In the previous Winter I built a HB9CV-in-a-box for 23cm for my uplink to the local ATV repeater PI6ATV. Although this antenna works nicely, its gain just isn’t enough when their 23cm preamp is broken (which, unfortunately, is the case most of the time). To achieve a more steady uplink, I decided to build an antenna with a bit more gain, at least 6 dB extra compared to the HB9CV. A short yagi should make this possible.
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
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. Unfortunately DF2CK’s website has vanished. Luckely I kept a local copy of the sheet to calculate your own yagi, click here to download the sheet. 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:
|Element||Length||Distance to reflector|
The finished antenna looks very good, but I have to admit that the driver is a bit wacky. Any hints to improve this are welcome.
The ATV repeater now receives a decent signal, resulting in a steady and colourful picture. Unfortunately I don’t have equipment to measure the impedance and resonance point of my antenna. Whenever I’m able to measure this, I will update this article.
Lex PH2LB managed to reproduce this antenna to examine whether it’s possible to make contacts at the 23cm band from his home. He send me some pictures:
If you’ve built your version of this antenna, please let me know your experiences, and send me some pictures of it!
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