Re: [time-nuts] Ball/Efratom MFS-209 Rubidium GPSDO...
Ok, time for a status report, and some modification information for the Ball/Efratom MFS-205, 209, ... family. First the status: I have the unit working properly now. I installed a nice 50db antenna on top of the radon mitigation pipe for my house, and now my unit has a nice view of the sky, and a good strong signal 24/7. As a result, it now regularly updates its frequency and time at the rate its setup prescribes. The rubidium's control voltage seems to be slowly dropping with each update, and each update is on the order of E-13, so that is probably normal. Now the modification: Tom Miller and I have been working on converting the 5MHz outputs, from the nice 24 channels of isolation amplifiers, to 10 MHz outputs. Tom identified the module marked MBF, which is really a type MBFD, as the source of the 5MHz for distribution to the MBF modules, which are the 4 channel distribution amplifiers. The MBF, and the MBFD modules really use the same PCB, only populated differently to handle their different requirements. The MBFD module takes the 10MHz signal from the master standard and sends it to an internal daughter board that contains a level shifter, and a 74HC390 that is used as a divide by two. The 5MHz output of the 'HC390 then goes through a 1K resistor, and back to the mother board where a band pass filter cleans it up, selecting out just the 5MHz component. The modification involves eliminating the 'HC390, and retuning the band pass filter to 10MHz. And then adjusting the isolation amplifier gains, and the thresholds for the fault detectors. 1) Remove the daughter board from the MBFD module, and remove the 74HC390 chip... it isn't necessary, and it isn't a good idea to leave its inputs floating... 2) Towards the middle of the daughter board beside the '390 chip is a grouping of 4 two pin holes marked EFGH. Remove the resistor that connects to the G holes... save it... and all jumpers from the EFGH holes. The resistor should be a 1K. 3) Locate the 4 holes marked E and F, and install the 1K resistor to the pair of holes farthest from where the 'HC390 chip was mounted. Ok, now the divide by 2 is eliminated, and the daughter board simply takes the signal from the input buffer, and converts it to TTL levels, and sends it back to the mother board. Next, find the toroid coil mounted near the center of the mother board. It is in the area that is underneath where the daughter board is mounted. Locate a pair of capacitors, usually rectangular epoxy coated ceramic type, that are in parallel, and quite close to the toroid. These capacitors resonate the toroid at 5MHz in the original circuit, and were a combined value of 1043pf on my unit. You need to pick a pair of capacitors that will resonate the filter at 10MHz. A ballpark starting point would be 1/4 the value of the capacitors you find on your unit. Mine required 191pf... which is a bit less than 1/4. To do this, it is best to power the board on the bench, and to solder a couple of wires to the input. The easiest way to power the board is to clip lead 20V to the pair of test terminal posts (TP1 and TP2) on the mother board. They go right to the main filter capacitor on the board ground is negative. The 10 MHz input connector is the top most coax connector on the MBFD board's main connector. 0.5Vrms into 50 ohms is the desired input level. I tack soldered a small coax to the board near the connector. I connected a scope set for 50 ohms to the output coax... everything on the MBFD is laid out in an obvious fashion, so you should have no trouble locating which output connector goes to which isolation stage. There are 4 gain pots, and one fault threshold pot on the mother board. The gain pots are grouped together one for each channel, and the threshold pot is set away from the others. Adjust the gain pots for 0.5Vrms output into 50 ohms. Adjust the fault threshold light so that it comes on when the output is less than 0.2Vrms. I first set the gain of all the isolation amp stages to 0.5Vrms, and then lowered the signal generator's signal until the scope showed 0.2Vrms, which is about 1/2Vpp. I then adjusted the fault pot to just come on. (as always, 0.5Vrms is 1.4Vp-p... If you happen to try and measure the outputs without the 50ohm loading, they will be double the 50 ohm value, or 2.8Vp-p) When everything is adjusted properly, you should get 4 very low distortion sine waves driving 50 ohms. That is all that I have in my notes. -Chuck Harris ___ 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] Ball/Efratom MFS-209 Rubidium GPSDO...
