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Saturday, 7 October 2017

23cm and 70cm yagi antennas in workshop are toast...:-)

In the workshop looked for the antenna bits for the 23cm transverter to find the 23cm antenna (and a 70cm one) had basically been crushed under some items that I had 'stored' in there... oops! So rather than try to fix as the booms were well mangled I am going to try to make from scratch.

Following I am going to basically try and create a short 23cm antenna on a Ali boom using welding rods and a length of 6mm copper tubing (was from an A/C unit I think).

I will use a copy of the DL6WU spreadsheet I have from previous as that site's link doesn't work now.

Copied from that site... I'll basically use materials I will either have to hand or will get. YEs understand 1mm out on the length is MHz so test of my skills.... Semi rigid hardline I have a few options for the matching section.

"Design criteria
There are lots of designs available for yagi antennas. Guenter Hoch DL6WU has researched this subject for decades, nowadays his design formulae are accepted throughout the world in both commercial and home made antennas. Many other designs are actually just small modifications of the DL6WU formulae. In the past I built a couple of 2m beams using DL6WU’s design, so I decided to use this again, now for my 23cm yagi. I started with my design criteria:
  • Center frequency: 1260 MHz
  • Bandwidth (3 dB): 1240-1280 MHz
  • Gain: 10 dBd or more
  • Polarization: horizontal
  • Mount: in front of mast
  • Lightweight


Because of low weight and easy handling I mostly use aluminium to construct VHF/UHF antennas. This material is also easy to drill, saw and grind. You can buy it in most DIY shops. For this antenna I bought an square bar (15x15mm), made of aluminium, length 1 meter. At one end I mounted a standard available mast mount, leaving about 90cm for the actual antenna. Using the DL6WU formulae, this results in a 14 element yagi, with a gain of over 13 dBd. I used the DL6WU spreadsheet calculator of DF2CK to calculate all measurements. I used AlMg3 welding rods for the radials. These rods have a diameter of 4 mm. The dipole is made of 6 mm2 copper wire, matched with a matching loop (1/2 wavelength coax or semi-rigid) and mounted to a female N connector.
These are my inputs for the spreadsheet:
  • Frequency MHz: 1260
  • Boom diameter cm.: 1.5
  • Element diameter mm.: 4
  • Element Thru Boom (“Y/N”): Y
  • Boom Length (Metres): 0.89
This spreadsheet returned these specifications, the real specifications will differ a bit, but it will give you an idea what to expect:
  • Gain: 13.6 dBd
  • Usable bandwidth: 1234.8 to 1285.2 MHz
And it returned these element sizes:

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