40-20 antenna?

[Bill, KD0HG]

Have done some research, but haven't found exactly what I'm looking for..

I am looking for an antenna, commercial or the design for one, that covers 40 and 20 only. I don't want to use a fan dipole that requires multiple end supports.

A trap-loaded aluminum dipole or a QRO-rated trap wire dipole would be ideal.

Antenna to attach to side of a Rohn tower.

Suggestions welcome!

Bill

[K3YA]

Mosley makes 20M and shortened 40M dipoles.  There 40M trapped add on kit is also pretty robust but may hove trouble with a yellow 304TL.

I would probably homebrew two parallel dipoles out of the old 20M yagi  parts that I have here. 

[kb3ouk]

i have saw designs for a dipole that was dual band and had two wires parallel to each other, one tuned for one band and the second was tuned for another. looks a lot like this:

40 m section> ____________________ ___________________
20 m section>                 __________/  \__________

Fed in the middle with coax, the 20 meter and 40 meter sections share the same feedpoint. the 20 meter wire has spacers between it and the 40 meter wire.

[WA1GFZ]

How about a lazy H with two 44 foot horizontal elements supported by the tower. It will work 40 through 10 with a tuner and have gain.

[W4NEQ]

I have done exactly that for portable operation - I bought some milsurp fiberglass poles for the 30 foot center support, and used a 40 / 20 inverted vee with traps.  Worked well.

Traps are about $50 storebought:

http://www.unadilla.com/?p=34

[Bill, KD0HG]

Wow! Those Reyco traps are just what I'm looking for. Seem to be useable with either wire or aluminum antennas. Thanks.

I sent an email off to Moseley asking about their 40 meter kits to add to a 20 meter aluminum dipole.

I need general transmit coverage on 40 and 20. I can't do a rotatable beam. I have been thinking of using an aluminum dipole arrangement of some sort, broadside E-W. That would have a height advantage over a droopy inverted vee arrangement, but I could live with that.

I *don't* want to use a multiband inverted V configuration using multiple parallel dipoles. Four end supports become a PITA.

I don't want to add another tuner at the base of the tower- No fun going out in the dark multiple times to tune the thing. In knee-deep snow or mud. Been there, no more.

;-)

Bill

[W1AEX]

Bill,

I also wanted to avoid multiple tie points and found this method that's very durable and very cheap to build. Buy some Fi-Shock electric fence post insulators or PVC tubing and use them as spacers to suspend the 20 meter wires below the 40 meter elements. I have done this with a 160/75 meter antenna and also a 160/40 meter antenna as well as a 20/17 meter dipole. The picture shows my 20/17 meter antenna. There is a little bit of interaction between the two bands but it didn't take long to trim each antenna to the desired resonance for each band. I used parachute cord at the end of the shorter elements and tied them off to the longer wires above. It's durable and works fine.

Rob W1AEX

 

[Steve - K4HX]

Build your own.

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=23263


Most commercial traps don't like high power AM.

[ke7trp]

Can someone take a moment to explain how the reyco traps work and how they are ordered?  I understand what a trap is.  But I do not understand how they are purchased for your application and how to know the length of wire between them

If I wanted 80 and 40 on a wire dipole for phone bands.  You need two sets?

C

[Steve - K4HX]

No, just one set (two). The trap would be placed at approximately 33 feet from the center. This would define the 40 meter dipole. Then you would add wire on the other side (outside) of each trap to make the 80 meter dipole. The length is usually less than the normal 80 meter length since the trap acts as a loading coil on that band. The manufacturer should give you approximate lengths required.

[ke7trp]

Ok.  But why do they sell them with Frequency specific ratings?  I guess thats what confused me. I guessed that you would tune the inside wire and outside wires until both bands got flat.

I bet those really sway around in the wind huh?

C

[Bill, KD0HG]

Build your own.

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=23263


Most commercial traps don't like high power AM.

Good article, Steve. I've prolly got the pieces to make AM-rated traps, but they would certainly be unwieldy. I'm really more interested in 40 than 20 anyway.

Bill

[Steve - K4HX]

Build that and add 20 meter legs with spacer and you're done.

[kb3ouk]

Bill,

I also wanted to avoid multiple tie points and found this method that's very durable and very cheap to build. Buy some Fi-Shock electric fence post insulators or PVC tubing and use them as spacers to suspend the 20 meter wires below the 40 meter elements. I have done this with a 160/75 meter antenna and also a 160/40 meter antenna as well as a 20/17 meter dipole. The picture shows my 20/17 meter antenna. There is a little bit of interaction between the two bands but it didn't take long to trim each antenna to the desired resonance for each band. I used parachute cord at the end of the shorter elements and tied them off to the longer wires above. It's durable and works fine.

Rob W1AEX

 

that is exactly what i was trying to describe.

[WD5JKO]

Back in the mid 1980's I used a 80-40m trap Inverted V and used Unadilla Reyco KW-40 traps on each side. I ran a AM Killo0watt (DC input days), 850 watt carrier with > 100% upward modulation. Those traps took the power for several years. I still have them, been outside for over 25 years, and they look fine.


The Reyco trap antenna dimensions are hard to find on the net. I did find them, and the link is here:

http://www.adurcomms.co.uk/pdf%20files/Unadilla%20traps.pdf

So for a 40-20m trap dipole using the Reyco KW-20 trap, each side of center we have"

*Center*16.6' wire * Trap* 12.3' wire*End Insulator*

Jim
WD5JKO