[TowerTalk] Boom correction 6m SQ boom

[Ian White GM3SEK]

Dan wrote:
>Looking for boom correction for 1.5 inch Sq. boom 6m with insulated  .625
>inch elements elevated above boom .25 inches.
>

Almost zero  -  don't  worry about it.

In more detail: if the element ran through the centre of the boom, 
electrically connected on both sides, the correction would be about 
0.15x the boom cross-section =  about 0.225in. This is based on the 
formula:

Correction (as a fraction of boom diameter) =
733 * BD * (.055 - BD) - 504 * BD * (.03 - BD)
where BD is boom diameter in wavelengths.

Since your elements are insulated *and* mounted above the boom, your 
correction will be less than half of that, ie about 0.1in - in other 
words, far too small to worry about at 6m.

You were right to ask the question, but 6m is the one band where boom 
corrections almost disappear.  This is because boom diameters are 
relatively small (in wavelengths) and large element mounting plates are 
not needed. On 2m and above, the boom diameter is becoming significant; 
while on 10m and below, element mounting plates may be needed and the 
corrections start to increase again. 6m is a kind of "sweet spot" where 
the practical boom-effect correction is almost always zero.

More information in links from:
http://www.ifwtech.co.uk/g3sek/diy-yagi/index.htm


-- 

73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek