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amplifying a received radio signal

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?

Reply to
occamsshavingkit
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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.

Reply to
mc

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 search if you pop up to many ready-made units.

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
Reply to
Tim Wescott

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.

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definition of a gyrator

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A simple gyrator based VLF receiver (you'd leave out the detector and just take the signal from the last amplifier.

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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.

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.

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.

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

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

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