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[Articles Home]  [Add Article]  

160/75/40/20-Meter Dipole in 130'

from Ken Bessler, KG0WX on July 28, 2010
View comments about this article!

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 04/04/2007





KG0WX 20/40/75/160 trap dipole

This antenna is the culmination of a weekend's worth of work with the goal being to make a physically small 160m antenna with the addition of the extra bands being a bonus. The target was to make an efficient 160m antenna that fits into a 75m antenna's space, is coax fed and requires NO tuner or ground radials. Total cost was under $40.

Materials list:

130' of antenna wire, plus extra for adjustments
16" of 3" id schedule 40 PVC pipe, cut into 4" lengths
6" of 2" id schedule 40 PVC pipe, cut in half
4 4'x.25" hardwood dowels (cut into 2" pieces) & sealer
36' of Tramflex RG-8X coax (25.9pf/ft)
5 brass coat hangers, hooks cut off, straightened & varnish removed
Superglue
Gorilla glue
28 solder eye lugs
14 #8-32 machine screws
14 #8-32 nuts
Center & end insulators

Tools:

Soldering gun & solder
Single edge razor blades or x-acto knife
Drill with 1/4" & 1/16" bits
Saw for PVC & dowels
Tape measure
Calculator
Grid Dip meter or MFJ analyzer with dip coils
Heavy wire cutters
Sandpaper
Pliers
Measuring tape
Google for "Coaxial Trap Design" freeware

Start with the 75m traps - cut 2 4" lengths of 3" id PVC. Drill a 1/4" hole 1" from the end (make the hole angled so the coax doesn't kink). Cut 44 2" lengths of 1/4" hardwood dowels and wrap the middle of the PVC form with them (like a belt). This extends the O.D. of the PVC pipe to 4" diameter, which nets a better performing trap. Cut a 9' length of coax and remove the jacket from the last 2" of one end. Insert this into the PVC and wrap 1/2 turn around the form then tack the end in the hole with a drop of superglue. Set aside to dry and repeat for the 2nd 75m trap.

Wrap 7.86 turns of coax around the dowels and mark/drill for the second hole. cut the to coax to length so it sticks through the hole by 1-1/2 inches or so, trim the jacket again to fit the second hole. Lay a small bead of Gorilla glue around the dowels and wrap the coax tightly around the form then insert the end into the second hole and tack with superglue.

Separate the center conductor and braid on each end of the coax. Solder the braid from one end to the center conductor of the other end. Drill 1/16" holes in the ends of the form (4 holes per trap) for the coat hangers. You straighten and strip the coat hangers then use half a hanger per trap end. Insert the hanger and fold it up on the outside (you will end up with the hanger in the same shape as it was in the beginning, just smaller and with the trap threaded onto the bottom of the hanger). Solder the coax to the hanger where it passes through the trap - Braid on one end and center conductor on the other end. Solder lugs to the ends of the coat hangers. NOTE: Don't just depend on the solder to keep the lug on the hanger when the antenna goes up - I did and the lugs just pulled off when I raised the antenna. I used spare antenna wire to tie the trap to the antenna wire like a safety wire.

Repeat for the 40m traps, with no dowels though and wind 5.46 turns. The 20m traps are a different monkey, though - the coil form is only 2" id and the resulting trap is sensitive to the number of turns you use - I found a 1/2" addition to the coax length changed the resonant frequency by 200 kHz! I wrapped just under 4.4 turns.

I used a Heathkit GD-1B Grid dip meter to verify that the traps all worked - this is optional but you could also use a MFJ analyzer with dip coils, too. Build your center feedpoint (I didn't use a Balun) and attach 17' of antenna wire to each side.

