I call that frequency translation but it will not work here
because the problem lies in the sensitivity profile of the sensor
itself.
I need to squish down the normal operating range
of the geophone so I can look at the signals
riding underneath the resonant point.

What I call equalization seems to work which is using
a LPF with a CF under the range you want to view
It serves to push down everything over the rolloff
including the noise you want to squish.
Then the range between the rolloff and resonance becomes
somewhat flat in response.

Thanks for your input.



"loedown" wrote in message ...
Hi All,
I know very little about radio and the like, but could some form of superheterodyning be done in this instance, the
idea of AM, or FM to combine the slow signal with much higher frequency?

Paul

"gmv" wrote in message
news:J7MNd.24453$C24.9065@attbi_s52...

"Watson A.Name - "Watt Sun, the Dark Remover""
wrote in message ...

"gmv" wrote in message
news:jJdNd.21541$C24.9629@attbi_s52...
Interesting,
I always thought the opamp buffered the output
so you could hook it to anything between 2K
and infinity.
I will keep in mind what you have said.
I have noticed a terrible ringing effect at Q
5 and above.
Maybe that is what you are talking about.
In any case I really need to see things between .5Hz
and 2Hz. It is only the noise in my local area that
keeps me from doing this as far as I can tell.

http://home.mchsi.com/~gmvoeth/index.html

will show a bit more of what I am doing.

Buy the RS printed circuit board that has the same layout as the
breadoard. Build the circuit on that board, and put it inside of a
metal enclosure, so that most of the noise is kept out of the
circuit.

What is "RS printed circuit board " ?

RS = Radio Shack AKA Radio Scrap, etc. They sell a PC board that has
the same layout as the breadboard. Makes it easy to transfer the
circuit to a permanent circuit board.

I have settled on using only a single filter
as is now posted to my web site. This will
limit one to only seeing P waves but in
this noisy environment it is the best I can do.
I agree with everything you say except I can not
put a preamp outside with the Geophone.

Well, that's probably the reason why you are getting so much noise!

There is a circuit I have included not on the
schematic and it is a 567 tone decoder on the back
end to decode WWV calibration marks.

Thanks for your advice, I can see a lot of
common sense to it. But I still do not
know how to buy a circuit board that already
has my layout on it. I figure I will have
to do the layout and etching etc... myself.

I'm not sure you understand. The hole patterns match those on the
breadboard.
Here it is, it's catalog # 276-170 and costs a bit over $3.
http://www.radioshack.com/product.as...category%5Fnam
e=CTLG%5F011%5F002%5F002%5F000&product%5Fid=276%2D 170&MSCSProfile=745D84
CBF04D14A48AA6FF9C89D722C0BA68C1B04FE384678A5285FC D6E056B17AF21627FDABE3
16B90B3C038D68EBD6B7F9F3BD1712EAA9951ACB2590A05C65 17EFE46941FEFDD1985D4E
FD6321F5E70B4DE9B6C1D45512DCD9FB3DBCACB9479D26760F AF1D7B193B4FEA078B5E09
80BDD61634ABB7D328B012D36915420A2B457BE162481F674B


All preamplification should be done as close as possible to the
geophone, to get the signal well above the noise _before_ it goes
any
distance.

Filtering should be done at the other end, to get rid of noise in
the
long transmission line between the sensor and the PC.

One other important point. The outside can of the electrolytic is
at
signal level, and is a large capacitance to the outside world. Just
shielding these from outside noise should help. You might consider
putting some aluminum foil over the ones at the input, and grounding
the
foil to common. Just to see how much it will help to put the whole
thing in an enclosure.

[snip]

"loedown" wrote in message
...
Hi All,
I know very little about radio and the like,

Yeah. I guess not.

but could some form
of superheterodyning be done in this instance, the idea of AM, or FM
to
combine the slow signal with much higher frequency?

If you mix the signal with a much higher freq, then the bandwidth of the
filter has to be much, much narrower. Which then makes filtering that
much more difficult.

Paul

I think this is the link you mean:
http://www.radioshack.com/product.as...5Fid=276%2D170

The one you gave me would not function.

Yes, I will eventually do this.
I am still debating whether or not to use
what I call equalization in my circuit.

Thanks for your input.

--
Regards;
gmv


"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ...

"gmv" wrote in message
news:J7MNd.24453$C24.9065@attbi_s52...

"Watson A.Name - "Watt Sun, the Dark Remover""
wrote in message ...

"gmv" wrote in message
news:jJdNd.21541$C24.9629@attbi_s52...
Interesting,
I always thought the opamp buffered the output
so you could hook it to anything between 2K
and infinity.
I will keep in mind what you have said.
I have noticed a terrible ringing effect at Q
5 and above.
Maybe that is what you are talking about.
In any case I really need to see things between .5Hz
and 2Hz. It is only the noise in my local area that
keeps me from doing this as far as I can tell.

http://home.mchsi.com/~gmvoeth/index.html

will show a bit more of what I am doing.

Buy the RS printed circuit board that has the same layout as the
breadoard. Build the circuit on that board, and put it inside of a
metal enclosure, so that most of the noise is kept out of the
circuit.

What is "RS printed circuit board " ?

