1 MHz frequency standard? - Page 1
Forum section: electronics / general

author: Chris Wilson
author_rank: Super Contributor
timestamp: March 19, 2012, 07:55:08 pm
content: My Racal-Dana 9908 frequency counter / timer will accept an external frequency standard, but only a 1 MHz unit. Most of the GPS and Rubidium based ones seem to be 10 MHz, Is there a cheap commercially available divider "thing" to give a 1 MHz signal from a 10 MHz source? I would rather buy something than wonder if a home made creation was working correctly. The whole idea is to have a known working and accurate piece of test equipment, without doubting its accuracy. Thanks.

author: wkb
author_rank: Super Contributor
timestamp: March 19, 2012, 08:59:11 pm
content: Well, if you put a simple 1:10 divider between the Rb oscillator and your counter your are in business.

author: Chris Wilson
author_rank: Super Contributor
timestamp: March 19, 2012, 10:01:36 pm
content: OK, will Google this, I take it the accuracy of the signal is not degraded at all by doing this? Thanks, may have more questions though ;( Sorry!

author: Rufus
author_rank: Super Contributor
timestamp: March 19, 2012, 10:25:12 pm
content: Quote from: Chris Wilson on March 19, 2012, 07:55:08 pmAre you sure it is worth doing? How many display digits has it? The 9908 seem to be a bit rare.Will feeding it a frequency standard really produce different readings compared to its own reference with occasional calibration?

author: ejeffrey
author_rank: Super Contributor
timestamp: March 20, 2012, 12:31:15 am
content: Quote from: Chris Wilson on March 19, 2012, 10:01:36 pmIt won't degrade the accuracy of the 10 MHz ref. A frequency counter that operates with a 1 MHz timebase is going to be less accurate one that uses a 10 MHz reference, but there is nothing you can do about that. On the other hand I don't know of any off-the-shelf frequency dividers that aren't more expensive than a new counter. DIY is super easy, but I still wouldn't recommend it to someone who isn't comfortable with that.In any case, I agree that it may not be worth it. It depends on what you are measuring and how good the rest of the electronics in there are. If the internal oscillator has aged you may be able to calibrate it. If not you can just drive the external input with an ordinary crystal oscillator.In any case, the first step should be to figure out how accurate it is right now. If you have any kind of device with a known frequency output you can just measure it for a week or two to get an idea of the offset and drift.

author: bingo600
author_rank: Super Contributor
timestamp: March 21, 2012, 07:48:57 pm
content: A 74HC390 should do the job/Bingo

author: saturation
author_rank: Super Contributor
timestamp: March 24, 2012, 11:52:05 pm
content: You'll need to convert the references sine wave output to square, then apply a divide by n counter or get something like this premade:http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320874664707

author: Chris Wilson
author_rank: Super Contributor
timestamp: March 25, 2012, 12:35:33 am
content: Thanks for the replies. I have had an idea.... Not always a good signWhat if I run my Marconi 2019A frequency generator from a Rubidium or GPS standard? It takes a 10 MHz external standard input on the rear panel. Then feed its output into the frequency counter? Does that degrade the accuracy compared to running the counter on a 1 MHz external frequency standard, or calibrating it directly against one? I probably DON'T need this level of accuracy, but would like my test gear to have some sort of in house reference to check against, and these standards are now not exactly hugely expensive. The divider board board looks ideal if I have to do things that way, thanks for the link saturation!

author: saturation
author_rank: Super Contributor
timestamp: March 27, 2012, 02:10:49 pm
content: If you can discipline the Marconi with a better external oscillator, you'll have more stable output frequencies. If the Marconi's output is faithful to a simple divide-by-n counter on a Rubidium clock, without introducing its own internal drifts, the accuracy should be as high, if you can detect it. What matters is the resolution of your counter. To detect the variation of a Rubidium clock, requires a counter to resolve a change at 10^-13.The actual frequency of a Rubidium clock is somewhere in the 6 GHz range. That disciplines an internal oscillator in the commercial package you buy to give an output of 10 MHz, which is a frequency standard, why 10 MHz is, I forget. I think it was arbitrarily selected during the early days of radio.Quote from: Chris Wilson on March 25, 2012, 12:35:33 am

author: lowimpedance
author_rank: Super Contributor
timestamp: March 27, 2012, 11:22:00 pm
content: Check out this pdf from J R Miller regarding his 10mhz GPS reference and his design of a post ref divider (at the bottom of the PDF page 6) which uses common cmos logic IC's and can accept a sign wave in to provide a number of useful logic level +5v divided frequencies out including 1 Mhz.Not a micro in sight.http://www.jrmiller.demon.co.uk/projects/freqstd/manual.pdf

author: radiomog
author_rank: Regular Contributor
timestamp: January 09, 2015, 04:40:55 pm
content: Quote from: lowimpedance on March 27, 2012, 11:22:00 pmBrilliant! This is what I need, having a mix of 1,5 and 10M based gear.I'm going to go about getting some boards made up (If I can not find them). maybe put together a few for others.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 10, 2015, 03:58:55 am
content: What happens if you overclock it by giving it 10MHz?