Attach the 20m coils to the wire - note - you MUST orient the traps so that they all "point" the same way. That is, the end of the traps with the center conductor soldered to the coat hangers must all face the feedpoint (or the reverse) - just keep 'em all lined up. Now, with 17' of wire on each side of the feedpoint and the 20m traps on the ends of the wire, raise the antenna and trim it for where you want on 20 meters. I found this section of the antenna very broad-banded - I only had to trim 2-1/2" off each leg to cover all of 20m

Now to the part where you have to start "guessing" - with my Tramflex brand coax, the nature of my traps as loading coils on the lower bands determined how much wire I needed for the lower bands. Your traps may be different! Here is what I ended up with:

20 meter section: 16' 9-1/2" each side
40 meter section: 9' 9" between the traps
75 meter section: 14' 8-1/2" between the traps
160 meter section: 33' 4-5/8" on the ends.
Total antenna length is just under 130'

I installed the antenna as a flat dipole @ 25' up. Here are the RF results I got:
20 meters: 476.2khz bandwidth centered on 14175.0 (Trap Freq 14017.8)
40 meters: 151.4khz bandwidth centered on 7207.0 (Trap Freq 7010.2)
75 meters: 97.5khz bandwidth centered on 3930.75 (Trap Freq 3891.4)
160 meters: 47.2khz bandwidth centered on 1877.0

Now comes the fun - making a few contacts! For reference I have a Cushcraft R7000 vertical ground mounted, a Mosley TA-33M @ 25', a ladderline fed 40m inverted V @ 25' and a 75m linear loaded inverted V @ 25'. Normally, the R7000, 40m inv V and the Yagi trade off as to which one works better - It's a matter of take off angles and target distances. The 75m linear loaded dipole was my only 75m antenna so I assumed it was OK. Now, the new antenna on 20m is always at least as good as the R7000. On 40m there is no contest - the new antenna beats the R7000 by 1-2 S units and 1 - 1-1/2 S unit over the ladder line fed inverted V. On 75m the new antenna beats the linear loaded by the same amount. I don't have another 160m antenna for reference but after a few evenings on the band I can tell it's working equally as well as the rest of the antenna.

OH - one more thing - I don't own a tuner but I might get one to extend the useable range on 160m...

Ken KG0WX

Member Comments:
This article has expired. No more comments may be added.
 
160/75/40/20-Meter Dipole in 130'  
by W0FM on July 28, 2010 Mail this to a friend!
Very detailed description but, personally, I could sure benefit from a drawing or two. Maybe a photo?

Thanks for submitting.

73,

Terry, WōFM
 
160/75/40/20-Meter Dipole in 130'  
by WX4O on July 28, 2010 Mail this to a friend!
Very interesting, but I agree, a photo or diagram would be great.
 
RE: 160/75/40/20-Meter Dipole in 130'  
by N0OKS on July 28, 2010 Mail this to a friend!
Difficult to understand why all this effort when a fan dipole fed with twin lead to a tuner would accomplish the same thing.

Mark, NōOKS
 
160/75/40/20-Meter Dipole in 130'  
by N1KDO on July 28, 2010 Mail this to a friend!
My 135' doublet will load up on 160-6 with a transmatch.

The cost might be a bit more, $50 for the antenna parts, $100 for the DX Engineering balun... and then there is the price of the tuner to consider, as well.

However: 200 KHz bandwidth on 160, 500 KHz bandwidth on 80/75, 300 KHz bandwidth on 40M... You get the idea. It can be made to work just anywhere! And it tolerates QRO operation -- I'm not sure how well those traps will do with a kilowatt...
 
160/75/40/20-Meter Dipole in 130'  
by KC8FRJ on July 28, 2010 Mail this to a friend!
Antenna results can be a quirky because of interactions with the environment it exists in/with.
While I understand that interactions with the vertical may be small, the radials under the vertical could have played some role in the tested antennaís results. Same can be said for the inverted Vís mentioned. Are the inverted Vís laid out perpendicular to the tested antenna? If not, how many wave lengths were the antennas placed?