RS = Radio Shack AKA Radio Scrap, etc. They sell a PC board that has
the same layout as the breadboard. Makes it easy to transfer the
circuit to a permanent circuit board.

I have settled on using only a single filter
as is now posted to my web site. This will
limit one to only seeing P waves but in
this noisy environment it is the best I can do.
I agree with everything you say except I can not
put a preamp outside with the Geophone.

Well, that's probably the reason why you are getting so much noise!

There is a circuit I have included not on the
schematic and it is a 567 tone decoder on the back
end to decode WWV calibration marks.

Thanks for your advice, I can see a lot of
common sense to it. But I still do not
know how to buy a circuit board that already
has my layout on it. I figure I will have
to do the layout and etching etc... myself.

I'm not sure you understand. The hole patterns match those on the
breadboard.
Here it is, it's catalog # 276-170 and costs a bit over $3.
http://www.radioshack.com/product.as...category%5Fnam
e=CTLG%5F011%5F002%5F002%5F000&product%5Fid=276%2D 170&MSCSProfile=745D84
CBF04D14A48AA6FF9C89D722C0BA68C1B04FE384678A5285FC D6E056B17AF21627FDABE3
16B90B3C038D68EBD6B7F9F3BD1712EAA9951ACB2590A05C65 17EFE46941FEFDD1985D4E
FD6321F5E70B4DE9B6C1D45512DCD9FB3DBCACB9479D26760F AF1D7B193B4FEA078B5E09
80BDD61634ABB7D328B012D36915420A2B457BE162481F674B


All preamplification should be done as close as possible to the
geophone, to get the signal well above the noise _before_ it goes
any
distance.

Filtering should be done at the other end, to get rid of noise in
the
long transmission line between the sensor and the PC.

One other important point. The outside can of the electrolytic is
at
signal level, and is a large capacitance to the outside world. Just
shielding these from outside noise should help. You might consider
putting some aluminum foil over the ones at the input, and grounding
the
foil to common. Just to see how much it will help to put the whole
thing in an enclosure.

[snip]

On Sat, 05 Feb 2005 09:06:45 -0800, Watson A.Name - "Watt Sun, the Dark
"gmv" wrote in message
"Watson A.Name - "Watt Sun, the Dark Remover""
"gmv" wrote in message
....
motor caps are too high power for my needs
I am just using small signal here.
NP caps are what i need.

Well, the motor caps are non-polarized. That's what you want.
And they are not electrolytic, I believe, but I'm not certain.

They are not. They are oil-filled paper. I don't understand the
"too high power", unless you mean simply that they're big fat
things. But they _do_ capacitate!

Aren't there digital filters that you can tailor the response
with smaller caps?

Good Luck!
Rich

On Sat, 05 Feb 2005 10:41:43 +0000, gmv wrote:
"Watson A.Name - "Watt Sun, the Dark Remover"" wrote in message ...
....
Anyway, what you need to do is use a mechanical filter, instead of
trying to make an electronic filter. One thought comes to mind. Use a
speaker and microphone coupled by a mechanical link, and add weight to
that link so that it would only respond to freqs below some low value,
such as 1 Hz. This also makes it a bandpass filter.

That sounds quite a bit more complex to me
then what I am already doing quite successfully.

Why not add some mass to the geophone itself? Do you have any pictures
of it, or design notes or anything?

Thanks,
Rich

forget about the RC oscillator, build a simple series RC circuit and
conect the input to a function generator producing 1hz output.

Find a proper value of R so the capacitor will just have enough time to
charge with the incomming square wave.

monitor the charging of the capacitor using an oscilloscope, you can use the
exponential equation for the charging of a capacitor in a series RC circuit
and solve it for C.


For more precise results, you can monitor the capacitor charging process
with a digital oscilloscope and hook up a computer to it using GPIB
(IEEE-488, HPIB)

Write a program to do a "data dump" from the oscilloscope to the computer
carefully look at your data and determine where 1 time constant is.

In an exponential curve, voltage changes quickly at the begining of the
charge curve and then things slow down.

TAKE your measurement at the begining (t,v) if you wait until the cap is
almost fully charged, a very small error in Vc can result in the wrong value
of t (curve is almost horizontal)


Option 2 don't use function generator, use a constant current source
instead!!

IF you charge a capacitor with a constant current source, the result is a
linear ramp, and the capacitance can be obtained from simple arithmetic!!!

V = (1/C) * I * t



"gmv" wrote in message
news:JQwMd.18007$C24.14251@attbi_s52...
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.

These capacitors are to be used at frequencies
under 1 Hz.

Everytime I try to use my meter to measure, the
capacitance will change from one range scale
to the next, I guess because the frequency changes too.
When I use a typical non-electrolytic capacitor
these changes in readings are not there.

I have been thinking of making
a simple RC inverter oscillator and using
the resulting frequency to determine the
true capacitance in the small signal
application I want to apply them to.

Maybe there are non-electrolytic capacitors
in the 10uf to 100uf range but if so
I have never heard of them before.

I do not know if any of you have ever seen
the SCI FI movie THIS ISLAND EARTH
but I am in need of several of those
fantastic capacitors.

I am trying to get a reading
within 1% of reality.

Help here is appreciated.


--
Regards;
gmv