captainkirksdog

Does anyone have a "crystal-radio", (i.e. NO power supply, NO batteries, just the signal itself) that will bring in WWV? I've built a few crystal sets, but try as I might, I can't tune in WWV. Any help?? Thanks.

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Nigel Goodwin

Crystal sets are short range only, it's not going to work from the outer limits of the solar system!.

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stevez

It is possible to do that with a crystal set - some factors that affect that:

A. How far you are from the transmitter.

B. Other stations that are on nearby frequencies.

C. Other nearby stations that your receiver can't keep out.

D. Time of day/band conditions.

E. Your antenna.

You might google on crystal radio sets as well as Shortwave Listening (SWL) to get some ideas.

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stevez

Gaston

as i understand it there is just way too much " noise" in the air these days to use a simple crystal set. i heard of a park ranger way back when before all of the noise that had a crystal set and a long wire from his tower streched out to a tree and every morning when the radio station would come up and play the star spangled banner and that would be his alarm clock. its ashame because i would love to have a setup like that. you can build a radio though whit a germainium diode. the germainium has less voltage drop that a silicon diode to pick up the relativly weak signal. i can look through my books and see if i can find a schematic if you need me too.

Roff

If you get your head out of Uranus and move to Fort Collins, Colorado, you might have a chance.

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Ron

k7elp60

In practical terms. The signal strength of the radio signal at the antenna terminals is in microvolts, that is 1 one millionth of a volt. If you consider a AA battery is 1.5 volts, you can see the difference. A pair of headphones probabley needs a few tenths of a volt to be heard. So a receiver that has amplification(requires power) and some selectivity(separates the stations)
is a minimum requirement.

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Roff

I think you can improve on that by using source and load impedance matching techniques on the coil, but a crystal set still needs a pretty strong signal. WWV transmits 2.5kW at 2.5MHz and 20MHz, and 10kW at 5, 10, and 15MHz. This is pretty weak compared to clear channel AM stations, which transmit at least 50kW.
Google "dx crystal" for ideas. Also, see this site for a crystal radio that is implied to receive WWV.

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Ron

RadioRon

I know this is not in keeping with your restriction of "just the signal itself" but would you be cheating if you added a small solar cell to give you some bias for a simple amplifier? I bet you would only need one amp to pull WWV out of the muck.

Of course, a crystal set normally gets all its power from the antenna so I hope that you have really pushed your antenna size and efficiency to the max before concluding it can't be done. Exactly what antenna have you tried so far?

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RadioRon

captainkirksdog

Hi all,
Thanks for the jokes and the help.
My antenna is a copper wire about 65 feet long between the eaves of my house and an old wood power pole. (no power, anymore). I am using a germainium 1N34 diode, an old 365pF tuner cap, and many different coils. The only thing I'm not sure of is the actual impedance of my headphones. I only have a DMM to measure it across the phone plug. I'm sure that's not a very accurate way to measure them, but I get about 1.8kohms.
So, if anyone has anything else to add, I'm certainly listening now that I've pulled my head out of Ur......no, no, no, NO! That's just not right! Whatever! I meant to say I'm listening. Thanks.

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RadioRon

The headphones sound like they are probably OK. I noticed back when I was playing with crystal sets a few years ago that there is a specific headphone type that is the mythical "best" headphones, and they are sought after but hard to find. Don't know if that is true or not, and can't help being skeptical, but I think that you should be OK if you use as high an impedance as you can find that still delivers some useful audio. If there is any doubt about the headphones, then just replace them temporarily with a powered audio amp to work out your antenna input optimization, then you can attack the headphone performance knowing that the input side is working well. To do this, it would be good if you attached a resistor in place of your headphones that has the same resistance (1.8Kohms?) and then use a high impedance audio amp (like what we used to call a "signal tracer"). This is important because the input is not isolated from the load (headphones) so the load should look the same whether you use a powered amp or not. This also gives you a way to vary the load resistance upwards from 1.8K to see if you need higher impedance headphones.

Your wire sounds good. Since you don't know what the impedance of your antenna is at whatever WWV frequency your trying to tune, your going to have to do a lot fooling around with your receiver input impedance by playing with different coil taps or series/shunt capacitors etc. to see if you can't tweak the sensitivity. You can't do any harm, so play around with the input tuned circuit configuration.

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RadioRon