Compact wire Tri-band Yagi for 10 -15m

2 active elements each band

 

By K1NQ (Rev 3/22/04)

 

Introduction

 

Specifications

300KHz 2:1 BW on 10-15m; 350KHz on 20m

Gain 5.5 dBi F/B ~10 dB

6 wire elements – 2 active on each band

Single feed point requiring no matching circuits.

Only 10 feet wide – makes a good portable antenna.

 

This is a wire version of a 2 element yagi antenna using a single feed point, no traps, and no matching circuits.  The antenna is based on the open sleeve dipole design employing a single dipole feed at the 20m driven elements.  The 10 and 15m driven elements are driven via the 20m dipole.  This antenna was designed for W1JQ to use at his contest station and has shown good results.  You may build this antenna for your own use and not for commercial resale.  See end for W1JQ’s notes on the antenna

 

 

 

 

 

 

The elements are cut from various wires.

 

 

Position            Length              Wire                 Notes

0”                     204”                 #8                    No center ins. 10m DE

-2”                   395.625”          #8                    DE 20m dipole feed at center

-6”                   270.625”          #8                    No center ins. 15M DE

-77.5”              208.5”              #14                  10m Ref

-86.25”            278.5”              #14                  15m Ref

-117”               420.375”          #14                  20m Ref

Center Frequency, 28.3, 21.2 and 14.175

 

For CW,

Make 10m DE, 207.75” long, 15m DE, 271.125”, 20m is the same length as above

No adjustments required for the reflectors.

The driven elements use # 8 wires to improve BW and keep losses down. You may use #10 but cut about ½” longer

 

Open sleeve insulators.

Make up insulators to hold the 2” and 4” separation distances constant.  This is an important step that must not be skipped.  Use ½” PVC pipe 8” long and drill holes to accept the #8 wires.  You will need to place the insulators ever 16 to 24”. Use 10 insulators of this style.  Cut 4 more 6” insulators and drill for #8 wires to slide over 15 and 20m wires. Space every 16-24”. Make up small wire jumpers to wrap around each wire and insulator to keep them in place. Solder each jumper.

 

Use an isolator at the end of each wire.  To the above chart add 2” to each wire length.

Install the end insulators temporarily, i.e. no solder, leaving about 2” of wire to trim.

 

Frame

Build the out of good quality 2”x2”x10’ lengths of wood. You can use other material if you like.  Attach the wires and ropes to the frame.  Let the wires sag slightly so the ropes will take up the strain.  Attach a coaxial cable to the 20m dipole, i.e. RG8X will work well. You should use a choke or 1:1balun. 6 turns of RG8X in solenoid form around a 4” dia. will work well.  Fasten coax to wood frame and leave enough to tune the antenna.

 

Tuning

Antenna should be at least 15 or 20 feet above the ground.

Tune the 20m DE fists and center at 14.175 MHz.  SWR should be good. Note how much wire you trimmed off.  Trim 20m REF the by the same amount as removed from the DE.

Tune 15m next in the same manor.  Do 10m elements last.  Recheck all band and Tweak if needed. Solder all the wires and make sure that the Dacron ropes are taking the load.

 

 

 

W1JQ’s Notes:

 

 

* The antenna is front-heavy, particularly if you feed it with RG-213.

  The solution is to tie a rope to the back end of each wood spreader,

  then tie these to trees or something to pull the reflector-end down.

  If you obsess about it, you can even account for the "sag" in the

  driven element.

 

* I got through 3/4 of the contest season using cheap pine for the

  spreaders, and then one of the spreaders snapped.  Fortunately, I

  had noticed it bending after CQWW CW, so I had bought some mahogany

  (standard mahogany decking from the lumberyard), and had already

  drilled the holes.  When I saw the antenna in pieces on Wednesday

  morning, it took me about a half hour to fix it.  The mahogany was

  very slightly more expensive, significantly heavier, and much less

  prone to bending under stress.  The guy at the lumber yard (who

  happens to be a ham) had some even heavier and sturdier lumber, in

  case the mahogany didn't cut it.  But I don't think I need it.

 

* Between contests, I drop the antenna, roll it up, and stow it under

  the deck.  If all goes well, it takes about 20 minutes to raise it

  or lower it.  (I leave the main support ropes up.)  Biggest problem

  when rolling it up: don't let a turn or two of the driven element

  slip off the end of the spreader, or you'll have to untie it,

  untangle it, and reattach it.  (I'm considering nailing one side of

  a cable spool onto the spreader to prevent that.)

 

I install the antenna facing S.  Performance is great for South

America, and it beats several dipoles that just didn't work (they were

outperformed by my Europe-facing dipole curtain, off the side).  For

some reason I don't understand, it's not all that good for the south

US or near Carib.  But then again, it's not hard to be heard down

there.  My *guess* is that the sag in the driven element, plus my

south-sloping property, give the antenna a bit of a down-tilt, so it's

got great low-angle properties for longer distances, but not that good

at moderate distances. (Maybe you have a terrain profile that Rocks South? – K1NQ)

 

I used #14 flex-weave (which I do

whenever I have an antenna that seems likely to turn into a tangled

mess of wire).  Haven't regretted that.

 

In practice, the SWR is fine across all of 20 and 15 (CW and PH),

though it's getting a bit high at the top of 15.  As long as the

auto-tuner in the Icom can handle it, I don't care.  On 10, it

resonates a bit higher than I'd like, but it still covers from the

bottom of the band up till about 28600, when the autotuner gives out.

That wasn't quite enough for CQWW Phone, but I doubt we'll be lucky to

see conditions that good for a few years.

 

73,

 

Mike, W1JQ

(From W1JQ email sent to K1NQ)

 

K1NQ is planning to put up one of these antenna at 40 feet facing south in the summer of 2004. This will be the south multiplier antenna. It also helps by getting the antenna away from the main run stacks to help in SO2R.