author: KJDS
author_rank: Super Contributor
timestamp: January 10, 2015, 12:40:03 pm
content: The Marconi 2945 uses a clever circuit that works out what input reference frequency from 1, 2, 5 or 10MHz is and divides it accordingly to 1MHz to phase lock the internal reference to it.

author: dannyf
author_rank: Super Contributor
timestamp: January 10, 2015, 12:44:05 pm
content: QuoteA divide by 10 counter would do.

author: dannyf
author_rank: Super Contributor
timestamp: January 10, 2015, 12:46:13 pm
content: QuoteAssuming it works at that frquency, your gate time is essentially 1/10, and your readings are 1/10 of their true value. So a 19.44Mhz signal would read 1.944Mhz now.

author: dannyf
author_rank: Super Contributor
timestamp: January 10, 2015, 12:47:47 pm
content: If you need more flexibility, you can run the 10Mhz through a PLL chip (cdce913 from Ti for example). A mcu can be used to either program the chip offlline or to provide the chip with real time division / multiplier to generate a whole host of output frequencies.

author: Flump
author_rank: Frequent Contributor
timestamp: January 10, 2015, 06:59:28 pm
content: done exactly this for my racal countersource 10mhz ocxoDM74LS9010:1 Frequency Dividerlink1114Vcc (+5)5GND3671010Mhz input11Mhz output12

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 10, 2015, 08:17:25 pm
content: Whilst we are this subject I would like to provide a low phase noise 15.6MHz GPS locked master oscillator for my Kenwood TS-590 transceiver. the stock Xtal controlled master oscillator is on a removable daughter board. Kenwood, (and some Chinese companies) do a low PPM Xtal upgrade, but being into very narrow bandwidth LF stuff I would like the most stable oscillator possible. I have a Trimble Thunderbolt GPS referenced standard, with 10MHz and 1PPS outputs. How could I generate 18.6MHz, locked, please?Thanks!Typo corrected, TS-590 is 15.6 MHz, *NOT* 18.6 as I put originally!

author: dannyf
author_rank: Super Contributor
timestamp: January 10, 2015, 08:23:51 pm
content: QuoteGoogle cdce913. It's a family of such chips.A much simpler solution that will provide performance comparable to your 10Mhz oscillator is to get a 18.6Mhz TCXO. I have a few Toyo 19.44Mhz TCXO (TCO912 I think) that are spec'd to 2.5PPM and all five of them came in within 0.1PPM.So if I were you, I would look into that as an immediate solution.

author: VK5RC
author_rank: Unknown
timestamp: January 10, 2015, 09:51:29 pm
content: A ham vk3hz has made some small pll boards Xref for unusual frequencies, I don't think it covers Kenwood yet but would be easily modifiable.http://www.vk3hz.net/XRef/XRef_Home.html

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 10, 2015, 10:04:41 pm
content: Quote from: VK5RC on January 10, 2015, 09:51:29 pmHim, thanks for the link, I mistyped 18.6 MHz, whereas the 590 is referenced on 15.6 MHz. It appears the TS-2000 shares the same frequency, so that looks very promising. I presume it's better than a TCXO? Thanks again.

author: dannyf
author_rank: Super Contributor
timestamp: January 10, 2015, 10:07:18 pm
content: SI4133 is fairly difficult to get and expensive as well.cdce913, if you simply want to fixed (but programmable) frequency output, is easy to do.

author: radiomog
author_rank: Regular Contributor
timestamp: January 24, 2015, 09:17:44 am
content: Quote from: radiomog on January 09, 2015, 04:40:55 pmI decreased the number of outputs (10(x2), 5 and 1 MHz) on the aforementioned divider and bread boarded it tonight. Using my Fluke 282 AWG, I put in the claimed Po of my GPSDO (+13 dBm). It divides, but the sine wave is not clean. The 1 MHz output was hard for my Analog Scope (2465A) to capture, my HP DSO (54201)was able to, including calculating the Freq.With a little finagling I was able to get my counter to lock on at all outputs. I think the majority of the problem lies in the input and breadboarding wiring vs a short-path optimized pcb.I wanted to proto this for functionality while I worked on the PCB design to have some boards made up and going with SMD's (vs the DIP's). Anyone interested in a more detailed post, let me know, I did take some photos.(thanks again to everyone and their help/input)