FE-5680b 1pps to 10Mhz - Page 1
Forum section: electronics / testgear

author: Bryan
author_rank: Frequent Contributor
timestamp: August 07, 2014, 08:21:02 pm
content: All:Occasionally see these rubidium oscillators with a 1pps output ONLY . Has anyone successfully been able to hack or modify it to output a 10mhz output. Not sure if the output of 1pps is derived from firmware or perhaps just divided down.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 07, 2014, 08:55:29 pm
content: Hi Bryan,The 5680s are a royal PITA. There are many different versions with many different options. Some have 1 PPS or 10 MHz or both. Some are programmable, some aren't. Some require 15V, some also need 5V. Some have EFC, some don't.If a particular unit is advertised as programmable, it is possible to change the frequency to 10 MHz, but it requires a little hardware hacking. The ones that output only 1 PPS take a frequency of 8.288608 MHz and put it through a fixed divider to get 1 PPS. You can reprogram that frequency so that it puts out 10 MHz. Of course, that blows the 1 PPS way off frequency. I have one that works like that. You then have to bring the 10 MHz signal out via a coax. Start googling. There's lots of info out there where people have done similar hacks.EdP.S. There's a couple of Trimble Thunderbolt up for sale on ebay that have a red label. Don't buy them! The red label units don't perform nearly as well as the plain units. Apparently the plain units were built with a better quality oscillator to meet the requirements of cellular carriers. The red label units also tend to be much pricier than the plain ones.

author: Bryan
author_rank: Frequent Contributor
timestamp: August 07, 2014, 11:09:13 pm
content: Well the seller is apparently quite knowledgeable with teh GPS items he sells and he can't figure it out so probably not a easy hack. With regards to the OCXO, this site does a comparison, and I believe the red labelled ocxo is referenced.http://www.ke5fx.com/tbolt.htm

author: edpalmer42
author_rank: Super Contributor
timestamp: August 08, 2014, 02:53:37 am
content: Did you buy one of those 1 PPS units? If so, you'll just have to wait for it to show up to see what you ended up with. I got mine some years back and got lucky. Hopefully, you will too.Regarding the Thunderbolt, I was actually referring to the red labelled Thunderbolt. I didn't realize that the OCXO also had a red label. But the phase noise graph certainly shows the difference between the 'old' red labelled Thunderbolt and the 'new' plain version.Ed

author: Bryan
author_rank: Frequent Contributor
timestamp: August 08, 2014, 05:52:03 am
content: No, I ended up buying a Trimble GPSDO re branded for Nortel. I hope it works well. Not a standard size, but for the price I couldn't do better. Looking around for a decent priced Rubidium that I can "discipline" with the GPSDO.

author: Bryan
author_rank: Frequent Contributor
timestamp: August 08, 2014, 04:12:42 pm
content: Quote from: mojo-chan on August 08, 2014, 11:01:31 amWould you mind sharing on how you hacked it at least for the 10Mhz output.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 08, 2014, 05:04:18 pm
content: Quote from: Bryan on August 08, 2014, 05:52:03 amI've seen those, but never played with one. What kind of antenna do you have? Have you discovered Lady Heather? You'll like Lady Heather. She's into discipline.Ed

author: dannyf
author_rank: Super Contributor
timestamp: August 08, 2014, 05:19:59 pm
content: QuoteA 1pps signal is a 1hz signal with very low duty cycle: the output is high typically for 1-2us and low the rest of the time.When you divide a high frequency signal, you get a 50% duty cycle signal - in this case, high for 0.5s and low for 0.5s. Not exactly a 1pps signal.You can, however, use other circuitry, sometimes as simple as a capacitor, to derive a 1pps signal from a 50% duty cycle 1Hz signal.

