-mail discussion with Brooks Shera (the man, who basically invented the idea of GPS pacification of OCXOs back in 1998) in summer 2000 about this aspect. And his opinion was that RbO is much better to be left alone as a free running frequency normal with excellent short term stability and that the "kicking" of RbO with 1PPS can only make things worse, especially if the time constant of FIR filter is not long enough (typically days or weeks). Same thing is valid when it comes to external steering by some component. Either the multi-turn potenciometer or some DAC. The thermal stability of those components is almost always much worse then the thermal stability of the RbO module without any external stimulus. 3. In my home lab, I am using GPS pacified OCXO (an old HP10811A) with Motorola OnCore UT+ (in position fix mode) built according to the Brooks Shera design - www.qsl.net/n9zia/wireless/QST_GPS.pdf for almost 25 years with only one interruption in 2002 (floods in Czech republic) and even today, the precision is really good. But the short time stability is not so good. So, if I want to measure something with better short term stability, I simply switch on my RbO, wait 3-6 hours or better to next day and do measurements. After this, I switch my RbO off until next measurement. RbO is not like OCXO and it does not need to be switched-on without interruption for decades. It will not become better after ten or twenty years, like good red wine or OCXO. :)
I just checked my data and during last comparison (approx. two months ago) and the difference between my free running RbO (overnight time to stabilise) and my GPSDO was only 20ns in 158 seconds. It means only 0.126 ns or 126ps per second. Because it is only relative measurement, I am not able to say which source is "right". I have neither hydrogen maser nor a cesium fountain at home. But both sources are good enough for my all purposes. BTW, the GPSDO is an old, vintage Brooks Shera design with original PIC program. My only modification was using one isp1032 Lattice CPLD instead of all those counters in original design to save space on PCB. Pretty good result for a 25 y.o. box which is silently working on the bench since 1999.
Great video! The attached article is well worth reading. Very similar to calibrating scope probes to your scope with the internal 1 Khz square wave oscillator. W2AEW has a great video on that. I like your style of videos and the way you show your mistakes as well. Also, along with it's intended purposes, a $10,000 service monitor is a GREAT table for storing junk on. Merry Christmas, happy holidays, 73's and all that garbage too.
Cool video! I played around a lot with Rubidiums back in the day when the FE-5680As were cheap and plentiful on eBay. As you know and mentioned, the more references you have, the less sure you are about which one is right. :) Rbs aren't perfect, with good enough equipment you can measure the drift and other weirdness that they exhibit, it's just further down in the noise of most people's test equipment. Getting that hooked up to your GPSDO, especially if you put it on a UPS to ride through power outages, should net you really nice long term stability. The OCXO version of your reference might still be useful if it ends up having lower phase noise. I'm looking forward to the follow up!
I have a similar rubidium oscillator and that also lost sync from time to time. When I attached a heatsink and addad a blower to keep the case cool, it didn't do that anymore. Just make sure the cooling is not too much or the heater will have a hard time...
what a fascinating video. i have now learned some things. thank you sir. i will hit that subscribe button. hmm my thoughts are that the drift is too much. the rate of rotation of that circle is pretty fast. my thoughts are that a magic cesium clock and gps satellite would not be off by that much. a little bit yeah but not that much
Hello. I have the same model of oscilloscope. It is much better and precise to use 1 and 3 or 2 & 4 channels at the same time. Because of internal architecture of this model of SIGLENT. When you use 1&2 (or 3&4) channels at he same time, ADC works in interlive mode and the real sampling rate is two times lower.
6:50 A-ha! That was on my mind since the beginning of the video - a useful bit of information there, saving us the trouble of finding out ourselves. I guess that makes buying a second hand one a gamble then.
Just a thought. There should be a C-Field trim to bring the frequency in. The hyperfine transition is influenced by the magnetic field and so the C-field trim compensates for this. That will likely be the external trim voltage you will be using your GPS disciplining board to control.
5:39 That is not the antenna, it is half of the antenna. The other "half" is the radio chassis and some capacitive coupling to your hand. As a result, the antenna is a specific length to marry up with the size of the chassis and the expected capacitive coupling effect. A wet piece of string will pick up RF, so not such a big deal, but I wouldn't expect a random stubby from another radio to work well on something with a totally different sized chassis. On the Moto DMR gear, you can drop into a service menu to see the RSSI displayed in dBm (not sure about the Kenwoods). Press the left navigation key 3 times, followed by the right navigation key 3 times. Try it - then swap antennas around whilst recieving a repeater (fixed signal). You'll see the RSSI change by a couple of dB with the "wrong" antenna.
A 50 terminator will definitely help clean up your waveform. My eBay FRS (an even older model) was pretty funky running straight in to the high impedance input of the Oscope. With the termination it was perfect. BTW, back in the '70s I used to work with the HP Cesium standard as shown in the video and have used various Cesium and Rubidium standards over the years.
WHEN KENWOOD PRODUCES DMR.. I’m buying it. I have missed Kenwood !!! Come back Kenwood to amateur radio HF/VHF. I want an all mode Kenwood Radio. VHF/UHF/HF.
You're thinking of toy radios. Kenwood radios already do DMR; the NX/VP line is the first and currently only radios that do multi-digital mode: P25, DMR and NXDN.
