On Sun, 10 Mar 2013 17:09:45 -0400, rickman wrote:

On 3/10/2013 1:32 AM, Jeff Liebermann wrote:

Holy crap! That's a lot of trouble to see a signal. By "see" I assume
you mean on the scope. How large was the signal?

Turning off the house was easier than finding the multiple sources of
noise at 60KHz. What drove me nuts for about an hour was that much of
the noise was coming from my bench oscilloscope. Argh.

This is typical. WWVH through an active preamp showing the effect of
power line noise (probably from attached switching power supplies).
http://www.prc68.com/I/Images/AMRAD110.GIF
and after adding some better line filtering:
http://www.prc68.com/I/Images/AMRAD_BT.GIF
Main page:
http://www.prc68.com/I/LF-Ant.shtml

I didn't log the setup or take pictures. So, let's do the math and
guesswork.
http://vk1od.net/calc/FS2RPCalc.htm
I plugged in some guesses and recollections as to what the antenna
(Q=30) and amp (+20dB gain) were doing and got:
http://802.11junk.com/jeffl/crud/WWVH-rx-signal-estimate.jpg
-15.8dBm or about 36mv into 50 ohms. I amplified this about 20dB with
two or three U310 JFET's (I forgot what I did) to about 3V rms on the
scope. I didn't bother with the 50 ohm to scope input Z conversion.
Most of what I saw was noise, noise, and more noise. However, if I
was patient, I could see the data fade in an out. As I vaguely
recall, it was less than 1 division or about 0.1v change.

The place where I am working currently is not very close to much and
there isn't much in the house. I'm told the fridge is the biggest
source of noise. We'll see how the CFL lamps do.

Sigh. Most of what I found at 60KHz was coming from lightning storms
over Florida. The local sources were all switching power supplies,
including those in my test equipment. I didn't have an CFL or LED
room lights at the time. I've recently found them to be a rather
nasty noise source. Also, the switching power supply wall warts were
rather awful. My standard test is to fire up my antique IC-735 HF
xceiver, attach a long length of RG-58c/u to the antenna with a
resonant loop at the end, tune it to 100KHz (as low as it will go),
and sniff around the house.

What you'll see on a spectrum analyzer.
http://www.prc68.com/I/Spec_0002.shtml
If you're thinking of removing all that junk with a 5Hz wide digital
filter in software, please note that you'll need to have the input A/D
handle the total power of almost all that junk. Also, the amplifier
that you're trying to avoid between the antenna and A/D will also need
to be rather linear, and therefore rather high power, in order to
avoid producing more spurious junk via intermodulation products.

Funny, last night my two RCC's both updated like they should. One is an
analog clock and runs at 8x speed to get the hour ahead. In the fall it
does this to go 11 hours ahead. Quite a sight! They both did the job,
but my PC didn't update until it had been on for awhile, without being
connected to the I'net.

So that's how they change daylight savings time. If I had known, I
would have stayed and watched. Thanks for the tip.

On the east coast, besides a weak signal, you also have the potential
for 60KHz interference from the UK:
http://en.wikipedia.org/wiki/MSF_time_signal

Loop antennas have a null that can be steered toward the source of
interference. I expect that will solve that problem...

The depth of the notch seems to be less as the antenna shrinks in
size. I'm not sure about this as I haven't attempted to recently
model a 60KHz magnetic loop with 4NEC2, but that's what my tinkering
shows. If there were a deep notch, most of the home "atomic clock"
receivers would be orientation sensitive and I would expect warnings
in the docs.

The BPSK signal is much better at rejecting interference and digging
the signal out of the noise. I don't know exactly how much, but I'm
sure it's in a NIST publication somewhere.

That's for an ideal receiver. I have my limitations and I have no idea
how that will impact the reception.

Well, you have to start somewhere, and an ideal receiver is a good
place to start. The advantage is that reality only makes everything
worse, never better. You should be able to build the BPSK
demodulator, and then use a PC to decode the data. I've seen several
such programs that do not require I/Q outputs. Here's one based on
FreeBSD intended to sync the system clock to WWV/WWVH:
http://docs.freebsd.org/doc/4.0-RELEASE/usr/share/doc/ntp/driver36.htm
I'm sure there are others.

In my case I am not worried that the SNR isn't better, I just need a
strong enough signal to drive the LVDS input.