author: Bryan
author_rank: Frequent Contributor
timestamp: August 08, 2014, 06:58:19 pm
content: Quote from: edpalmer42 on August 08, 2014, 05:04:18 pmI have not sourced an antenna yet. Any suggestions. I believe any GPS timing antenna, either passive or amplified, would work.? Yes Lady Heather I have downloaded, but not sure if it will work with the board, haven't really looked into that aspect of it yet.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 08, 2014, 11:19:55 pm
content: The traditional timing antenna is one of the bullet or cone shaped ones. I think a timing antenna has more filtering than a navigation antenna. Not totally sure about that. You definitely want an active antenna. Most of the GPSDOs that show up for auction are 5 - 10 years old and are a bit deaf by modern standards so they need lots of signal. Don't buy an antenna unless they state what the gain is - e.g. 26 dB unless you can find a data sheet. Check your GPSDO to see what voltage is running up the antenna cable. Older systems are usually 5V, newer ones are 3V3. Strange ones are 12V. The antenna has to match that voltage. I see some cheap mushroom-shaped timing antennas for sale. I don't know anything about them. If you have or can borrow an active patch antenna give it a try - won't hurt (as long as it's the right voltage).Lady Heather should work with your board. I think you've got one of those NTGS50AA units.Ed

author: Bryan
author_rank: Frequent Contributor
timestamp: August 09, 2014, 01:17:36 am
content: Any recommendations for the gain. I have seen on eBay most are around 20db to 26db gain. I did manage to find what I think is a manual for the GPSDO and yes it appears to be a NTGS50AA. It says the antenna outputs +5v on the center pin, so pretty sure a 3.3-5v timing antenna will do. I think something like this should dohttp://www.ebay.com/itm/NEW-PCTEL-26db-GPS-TMG-26N-GPS-Timing-Reference-Antenna-/291208295462?pt=US_Ham_Radio_Receivers&hash=item43cd5df426Did see some posts about on the board using Lady Heather, seems a bit of fiddling is required and the recommendation is too get it working with the Trimble software first.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 09, 2014, 04:23:18 am
content: Sorry Bryan, but I'm not sure how much gain you should use. In your case - north facing, right? - you'd think that more gain is better, but you could have a lot of multipath. More gain will just make that worse. 26 dB is not really high by timing standards so that might be okay. I've seen antennas with 38 dB gain. Do you have a little patch antenna available that you can test with before you buy a good one? That would tell you how deaf your receiver is. Maybe it needs all the gain you can give it just to get a good signal. I don't suppose you're on the top floor are you? I am and I can get a decent signal through the roof with a good antenna.Ed

author: Bryan
author_rank: Frequent Contributor
timestamp: August 09, 2014, 10:44:30 am
content: Ed:Yes, facing north on a bottom floor condo in Vancouver. Holding my cell phone out the window I can pick up 3 satellites (GPS Logger II), so think I should be ok with a decent GPS timing antenna. May as well just order one of the 26db ones, cheap enough and if it works great, if not then going to go with another option.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 09, 2014, 05:24:43 pm
content: OK, sounds good.Don't forget to get some cables and/or adapters to connect to the board. The RF connectors look like SMB.Good luck,Ed

author: Bryan
author_rank: Frequent Contributor
timestamp: August 10, 2014, 01:05:06 am
content: Good that you mentioned SMB, already had some SMA's sorted out and had to have a second look at the listing, yes they are SMB. Did find some crimp SMB connectors on EBay that can use RG58 coax

author: larry42
author_rank: Regular Contributor
timestamp: August 10, 2014, 07:25:50 pm
content: Quote from: edpalmer42 on August 09, 2014, 04:23:18 amMore gain will not make multipath worse. The multipath problem is an SNR issue.The gain required depends on the Rx sensitivity and the antenna cable loss. Acq. power required is probably around -145dBm. If GPS signal at ground level is -160dBm, then need at least 15dB + cable loss.Sent from my One S using Tapatalk

author: edpalmer42
author_rank: Super Contributor
timestamp: August 10, 2014, 08:40:32 pm
content: Quote from: larry42 on August 10, 2014, 07:25:50 pmMore gain could raise a multipath signal from a too-low level to an annoying level.In this case, more gain might be required due to a very poor antenna location. The OP is on the ground floor of a north-facing condo.Ed

author: h572
author_rank: Newbie
timestamp: November 24, 2014, 09:53:07 am
content: in fe-5680b,there is a 20MHz square wave point.used 74hc393 to 2 divider.can output 10MHz.

