Adjusting frequency counter to match WWV - Page 1
Forum section: electronics / testgear

author: Aaron D. Parks
author_rank: Contributor
timestamp: December 16, 2014, 02:31:17 pm
content: I had a suspicion that the oscillator in my RD 1992 frequency counter might be out of whack (that's a technical term). I remembered seeing a video by W2AEW about using a SSB receiver to adjust an oscillator to match the 10MHz carrier of WWV. So I did that, and it did turn out to have been quite far off.I thought it would be cool, though, to see the WWV carrier on a scope along with the oscillator output like in EEVBlog #457. With that idea in mind, I undertook to design and build a receiver (really just a filter and amplifier). It came out pretty well, so I thought I'd share a video about it.I'd be curious to know if anyone else has done something like this. I seem to recall some kind of commercial product that had an oscillator disciplined by a radio signal, but I think it might have been WWVB, not WWV?I think I've heard that over-the-air frequency transfer is less accurate at HF (WWV) than LF (WWVB). I'd love to know what the causes are, but a quick search didn't reveal a satisfactory answer.It was just a quick one-off for this particular project, but I'd still be interested in feedback on the design.I also welcome feedback about the video itself. I'm still a bit new to this style of video and working to improve my technique. Feedback helps.

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2014, 03:21:37 pm
content: Quite liked that. Here half way around the world I can get a very noisy WWV all the time, though at night I get a clearer one and occasionally WWVH overlaid with it. I can also see my receiver oscillator is 1kHz too high, as the zero beat is at 9.999MHz. But not bad for a PLL with an unheated crystal.Even now with a daylight path all the way, and an antenna that is not quite the best for this band. 5MHz and 15MHz though is no signal at all in the noise.

author: aroby
author_rank: Regular Contributor
timestamp: December 16, 2014, 04:18:27 pm
content: Very nice. I like the overall video style, especially seeing the circuit diagram in very readable form. A block diagram would be useful to visualize the various pieces. Obviously lots of patience putting that together!

author: Rigby
author_rank: Super Contributor
timestamp: December 16, 2014, 04:38:41 pm
content: Yeah, what software did you use for the schematic? It looked great.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 16, 2014, 05:45:49 pm
content: Quote from: SeanB on December 16, 2014, 03:21:37 pmBut the modern GPS system provides similar functionality that is sufficient for most home users.Unless you are operating a calibration lab at home in which case you probably wouldn't be asking about cal reference standards in this forum.Inexpensive GPS receiver modules provide frequency reference outputs that are synchronized to the satellite signals.

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2014, 06:18:01 pm
content: They do work, but using NTP servers and synchronising the PC clock works just as well, less than a second difference between PC clock and WWV here, and if I connect the cheap GPS module it also agrees, though there I have to manually parse the NMEA data stream to get the time to compare.

author: Aaron D. Parks
author_rank: Contributor
timestamp: December 16, 2014, 09:06:24 pm
content: Quote from: SeanB on December 16, 2014, 03:21:37 pmThat's cool to know! Sometimes I can hear WWVH here too. The announcements are on opposite sides of the minute mark, so you can hear both of them.Quote from: aroby on December 16, 2014, 04:18:27 pmQuote from: Rigby on December 16, 2014, 04:38:41 pmYeah, I thought about also doing a block diagram. It sounds like I should have. Thanks for the feedback!I used Adobe Illustrator. It doesn't have any of the helpful things a schematic capture package would, but for presentation it's hard to beat.

author: KD0RC
author_rank: Regular Contributor
timestamp: December 16, 2014, 10:41:58 pm
content: Nicely done Aaron!Here is a link to a thread about calibrating the Rigol DSA 815 directly from WWV (it looks like you have a Rigol 815 or 1030 on your shelf...).https://www.eevblog.com/forum/testgear/tried-a-new-method-for-calibrating-a-rigol-dsa-815/msg396134/#msg396134Here is a link to a YouTube video that I did about ithttp://youtu.be/E82NL086VrEOne thing you can do if you get the spectrum analyzer properly calibrated is to take the 10 MHz sig out of the SA and beat it with your oscillator (or just measure it with the SA). I think you can count on getting within a Hz using techniques like this.Adding your amp to the input of the SA should yield really good results, and would be interesting to see if you feel like making another video...Len

author: Aaron D. Parks
author_rank: Contributor
timestamp: December 17, 2014, 02:06:21 am
content: Quote from: KD0RC on December 16, 2014, 10:41:58 pmThanks, I really enjoyed that!I'll give it a try tomorrow.A convenient way to compare the oscillator frequency in the SA to the one in frequency counter is to use the frequency counter to measure the reference output from the SA.

author: Aaron D. Parks
author_rank: Contributor
timestamp: December 17, 2014, 04:01:21 pm
content: Quote from: KD0RC on December 16, 2014, 10:41:58 pmI gave it a try. The receiver output is designed to drive a high-impedance scope probe, not a 50 ohm load, but it was still able to provide about 50dB of gain.From it's own internal counter, it looks like the SA oscillator is within a couple of Hertz.Using the oscillator in the frequency counter that you saw me adjust in the video as an external reference for the SA gives some improvement.I measured the 10MHz output of the SA with the frequency counter from the video: 10,000,000.79 Hz and quite stable.