2M/70cm Dual Band Handi-Yagi Home-Brew Antenna Based on a design by AD1B

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K3CDY, Oct 16, 2020.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Left-3
ad: Subscribe
ad: abrind-2
ad: L-MFJ
  1. K3CDY

    K3CDY Ham Member QRZ Page

    I'd like to share the results of my first home-brew antenna, the "Dual Band Handy Yagi," based upon a design by AD1B, published in the May 2008 issue of QST Magazine, with a couple of tweaks.

    Concept

    The antenna design is interesting in that it has no reflector element, driven element or matching network. Instead, the HT radio's own dual-band antenna (a Super Flexible Signal Stick in my case) is the "driven" element. The HT mounts directly on the boom using a wooden bracket, and RF-couples with three 2 meter director elements. Also on the boom are seven 70 cm director elements that couple with the HT antenna. The three 2 meter elements can be rotated for more compact storage. This design makes setup & teardown quick and easy.

    My Implementation

    Below is a photo of the finished product:

    upload_2020-10-16_1-0-52.png

    I use a Yaesu FT3D HT, with a home-made "rat tail" counterpoise wire attached to the base of the antenna, which is the same length of the Signal Stick. I operate the radio using a bluetooth headset (Anker Soundcore Life NC). Pressing the headset play/pause button results in a latched PTT on/off action. I can get about about 30-40 feet away from the radio before losing the headset/radio bluetooth connection, allowing me to slip indoors while my rig sits out in the heat or cold.

    One major departure from the QST article was adding a tripod mount, extending the boom and adding a counterweight. The antenna is balanced at the tripod attachment point, and pivots nicely in all directions with fingertip pressure. Without a tripod mount, I believe this antenna would get too heavy to hold pretty quickly.

    The counterweight is a leftover ankle weight, simply wrapped around the boom with a tie-wrap to prevent it from sliding off the end. I can slide the weight along the boom for fine adjustment to balance. The eye hook is for storing the antenna.

    upload_2020-10-16_1-1-54.png

    Here are some closeups of the tripod mount, front and back:

    upload_2020-10-16_1-2-30.png

    upload_2020-10-16_1-2-42.png

    To the boom, I attached a piece of ¼" thick scrap aluminum as a mounting plate, in which I drilled and tapped ¼" mounting hole for the tripod quick-disconnect adapter. The mounting plate is securely attached to the boom with machine screws, nuts and fender washers to help distribute pressure. I also installed a machine screw and star lock washer through the quick-disconnect adapter to prevent it from twisting; the machine screw mates with a drilled and tapped hole in the aluminum mounting plate.

    I modified the radio mounting bracket by adding a small notch at the bottom to accommodate the radio's belt clip, and altering the depth of the "top notch" so the bottom of the antenna is precisely on the same plane as the top of the boom. This ensures that when the radio is mounted, that the antenna height is about 0.375" longer than the 2 meter D1 element, giving that nice long-to-short Yagi progression. On the back of the mounting bracket, I glued a piece of furniture glider felt as a spacer to keep the radio perpendicular to the boom.

    upload_2020-10-16_1-3-17.png

    upload_2020-10-16_1-3-54.png

    The radio antenna's centerline is the "reference point" against which all director elements are positioned along the boom. To assure accuracy, I established that reference point first, and then constructed the bracket to position the radio's antenna to align precisely with that reference point.

    upload_2020-10-16_1-4-18.png

    The 2 meter rotating elements were constructed using 1" x 2" x 2" blocks, cut from the same stock as the boom's 1x2. This differs from the dimensions in the original QST article.

    The director elements were secured to the boom using gel-style superglue, and the whole assembly was sprayed with primer, then flat black paint.

    Probably the biggest construction challenge was drilling perfectly perpendicular holes for the antenna elements. I don't own a drill press, and I had to rely on a "DrillBlock" handheld drill guide. Nonetheless, I managed to get pretty good alignment as can be seen in the picture below:

    upload_2020-10-16_1-5-1.png

    Performance

    Today, from my home in Broomfield, CO I managed to hit a repeater 79 miles south, located on the top of Pikes Peak near Colorado Springs, CO (KBØSRJ), operating at 146.97 MHz and 448.45 MHz. My best performance was on 70 cm, with two evening QSLs that reported a strong, clear signal from me. I could hear them both just fine, with only minimal noise. I think that repeater was the theoretical limit for my little rig which is pretty impressive.

    I'm anxious to do more experimentation (with and without the "rat-tail," different repeaters, simplex operation, satellites, etc.) and will update this post with the results.

    Clearly, this was a very rewarding project for me and I hope this experience is useful for my fellow hams thinking of a home-brew Yagi. Many thanks to AD1B for this very intelligent design. Highly recommended!

    73
     
    N5TJD, AK5B, KC3RN and 1 other person like this.

Share This Page

ad: KE5EXXad-1