WWVB cheap chip saa6579 RDS decoder back to the chip
Hello to the group.
I see the thread took a left turn a day or so ago so thought I would fire
up a new one for the interested in the phillips saa6579 RDS chip.
Several others have purchased this chip. Jameco electronics had them for 10
or 20 cents. I picked up 10. You had order that many as I recall. Its a
costas loop but will say the documentations skimpy.
My interest
Restoring the old style frequency rcvrs to operation. Like the HP vlf117,
tracor 599, fluke 207....
A byproduct of accomplishing that is you can restore the old time rcvrs
also like the spectracom 8170s.
Lastly end up with the new wwvb code to do something with. Thats really low
on my list of interests actually.
Have tried many approaches to date. The doubling and dividing stuff.
Fades and noise are a killer for this approach. So stopped work on those.
One hack that works is a small fast uproc that detects phase flips using a
spectracom 8163 VCO chain as the reference.
When a flip occurs you flip an rf amplifier phase to invert it.
Its a hack and you need a spectracom. But this voids a favorite requirement
of mine KISS.
So currently building a discreet costas loop using ad633s see how that
works.
To the saa6579
As mentioned in the other thread.
Simple to hook up.
Cheap
Requires 1000uv or more so that ends up making things more complicated.
But in my case simply did not really work at 57 or 60 Khz.
As some someone pointed out you may have to take the clock and data to a
flip flop to get the correct information.
Regards
Paul
WB8TSL
paul swed schrieb:
To the saa6579
As mentioned in the other thread.
Simple to hook up.
Cheap
Requires 1000uv or more so that ends up making things more complicated.
S/N is important, not so absolute amplitude.
But in my case simply did not really work at 57 or 60 Khz.
The chip looks for correct phase for about 50ms (max. 100ms). Did you
check carefully that in this time-frame the phase never inversed or
amplitude dropped down temporary?
Maybe you misunderstood the modulation scheme anyway? It is not native BPSK!
As some someone pointed out you may have to take the clock and data to a
flip flop to get the correct information.
Where is "someone"?
As I understood the datasheet you get maximum processing time (set-up
time) for the data-bit if you use a D-FF delaying DATA strobed by CLOCK.
- Henry
--
ehydra.dyndns.info
Henry
Its been a while since that thread and I have not done anything with the
chip. But to answer your questions.
Really good signal to noise. The modulator is 6" from the saa6579. Its a
home brew BPSK modulator and the transitions are programmable. But I am
following wwvbs 1sec per bit. So the phase is quite stable for long periods
of time. Signal level is 1000uv but again that can be adjusted.
Were is someone. My comment was someone on time-nuts suggested that you had
to use the clock and a flip flop to properly see the data. Thats what you
are also saying.
As to the wwvb modulation scheme I fully understand that. But I actually do
not know a lot about RDS and how it might be different from wwvbs method of
transmission.
I believe there is plenty of information on RDS. I just don't have a lot of
time to figure it out.
I will get back to the chip at some point it is really interesting but very
poorly documented unfortunately.
Regards
Paul
WB8TSL
On Thu, Nov 15, 2012 at 7:14 PM, ehydra ehydra@arcor.de wrote:
paul swed schrieb:
To the saa6579
As mentioned in the other thread.
Simple to hook up.
Cheap
Requires 1000uv or more so that ends up making things more complicated.
S/N is important, not so absolute amplitude.
But in my case simply did not really work at 57 or 60 Khz.
The chip looks for correct phase for about 50ms (max. 100ms). Did you
check carefully that in this time-frame the phase never inversed or
amplitude dropped down temporary?
Maybe you misunderstood the modulation scheme anyway? It is not native
BPSK!
As some someone pointed out you may have to take the clock and data to a
flip flop to get the correct information.
Where is "someone"?
As I understood the datasheet you get maximum processing time (set-up
time) for the data-bit if you use a D-FF delaying DATA strobed by CLOCK.
- Henry
--
ehydra.dyndns.info
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Hi Paul -
If you can spend time on that:
- Look for the different modulation spectrum between BPSK and RDS. The
phase modulation angle is different, the bits are manchester encoded or
such to get a hole on the carrier frequency (For the ARI carrier), the
baseband is DBPSK. - Carefully adjust the clock generator. Very sensitive to it!
- The demodulator can lock on two different phase states. But the
difference is just where the clock transition is positioned in the
data-bit. In locked state this should be constant and can only change
the next time the chip switches von search to lock state (with a 50%
probability). - Yes, often such chips are interesting but poorly documented.
Sometimes it helps to look for similar devices like the SAA6588, TDA7330
, etc. Older datasheets often show more details. - I don't think you can use the chip with 1bit/sec. It is made for
1200bits/sec. I don't know if the internal digital part of the circuit
is fully static. But surely the capacitors of the filter are to small
for a 1200:1 dynamic range. Maybe I misunderstood this in your application.
Have fun -
Henry
paul swed schrieb:
Henry
Its been a while since that thread and I have not done anything with the
chip. But to answer your questions.
Really good signal to noise. The modulator is 6" from the saa6579. Its a
home brew BPSK modulator and the transitions are programmable. But I am
following wwvbs 1sec per bit. So the phase is quite stable for long
periods
of time. Signal level is 1000uv but again that can be adjusted.
Were is someone. My comment was someone on time-nuts suggested that
you had
to use the clock and a flip flop to properly see the data. Thats what you
are also saying.
As to the wwvb modulation scheme I fully understand that. But I
actually do
not know a lot about RDS and how it might be different from wwvbs
method of
transmission.
I believe there is plenty of information on RDS. I just don't have a
lot of
time to figure it out.
I will get back to the chip at some point it is really interesting
but very
poorly documented unfortunately.