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Martian Special Radio

Started by TelePlay, November 16, 2014, 12:20:21 PM

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DavePEI

Quote from: TelePlay on May 11, 2015, 10:36:32 PM
Sent an email to the radio station asking for their tower location and power.

The tower is about 10 miles from me and they put out 1,000 watts at night. Guess that's about right for a crystal radio. Anyone ever get a station father away?
Absolutely! When I was a kid, I used to listen to radio stations right across N. America at night with my crystal set. Right down to the Mexican border. You do need a good long wire antenna and ground, though!
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NorthernElectric

Quote from: DavePEI on May 12, 2015, 06:37:03 AM
When I was a kid, I used to listen to radio stations right across N. America at night with my crystal set. Right down to the Mexican border.

Mexican radio?   ;D
Cliff

DavePEI

#62
Quote from: NorthernElectric on May 12, 2015, 06:51:30 AM
Quote from: DavePEI on May 12, 2015, 06:37:03 AM
When I was a kid, I used to listen to radio stations right across N. America at night with my crystal set. Right down to the Mexican border.

Mexican radio?   ;D
XERF 1570 khz, home of Wolfman Jack! It was a 250,000 watt border radio station (and even at one point was expanded to 500,000 watts) in Ciudad Acuña, Coahuila. with enough power to be heard clear across N.America at night after the non clear channel stations reduced their power (as the regular stations were required to do). Most nights it came in just fine, with a bit of fading at times, in Ontario where I grew up, yes, even on my crystal radio! Unlike the stations the song refers to, it broadcast only in English.
The Telephone Museum of Prince Edward Island:
http://www.islandregister.com/phones/museum.html
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TelePlay

Connected the ground to a copper pipe driven into the ground and ran an external 50 ft long wire antenna 15 ft above the ground. Am receiving only one station broadcasting on 620 AM from a tower about 30 miles away. They put out 10,000 watts at night.

The true ground really made a difference. A real antenna got rid of the buzz I was getting off of the finger stop. Was expecting to get more than one station tonight but at least I now know the radio works on the full AM band - 1620 days and 620 nights. The 10,000 watt day station is only 8 miles away but drops down to only 1,000 watts at night. 620 has 50,000 watts days but drops down to 10,000 nights. Have to see what I pick up tomorrow, daytime. We have a couple of 50,000 watt stations in the area days so should be interesting to see what I get with the external antenna tomorrow.

Reception tonight is strong, clear and steady. Never used one of these before so this is all brand new to me, and quite fun.

19and41

Good work!  That antenna and ground can serve you well for tube type radios also.  You can get a lot from it. 
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

TelePlay

Hooked it up this morning and even with my age reduced hearing had the first thought of where is the volume control. 50,000 watts 30 miles away does come in strong. That station also takes up a good third of the tuning on my Martian. I am getting a few other stations up in the 1,000 to 1,670 range but they are competing and hard to distinguish. I can make out the 1640 station but it is getting walked on by a local 50,000 watt station on 1130.

Somewhere I read that the antenna can be tuned with a variable air capacitor. Think that would work, would help?

And yes, going to hook up my Froggy 7 tonight to see what I can pull in.

19and41

The capacitor should help.  It's interesting how such a unit leads one through each of the characteristics of radio reception.  last night you wanted sensitivity, today you need selectivity.  It's like discovering radio all over again!   :D
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

DavePEI

#67
Quote from: 19and41 on May 17, 2015, 10:00:34 AM
The capacitor should help.  It's interesting how such a unit leads one through each of the characteristics of radio reception.  last night you wanted sensitivity, today you need selectivity.  It's like discovering radio all over again!   :D

I have to echo his thoughts. Your radio is the simplest form of crystal radio. It is basically a coil with only a cat's whisker, which was great in the days where radio stations were sparse.

That is why, when I build mine, I used a design which also had capacitive tuning. Yours has poor selectivity, which was pretty normal with the simpler designs of crystal radios. Actually, I am surprised yours isn't more sensitive - it should be. You might just for a trial, try cleaning up all of the connections, and temporarily replacing the cat's whisker with a IN34 diode, and see if it becomes more sensitive. If it does, your crystal could benefit from a replacement. But I think if I remember correctly, you had to get a new crystal for the radio since the crystal was missing when you first got it. Try the diode temporarily to see if it improves things.

As I mentioned, with crystal radios, local stations running with high power will bleed through over weaker signals. The solution is to wait until night when they reduce power. I used to be able to tune in 20 or more signals at night using my childhood crystal radio.

You could try a 365 pfd. variable capacitor across the end leads of the coil, which will give you some selectivity. But then, you would be destroying the ultimate value of your radio, which as an interesting antique and collectible, just as surely as a person converting a 1317 wall phone so it will run on common battery, and hiding a dial in it  ::) However, playing with temporary replacement of the cats whisker to see if you get better sensitivity can't hurt, and even playing with a variable capacitor using clip leads to connect it can't hurt.