An ADC0808 directly connected to the GPS antenna? Not even a DC blocking capacitor? So it receives also the 5V antenna supply? On Wed, Dec 24, 2014 at 7:42 AM, Chuck Harris cfhar...@erols.com wrote: It's Alive!!! The MGPS module was saying there was an A-to-D fault and a Feedline fault. Suspicious of the common element, I traced the signal path from the GPS antenna connector to the input of the ADC, and it was a straight DC path. Sure, there were a few chokes, and capacitors to ground to filter out any stray 1.5GHz signal, and to keep the DC circuitry from loading the antenna signal. I ordered up a new ADC converter, which was an ADC0808 by National and TI. A small 28 pin quad J lead surface mount package. It finally came, and I swapped it out this afternoon. I was rather worried, as the failure mode could have been simply a faulty converter, or it could be that something happened on the antenna line that killed the converter. It was not evident how the GPS module knew there was an A-to-D fault. It could have been something like a lack of an end of conversion flag, or they could have been using some extras of the 8 analog inputs to measure things like power, ground, resistor dividers... I really don't know... Powering the GPS module on the bench showed an immediate improvement: The A-to-D converter fault condition was no longer set! It was still showing an antenna line fault, but since I didn't have an antenna connected, that was to be expected. I put the GPS module back into the MGPS chassis, and installed it in the MFS-209, and as soon as I connected a good antenna, the antenna line fault indicator went away So far so good. Some satellites started appearing on the display, and after waiting for what seemed like forever, and the almanac was finally updated. And... The system status changed to GPS Lock! And reports normal operation. Now to let it cook for a few weeks and see how well this ancient GPS RbDO performs. Thanks to all that offered tips and moral support. -Chuck Harris Chuck Harris wrote: And as I feared, the MGPS display is telling the truth, there is something wrong with the GPS module's ability to check the feed line for shorts and opens, and something wrong with the motherboard's ADC module. At least the communication between the MGPS and the GPS engine is working properly... -Chuck Harris ___ 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 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] Ball/Efratom MFS-209 Rubidium GPSDO...
Hi The ADC0808 is a (relatively) slow multi-input 8 bit ADC. It’s a good candidate for built in test chores on a board that does not have a MCU with built in ADC capability (or where you have used all the pins). They are cheap and easy to use. Current limiting the antenna supply is a pretty good idea. They do short from time to time. Monitoring the voltage going to the antenna is a quick way to see if the supply is limiting. So far a great idea. Get a bit of over voltage on the antenna and the ADC probably isn’t going to last very long …Over voltage might be lightning, it could be other things. Bob On Dec 24, 2014, at 4:58 AM, Azelio Boriani azelio.bori...@gmail.com wrote: An ADC0808 directly connected to the GPS antenna? Not even a DC blocking capacitor? So it receives also the 5V antenna supply? On Wed, Dec 24, 2014 at 7:42 AM, Chuck Harris cfhar...@erols.com wrote: It's Alive!!! The MGPS module was saying there was an A-to-D fault and a Feedline fault. Suspicious of the common element, I traced the signal path from the GPS antenna connector to the input of the ADC, and it was a straight DC path. Sure, there were a few chokes, and capacitors to ground to filter out any stray 1.5GHz signal, and to keep the DC circuitry from loading the antenna signal. I ordered up a new ADC converter, which was an ADC0808 by National and TI. A small 28 pin quad J lead surface mount package. It finally came, and I swapped it out this afternoon. I was rather worried, as the failure mode could have been simply a faulty converter, or it could be that something happened on the antenna line that killed the converter. It was not evident how the GPS module knew there was an A-to-D fault. It could have been something like a lack of an end of conversion flag, or they could have been using some extras of the 8 analog inputs to measure things like power, ground, resistor dividers... I really don't know... Powering the GPS module on the bench showed an immediate improvement: The A-to-D converter fault condition was no longer set! It was still showing an antenna line fault, but since I didn't have an antenna connected, that was to be expected. I put the GPS module back into the MGPS chassis, and installed it in the MFS-209, and as soon as I connected a good antenna, the antenna line fault indicator went away So far so good. Some satellites started appearing on the display, and after waiting for what seemed like forever, and the almanac was finally updated. And... The system status changed to GPS Lock! And reports normal operation. Now to let it cook for a few weeks and see how well this ancient GPS RbDO performs. Thanks to all that offered tips and moral support. -Chuck Harris Chuck Harris wrote: And as I feared, the MGPS display is telling the truth, there is something wrong with the GPS module's ability to check the feed line for shorts and opens, and something wrong with the motherboard's ADC module. At least the communication between the MGPS and the GPS engine is working properly... -Chuck Harris ___ 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 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 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] Ball/Efratom MFS-209 Rubidium GPSDO...