Gain at 60KHz is very cheap. Watch out for overload issues. If you
design it to work at full scale with whatever you get at 50uV/m, and
the signal climbs to 100uV/m, your input A/D isn't going to be very
happy. AGC will help, but I don't think it will be needed if you
calculate your signal levels so that the A/D input amp isn't clipping.

Out of service for a day. It seems that about 30 years of chemistry
experiments has finally destroyed much of the kitchen sink plumbing. I
hate plumbing.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 3/10/2013 11:42 PM, Jeff Liebermann wrote:
On Sun, 10 Mar 2013 17:09:45 -0400, wrote:

On 3/10/2013 1:32 AM, Jeff Liebermann wrote:

Holy crap! That's a lot of trouble to see a signal. By "see" I assume
you mean on the scope. How large was the signal?

Turning off the house was easier than finding the multiple sources of
noise at 60KHz. What drove me nuts for about an hour was that much of
the noise was coming from my bench oscilloscope. Argh.

Yes, like I said, not much in this house and there is not much near it.
I have a laptop and my roommate (when he is here) uses one along with
an iPhone. I suppose they might generate some noise, but he turns off
his laptop at night I'm sure. Otherwise, there just isn't much in the
house that isn't 10 or 15 years old. I have a car radio on a linear
regulator and an electric shaver that sits charging (part of the time).
Otherwise it should be pretty quiet electrically here.


This is typical. WWVH through an active preamp showing the effect of
power line noise (probably from attached switching power supplies).
http://www.prc68.com/I/Images/AMRAD110.GIF
and after adding some better line filtering:
http://www.prc68.com/I/Images/AMRAD_BT.GIF
Main page:
http://www.prc68.com/I/LF-Ant.shtml

I didn't log the setup or take pictures. So, let's do the math and
guesswork.
http://vk1od.net/calc/FS2RPCalc.htm
I plugged in some guesses and recollections as to what the antenna
(Q=30) and amp (+20dB gain) were doing and got:
http://802.11junk.com/jeffl/crud/WWVH-rx-signal-estimate.jpg
-15.8dBm or about 36mv into 50 ohms. I amplified this about 20dB with
two or three U310 JFET's (I forgot what I did) to about 3V rms on the
scope. I didn't bother with the 50 ohm to scope input Z conversion.
Most of what I saw was noise, noise, and more noise. However, if I
was patient, I could see the data fade in an out. As I vaguely
recall, it was less than 1 division or about 0.1v change.

I'm not sure why you used 1900 meters for the distance. I also don't
get why you used 5 ohms for the receiver input impedance.


The place where I am working currently is not very close to much and
there isn't much in the house. I'm told the fridge is the biggest
source of noise. We'll see how the CFL lamps do.

Sigh. Most of what I found at 60KHz was coming from lightning storms
over Florida. The local sources were all switching power supplies,
including those in my test equipment. I didn't have an CFL or LED
room lights at the time. I've recently found them to be a rather
nasty noise source. Also, the switching power supply wall warts were
rather awful. My standard test is to fire up my antique IC-735 HF
xceiver, attach a long length of RG-58c/u to the antenna with a
resonant loop at the end, tune it to 100KHz (as low as it will go),
and sniff around the house.

There's just not much of that in this house.


What you'll see on a spectrum analyzer.
http://www.prc68.com/I/Spec_0002.shtml
If you're thinking of removing all that junk with a 5Hz wide digital
filter in software, please note that you'll need to have the input A/D
handle the total power of almost all that junk. Also, the amplifier
that you're trying to avoid between the antenna and A/D will also need
to be rather linear, and therefore rather high power, in order to
avoid producing more spurious junk via intermodulation products.

What A/D? Oh, you mean the LVDS input. How do you saturate a 1 bit ADC?


Funny, last night my two RCC's both updated like they should. One is an
analog clock and runs at 8x speed to get the hour ahead. In the fall it
does this to go 11 hours ahead. Quite a sight! They both did the job,
but my PC didn't update until it had been on for awhile, without being
connected to the I'net.

So that's how they change daylight savings time. If I had known, I
would have stayed and watched. Thanks for the tip.

On the east coast, besides a weak signal, you also have the potential
for 60KHz interference from the UK:
http://en.wikipedia.org/wiki/MSF_time_signal

Loop antennas have a null that can be steered toward the source of
interference. I expect that will solve that problem...

The depth of the notch seems to be less as the antenna shrinks in
size. I'm not sure about this as I haven't attempted to recently
model a 60KHz magnetic loop with 4NEC2, but that's what my tinkering
shows. If there were a deep notch, most of the home "atomic clock"
receivers would be orientation sensitive and I would expect warnings
in the docs.

