Re: [time-nuts] Changing FE-5650A frequency?
On 20/04/13 10:03, Robert Atkinson wrote: Hi Alec, Well done and thanks for the credit. I had not looked under the board for the crystal or spotted the divider. One comment. in your blog and ebay description you say that the unit runs on 15V. The "M" suffix 5650A is actually designed for a normal aircraft 28V DC supply (typical specification range 22-32V). It may run on 15V but it may be stressing the power supply circuit and / or under-running the oven. The external (28V) supply to the Marconi unit is just filtered, switched and connected to the FE-5650A without regulation. It appears that these units have options 08, 09, 22 and 25 rolled up into the "M" military suffix. By the way, these units can cost $10,000 or more each for specials see http://www.dlis.dla.mil/webflis/pub/pub_search.aspx Robert G8RPI. Robert, Good point, well observed! The power-trends thing inside the package is an adjustable 3A switching regulator which seems to be set to nominally ~15.3V (91k setting resistor to ground). When i crank up the input voltage, the output voltage of the regulator settles to around 15.5v once the input voltage reaches around 19v. According the the datasheet the dropout voltage of those regulators is 4V, which means these frequency standards should be happy with any input from 19.5-38v. Where did you find the info about pricing for these? I searched in that form for FE-5650A and couldn't find it. I tried searching the whole "stable oscillator" thing's NSN to no avail. I did expect these must have been very expensive when they were new though! On 20/04/13 04:10, WB6BNQ wrote:> > Hi Alex, > > Your alternate assumption is the correct one. Working the formula backwards with the assumptions that the 800 KHz is spot on would then dictate that the DDS out is exactly 12.8 MHz with the final value of the physics package being > > 50,255,058.6495 > > based upon my HP-35s calculator. > > Many construction and environmental factors affect the actual final frequency of the physics package. Plus there is some small variance about the center frequency with which signal levels are still strong enough to allow functionality. The C-field adjustment allow for tweaking within that small variance. Fortunately, this ability allows for putting the Rb right on the assumed true frequency. > > Provided you have a higher reference source (i.e., Cesium or a well tamed GPS arrangement), the way to properly adjust the Rubidium is to adjust the physics package C-field pot to it minimum frequency point, then set the DDS to the closest point just below the desired frequency and then re-adjust the C-field pot to come up onto the proper frequency. This is a slow repetitive process requiring time and patience. The degree of patience will directly correlate with the precision obtained. > > However, if you are not dying to have absolute accuracy, but more interested in the stability provided by the Rb, then do not mess with the C-field pot. If you do not have the means for the calibration, it would, most likely, be safe to assume that the Rb is within 1x10-9 if other means are used to make sure some gross error is not evident. > > I read your blog and, besides the success, it looked like you were having fun. Good luck, > > BillWB6BNQ > > Bill, I thought as much, thanks for confirming! I'll keep an eye out for any callibrated frequency reference I can borrow for 10 minutes to set this with, but otherwise I'll leave it as is. On 20/04/13 09:37, gandal...@aol.com wrote:> Hi Alec > I see your web page and Ebay auction, are you able to supply one still > complete and unmodified in its original enclosure? > Regards > Nigel > GM8PZR Nigel, You mean just the FE-5650A enclosure or the whole "stable oscillator" thing? Do you want to ping me off list? Regards, Alec ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Changing FE-5650A frequency?
Success! I've managed to set mine to 10MHz. I've documented this on my blog: http://blog.m0tei.co.uk/post/2013/04/20/Mystery-Aircraft-Parts-and-Atomic-Clocks Thanks to those who offered suggestions. Regards Alec ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Changing FE-5650A frequency?
On 07/04/13 21:55, WB6BNQ wrote: Hi Alec, I am going to agree with Robert (G8RPI) on his assessment, particularly as the dip switches are clearly visible in one of the pictures. Although I wonder why Robert feels unfortunate about the [ two chip DDS arrangement ] ? It matters not the number of chips that make up the DDS. Why ? Because the actual physics package and its electronics has nothing to do with the DDS in the older designs. That is, the signal output of the physics package is a fixed frequency (around 50.255 MHz) that you could capture and feed to a more modern DDS if necessary as replacement of the old one is probably not going to happen. However, if it is working then once you get to a frequency you need you probably not touch it again. So no loss there. As for calibration, there is a hole on one side of the can that has a multi-turn pot that adjusts the "C-field" current. The C-field is a very fine frequency adjustment. You first adjust the C-field pot to its lowest setting (as in frequency), then set the DDS to the closest frequency on downside of where you want to go and then adjust the C-field pot to come up on to the frequency. The C-field pot is a really fine adjustment, so we are talking very small movement that will require patience, a better reference and at least a oscilloscope to watch the drift rate over a very long time. A truly time consuming experience. However, if you leave that C-field pot alone, you will most probably be inside 1 part in 10 to the minus 9th. The most recent designs have the DDS in the control loop for the physics package. In the new internal design in order to change frequencies you need to actually change the BASE crystal frequency, the DDS and the firmware to get a new output frequency. So basically a real pain in the ass. As for the foam that is sandwiched in between the boards, I agree with Robert that it is for temperature stability in varying environments. If the unit is kept in a normal room all the time then the foam is not a concern and could be carefully cleaned off. There is some other components that have white stuff that looks more like an RTV type substance used to hold down a component like what is seen in photograph IMG_20130407_102937.jpg at the two toroids, That I would leave alone. Your finding the 12+ MHz just confirms that the design is very similar to that described in the FTP file I provided. Make sure you record the switch settings before you change them so you can return to a reference point. Although you did not indicate, I assume you downloaded the FTP file ? Please let me know so i can reduce the storage level as it is not my site although I have use of it on a short term basis. Thank you, BillWB6BNQ Bill, Thanks for your input and sorry for the slow reply! So, I've had a look at the datasheet and it looks like the output frequency should be Fin*(tuning word)/2^32... I thought I'd check if this matches up. The tuning word was set to x4134111F (towards the inside of the board seems to represent 1 and towards the outside, zero. Assuming 50.255MHz going in that gives 12.799985 MHz output! Perfect. Pretty much exactly what I'd measured. Alternatively I could assume that the output is 12.8MHz exactly which sets the input frequency to 50.2550586MHz - i wonder which assumption I should use when changing the frequency? I'd like to adjust it to put 10MHz out, skip the 4000 series logic divider and remove/change the output filter. Regards, Alec ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Changing FE-5650A frequency?
