[TowerTalk] Two 15M yagi stacking

Jim Lux jimlux at earthlink.net
Sat Feb 24 15:20:43 EST 2007

At 09:55 AM 2/24/2007, Stan Stockton wrote:
>K1TTT wrote:
>  >With 5 or 6 elements from here you can not
>cover all of Europe without rotating them.
>W4ZV wrote:
>          I strongly disagree.  My 6 element KLM array
>has a 3 dB beamwidth of about 54 degrees, which
>is plenty for Europe.
>I guess when people talk about 3 dB beamwidth it is just a measure 
>of reference, so I will use it as well.  Let's say you could double 
>the boomlength and realize about 3 dB more of gain than the original 
>antenna.  Now if you want to compare the two antennas look at what 
>the 6 dB beamwidth is of the new antenna.  However many degrees that 
>is will be the place where the two antennas would be equal and 
>everything less than that, the larger antenna will be better!

The only problem with this is that some of the time, the advantage of 
a directive antenna is in the rejection of signals you don't want, 
rather than the forward gain  (that is, you might be willing to give 
up efficiency to achieve a higher directivity).  It might be that the 
point at which the gain is down, say, 20 dB is the important thing. 
(An example is antennas for receiving DBS satellite signals.. you 
especially want to reject the signals from satellites that are 
adjacent in the equatorial band...  Or, maybe you're in southern 
Californiai and  want to suppress all those big signals from 5 land, 
when you're shooting north to EU)

Especially when it comes to suppressing atmospheric noise (which is 
very unevenly distributed) this might actually be more important than 
raw gain (at least on receive).  On transmit, of course, you want all 
the gain you can get in the desired direction.

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