Thread: Optibeam
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Old July 5th 06, 02:53 PM posted to rec.radio.amateur.antenna
Dave Dave is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 444
Default Optibeam

Dave wrote:

I looked at their web site and did not see a 'Log Periodic'.

Their antennas seem to be Yagi based. A L-P is a driven array, not
parasitic, and broad banded so that the VSWR never exceeds a max value,
typically 1.7:1, ANYWHERE in the spectrum from 14 to 30 MHz in the
bandwidth you mentioned.

Do you have a model number?

/s/ DD W1MCE


Additional info Log Periodics.

Typical VSWR values for a 13 to 30 MHz LP are as follows:

13.5 MHz ... 1.7:1
13.7 MHz ... 1.6:1
13.9 MHz ... 1.4:1
14.1 MHz ... 1.3:1
14.3 MHz ... 1.4:1
14.5 MHz ... 1.5:1
14.7 MHz ... 1.7:1
14.9 MHz ... 1.7:1
15.1 MHz ... 1.6:1
15.3 MHz ... 1.5:1
15.5 MHz ... 1.4:1
15.7 MHz ... 1.3:1
15.9 MHz ... 1.3:1
16.1 MHz ... 1.4:1 ... continuing through 30 MHz for a 13 to 30 MHz antenna.

Note: On 10 meters my VSWR does not exceed 1.4:1 anywhere from 28.0 to 29.7 MHz.
I don't believe a Yagi design is that broadbanded.

The VSWR on my LP does not exceed 1.7:1 anyplace between 13.5 and 31 MHz. It
varies slightly between 1.7:1 and 1.3:1 minimum.

Gain is effectively constant between 13 and 30 MHz. However, it is slightly
lower than a well designed 3 element Yagi. [~-0.5 dB]
Efficiency, however, is slightly better than a trapped Yagi [no trap losses].
Physical size is larger than a trapped Yagi.
F/B ratio on 14 MHz is lower than a Yagi but will match a yagi on 18 through 30 MHz.

I chose a LP because I wanted full coverage of the HF spectrum from 13 to 30
MHz. [Including USAF MARS & 17 and 12 meters] A 5 band Yagi only covers 5
segments of that spectrum.

If I were interested in one or two bands only, I would go to a full sized 4 or 5
element Yagi for for each band and get excellent gain, efficiency and F/B.
[Assuming I had the $$$$]