Topband: Caged Inv-L - Pros and Cons ? (Dan Bookwalter)

[Herb Schoenbohm]

Several NAB engineering papers have be written with field tests on the 
caged feed and demonstrate that whether you feed the cage or if merely 
connect the cage to the bottom of an insulated tower both the field 
strength and bandwidth remains the same. All agree that for a lower Q 
cage fed antenna the station actually sounds better than higher Q feed 
systems which could and often reduce the band pass fringes so the signal 
"sounds narrow rather than fat" on the BC frequency assignment.  I know 
the later is anecdotal but many broadcaster who use the cage prefer them 
over the straight feed.

On 160 if you wish to operate across the band and don't have a remote 
tuner to accomplish this a cage can help.

Herb Schoenbohm, KV4FZ

On 1/26/2012 10:25 AM, W9UCW at aol.com wrote:
> During the 1980's we had  a 120 foot, insulated base tower with an
> appropriate radial system. I wanted to  improve it's performance and increase its
> bandwidth. I also wanted to add an 11  foot conical monopole to our collection
> of antennas.
> With the help of friends,  we mounted the 14 to 60 MHz conical monopole on
> top of the tower. Then we  "caged" the tower from top to bottom at 10 feet
> in diameter using #12  wire and 10' PVC pipes as spreaders at three levels.
> On 160 it was fed as a  folded monopole with the tower grounded and it was
> below 1.5 to 1 SWR  for most all of the band. On 80 where it was voltage fed
> as an  insulated base, very fat half wave monopole, it was below 1.5 to 1 SWR
> for  nearly the entire band. The cage doubled the bandwidths.
> IMHO, having also worked  with using a "cage" as the gamma rod on grounded
> towers in  several cases, I would say the positive effects are worth the
> trouble, Dan. It's  hard to predict the results on your inverted "L" but I
> would urge you to try  it.
> BTW, I had a remotely  controlled tuner/matcher at the base of that big fat
> vertical. It allowed us to  switch configurations, tweak the capacitance
> and inductance settings and either  connect or disconnect the coax up to the
> conical monopole on top. I wish we  still had that set up.
> 73, Barry,  W9UCW
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