[time-nuts] FE-5680B Rubidium and DDS

Don Latham djl at montana.com
Tue Sep 29 16:20:36 EDT 2015


definitely interested.   I'd especially like to know about using the 30 MHz
with the Chinese dds block.
Don

Clint Jay
> I've made some investigations and re-confirmed my earlier findings on the
> FE-5680B I have.
>
> It locks from cold in under five minutes and runs at approximately 700mA
> steady with the expected PPS signal on the output connector when locked.
>
> The particular 5680 I have has a Hi Density 15p male connector on the
> output and uses a single 15V supply, part number FE5680B UN 77672.
>
> The device does not have the optional DDS daughterboard which means that
> it's not usable as a programmable signal source as it stands (but see
> later).
>
> For approximately six seconds after power is applied a 10MHz signal
> available on the output connector, this signal comes directly from the
> XC9572 CPLD via a filter network and appears to be a clean sine wave.
>
> The 10MHz signal seems to be 'switched off' by some event in the unit, I
> don't yet know if this is in response to an event or just a timed shutdown
> but power cycling the unit re-enables the 10MHz output for a further six
> seconds. It doesn't appear to be related to rubidium lock as it takes
> consdierably longer than six seconds to lock.
>
> There is a solid 30MHz signal inside the unit, stable once the rubidium has
> locked and the PPS output is also available once locked.
>
> Other observations show that the MAX3232 serial driver chip is missing and
> in it's place there is a tiny 8 pin device marked M09 or MO9 which is
> connected to the TXD/RXD pins on the output connector and the TXD/RXD pins
> on the 80C323 CPU.
>
> I'd be very interested in suggestions as to the part number of that device,
> it may yield clues as to the communication method needed.
>
> Attempts to communicate with it via a terminal program have given no
> responses at several 'standard' baud rates. Voltage levels are LVTTL.
>
> I'm wary of applying 5V to any of the pins on the interface connector
> directly and probing them with 3.3v via a 10K resistor has made no
> difference to any of the signals I can monitor (30MHz, PPS etc.) with the
> exception of pin 13 which I *think* is reset, obviously this causes the
> frequencies to skew for a few seconds until reset is completed.
>
> My intent is to use the 30MHz signal from the CPLD to clock a DDS chip
> (probably one of the eBay DDS modules) that's controlled by a PIC chip (I
> already have code to run a DDS VFO I developed earlier this and late last
> year. Hopefully this will be small enough to fit inside the casing though I
> don't see a problem with bringing the 30MHz signal out if necessary.
>
> My apologies if this is outside of the scope of this list, I will also be
> writing up my findings and experiments with this standard on my blog if
> anyone is interested?
>
>
>
> On 26 September 2015 at 11:23, Bryan _ <bpl521 at outlook.com> wrote:
>
>> Thanks Hal, that's interesting, will try and see how far I can get.
>> -=Bryan=-
>>
>> > To: time-nuts at febo.com
>> > From: hmurray at megapathdsl.net
>> > Date: Fri, 25 Sep 2015 23:40:40 -0700
>> > CC: hmurray at megapathdsl.net
>> > Subject: Re: [time-nuts] FE-5680B Rubidium and DDS
>> >
>> >
>> > > I as well wish there was a quick way of converting it back to 10Mhz. I
>> am
>> > > sure it can be done, just not sure how or where to look
>> >
>> > If the 10 MHz is visible for a second or two, there is probably a gate to
>> > turn it on/off.  If I wanted 10 MHz, I'd open it up and trace the wire
>> back.
>> > If it goes to a gate, you might be able to lift the pin for the other
>> input
>> > and wire it hi/low.  There is a good chance it goes to a FPGA where you
>> can't
>> > get at the gate.
>> >
>> >
>> >
>> >
>> > --
>> > These are my opinions.  I hate spam.
>> >
>> >
>> >
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>
>
>
> --
> Clint.
>
> *No trees were harmed in the sending of this mail. However, a large number
> of electrons were greatly inconvenienced.*
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>


-- 
Felix qui potuit rerum cognoscere causas.
Lucky is he who has been able to understand the causes of things.
Virgil
-------------------------------
"Noli sinere nothos te opprimere"

Dr. Don Latham, AJ7LL
Six Mile Systems LLC, 17850 Six Mile Road
Huson, MT, 59846
mailing address:  POBox 404
Frenchtown MT 59834-0404

VOX 406-626-4304
CEL 406-241-5093
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