Donít get me wrong, I love the information; particularly how you build them. But one of the reasons I do not post much information about my antennas is that I am unsure of all their interactions with the objects in their space restricted environment. (Houses with foiled covered sheathing, aluminum siding, aluminum gutters, chain link fencing, utility cables, buried cables & pipesÖ..Itís maddening!) Accurate modeling seems to be a monumental task.

Best Regards,

Chris
 
160/75/40/20-Meter Dipole in 130'  
by K8QV on July 28, 2010 Mail this to a friend!
I don't know if this antenna works any better than the simpler solutions, but it's surely got to weigh a lot more!
 
160/75/40/20-Meter Dipole in 130'  
by KG6YV on July 29, 2010 Mail this to a friend!
Interesting antenna and congratulations that it works well. One consideration to keep in mind using PVC as a core for traps or loading coils is that fact that the "PVC tube" is open.

It may sound funny, but several of my fellow hams have the old W9INN 160/80/40 dipoles which use coils wound on PVC tubes.

Here is the danger. Critters build nests inside the tube (moths/wasps/etc), Their nest material can cause a short/flame/fire thru the PVC which is not designed to be a super RF insulator anyway. Wham, bam, boom you load up with something more than 100W and the whole form goes up in flames. I have seen 3 cases of this with W9INN dipoles. Its really cool the way the PVC lights, burns and the coil turns into a useless-shorted mess. No fun for the owner who has to take the dipole down and build a new trap.

I would put some end caps of some kind on any PVC trap or coil used in this manner.

FYI,

Greg
KG6YV

 
RE: 160/75/40/20-Meter Dipole in 130'  
by N4JTE on July 29, 2010 Mail this to a friend!
Ken, nicely detailed article and appreciate the work you put into it. My concern is with your statement that this antenna is "efficent" on 160 meters. I am aware that your comparisons on the other bands seem to indicate some improvement, not surprising considering that you are now comparing a straight flat top antenna against various loaded and unloaded inverted vees with perhaps their ends around 8 or so feet off the ground along with a ground mounted vertical of conservative height. Any flat top antenna will out perform your comparison antennas even at that 25 foot height. Because an antenna "loads" is the last reason for giving it high marks.
Your coil building techniques are very helpful and well documented, but if 160 meters is as important to you as the other bands, your antenna might be a disappointment, always a subjective expectation, but an inverted L on 160 is easily matched and constructed without coils and could quickly be switched between your experimental antenna with a remote antenna switch to acheive your multiband goal.
Thank you and keep on building.
Bob
 
RE: 160/75/40/20-Meter Dipole in 130'  
by W7ETA on July 29, 2010 Mail this to a friend!
This article was originally published on: 04/04/2007
 
RE: 160/75/40/20-Meter Dipole in 130'  
by W4VR on July 30, 2010 Mail this to a friend!
I bought my brother a W9INN 160/80/40 dipole about 10 years ago. The antenna had what W9INN called Resonactors. It was about the same length as your antenna. It worked fine on 80 on up, but on 160 it's performance left a lot to be desired...it was very inefficient to say the least.
 
RE: 160/75/40/20-Meter Dipole in 130'  
by W7ETA on July 30, 2010 Mail this to a friend!
This article was originally published on: 04/04/2007

Maybe you are describing how any low dipole or inverted Vee for 160 meters "acts", leaves a lot to be desired?
73
Bob
 
160/75/40/20-Meter Dipole in 130'  
by KB2DHG on August 3, 2010 Mail this to a friend!
As they say a picture is worth a thousand words... This article needs pictures to see exactly what the antenna is suppised to look like and see how it is built.
 
RE: 160/75/40/20-Meter Dipole in 130'  
by WB4TJH on August 3, 2010 Mail this to a friend!
Why go to all the trouble and expense of building a "Rube Goldberg" trap dipole? A simple 130 foot dipole fed with balanced feedline, which some people call a center fed Zepp, and a tuner will run rings around this trapped monstrosity any day of the week, be easier to put up and keep up, and so much more simple and little or no loss. I have been running this system for over 30 years and nothing in a simple antenna can beat it for all band service.
 