Getting some cheap chinese 50 ohm in-line terminators for your scope might be a cheap investment. Will they be flat, capacitance-less response up to 1Ghz? lol no. Will they do the job for 99.9% of cases up to 100Mhz? Yeah. That slow of a lissajous plot for a 20 year old, completely free-running, clock is amazing. Atoms, man.
The external trim is there to take care of the last few decimals of error. A stable voltage there, whether from a GPS disciplined servo, or just days of manual adjustment, should get you to (or near) the rated accuracy. You may need to do some tweaking of the servo coefficients on the GPSDO board to better suit the stability characteristics of the Rb relative to Quartz oven.
Thats cool, super high precision, 10E11 available. A practical use of what such a Rb frequency standard is for, if anyone is interested: In the last millennium, at the end of the '80s, I built my own DIY NMR device. With this, I was able to determine the material composition with hyperfine resolution in a test tube. This required a frequency standard, but the thermally stabilized Quartz oscillator, the 10E-9 OXCO was scarce, then I found that such a Rubidium Oscillator Standard exists, but it was prohibitively expensive. My idea was much cheaper: it is possible to get to a frequency standard, from the GPS signals, somehow extract the signal, because I knew that they emit a highly accurate atomic clock-based signal. It worked. An Operational Amplifier with very accurate phase noise is the essence. I only made 1 piece as a sample for a science demonstration, I didn't make a product out of it, now anyone can build it for themselves, the idea has become well known. Years later, many others began to manufacture and distribute them. It's GPSDO today and it's a huge thing, that today it is possible to do this even with an amateur wallet. The only problem with this is that if there is no GPS signal, our equipment does not work, so the Rubidium Clock is better for spectrum analyzer as a reference point 10MHz source oscillator. The coveted desired Rubidium-Vapor Discharge Lamp, Rb Glass Cell luckily I can made DIY, so I started to build such a Rubidium clock, but it wasn't finished, instead I used the Rubidium for something else: It became the hypersensitive magnetic sensor of the NMR device. I measured the spin response of the molecules to be determined, so that a laser beam must be passed through the rubidium glass tube placed in the magnetic field to be measured, it changes the polarization properties of the laser beam and we can easily measure it. I'm not a radio operator, but (I learned Morse code and radio as a child) 73
I used these in a positioning system called Starfix. Starfix was a positioning (navigation) system that was designed for providing precise positioning information for offshore work in the Gulf of Mexico. It was similar to a differential GPS system but we used geosynchronous satellites and put up our own spread spectrum signal. GPS was not available at the time. As I remember we built 62 systems. They were great little oscillators, very low phase noise. I still have an Efratom FRT in my lab that has been running since 1987.
Were those made before people realized that general relativity needs to be compensated for? I’ve always heard stories that the first attempts at satellite positioning had accuracy problems relating to forgetting that you’re dealing with relativistic dilation
@@markhaus The relativistic problems were anticipated very early in the development of GPS. With Starfix we did not have that problem because our clocks were all on the ground, not flying clocks as in GPS.
I've long wanted to build a 10MHz Rubidium frequency standard for my lab, but the formerly plentiful modules from the old GSM stations have turned rather rare by now, and usually go for 250$+, which just isn't worth it for me anymore.
I repaired some rubidium oscillators in the 80s. They were pretty accurate. (10E-11 if memory serves) We compared them to national standard broadcasted during a few hours (they were 10E-12 or -14 at the time. I’m not sure)
Yeah, we get better than 10E-11 on the rubidium we have at work and it is around 20 years old. Every four years (or thereabout) it requires some adjustment from the front panel (C-Field).
I built a totally digital GPSDO/NTP server around an Rb (Symmetricom X72 or SA.22c - now owned by Microchip, by way of Microsemi) some years back. It did all of the PLL stuff in software, using the Rb's digital frequency adjustment, and it output a whole bunch of stats over the network so you could monitor it in real time. I got the control loop dialed in real nice and it worked great. Ironically, I built it before I became a ham, and disassembled it shortly after becoming a ham, because I'm terrible at hardware design. The thing had RF (10MHz and some other frequencies) flying around all over the place on unshielded wires, and it was in the same room where I was building my HF shack, so I had to kill it to get rid of the interference! For a long time I've wanted to bring it back in a better version without the random mass of wires, but learning PCB design is on my "maybe someday" list.
I started out with an FEI 5650A but I decided that trying to use a DAC to digitally control an analog tuning input wasn't my cup of tea. Too many unknowns and nonlinearities for me.
Your FE5650A didn't have an RS232 port on it? The only way I found to tune the ones I had was over serial, although FEI were famous (notorious?) for making a wide range of products with disjoint feature sets but the same P/N @@hobbified
@@aftbit it was a real "project" device so it changed over the years, but the nicest version was: an Arduino Due clone board (ATSAM3X8E CPU), the X72 connected to external timer inputs, a uBlox M8T GPS, and the uBlox set to timestamp a PPS coming *out* of my board, which offered a bit more resolution than having my board timestamp the GPS's PPS. A 32-bit timer could handle counting up to 10,000 trivially. The timestamp offsets were fed into a dual FLL/PLL (which I think of as the P and I of a PID loop only with a time derivative thrown in), with adaptive time constants so that it would run low tau at startup when still warming up, and increase up to tau=3 hours once stable.
