john, whats a good rule for height of the antennas to avoid large back lobes reflecting, ie how many wavelengths up should the antennas be? Thanks...
--STeve Andre' wb8wsf en82 On Saturday 05 June 2010 17:07:15 John Belstner wrote: > Just another $0.02 to add. > > You will find that the size and shape of the reflector will not affect the > forward gain as much as it does the F/B ratio. It depends on what is > important to you and (of course) how high you are above the ground. Even > for satellite operation pointing up, large back lobes reflecting off the > ground can adversely affect the forward pattern when the antenna is mounted > only 6-8 feet above ground. > > On Jun 4, 2010, at 10:13 PM, Clare Fowler wrote: > > To add to the discussion the July/Aug 2007 Amsat Journal has an article > > covering some gain comparisonmeasurements I made between four > > 13 turn (2.88 wavelengths) 13cm antennas with different square solid > > aluminum reflectors. > > The sizes were 0.56 wavelengths, 0.84 wavelengths, 1.0 wavelength and 1.4 > > wavelengths. > > There was no difference between the 0.84, 1.0 and 1.4 wavelengths but the > > antenna with the0.56 wavelength reflector had 1.5 db less gain. > > > > However for my 70cm helix antennas I followed the Satellite Handbook > > minimum > > size of 0.6 wavelengthsor slightly over 16 inches. I used 1/2 inch > > hardware cloth > > mesh to keep the weight and windloading down. > > These antennas have performed well however it appears that they would be > > a bit better with a somewhat larger reflector. > > > > A brief description and picture of the 70 cm reflector is in the > > November/December 2005 Amsat Journal article on > > The Development of a Quarter Wave Match for helical antennas. > > > > Clare VE3NPC > > > >>> Hi All: > >>> I am rebuilding a 440 MHZ Helix that I built several years ago . It > >>> worked very well, but I would like to reduce the size of the reflector > >>> to a more manageable size than I had before. The only reference to > >>> reflector size I can find is, "minimum 20" ". I may be looking in the > >>> wrong places. I would appreciate it, if someone would steer me in the > >>> right direction. Thanks, > >>> Pete, K1HZU _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