Nice work Chuck. So now you have a many port house reference that should last for many years. My unit took a long time to start from cold, I think it is operating in position mode and takes time to settle on the location. Regards - Original Message - From: Chuck Harris cfhar...@erols.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, December 24, 2014 1:42 AM Subject: Re: [time-nuts] Ball/Efratom MFS-209 Rubidium GPSDO... It's Alive!!! The MGPS module was saying there was an A-to-D fault and a Feedline fault. Suspicious of the common element, I traced the signal path from the GPS antenna connector to the input of the ADC, and it was a straight DC path. Sure, there were a few chokes, and capacitors to ground to filter out any stray 1.5GHz signal, and to keep the DC circuitry from loading the antenna signal. I ordered up a new ADC converter, which was an ADC0808 by National and TI. A small 28 pin quad J lead surface mount package. It finally came, and I swapped it out this afternoon. ___ 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] Ball/Efratom MFS-209 Rubidium GPSDO...
I agree that in some ways it is not too swift, but it is as I said, a direct DC path... not even a resistor, nor, as far as I can tell, any diode clamp. The GPS RF path does have a blocking capacitor, and all sorts of protection diodes and bandpass filters. Because the antenna of the 40dB preamplified variety, the receiver doesn't have much in terms of on board gain. [Remember, once you have loss, you can't get your nice low noise figure back. It always pays to put your best low noise preamp up at the antenna end of the coax.] As far as I could determine, the ADC0808 is used for only two things: 1) To measure the voltage at the antenna feed. This allows the GPS to detect shorts and opens. The antenna preamp power supply has a small resistor in series with its 5V output, so the ADC can measure how much the antenna preamp's current draw drops the voltage across that resistor, and calculate the feed line current. 2) To measure the temperature of the Rb oscillator's heat sink. Rb oscillators Achilles heel is temperature sensitivity. The MGPS controller takes the Rb oscillator's temperature, and tweaks the control voltage, hopefully compensating for changes in ambient temperature. With the ADC having a 5V maximum input voltage, and a direct connection to the feed line, all one would have to do to kill it is to attach a long feed line to the antenna connector with an open on one end. A nearby lightning strike could do the deed too. I am quite pleased that the RF section of the MGPS unit didn't get affected by whatever killed the ADC0808. -Chuck Harris Azelio Boriani wrote: An ADC0808 directly connected to the GPS antenna? Not even a DC blocking capacitor? So it receives also the 5V antenna supply? On Wed, Dec 24, 2014 at 7:42 AM, Chuck Harris cfhar...@erols.com wrote: It's Alive!!! The MGPS module was saying there was an A-to-D fault and a Feedline fault. Suspicious of the common element, I traced the signal path from the GPS antenna connector to the input of the ADC, and it was a straight DC path. Sure, there were a few chokes, and capacitors to ground to filter out any stray 1.5GHz signal, and to keep the DC circuitry from loading the antenna signal. ... ___ 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] Ball/Efratom MFS-209 Rubidium GPSDO...
It's Alive!!! The MGPS module was saying there was an A-to-D fault and a Feedline fault. Suspicious of the common element, I traced the signal path from the GPS antenna connector to the input of the ADC, and it was a straight DC path. Sure, there were a few chokes, and capacitors to ground to filter out any stray 1.5GHz signal, and to keep the DC circuitry from loading the antenna signal. I ordered up a new ADC converter, which was an ADC0808 by National and TI. A small 28 pin quad J lead surface mount package. It finally came, and I swapped it out this afternoon. I was rather worried, as the failure mode could have been simply a faulty converter, or it could be that something happened on the antenna line that killed the converter. It was not evident how the GPS module knew there was an A-to-D fault. It could have been something like a lack of an end of conversion flag, or they could have been using some extras of the 8 analog inputs to measure things like power, ground, resistor dividers... I really don't know... Powering the GPS module on the bench showed an immediate improvement: The A-to-D converter fault condition was no longer set! It was still showing an antenna line fault, but since I didn't have an antenna connected, that was to be expected. I put the GPS module back into the MGPS chassis, and installed it in the MFS-209, and as soon as I connected a good antenna, the antenna line fault indicator went away So far so good. Some satellites started appearing on the display, and after waiting for what seemed like forever, and the almanac was finally updated. And... The system status changed to GPS Lock! And reports normal operation. Now to let it cook for a few weeks and see how well this ancient GPS RbDO performs. Thanks to all that offered tips and moral support. -Chuck Harris Chuck Harris wrote: And as I feared, the MGPS display is telling the truth, there is something wrong with the GPS module's ability to check the feed line for shorts and opens, and something wrong with the motherboard's ADC module. At least the communication between the MGPS and the GPS engine is working properly... -Chuck Harris ___ 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] Ball/Efratom MFS-209 Rubidium GPSDO...
