A Converted CB Yagi-Uda Antenna for the 10-m-band

A local ham, Manfred, DK9TG recently found a very attractive ad of a 3ele Yagi-Uda beam antenna originally produced for CB use. As a great fan of the 10m band he purchased the beam after a short check of the datas. The prize was allright and the antenna itself turned out as a real winner..

He built up the antenna very soon. During that time I searched the web and found the same antenna already used and modified for ham purpose at:

http://www.df9cy.de/cy3ele28.htm

Christoph already used this antenna since nearly 1 year and was very satisfied with the results. He redesigned the antenna using the software EZNEC and the results are quite good.

Basically it can be used at the lower portion of 10m (CW/SSB part) using the measurements provided.

Another report about this antenna was done by Martin, DK7ZB in the magazin Funkamateur issue 8/2000 (german language).

Mechanical datas:

• boom: 275 cm / 33 mm

• radius: 320 cm (R: 283cm / DE 267 cm / D 250 cm)

• tapered elements: 16 - 12 - 8 mm

• gamma match feeding

• weight 4.7 kg

Electrical datas (YO 6.58 de K6STI)

• Gain: > 7,5 dBi

• F/R: 20 db @ 28 MHz 15 db @ 28.8MHz, peak of 23.5 dB @28.25 MHz

• Z: 28 Ohm @ 28 MHz, 14 Ohm @ 28.8 MHz

• SWR-bandwith for 1:2 is ~700 kHz

Tuning for 10m amateur radio band

The tuning resulted in a shortening of 4cm of every element half. That is quite easy to realize. Just pull back the outer aluminium tube and redrill another fixing hole 4 cm nearer the end of the element for use with phillips screws/metal screw or you can slice the middle segment and fix the 8mm tube with a hose clamp. If you are using screws you should replace the original ones by some higher quality stainless steel (VA) to avoid rusty junctions. The element spacing remains as original.

Here we are with a shiny new 10m beam at QTH de DK9TG

Some more mechanical details

Watch the DE holder with the SO-239 socket. All 3 element holders are such robust. In deed a very nice piece of antenna. Maybe the connector should be replaced by a better one.

Feeding system

The antenna will be fed with the classic gamma matching system. It is appropiate for such low impedences.

The measurements used by Christoph, DF9CY:

Position of the gamma match as approximately moving the bracket as far inside as possible and the inner conductor "looks out" by 70 mm at the end.

The measurements used by Manfred, DK9TG:

The end tube looks out 220mm out of the inner tube and the bracket is positioned 150mm from the end of the tube.

The measurements used by Martin, DK7ZB:

Using the original datas for mainly SSB operation. The measurements are varying with the height of the installed antenna.

These are the original lengths of the gamma match, resulting in an VSWR of 1,1 at 28,65 MHz (best F/R at 28,4 MHz).

The outer 8mm tubes were here shortened by the following amount:

This measurements give you a coverage of 28 - 29 MHz. The Satellite and FM portion can be used with an additional tuner (although with bad F/R )

Performance

The antenna is up since October 1998 and performance is good. Contacts were made with all continents using my TS690 with about 90 Watts output. It does not perform as our "pile-up-cracker" does, but I feel it works better than a tribander. The antenna is installed at about 9 m above ground. This is indeed not very high, but the surrounding terrain descents in most directions putting the antenna virtually to a higher position. The feedline I use is a low-loss UHF cable (AirCell 2000) with less than 0.4 dB of loss on the 22m run. I also used it with 750 Watts output from a 3-500 for a while and it did a fine job.

Manfred, DK9TG:

Fed with up to 1200W without any problems. The SWR reading is 1:1.2 from 28.3 - 28.55 with gamma match bracket 150mm outside the end of inner tube.

He is very satisfied with the performance. Especially the directivity is very good. The signals are about '2 S units' better than the original antenna a GPA30 (triband vertical by Fritzel) using the Icom IC-751.

Martin, DK7ZB:

A very good alternative to a completly homebrewed antenna. The result is a directional antenna, providing excellent mono band results and an additional use as portable or fieldday antenna is possible. The beam can be rotated with a small TV rotator, pay attention on the relativly soft boom when tightening the boom-to-mast-clamp.

[1] SIRIO ANTENNA Italia, model SY-27-3, also PAN International Part-Nr. 11120