author: h572
author_rank: Newbie
timestamp: November 24, 2014, 09:58:20 am
content: 20MHz point

author: h572
author_rank: Newbie
timestamp: November 24, 2014, 10:01:15 am
content: REMOVE SOME COMPENT

author: h572
author_rank: Newbie
timestamp: November 24, 2014, 10:03:26 am
content: install 74hc393

author: h572
author_rank: Newbie
timestamp: November 24, 2014, 10:05:54 am
content: 10MHz output point

author: nixxon
author_rank: Frequent Contributor
timestamp: November 24, 2014, 07:43:26 pm
content: Quote from: h572 on November 24, 2014, 09:53:07 amDo you know if the "20MHz square wave point" output works also in the units that are sold with only 1pps (cripled unit)?The example chip (in photo), MC74HC393, has status "OBSOLETE" in datasheets. Could you recommend some other Ripple Counter chip that would work as well with the "20MHz square wave point"? (also, how can we tell from the datasheet that the MC74HC393 can handle the 20MHz input on one of the "CLOCK" inputs?)

author: David Hess
author_rank: Super Contributor
timestamp: November 24, 2014, 07:58:57 pm
content: Quote from: nixxon on November 24, 2014, 07:43:26 pmOther companies make the 74HC393 including NXP, TI, and On. Any of them should work.The datasheet will either list the minimum clock input toggle frequency or the minimum clock input pulse width.

author: nixxon
author_rank: Frequent Contributor
timestamp: November 24, 2014, 08:30:54 pm
content: Quote from: David Hess on November 24, 2014, 07:58:57 pmIt seems that user: h572 suggested to power the chip with the 3.3V output. The datasheet for the MC74HC393* guarantees operation with a CLOCK pulse width of 100nS @ 2Vcc and 20nS @ 4.5Vcc (Both at <=85 deg C). Real life interpolation of a 3.3Vcc better be <= 50nS (20 MHz)...*)http://www.onsemi.com/pub/Collateral/MC74HC393-D.PDFIt would be way better to find a 5V source inside that Rubidium standard.And then you have the recommended rise time of the CLOCK pulse being nothing less than 400nS, even with a Vcc of 6V.

author: David Hess
author_rank: Super Contributor
timestamp: November 25, 2014, 12:42:26 am
content: Quote from: nixxon on November 24, 2014, 08:30:54 pmI agree that at 3.0 or 3.3 volts, the 74HC393 and 74HCT393 would probably not be fast enough. There are faster direct replacements for the them like the 74VHC393 and 74LV393 which would work and are specified for 3.3 volt operation.For dividing 20 MHz down to 10 MHz lots of flip-flops could be used like the common '74 dual D flip-flop. Pick the right logic family like AC and it will provide plenty of drive as well.

author: h572
author_rank: Newbie
timestamp: November 25, 2014, 02:53:27 am
content: I suggested power the chip with the 3.3V .used 74XX393 is reduce wiring?

author: h572
author_rank: Newbie
timestamp: November 25, 2014, 03:13:46 am
content: about the frequency.in philips semiconductors datasheet ,power in 2.0V,25 degree the typ fmax is 30MHz.if in 3.3V power the fmax more then 30MHz.what is "typ fmax" ,it means lots of this chip can reach parameter.But strictly? power in 3.3V? the 74hc393 can not good work.the best choose is 74vhc393 or 74lv393.why did i choose 74hc393,because it is easy to buy and unexpensive.