As 19and41 says, "It's like discovering radio all over again!" The lack of selectivity with crystal radios was the reason TRF, then Superhetrodyne circuits flourished. By nature, crystal radios lacked selectivity. However, you should be able to hear more than two stations at night.

One thought: I wonder if your headphones really are high impedance, or have they lost sensitivity over the years. Headphones for crystal radios should have an impedance of 20-40 K ohms. Your headphones due to moisture, and environmental causes during storage for all these years could have wavered from these specs. If they have, they could be loading down the signal from the radio - that would effect sensitivity, and not selectivity, and could cause you not to hear weaker stations even though the radio was working correctly.

Keep on playing - that is part of the fun of crystal radios. But bear in mind, yours is a very early design, using only a slider on the coil to tune it...

P.S. A final thought added later - you might try cleaning the coil where the slider goes up and down. A very light sanding of that spot only with extremely fine sandpaper should suffice.

Dave



The Telephone Museum of Prince Edward Island:
http://www.islandregister.com/phones/museum.html
Free Admission - Call (902) 651-2762 to arrange a visit!
C*NET 1-651-0001

TelePlay

#68
Quote from: DavePEI on May 17, 2015, 12:37:34 PM
I wonder if your headphones really are high impedance, or have they lost sensitivity over the years. Headphones for crystal radios should have an impedance of 20-40 K ohms. Your headphones due to moisture, and environmental causes during storage for all these years could have wavered from these specs. If they have, they could be loading down the signal from the radio - that would effect sensitivity, and not selectivity, and could cause you not to hear weaker stations even though the radio was working correctly.

I'm using a relatively new (mid '30s) set made by Telephonics. I think they are military. The back of each Bakelite can is stamped into the Bakelite is 8500-Z. So, I guess these are a bit low.

But, looking through the specs on a lot of headphones at this link

http://oldheadphones.com/crystal/gallery/gallery.html

it seems the top end is 4K ohms DC resistance. How does Z impedance compare to ohms - just the same thing but different word when it comes to headphones?

I have another set I'll have to dig out of storage. They are piezo crystal headphones and haven't tried them yet.

DavePEI

Quote from: TelePlay on May 17, 2015, 10:45:16 PM
Quote from: DavePEI on May 17, 2015, 12:37:34 PM
I wonder if your headphones really are high impedance, or have they lost sensitivity over the years. Headphones for crystal radios should have an impedance of 20-40 K ohms. Your headphones due to moisture, and environmental causes during storage for all these years could have wavered from these specs. If they have, they could be loading down the signal from the radio - that would effect sensitivity, and not selectivity, and could cause you not to hear weaker stations even though the radio was working correctly.

I'm using a relatively new (mid '30s) set made by Telephonics. I think they are military. The back of each Bakelite can is stamped into the Bakelite is 8500-Z. So, I guess these are a bit low.

But, looking through the specs on a lot of headphones at this link

http://oldheadphones.com/crystal/gallery/gallery.html

it seems the top end is 4K ohms DC resistance. How does Z impedance compare to ohms - just the same thing but different word when it comes to headphones?

I have another set I'll have to dig out of storage. They are piezo crystal headphones and haven't tried them yet.
No the net resistance of the phones doesn't directly co-relate to the impedance. Remember there is an inductive component in determining impedance... Try the Piezo headphones and see if they make a difference.

Dave
The Telephone Museum of Prince Edward Island:
http://www.islandregister.com/phones/museum.html
Free Admission - Call (902) 651-2762 to arrange a visit!
C*NET 1-651-0001

19and41

I was thinking, there is another mineral that was used in open detectors for crystal sets and it is something we have a lot of down here In Georgia:  Iron pyrite.  There is so much of it here the dust looks like there is glitter blended in it.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

DavePEI

Quote from: 19and41 on May 19, 2015, 02:14:37 PM
I was thinking, there is another mineral that was used in open detectors for crystal sets and it is something we have a lot of down here In Georgia:  Iron pyrite.  There is so much of it here the dust looks like there is glitter blended in it.
That's right. Iron Pyrite - Fool's Gold!
The Telephone Museum of Prince Edward Island:
http://www.islandregister.com/phones/museum.html
Free Admission - Call (902) 651-2762 to arrange a visit!
C*NET 1-651-0001

mdodds

In retrospect, the finger-stop antenna connection probably worked well for me for a couple reasons.
I was in a small village in the Adirondacks in the mid-late 60's with very little QRM to worry about, plus there were really only 2 stations that were receivable in the daytime anyway, WIRD (a 5KW daytime only) and WNBZ(1 KW daytime, 250W at night).
Plus, the POTS infrastructure at that time was copper pairs all the way to the CO. It worked very well for those 2 stations and actually worked at night for the blowtorch stations of the day, except you tended to hear several at once :)
For night time use I had a bakelite Sears Silvertone 6 tube series string AC/DC radio with a pillow speaker jacked in so I could listen after I was supposed to be asleep  8) I don't know if that 6th tube really helped over the traditional 5 octal tube complement, but it was a sweet performing radio.

