TheRadioBoard

I'm glad to see me reviving this old post has sparked some interest here Sounds like a couple of us are gonna have some fun building this

One more question, how critical is the diameter and wire length ? I ask because I'm a More is better type and I have a 48 inch piece of 1 1/2 inch dia dowel and probably 150 feet of 16 Gage magnet motor wire.


I'm using it on a shortwave crystal radio I'm playing with and will have it hooked up to an antenna tuner.

Thanks guys !
Dan

It's a compromise antenna, so diameter is less of an issue. As for length, it depends on the frequencies of interest and the ability of your matching network to match it to your receiver. The latter is unknown until you build it. For receiving, if you find it doesn't tune high enough in frequency, you can remove turns. If you later have to add some back, a soldered splice won't affect performance as long as it doesn't short to adjacent turns. A piece of electrical tape under the splice, or heat-shrink tubing over it, should suffice.

If you've got room, you might try spacing the turns the diameter of the wire (use a spare roll of wire or stiff twine and remove after winding). That will aid in getting the antenna to tune higher in frequency. As you'll be using it with a crystal set, you'll still want a good ground system.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

Thanks for all that advice it might be a little tricky getting that spacing, but it's winter, I'm stuck in the house and want to play with this project this weekend. I'm glad you pointed that out to me.
Dan

AWG 16 wire has a diameter of 0.0508 inch (https://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes) Neglecting coating thickness, that works out to 944 turns over a 48-inch length. Your 1-1/2-inch dowel has a circumference of 4.712 inches. Even for a spiral winding, the circumference won't be much longer. If you have 160 feet of wire, that works out to 407 turns; we'll say 400. The dowel can contain almost 2.4 times as many turns, so you can use the whole spool and space by the diameter of the wire without overfilling the dowel.

Using another piece of wire, or twine, makes it easier to evenly space the turns, but if you're patient and your hands don't cramp up, you could do it by eye. Put a Ty-wrap on every time you start to get tired, to keep the existing turns in place. If the dowel dries after winding, it will shrink, so setting it in a sunny window and then giving it a coat of sprayed polyurethane before winding would be a good idea. Another shot of poly after winding won't significantly affect performance and will help keep the wire in place.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

Thank you so much for all your help ! I was wondering how much wire that dowel would hold I actually was wondering if it would hold 160 feet after I posted that I'm in-between meetings and checking this post, I plan to do this project this weekend and must admit I haven't given it a lot of thought, your making this easy for me, Thank You !

I appreciate your thoughts on sealing the dowel, I was thinking of using the polyurethane after I finished to hold the wire in place, I didn't think of the dowel shrinking & expanding But you are correct on that problem. I need to do some more homework on this as I don't know if you can polyurethane over top of dried polyurethane ? Maybe I should do as you say and make sure the dowel is dry (shouldn't be a problem in my home as my furnace drys my house right out) and polyurethane it after I wind the wire on it and seal it up as well as hold the wire in place.

I'm looking forward to this project, I will post pics when I get it done
Dan

One more question (you might hear that a few more times this weekend ) I was reading this topic (along with the link posted here already) on broomstick antennas.

http://www.ehow.com/how_4855036_build-s ... tenna.html

#2 Says: Fasten the aluminum disk to the top of the pole. How you do this will depend heavily on what kind of disc you have scavenged. If it has holes in it, for example, bind it with a cord. If not, you should drill holes in it and then bind it. The main thing is not to attach it to the pole with screws or bolts or anything made of metal

Why can't I fasten the aluminum disk to the top of the dowel with a steel screw ? The wood is going to prevent any connection being made anywhere ? Maybe I'm missing something here (wouldn't be the first time
Lol ) how else do you fasten it ? Superglue ?

Off to another meeting !
Dan

A brass wood screw should not cause any problems?

..............................................

Dan,

You can apply polyurethane over dried polyurethane. I've done it many times, including on my workbench. It doesn't hurt to rough the surface a bit if you use glossy poly; I used semigloss. I also used multiple coats on the Hoop Loop antenna project. After staining the hoop I put on one coat, then another after adding the winding. Had to do that because half the winding is exposed and I didn't want to accidentally bump the wires off the hoop.

As your antenna will not fill the dowel, start the winding a couple of inches below the top, to keep the winding as high above ground as possible. You can drill a small hole through the dowel and run the wire through to hold it in place. Then, a disk-fixing screw of any material will have no effect, as it will be far from the winding. You don't need a long screw. Brass would be better from an rf standpoint, but in this application I don't think it matters.

Things get a little different when you use an antenna like this to transmit. I sure wouldn't put much power into it, as the voltage at the top could get pretty high. If the disk had sharp edges you might even see corona discharges, just before the winding went SNAP!

This antenna will be greatly affected by nearby conductors, so plan to move it around while listening if you use it indoors. A couple of feet could make a difference.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

Thanks for all the advice !
Dan

I figured I would ask another question on this post, that way in the future if someone references this post they will have lots of info.

If you read my crystal radio broomstick antenna project, you will see I found out I have more coated 16 gauge magnet motor wire than I know what to do with

If I build an outdoor broomstick antenna, using PVC pipe and swing this thing 20 feet up on a pole, will it work as an AM antenna ? From what I have read, most of these types of antenna's are used for shortwave.

Thanks,
Dan

Almost anything will work on the BCB. As you're building a crystal set I think a longer, straight wire antenna would be a better idea. You could try both and compare results, though. Hard to know how a random antenna will work without building it.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

Ok, I am once again reviving this old post as I finally got around to building my broomstick antenna (only a year later )

Last night I played with my setup & couldn't pick up anything !

I only picked up 2 signals using my long wire setup, but I picked up nothing using this setup I'm a little thickheaded on throwing in the towel that a long wire is the only way to go, I was hoping to tear down my Short 30 foot long wire and just use this. I have it in my head that a long wire is ugly & after once watching a dove do a cartwheel in midair after hitting it I kinda want to take it down.

Looking for advice on making this work ? If not I guess I re-route my long wire over the peak of my house & try to hide it & make it bird proof.

Since that pic, I have added a 6 inch aluminum pie plate cutout to the top of the broomstick . It has 168 feet of wire on it, the winding is 34 inches long using coated electric motor winding.

All advice appreciated,
Thanks,
Dan




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You essentially have a very short indoor antenna. Maybe if you put little flags on the wire -- plastic tape used by surveyors -- the doves will avoid it.

73,

_________________

http://kr1s.kearman.com/
http://qrp.kearman.com/

KR1S, I always appreciate your quick helpful advice !  Thank You !

I am assuming the way you answered that question I had better get it in my thick skull that a long wire antenna is the only good way to go & to give up fighting the losing battle of an indoor replacement.
Dan