### Network

O

#### [email protected]

Jan 1, 1970
0
I'm interested in making my own WWVB time clock. (the WWVB is a 60kHz
signal sent out by the US NIST with an encoded time signal) I have
many questions.

As I understand it, a radio receiver is an antenna, an inductor and a
capacitor. I assume I can connect them in series in that order?

WWVB broadcasts its time signal at 60kHz, so all I need to do is take
2*pi*f = 1 / sqrt(L * C) and choose an inductor and capacitor that
will make f 60000, attach a length of wire as the antenna to the
inductor, and I'll be getting the signal, right?

Obviously the signal will be weak, what is an appropriate method for
amplifying it? What is an appropriate amplification factor? The WWVB
website at NIST says that it broadcasts "loud" enough to give at least
50uV signal over almost all of the continental US. Let's assume that
is the strength I am dealing with.

The time on WWVB is encoded by dropping the dB level by 17 dB and
raising it again. (I am not sure how that translates into a voltage
strength equivalent) Is there a way to make the "low" signal come out
the amplifier as 0?

Should I send it through an op-amp? I plan on sending the signal to an
input (ADC input?) on an attiny chip.

I found plenty of schematics for audio amplifiers for crystal radios
on the web, but WWVB's signal changes from low to high at most every
0.2 seconds, which I think would make the capacitors in those
schematics eat my signal.

I assume I'd also want to put some kind of voltage regulator on there,
just in case I take my clock a lot closer to the signal source. Would
a Zener diode do?

M

#### mc

Jan 1, 1970
0
Let me suggest that you find some published circuits for WWVB receivers.
There's more to it than that. Longwave reception is tricky because there is
a gigantic amount of ambient noise on those frequencies.

T

#### Tim Wescott

Jan 1, 1970
0
I'm interested in making my own WWVB time clock. (the WWVB is a 60kHz
signal sent out by the US NIST with an encoded time signal) I have
many questions.

As I understand it, a radio receiver is an antenna, an inductor and a
capacitor. I assume I can connect them in series in that order?

WWVB broadcasts its time signal at 60kHz, so all I need to do is take
2*pi*f = 1 / sqrt(L * C) and choose an inductor and capacitor that
will make f 60000, attach a length of wire as the antenna to the
inductor, and I'll be getting the signal, right?

Obviously the signal will be weak, what is an appropriate method for
amplifying it? What is an appropriate amplification factor? The WWVB
website at NIST says that it broadcasts "loud" enough to give at least
50uV signal over almost all of the continental US. Let's assume that
is the strength I am dealing with.

The time on WWVB is encoded by dropping the dB level by 17 dB and
raising it again. (I am not sure how that translates into a voltage
strength equivalent) Is there a way to make the "low" signal come out
the amplifier as 0?

Should I send it through an op-amp? I plan on sending the signal to an
input (ADC input?) on an attiny chip.

I found plenty of schematics for audio amplifiers for crystal radios
on the web, but WWVB's signal changes from low to high at most every
0.2 seconds, which I think would make the capacitors in those
schematics eat my signal.

I assume I'd also want to put some kind of voltage regulator on there,
just in case I take my clock a lot closer to the signal source. Would
a Zener diode do?

There's more to it than that -- unless you're right next door to the
transmitter, probably much much more.

Do a web search on "WWVB receiver", possibly include "schematic" in your

You'll find a suitable project.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

D

#### default

Jan 1, 1970
0
I'm interested in making my own WWVB time clock. (the WWVB is a 60kHz
signal sent out by the US NIST with an encoded time signal) I have
many questions.

As I understand it, a radio receiver is an antenna, an inductor and a
capacitor. I assume I can connect them in series in that order?

You can use either a series resonant or parallel resonant circuit.
Receivers usually employ parallel resonant circuits (LC in parallel) -
check out some crystal radio schematics.

At 60 KHZ the inductor size may be unwieldy, but at that low a
frequency a band pass filter or gyrator tuned circuit probably makes
more sense.

http://en.wikipedia.org/wiki/Gyrator definition of a gyrator

http://aavso.org/observing/programs/solar/gyrator.shtml A simple
gyrator based VLF receiver (you'd leave out the detector and just take
the signal from the last amplifier.

http://www.auroralchorus.com/bbb4rx3.htm Schematic of a very simple
VLF (11KHZ) receiver. To get the inductor needed he uses an audio
transformer as part of the band pass filter.
WWVB broadcasts its time signal at 60kHz, so all I need to do is take
2*pi*f = 1 / sqrt(L * C) and choose an inductor and capacitor that
will make f 60000, attach a length of wire as the antenna to the
inductor, and I'll be getting the signal, right?

Sure. In theory at least. How close are you to the transmitter? How
close are you to a Loran site? They transmit at 100 KHZ and may
interfere.
Obviously the signal will be weak, what is an appropriate method for
amplifying it? What is an appropriate amplification factor? The WWVB
website at NIST says that it broadcasts "loud" enough to give at least
50uV signal over almost all of the continental US. Let's assume that
is the strength I am dealing with.

The time on WWVB is encoded by dropping the dB level by 17 dB and
raising it again. (I am not sure how that translates into a voltage
strength equivalent) Is there a way to make the "low" signal come out
the amplifier as 0?

Should I send it through an op-amp? I plan on sending the signal to an
input (ADC input?) on an attiny chip.
An op amp will have an open loop amplification of 200,000 or so, but
to get some reasonable gain and stability you'd probably use two or
more stages.
I found plenty of schematics for audio amplifiers for crystal radios
on the web, but WWVB's signal changes from low to high at most every
0.2 seconds, which I think would make the capacitors in those
schematics eat my signal.

Crystal radios detect the signal in the 500 - 1,000 KHZ range and
produce an audio output - you don't want or need that kind of
filtering or detection on the output
I assume I'd also want to put some kind of voltage regulator on there,
just in case I take my clock a lot closer to the signal source. Would
a Zener diode do?

Voltage regulator? Do you mean to say "automatic gain control?"

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