RE: 160/75/40/20-Meter Dipole in 130'  
by W8YG on August 8, 2010 Mail this to a friend!
Thanks for the dipole construction post. Its great!!
And to those who say an 80 meter doublet will load up on 160 it will at 5 or 10 watts and it wont get out at all.
What this gentle man has done is put more wire in the air and made his dipole resonant on 160. Resonant is the key.
Ladder line be it 450 or 600 or 300 is not the genie in the bottle and it will not make a wire resonant and workable unless its a harmonic of the lowest frequency its cut for. Hello radio? Read a book or article on this theory its even in the ARRL antenna handbook.
That is why some hams like to make dipoles of this nature.
As for the reference to a fan dipole. You still have to have the different wire to be resonant on the bands you cut it for and 160 is more than 30 feet so there goes the city lot it will be to long.
Ham radio is a hobby where people try new things. Even though some have grown lazy and can no longer work on radios I draw the line on antennas. This is the last part of our hobby that is still in reach of the average ham.
Trapped dipoles do work and very well.
 
160/75/40/20-Meter Dipole in 130'  
by CT1DOV on August 9, 2010 Mail this to a friend!
Hi Ken

Great description on the antenna and no dowbt it work. We are a group of CT hams that like to spend the weekends building and experimenting antennas. The problem is that we dont have the hardware and surplus stores you have. Could you be so kind as to send some pictures or detailed photos ?
Thank you and sorry about the English.
All the best
CT1DOV John ct1dov@gmail.com
 
160/75/40/20-Meter Dipole in 130'  
by KD7DCR on August 11, 2010 Mail this to a friend!
I have never been a big fan of anything "trapped".. My taste ran more to the "Rattler" antenna from an old 73 mag, back in the early 90's..

Start with two chunks of ROMEX house wire...I used 14/2 and it worked great...still works after 4 up and downs' qth moves.. Each chunk is 70ft long as I remember.

Strip back the outer cover for 2 to 3 inches, from both ends..all 4 of them! On two ends, cut off all but the "white" wire 1" back from the end. Connect the "black" wire to the "bare" ground wire...strip the end of the White wire back enough to make the center connection to your WINDOW LINE feedline...YES, you will need a wide range antenna tuner for open feedline! At the "other" end of each chunk... strip back and connect the "white" and "black" wires...bend them back from the end of the bare ground wire..no shorting allowed.

Now, "stress relieve" these ends when mounting them by any means you choose to use...(big grips are overkill). I used some 2" pvc pipe chunks..drilled 3 each 1/2" holes about 1.5" apart..and "threaded" the romax thru them like a snake.. Used a 4th hole at the other end for the rope support... For the center I used a longer chunk of the same 2" pvc...same 3 holes in the outer ends...it was about 2 ft long... brought the Ladder Line up and over the pipe center point..matched up the "ends of the romax with the bared "white" wires to it and connected...a few wraps of Super88 tape to secure everything and it was ready... Keep the Ladder Line over 72ft, but under 220ft, if I remember right...haul it up as high as you can get it...mine has worked from a "slight sloper" of 48ft down to 24ft heigh and well over 85ft on both ends in our trees...

IF you have "length" problems, you can just move your strss relief ends in a little closer, say 15 to 20ft or so...and let those ends hand down like a tail...I tied mine off to keep them from swinging during winds. Use one of those 9:1 baluns to change over to coax coming into the shack...

This thing never failed to tune and load!... I have used it on everything from 10m to 160m without failure. I have never tried to load it on 6m. I did have to change the length of my window line once, then all was well. Keep it "free" from any metal "amythings" and it will worky-worky..
 
RE: 160/75/40/20-Meter Dipole in 130'  
by K1XT on September 7, 2010 Mail this to a friend!
What's the deal with quote marks around various words. Is "black" not black? Is "white" not white? Why WINDOW LINE instead of window line?
 
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