[TowerTalk] Feeding a Quad

[CubexCo@aol.com]

Bob,
The problem to be solved when feeding a multi-band quad is matching the 
impedance that each band presents.  Typically 20m will range from 50 to 75 ohms, 
15m 75 to 90 ohms and 10m typically is about 100 to 110 ohms.  These numbers can 
vary depending on element spacing and dimensions.   The preferred method of 
feeding a quad is with individual feed lines for each band, remotely switched.  
This permits using odd quarter wave 75 ohm series matching cables for a 2:1 
transformation, and combinations of 75 ohm (or cabe with other characteristics) 
and 50 ohm cable to achieve a broad range of impedance matching (see series 
matching in ARRL antenna book).

Gain is the least likely characteristic of the antenna affected by the 
matching system.  Front to back, depth of side nulls, and bandwidth are more likely 
to be compromised.

Cubex also has available a matching transformer with three balanced outputs 
for 10, 15, and 20m.  We do feed 17m common with 20m and 12m with 10m with 
acceptable results.  There definitely is degradation in operational bandwidth, and 
other characteristics, but it is a simple cost effective method of feeding up 
to 5 bands with one coaxial cable.  

Regard integrating a 6m antenna, that works but I suggest if you have a boom 
at least 8ft long that you consider 4 elements on 6m.  Remember odd number 
element arrays always puts one element very near the center and that can be a 
problem with physical interference the the antenna supporting structure.

Regards,
Norman W4QN
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From: "Bob T." <bobt at gloryroad.net>
Subject: [TowerTalk] QUAD FEEDING

I'm ready to put a Lightning Bolt 2 element, 20/15/10m quad up at 80ft. I 
want to do this right the first time, and get the best reasonable performance 
from the antenna. Lightning Bolt supplies a 2:1 balun for a common feedpoint. The 
owner of the company sez this is the best way to feed the antenna for max 
performance, anyone who sez otherwise is wrong. But...he can't supply figures or 
pattern pics. Others favor the gamma match method, but still I haven't seen 
any concrete evidence that this is the best way. (believe me, I've scoured the 
web) Still others say a common feed point (feed line)is just no good; the only 
way to go is seperate feedlines for each band. Still no facts or figures to 
back up this claim. I am primarily concerned with maximum forward gain and a 
fairly good pattern. I won't quibble over .5-1.0 db or so. If it makes any 
difference, I am also interested in integrating a 3 element 6 meter quad on the same 
boom. (seperate feed) and/or mounting a loaded 40 mete
r dipole along the boom of the quad. So, who has the facts? Please, no 
educated guesses or second hand anectdotes. Thanks
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Regards,
Cubex Sales


"The Power of a Cubex Quad"

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