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Tape Measure Yagi

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W0BDT
(@w0bdt)
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Joined: 3 years ago
Posts: 15
Topic starter  

Here is a thread to discuss the 70cm Tape Measure Yagi that we constructed at the Elmer Night meeting in September.

I did not design the antenna, it was based on these plans: http://www.nrharc.org/UHF%20Tape%20Measure%20Yagi.pdf

The only modification that I made was to use ring terminals and a sheet metal screw with a star washer to connect to the driven elements, instead of soldering directly to the steel. Jerry Jenkins (AG7U) and I surmise that because the screw is attached about 1/4" from the end, we have effectively shortened the driven element slightly, which may be why most people weren't able to see a low SWR at 446.0MHz where we expected it. Jerry will likely add his own post below, but through some experimentation and testing, he found that to get a better tuning he had to lengthen the driven elements. He has some extra tape measure material, and may make longer elements available at a future meeting.

For those who might be interested in building a 2m band version of the tape measure Yagi, here is a link: http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm

Marvin (KE6HTS) notes a useful addition to the WB2HOL antenna: “A choke balun consisting of 6 - 8 turns of coax around the beam will help reduce the pattern skew significantly. It is not shown on the plans for the WB2HOL Tape Measure Beam, but should still be added to the antenna.”

There are many variations on this theme, including straightened coat hanger wire on a wood beam, or threaded rod through a square PVC pipe, or others made from welding rods, arrow shafts, etc. Use your imagination, the materials that you have on hand, and Google -- experiment!

Arrow Antennas in Wyoming manufactures very nicely made portable, handheld Yagis for satellite contacts and fox hunting, etc. if you would rather purchase a commercial antenna instead of building one.

Below are the instructions that we provided with the 70cm kits that we built at Elmer Night:

Parker Radio Association

Tape Measure Yagi for 70cm Band

 

In the Kit:

 

PVC Pipe:

Schedule 40, 1/2" ID

Piece 1 6"

Piece 2 2"

Piece 3 3 3/32" (already in Cross Tee)

 

PVC Fittings:

Tee

2x Cross Tee

 

Steel Tape Measure: Caution — Extremely Sharp!

Reflector 13 19/32"

2x Driven Elements 5 3/8"

Director 11 1/16"

 

Additional Materials:

2x #8 Self-tapping sheet metal screws

2x #8 star washers

4x #8 crimp-on ring terminals

8x Nylon wire ties

3' RG-58 w/BNC Male

1.5" solid copper wire

Sandpaper

Electrical tape

 

Assembly Instructions:

 

  1. Carefully wrap the ends of the steel tape measure with electrical tape to cover the sharp edges.  Only wrap one end of each of the (2) 5-3/8” driven elements; the other end of the driven element will be sanded.
  2. Assemble the sections of PVC pipe into the cross tees according to the diagram. Make sure to align the sides of the fittings so they lay flat.
  3. Using the sandpaper, remove ~1/2” of the paint down to bare metal from the non taped, convex end of each driven element.  Paint does not need to be removed from the concave side.
  4. Using the paper template, align the driven elements.  Use the hammer, nail, and wood block to pierce the sanded end of each driven element.  Alignment demo will be given during Elmer night.
  5. Align the paper template on the center PVC cross tee.  Mark and drill (2) 7/64" holes, which will be used to fasten the driven elements with sheet metal screws.
  6. Carefully strip about 1" of the jacket from the RG-58 coax cable.
  7. Untwist the copper braid shielding, and twist the braid shield wires together into a single strand.
  8. Strip about 1/4" of the center conductor of the coax cable.
  9. Strip about 1/4" of the insulation from each end of the solid copper wire for the hairpin match.
  10. Crimp (1) ring terminal onto the coax center conductor, (1) ring terminal on the coax braid coax and (1) ring terminal to each end of the solid copper wire.
  11. Bend the solid copper wire in half, creating a U about 3/4" wide.
  12. Connect the ring terminals for the coax and hairpin match to the driven elements using a sheet metal screw and star washer.  The star washer needs to make direct contact with the convex sanded end of the driven element.
  13. Place a nylon wire tie to anchor the coax at the base of the middle cross tee.
  14. Wind the coax around the center section of PVC pipe five turns to create a choke, anchor the end with another nylon wire tie.
  15. Use a nylon wire tie around the cross tee and driven elements to stabilize the tape measure. Pull tight and cut flush.
  16. Attach the longer reflector element to the rear cross tee with a nylon wire tie on each side of the cross tee. Pull tight and cut flush.
  17. Attach the shorter director element to the tee with a nylon wire tie on each side of the tee. Pull tight and cut flush.
  18. Center the Reflector and Director from side to side.
IMG 2337
IMG 2316
IMG 2338
IMG 2318
IMG 2317
IMG 2319
IMG 2340
IMG 2339
IMG 2341

Brad Tombaugh (W0BDT)

Brad Tombaugh (W0BDT)
Yaesu FT-60R - AnyTone AT-D878UV Plus - AnyTone AT-D578UVIII Pro - Yaesu FT-991A - Diamond X50A - MFJ-2299 - PreciseRF HG-1 "WR" Magnetic Loop Antenna


   
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Jerry Jenkins
(@ke0lpp)
Member
Joined: 2 years ago
Posts: 3
 

I experimented with and tested over 50 different combos of hairpin lengths/shapes plus additional feed line combos (+3ft, +6ft) and did not find an acceptable solution to the high SWR @ 446.500 MHz.

I then experimented with driven element lengths, which did make the biggest impact.  In the end I found that a driven element length of 5 – 5/8” was the best solution to achieve good performance @ 446.500 MHz. 

I will be making and providing replacements sets of driven elements and will hand them out at our next face-to-face meeting as well as the fox hunt event.  Replacement should be a simple matter of unscrewing and removing old driven elements and reattaching the new driven elements with same screws in same holes.  The hairpin should be reused as-is; there no change to the original hairpin spec. 


   
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W0BDT
(@w0bdt)
Member
Joined: 3 years ago
Posts: 15
Topic starter  

Folks, we still have kits available for $15 each. I'll bring them to the face-to-face meeting on Tuesday 10/11. There is still plenty of time to build one before the Fox Hunt on 10/15.

Brad Tombaugh (W0BDT)
Yaesu FT-60R - AnyTone AT-D878UV Plus - AnyTone AT-D578UVIII Pro - Yaesu FT-991A - Diamond X50A - MFJ-2299 - PreciseRF HG-1 "WR" Magnetic Loop Antenna


   
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