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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