After chatting with John Miles, and Paul (ziggy), I was reminded that TTL RS232 is not a good thing around a pedantic protocol analyzer. 4V signal swings would work with the analyzer's strict +/-3V thresholds, except for that wonderful excuse for a UART that Trimble used, putting a big glitch dead center in each sent bit position. The protocol analyzer saw that glitch drop below 3V, and just knew it was a start bit. And, that coupled with using 9600,8,N,1 instead of Trimble's favorite 9600,8,O,1 settings made for the interesting data smearing I was seeing. Now, I am getting properly formed TSIP packets. Time to decode them and see what they mean. More later, -Chuck Harris Chuck Harris wrote: Hi gang! I am in the process of repairing a Ball/Efratom MFS209 GPSDO. The MGPS unit reports that I have an ADC fault, and a feed line fault. I have done some testing and can easily see that the feed line has the proper +5V on the unit's N connector, and that it can source the required 200ma, but with a known good antenna, the MGPS controller still reports the fault. ___ 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] Ball/Efratom MFS-209 Rubidium GPSDO...
And as I feared, the MGPS display is telling the truth, there is something wrong with the GPS module's ability to check the feed line for shorts and opens, and something wrong with the motherboard's ADC module. At least the communication between the MGPS and the GPS engine is working properly... -Chuck Harris Chuck Harris wrote: After chatting with John Miles, and Paul (ziggy), I was reminded that TTL RS232 is not a good thing around a pedantic protocol analyzer. 4V signal swings would work with the analyzer's strict +/-3V thresholds, except for that wonderful excuse for a UART that Trimble used, putting a big glitch dead center in each sent bit position. The protocol analyzer saw that glitch drop below 3V, and just knew it was a start bit. And, that coupled with using 9600,8,N,1 instead of Trimble's favorite 9600,8,O,1 settings made for the interesting data smearing I was seeing. Now, I am getting properly formed TSIP packets. Time to decode them and see what they mean. More later, -Chuck Harris ___ 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] Ball/Efratom MFS-209 Rubidium GPSDO...
Hi gang! I am in the process of repairing a Ball/Efratom MFS209 GPSDO. The MGPS unit reports that I have an ADC fault, and a feed line fault. I have done some testing and can easily see that the feed line has the proper +5V on the unit's N connector, and that it can source the required 200ma, but with a known good antenna, the MGPS controller still reports the fault. The MGPS communicates with an internal Trimble GPS receiver board using RS422, and the MGPS pins the - input/outputs of the RS422 signal to ground, the communication is essentially TTL RS232. The ADC, and the detector for the feed line faults are on the Trimble board, so I thought I would sniff at the serial lines to see what packets were being sent to and from the GPS. I tagged a couple of wires onto the interface connector for the Trimble board, and hooked them up to a scope, and verified that they were 0-4V and 9600 baud, and then hooked up a protocol analyzer to capture some messages. Since the Ball/Efratom advertising blerbs I found on John Ackermann's website say it is a 6 channel GPS receiver, and at that time, Trimble made a common 6 channel receiver called the SVeeSix, I went there for hints on the communication protocol. Trimble provides a serial 8 bit protocol called TSIP on their GPS engines, so I looked at that first. TSIP is a packet protocol, which uses frames that look like this: DLEpacket IDpacket data bytes...DLEETX Where DLE is an ascii 0x10, the packet id is one or two bytes and ETX is an ascii 0x03. I get the following packet, sent by the Trimble, about every 15 secs: FF 90 14 20 20 20 06 41 96 65 1E 01 41 06 FF After 3 such packets, the MGPS sends: FF 90 22 D0 Then immediately the Trimble sends: FF D0 24 01 01 01 0101 01 41 06 Where there are 25 of the 01 bytes in a row. and the MGPS again sends the packet: FF 90 22 D0 After which the whole process repeats. Clearly, this isn't regulation TSIP! The other protocols proffered by Trimble send plain text messages intended for printing, so it isn't one of them (TSIA, or NMEA). Does anyone recognize this protocol? I have a little trouble believing that Ball/Efratom got Trimble to roll a custom data protocol just for this MGPS unit, but documentation is so sparse, that who knows? Any ideas? -Chuck Harris ___ 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.
