Good homebrew AM antenna plans

I just found this forum!

This antenna has *sharp* tuning so
an MFJ-259 antenna analyzer is a good way to tune it up.

Here's the link...enjoy....and comments welcomed:

http://charliethompson.50megs.com/1610khz.htm

-=Chazro=-

What did you do to bring the MFJ down to 1610?

Hi all,

This is an interesting link and it is good to see someone who experiments posting the results. Unfortunately the sub links would not open for me...probably the server is getting overloaded due to the part15.us folks going there?

I don't mean to be too picky but rather to clairfy that the FCC 15.219 rules do not limit antenna height, rather they limit the total length of the antenna, transmission line, and ground lead.

Also, it is not the output power but rather the input power which is limited to 100 mW. Practically this means the output power will range from about 10 mW. to 80 mW.

Experimentation is wonderful, especially when the results are reported on this board. I just wanted to add a bit so the rules are interpreted properly.

Neil

Too cool that you posted that plan and links here - awesome!

Experimental broadcasting for a better tomorrow!

It is really nice.

I'd be interested in seeing more peoples antennas.

I'm thinking of the 102" CB whip base loaded somehow for my AMT3000. Still learning... I can cut a doublet to fit but that's not legal 🙂

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So, how do you determine the coil size needed for a given frequency? Or alternatively, what type of variable could be used to tune say 1610-1710 to give more use to the antenna?

Also, we'd talked about tuners (transmatch) a while back. I see none commerically made for the AM (MW) band (180m). So I assume this would be a homemade job (see paragraph above).

Just bringing this up to the top. I see some info in another thread...

I'll cut & paste after while.

Have you looked at the plans for the antenna on the SStran web site? If I can get my boss to go AM, that's what I intend to build. Seems simple enough, and everything can be bought locally (though ordering the wire might be cheaper).

Try the lpam.info link on the left side of this page. They have an article about loading coils which gives dimesions, turns, and frequency. I just tried the link but it is down though it usually works.

Neil

So, how do you determine the coil size needed for a given frequency? Or alternatively, what type of variable could be used to tune say 1610-1710 to give more use to the antenna?

Here is a link: http://www7.brinkster.com/yvesroy/10ft-antenna.asp

Regards
Yves

HA!

I just found that one this morning. It's based on copper pipe, but it should get me close enough.

I also found this today just to share info with everyone. http://www.northcountryradio.com/Articles/am88vert.htm

The only thing I'm not quite understanding is when/where to insert taps into the coil. I understand the principal but not how to determine where they go.

In the North Country Radio link, they suggest using as many ground radials as possible. Doesn't this go against the FCC rules concerning the total length of the antenna, feedline, and ground lead? Aren't those buried radials an extension of the ground lead?

Aren't those buried radials an extension of the ground lead?

From an electrical viewpoint, the radials constitute the r-f ground itself, and only the exposed conductor leading up from the intersection of the buried radials to the Part 15 AM tx chassis is part of the 3-meter radiating length defined by 15.219.
//

Check this article for some tips on this. Also, look at the variometer discussion.

http://lpam.info/index.php?page=antennas

The idea behind the taps is to provide adjustment of the inductance by selecting the appropriate tap. If you want to modify North Country's coil, add a few more turns than specified. The taps should be placed about every turn from one end of the coil until the turns between the innermost tap are fewer than those in the original coil. Keep in mind that we are trying to provide adjustment below and above the value of the nominal inductance so we want the taps to change the number of turns below and above the original number.

Neil

Cool! Thanks! That makes more sense.

Good question! How do you design the coil?
Here's a link to a program that will walk you
through the process:

http://www.btinternet.com/~g4fgq.regp/solnoid3.exe

This is a little DOS program that works OK in XP.

Also...if you can find it.... I like Brian Beezley's COIL.EXE
program. I can't seem to find it via Googling so I don't
know if Brian is still offering it to the public or not.

In general you'll find that the 3 meter whip has approximately
30pF of capacitance (give or take). So you want to resonate
the 30pF with a coil that you design using the above program.
Use the F=1/(2*pi*sqrt(LC)) equation to solve for "L" and then
the program above helps you wind the right coil size. "F" in this
case is your transmit frequency in Hz.

Have fun!

-W5CDT