I wouldn't say the *depth* of the null depends on the size of the loop.
I think it is a null with a Q, much like a resonance peak, but a null
of course. The smaller the loop, the sharper the null like a high Q
resonance, so the orientation becomes very critical. In theory at
least, the null is perfect, 0 signal.


The BPSK signal is much better at rejecting interference and digging
the signal out of the noise. I don't know exactly how much, but I'm
sure it's in a NIST publication somewhere.

That's for an ideal receiver. I have my limitations and I have no idea
how that will impact the reception.

Well, you have to start somewhere, and an ideal receiver is a good
place to start. The advantage is that reality only makes everything
worse, never better. You should be able to build the BPSK
demodulator, and then use a PC to decode the data. I've seen several
such programs that do not require I/Q outputs. Here's one based on
FreeBSD intended to sync the system clock to WWV/WWVH:
http://docs.freebsd.org/doc/4.0-RELEASE/usr/share/doc/ntp/driver36.htm
I'm sure there are others.

PC?!!! We don't need no stinking PCs! The demodulator is simple. The
signal is beat with a quadrature reference which will bring it down to 0
Hz. This gives two values, a sin and a cos signal. Take the ratio and
do an arcTan. This is a simple table lookup made simpler by some
convenient math relations. For example, the table only needs to cover
0° to 45° since the ratio can be swapped for 45° to 90° and the other
three quadrants distinguished by the sign bits.

Some folks would like you to think this has to be done like a high
fidelity receiver, but it only has to pull the signal out of the noise.


In my case I am not worried that the SNR isn't better, I just need a
strong enough signal to drive the LVDS input.

Gain at 60KHz is very cheap. Watch out for overload issues. If you
design it to work at full scale with whatever you get at 50uV/m, and
the signal climbs to 100uV/m, your input A/D isn't going to be very
happy. AGC will help, but I don't think it will be needed if you
calculate your signal levels so that the A/D input amp isn't clipping.

If this is *signal* strength then it won't matter. If this is noise you
are talking about, I'm not sure it will be a problem, the signal will
still be able to be dug out with enough processing gain.


Out of service for a day. It seems that about 30 years of chemistry
experiments has finally destroyed much of the kitchen sink plumbing. I
hate plumbing.

Not much fun, but then what it if you have to work on your knees and get
dirty? I don't enjoy working on my car anymore either.

--

Rick

On Mon, 11 Mar 2013 18:10:23 -0400, rickman wrote:

So, let's do the math and
guesswork.
http://vk1od.net/calc/FS2RPCalc.htm
I plugged in some guesses and recollections as to what the antenna
(Q=30) and amp (+20dB gain) were doing and got:
http://802.11junk.com/jeffl/crud/WWVH-rx-signal-estimate.jpg
-15.8dBm or about 36mv into 50 ohms. I amplified this about 20dB with
two or three U310 JFET's (I forgot what I did) to about 3V rms on the
scope. I didn't bother with the 50 ohm to scope input Z conversion.
Most of what I saw was noise, noise, and more noise. However, if I
was patient, I could see the data fade in an out. As I vaguely
recall, it was less than 1 division or about 0.1v change.

I'm not sure why you used 1900 meters for the distance. I also don't
get why you used 5 ohms for the receiver input impedance.

(Quick reply... still working on my expanding plumbing problem).

The 1900 meters is because I screwed up. It should be about 1900Km
from San Francisco to Denver. However, any distance greater than zero
will suffice for this calculation. The controlling numbers are the
100uV/m field strength, the -3dB antenna gain, and the receiver
bandwidth (5Hz). All of the other numbers can change without having
any effect on the recovered power. The 5 ohms rx input Z was because
the original antenna that I used, was a base loaded 100ft "whip"
antenna with a rather impedance. I couldn't decide if the field
strength to receive power form wanted the antenna impedance before the
50 ohm matching network, or if it treated the matching as part of the
antenna. I flipped a coin and chose 5 ohms. I guess for a loop,
100-200 ohms would be more appropriate. Again, the value makes no
difference in the calculations.

(Back to plumbing and fixing the 48" farm jack that my neighbor
borrowed and returned looking like a pretzel).




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

(Back to plumbing and fixing the 48" farm jack that my neighbor
borrowed and returned looking like a pretzel).


It sounds like your neighbor doesn't know jacks. ;-)