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UHF Beams

Introduction

Due to the point to point nature of UHF, beams are quite popular on these bands.  Most hams can handle the construction skills needed for 70 cm antennas, though its challenging to scale Yagi designs as you move up in frequency.

Articles

Small 70-cm Yagi (671,292 bytes, PDF file
QEX July/August 2001. pp. 55-59
A 6-element Yagi designed for a wide bandwidth.

Controlled Impedance “Cheap” Antennas Kent WA5VJB’s computer optimized 144MHz to 1296MHz antennas with a clever asymmetrical feed.

A 902 MHz Loop Yagi Antenna QST Nov 1985, pp. 20-21
A great classic design for a 33 cm band loop yagi antenna. Great for point to point links, mesh networks, and as a feed for Parabolic Dish antennas. A similar design can be used for higher frequencies such as 2.4 GHz.

The Long-Boom Quagi
QST February 1978, pp. 20-21 Build a 15-element Quagi antenna for 432MHz.
Including "Additional Bands for the Quagi" QST April 1978, Technical Correspondence, p. 34 (Also see www.n6nb.com)

25 and 45 element Loop Yagis and test data on the North Texas Microwave Web site.

Dishes and Alternative Beams

Because of the increased precision and accuracy required as you move up in frequency for good antenna performance, it is difficult to scale traditional yagi-uda or similar beams in the microwave ranges using conventional techniques. However, because of the smaller wavelengths involved, it is possible to use different types of beams not practical at lower frequencies because of size constraints and movability. For instance, a directional waveguide antenna, often known as a cantenna, which often made from pringles and coffee cans, exhibits similar gain to an equivalent sized yagi antenna, but is much easier to build for the higher microwave bands than an equivalent yagi due to the lack of precise element spacing and sizing involved with the cantenna design. Similarly, many amateurs use a parabolic dish as a reflector, which itself tends to be frequency independent, while "feeding" the dish antenna using a resonant directional antenna that has the proper beamwidth corresponding to the focal width (distance from the center of the dish to the focal point) to maximally "illuminate" the dish.

Parabolic Dishes QST July/August 2001. pp. 55-59
A Primer on Parabolic Dish antennas for the microwave experimenter. These are the most common way of entering moonbounce communications. 

Understanding Feed Horns for Parabolic Dishes  QEX July/August 2001. pp. 55-59
A good discussion on the different feed types available and what effect they have on the antenna system of a Parabolic dish. If you plan on using a dish, expect to construct multiple different feeds.

Small dishes and Digital EME QEX July/August 2001. pp. 55-59
A misconception for moonbounce communications is that one needs a massive dish antenna and a lot of power, but using digital techniques and SHF frequency bands, it is possible to get to the moon and back without a massive setup, albeit in a somewhat compromise fashion

A High Performance UHF and Microwave System Primer QST, May 1991
A fantastic article summarizing the various design considerations for microwave communications. Although published in 1991, before the advent of digital techniques and the widespread availability of commercial microwave equipment, the issues and design considerations discussed are still very much true today

Cantenna online calculator - 3G-aerial
A calculator for building a directional waveguide antenna, aka, cantenna. For wide diameter cans, venting duct is often a good substitute for a "can".

 

 

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