[time-nuts] FE-5680A help/identification (again!)

[Ed Palmer]

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
>
>
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