[amsat-bb] Re: Cross Boom

[Roy]

It seems that this subject comes up  once or twice every decade.  I have 
never used anything but a metal cross boom since I joined AMSAT in 
1974.  Later there were some tests run by Kent Britain, WA5VJB.  His 
measurements resulted in the following recommendations:

1.  Mount the antenna  with the tips of the elements as far from the 
support boom as possible.  Instead of mounting them in a + form, mount 
them as an X in relation to the cross boom.

2. Saw off any excess cross boom so that it doesn't extend past the 
antenna boom.

3.  Avoid mounting the boom 1/2 or 1 wavelength from the driven 
elements.  (I would modify that to multiples of 1/2 wavelength)

4.  Run the coax out the metal boom and down the antenna boom.  Keep the 
turning radius of the coax small but not to the extent of damage to the 
coax.

I have never detected any bad effects of this arrangement and had 
stumbled into this configuration years before Kent published his 
findings in the 1993 AMSAT Symposuim Proceedings.  I did it to avoid 
having the coax  from hanging off the rear of the antennas and dragging 
on the roof of my house and changing fore/aft balance with ice loads.  
Incidentally, I think I recall that Jim, G3RUH was also using this 
method.  If anyone wants a photo of the antenna setup and contacts me 
directly I will send it to him.

Roy -- W0SL
AMSAT  410