[TowerTalk] 160-m Inverted L or Sloper?

K4SAV RadioIR at charter.net
Mon Nov 14 15:52:06 EST 2005

Two to three S units is a lot of DBs.  I can only think of two 
possibilities that could cause this.  The first, and not very likely, is 
that there is something wrong with the inverted L. This is not a 
complicated antenna, and this is not likely the cause.  The second is 
more likely.  When you have two antennas resonant on the same band, they 
interact.  One will act as a reflector for the other.  When you compare 
signals from a certain direction, it is possible to get this much 
difference. If you then compare the signal strengths for a station in 
the opposite direction, you should get a reversal of which antenna is 
best.  For 160 meters the spacing required for antennas to not have 
significant interaction is very large.  You need at least 500 ft 
separation to reduce this maximum gain difference which you may detect 
to something like 3.5 dB.

If you still have the antenna, this would be an interesting test.

Receive-only test should be perfectly valid as long as you are comparing 
S unit differences on DX stations and not signal to noise ratios. 

Jerry, K4SAV

Doug Renwick wrote:

>Well last year I put up an Inverted L (100' vertical, 70' horizontal)
>with 20 full size radials on a separate tower and compared it
>to my half slopers. I didn't do any transmit comparisons but my receive
>comparisons were 2-3 S units down from the half sloper.  Admittedly I
>didn't do the comparison using good specific comparison techniques for
>a technical report.  But my 'ballparking' comparison gave me enough
>information to decide whether to continue the testing or not.   My initial
>evaluation did not warrant further Inverted L testing.  The test
>is still in place as I haven't taken it down yet.  Maybe I will look at
>it again as we all know that you cannot have too many antennas.
>That's right Jerry, and that's really the bottom line. The
>best we can hope for is a tie with a shunt fed or series fed
>vertical or Inverted L. The worse is something much worse
>than that.
>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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