On 07/04/13 15:10, Herbert Poetzl wrote: The purpose of the polymer foam is isolation to keep a stable temperature throughout the boards. http://www.qsl.net/z/zl1bpu/PROJ/FE5650-2.jpg The top layer in this image is the DDS board, and it is basically identical to the FE5680A, which means it can be adjusted in a wide range, but only does digital synthesis based on the reference frequency. But let's see what Bill says to the pictures ... :) best, Herbert Herbert, the board doesn't seem to be the same, the chips which are visible don't line up with the ones in that picture. Anyway my curiosity got the better of me and I dug through the foam some more to find a long row of DIP switches. I bet i can change the divider ratio with some combination of those: http://m0tei.co.uk/fe5650pics/IMG_20130407_170929.jpg Also, you can see that the chip is an AD9955 DDS chip: http://novatech-instr.com/PDF_files/AD9955.pdf - Alec ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Changing FE-5650A frequency?
On 07/04/13 17:56, Robert Atkinson wrote: Hi Alex, These units were used as timing references for secure communication systems (Havequick). see ebay item 130832014630. Unfortunatly they are an older design with a two chip DDS. The other problem is that the "M" designation is for military and means they have been partially encapsulated with polyurethene foam. You can cut it away but it is very easy to damage the PCB. Frequency setting is by DIP switches (under the foam) allowing full range of frequency selection. However the output filter is narrow so you can't go far from 800kHz. Did you buy all seven? Robert G8RPI. Robert, Thanks for the info! I bought one of these wondering what they were, took it apart and found the rubidium clock and figured it must be worth something (more than the 15 quid he was asking) so I bought the remaining 6! I've taken the foam off the top PCB and i've found that there's a 12.8MHz signal being produced which is then being divided down with an 800kHz logic chip. I should imagine the filter must be on the circuit board below? I might try changing the frequency of the DDS chip, removing the frequency divider and tinkering with the output filter. Do you have any info on what sort of filter I should expect to find? Thanks, Alec M0TEI ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Changing FE-5650A frequency?
On 07/04/13 05:01, WB6BNQ wrote: Hi Alec, You may be in luck. However, I would need some additional pictures, particularly of the connector on the bottom, also some of the inside. Bill, Thanks for your reply! Here are some photos of the inside: http://m0tei.co.uk/fe5650pics/ You'll see that it comes with a custom machined plate screwed onto the front - this was how it was mounted in the thing i pulled it out of. It can be removed but i found it easier to take the thing apart with it on. A thermostatic switch used to bolt onto it to (presumably) act as a thermal cutout. You'll also notice that the boards we're probably interested in are potted it some sort of white compound - it's hard but crumbly - feels like some sort of polymer foam. I've started to pick it off a bit but could you just confirm that this is actually a sensible thing to do before I go all out scraping it off? Thanks! The primary physics package is a stand alone analog Rubidium frequency standard that outputs 50.255* MHz frequency. That signal is used to drive various output board configurations, included inside the unit, to provide a customer required output frequency. The more recent revised units (they look the same) use a new digital scheme that is much more of a hassle. This unit is probably from late 1996/1997 if that helps? The one that I and a number of people are familiar with is the 5650-option-58 model whose output was a 1pps. To get the 1pps the 50.255+ MHz signal was used to drive a Direct Digital Synthesizer (DDS) that produced 8.3+ MHz signal that was then divided down via normal TTL dividers to produce the 1pps. The DDS is capable of being changed to other frequencies up to about 20 MHz, however, the filter following the DDS needs to be changed or bypassed to properly filter the new frequency. Bypassing is the easiest method but would require using an external filter to get rid of aliasing and spurs. I put together a zip file of various information on FEI-5650-option 58 that will help you get familiar with the family line. If you have problems with the link let me know. Also, after you get a successful download let me know so I can reduce the FTP storage level, thank you. http://pages.suddenlink.net/stevewingate/cryptic1/for alec on 5650-option-58.zip BillWB6BNQ Awesome, looks like there's some great info there! Unfortunately i'm not sure hoe relevant it is to mine since my option doesn't seem to do RS232 On 07/04/13 04:17, Herbert Poetzl wrote: > > Open it up, take some nice pictures of the circuit boards > and components and I can probably tell you what might be > possible (after looking at them :). > Thanks Herbert! Pictures above^ >> As far as i'm aware this model doesn't have serial control. > > best, > Herbert > Best regards, Alec ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Changing FE-5650A frequency?
Hi all, I've recently ripped some FE-5650A's out of some old equipment, but they seem to be a custom build, here you can see they have the option just listed as "-": http://cambridge.m0tei.co.uk/files/IMG_20130330_232647.jpg They seem to be single rail (15v) supply with an 800kHz output. I wonder, does anyone know if it's possible to change its frequency? As far as i'm aware this model doesn't have serial control. Thanks, Alec M0TEI ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