author: nixxon
author_rank: Frequent Contributor
timestamp: November 25, 2014, 12:39:50 pm
content: Quote from: h572 on November 25, 2014, 02:53:27 amMay I ask why you suggest connecting the 3.3V operating voltage also to the unused CLOCK input pin ("1CP") and the RESET ("1MR") pin?

author: h572
author_rank: Newbie
timestamp: November 26, 2014, 02:33:21 am
content: Connect pin-1CP and pin-1MR to 3.3V is easy to connect.

author: nixxon
author_rank: Frequent Contributor
timestamp: November 26, 2014, 09:15:33 am
content: Quote from: h572 on November 26, 2014, 02:33:21 amYes, it is easy to connect. But what are the benefits of connecting the unused half of the chip like suggested?One more thing: How sure are you that the 20MHz signal is present in all (1pps-only) FE-5680B?

author: David Hess
author_rank: Super Contributor
timestamp: November 29, 2014, 07:56:46 am
content: Quote from: h572 on November 25, 2014, 03:13:46 amTyp fmax is the frequency that the parts will typical operate at but it is neither tested nor guaranteed. Min fmax is the guaranteed minimum specification. If you want higher than that, then you should grade them yourself for operation at the frequency of interest over temperature and voltage.

author: jimon
author_rank: Regular Contributor
timestamp: January 19, 2015, 10:35:10 pm
content: Today I've poked different test points & pads with oscilloscope (DS1054Z\hacked), and look what I've found !Point 1 that was mentioned inQuote from: h572 on November 24, 2014, 09:58:20 amLook how strange signal looks. Dunno why is that, I've poked other test points in that area - they are all digital or power.Point 2 is on other side of board, looks like DDS generator should be there, look how clean waveform is and how big V peak-to-peak. Poking around with this test point doesn't mess with PLL, on other hand if I poke around VCO that whole unit goes out from lock really fast (1-2 sec)Any good ideas how to use this 60 MHz point ? I have AD9850 laying around.PS. If I trigger on this 60 MHz and then scroll for couple of microseconds then the waveform start to look really jittery (on point 1 or 2), is it a issue with time domain oscillator in the scope ? I assume frequency standard is a standard for a reason(Reposted this questionhere)PS2. Is it safe to operate this unit without a case ? Rubidium 87 decays by beta emission, so maybe the case is there for a reason ? Also it's getting pretty hot without the case.

author: Bryan
author_rank: Frequent Contributor
timestamp: March 09, 2015, 08:39:50 am
content: Picked one up and it is testing out fine. I do have question, does anyone know if the frequency can be tuned with a serial connection. Appears some of the 5680A models with option 02 can be tuned with a serial connection. Once I have it outputting 10MHZ I would like to tweak it to match my GPSDO. The datasheet from the seller seems to suggest their is a serial connection on pins 14 and 15, but I can't seem to find a Max232 onboard so wondering if perhaps this model does not support this option.

author: smgvbest
author_rank: Unknown
timestamp: April 19, 2015, 05:26:28 pm
content: This is not a topic I'm strong on so excuse a dumb questionis there any value in trying GPS Stabilize a Rubidium standard or is it a case diminishing returns?

author: Bryan
author_rank: Frequent Contributor
timestamp: September 21, 2015, 08:08:12 am
content: Quote from: h572 on November 24, 2014, 10:01:15 amDoes anyone know why the components need to be removed. Not sure what the purpose is if the 20Mhz point is there.

author: andre.lubbock
author_rank: Contributor
timestamp: September 30, 2015, 09:43:36 am
content: I've modified my FE-5680B to output 10MHz square wave. I've posted a couple of pics below but there's a full writeup here.http://andrelubbock.blogspot.co.nz/2015/09/rubidium-frequency-standard.htmlEssentially though I found a 20MHz which I brought out on the DB15 and divided it by 2 with a D-type flip flop. My standard also has 5V that I used to power the external circuitry.

author: AnalysIR
author_rank: Contributor
timestamp: September 30, 2015, 10:37:24 am
content: excellent write up - tnx for sharing