Hello Nuts, I know the FE-5680 (and FE-5650) have been discussed at length here. However, I'm trying to figure one out and need a bit of help. Yes, there are MANY variations - but I have found the telecom units to generally fall into three classes. 1. The "10MHz and 1pps" units. These need +15V on DB9-1 and +5V on DB9-4 and have both 10MHz (DB9-7) and 1pps (DB9-6) outputs. RS-232 is on DB9-8 & 9. These units have two labels on the top of the unit - one large and one smaller. These units are programmable over a small range using the RS-232 interface. 2. The "1pps only units". These need only +15V on pin 1 and only have the 1pps output on pin6. These units have only the smaller label on the top of the unit. FLL runs at 50.xx MHz, DDS outputs 8.3xx MHz. The DDS is presumably programmable over a wide range, but the RF signal and RS-232 lines must be brought out of the box. A photo is attached of the inside of this unit. 3. The "new(est) FE-5680A". I have not had one to examine, but pictures are on Diders website. These units have only the single board inside (and not the stacked configuration). I don't know the I/O configuration. FLL runs at 60MHz. I have several questions: 1. How do the older units with both 10MHz and 1pps (#1) get both outputs? (perhaps they had decade dividers, as opposed to the 2E23 division of variation '2'? 2. In the photo of variation '2', What is the function of the small board at the left? I know it has been mentioned before, but can't find the reference. It only seems to have three connections - power (red), ground (black), and analog voltage out (orange). The orange wire is connected to one side of an optional component, the other side of which goes to DB9-9 (Are there options of the 5680 that use pin 9 for EFC or C-field adjustment? - the optional component being a resistor). This board has its own microprocessor and lots of associated circuitry, but does not seem to have any input unless it is the device that is thermally bonded to the center support/heatsink (a LOT of harware for temperature compensation). This small board also has an RS-232 converter, the signals come out to two pins on the small 5-pin connector on the bottom of the board. Anybody have a clue as to protocol? Any help would be appreciated. Thanks in advance. Regards, Skip Withrow

Hi Skip, You might have seen my reference to the small board in the 'variation 2' FE-5680. I looked at the signal on the orange lead and found only about 2.02 Vdc. The orange lead goes to the output of a D-A converter on the small board. So, on a hunch, I used a 10-turn pot to put 0-5V into the main board at the point where the orange lead connected. My hunch was good. It's the analog tuning input. Range on my unit is about 3e-9 for 0-5 volts input. Higher voltage = higher frequency. So I know *what* the board is doing, but I can't imagine *why*. Is it nothing more than temperature compensation? Is it just a factory calibration adjustment? Are they attempting to compensate for the Rb aging by following some model and gradually changing the frequency of the DDS or the C-field? Maybe a model, even an inexact one, helped them to meet a more stringent aging spec. No clue. You'd have to watch the output voltage of the small board and track it over time to see how or if it changes. I didn't attempt to talk to the board so I can't help you there. Ed On 4/19/2013 3:46 PM, Skip Withrow wrote: > Hello Nuts, > I know the FE-5680 (and FE-5650) have been discussed at length here. > However, I'm trying to figure one out and need a bit of help. > > Yes, there are MANY variations - but I have found the telecom units to > generally fall into three classes. > > 1. The "10MHz and 1pps" units. These need +15V on DB9-1 and +5V on DB9-4 > and have both 10MHz (DB9-7) and 1pps (DB9-6) outputs. RS-232 is on DB9-8 & > 9. These units have two labels on the top of the unit - one large and one > smaller. These units are programmable over a small range using the RS-232 > interface. > > 2. The "1pps only units". These need only +15V on pin 1 and only have the > 1pps output on pin6. These units have only the smaller label on the top of > the unit. FLL runs at 50.xx MHz, DDS outputs 8.3xx MHz. The DDS is > presumably programmable over a wide range, but the RF signal and RS-232 > lines must be brought out of the box. A photo is attached of the inside of > this unit. > > 3. The "new(est) FE-5680A". I have not had one to examine, but pictures > are on Diders website. These units have only the single board inside (and > not the stacked configuration). I don't know the I/O configuration. FLL > runs at 60MHz. > > I have several questions: > > 1. How do the older units with both 10MHz and 1pps (#1) get both outputs? > (perhaps they had decade dividers, as opposed to the 2E23 division of > variation '2'? > > 2. In the photo of variation '2', What is the function of the small board > at the left? I know it has been mentioned before, but can't find the > reference. It only seems to have three connections - power (red), ground > (black), and analog voltage out (orange). The orange wire is connected to > one side of an optional component, the other side of which goes to DB9-9 > (Are there options of the 5680 that use pin 9 for EFC or C-field > adjustment? - the optional component being a resistor). This board has its > own microprocessor and lots of associated circuitry, but does not seem to > have any input unless it is the device that is thermally bonded to the > center support/heatsink (a LOT of harware for temperature compensation). > This small board also has an RS-232 converter, the signals come out to two > pins on the small 5-pin connector on the bottom of the board. Anybody have > a clue as to protocol? > > Any help would be appreciated. Thanks in advance. > Regards, > Skip Withrow > > > _______________________________________________ > 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.