See the G3SEK VHF/UHF Long Yagi Workshop at http://www.ifwtech.co.uk/g3sek/diy-yagi/index.htm
This article was first published in Amateur Radio Magazine in March 1999 (pp11-15)
and subsequently reprinted in QEX in January 2000. The article gives details on how
to calculate corrections to yagi element lengths at 144, 432 and 1296MHz when those elements
are mounted through the middle of a circular metal boom and in electrical contact with it.
For square booms VK2ZAB has shown that the correction is 20% greater than for a round
boom of diameter equal to one side of the square.
For elements mounted on top of and in electrical contact with the boom, the corrections
are approximately halved.
For elements insulated from the boom, the proper corrections depend on the exact form of the
insulators used, and must be determined by experiment.
This is the text of a lecture given by Gordon VK2ZAB on 16 March 1999 to the NSW VHF DX Group.
It gives practical information about how to decide the correct stacking distance for pairs of yagis.
There are many sources for data on the properties of Coaxial Cables.
Manufacturers include:
Loss in dB is directly proportional to cable length.
USA catalogues quote losses in "dB per 100 feet".
To convert the loss to "dB per 100m", divide the figure for "dB per 100 feet" by 0.3048.
Example: RG213 at 400MHz: 4.6 dB per 100 feet = 4.6/0.3048 or 15.0 dB per 100m.
Cable losses are usually given at non-amateur frequencies such as 400MHz.
To convert losses from one frequency to another, first look up the data for the nearest
frequency given.
Then multiply this by the square root of the frequency ratio.
Example: RG213: 15.0 dB per 100m at 400MHz = 15.0 * SQR(432/400) or 15.6 dB per 100m at 432MHz.