TelePlay

Quote from: mdodds on May 20, 2015, 05:43:27 PM
In retrospect, the finger-stop antenna connection probably worked well for me for a couple reasons.
I was in a small village in the Adirondacks in the mid-late 60's with very little QRM to worry about, plus there were really only 2 stations that were receivable in the daytime anyway, WIRD (a 5KW daytime only) and WNBZ(1 KW daytime, 250W at night).
Plus, the POTS infrastructure at that time was copper pairs all the way to the CO. It worked very well for those 2 stations and actually worked at night for the blowtorch stations of the day, except you tended to hear several at once . . .

Yes, and back then was the copper wire hung from poles back to the CO? I have a land line with copper back to the CO but it's all under ground which might reduce the signal.

Anyway, hung the antenna again tonight, about 60 feet, to try out a few different head phones. I use 24 gauge line cord, pull apart so only one conductor is being used. I tied 2 one ounce fishing lead sinkers on the end and launched it high over a tree branch. The two ounce weight was enough to hit the ground so pulled the wire up so the weight was just into the bottom canopy of the tree, out of reach and hidden. Comes down by releasing the other end of the wire from the house and winding up the antenna from below the tree. Tried just one ounce but that was not enough to pull the wire tight.

The first head phones I tried were my Telephonics to get the radio working and tuned. I then switched to a pair of Acme Trim head phones and they produced the same results, the same volume as the Telephonics head phones.

So, I dug out my Brush Model 200 piezo crystal head phones. According to specs from another site, "The phones have a wide range response from 60 to 10,000Hz. These phones have an impedance of approximately 50,000 ohms at 400Hz"

These gave me a gain in volume of about 100%, doubled the volume. Was able to hear the local late night blow torch over half of the coil (not what I would call fine tuning) and within the other half, could make out about 4 stations, all walking on each other.

I did notice that with each of the head phones, I was picking up a low volume buzz, sounded like 60 cycle, not related to the TV or lights. But by accident, I discovered if I placed the palm of my hand on the top plate of the radio coil, the buzz went completely away and the volume was not affected. That made for good listening.

Another thing I noticed was the more I use the crystal, the easier it is to find sweet spots and they are louder. I wonder if raking the wire over the crystal is removing some coating that developed of the years since it was made. It was sold as NOS from more than a few decades ago. If that is the case, is there any way to clean or refresh the surface of the crystal?

DavePEI

#74
Quote from: TelePlay on May 23, 2015, 01:00:55 AM
So, I dug out my Brush Model 200 piezo crystal head phones. According to specs from another site, "The phones have a wide range response from 60 to 10,000Hz. These phones have an impedance of approximately 50,000 ohms at 400Hz"

These gave me a gain in volume of about 100%, doubled the volume. Was able to hear the local late night blow torch over half of the coil (not what I would call fine tuning) and within the other half, could make out about 4 stations, all walking on each other.

I did notice that with each of the head phones, I was picking up a low volume buzz, sounded like 60 cycle, not related to the TV or lights. But by accident, I discovered if I placed the palm of my hand on the top plate of the radio coil, the buzz went completely away and the volume was not affected. That made for good listening.

Another thing I noticed was the more I use the crystal, the easier it is to find sweet spots and they are louder. I wonder if raking the wire over the crystal is removing some coating that developed of the years since it was made. It was sold as NOS from more than a few decades ago. If that is the case, is there any way to clean or refresh the surface of the crystal?
Ok, so now you have the sensitivity... Re: your buzzing problem. I still wonder if there is some corrosion somewhere in the set which could be causing this. Have you tried cleaning up all the connections in the set? Make sure the screws on the lid don't have any corrosion between them and the plate.

Now you have the sensitivity, you may want to play with ways to make it more selective, specifically putting a 365 pfd. variable capacitor across the coil with clip leads, and use that to see if you can tune out some of the splatter from other stations.

When you had mentioned the low signals you were getting, I thought it might be related to the headphone impedance.... Glad that turned out right....

This was a very basic radio, only a coil and slider, cat's whisker, and therefore didn't offer much tunability. But you can have fun experimenting with a capacitor...

Insofar as cleaning the galena, I have never tried that. The detector relies on the impurities in the galena to rectify the signal. I would be worried that if you tried to clean it the wrong way, you might remove the sulphides which help it rectify... Tuning a cat's whisker is an acquired skill - you may just be getting better at it...

The main thing, is have fun with it. It must be close to 100 years old, and still working, so you should be pleased!

Dave
The Telephone Museum of Prince Edward Island:
http://www.islandregister.com/phones/museum.html
Free Admission - Call (902) 651-2762 to arrange a visit!
C*NET 1-651-0001