You've got too may variables to compare them directly. What band,
different heights, etc.? Put them on an antenna range under controlled
conditions and see what happens. The additional height of your LP
most likely gives it an advantage over the quad at the path distances
you happen to compare.
The 12 element LP (probably on a 32 foot boom) will have a slightly
larger "active cell" than the 8 element LP but will still not be within
3dB of an optimally designed yagi (Force 12 C31xr, 4 element SteppIR,
etc.) on a similar size boom - the physics just doesn't support it.
73,
... Joe, W4TV
On 10/25/2013 3:51 PM, Bill Winkis (KC4PE) wrote:
I really don't find the below...
In the real World ....
My 12 element Log at 110" stays with my 4 element Quad at 80 feet ...but is
behind a 4 element 44 foot W2PV mono at 140 feet at band opening and closing
... and there are times when the 18HT Hytower vertical with 4000 feet of
wire under it beats them all....
-Bill
http://www.kc4pe.com/amateurshack.htm
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Joe
Subich, W4TV
Sent: Friday, October 25, 2013 1:39 PM
To: Chris
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Tower and antenna decisions
I did the same study almost 10 years ago using AO (the results should be in
the archives) comparing the Cushcraft 20-10 meter LP, the Force
12 C3e and original three element SteppIR.
The 18 foot Cushcraft was nowhere near close to even the C3e on any of the
three "primary" bands with the gain deficit running between 1.5 and
2 dB and pattern deficit (F/R) on the order of 5 to 7 dB. Remember the
C3 is a *two element* tribander - it has only two active elements per band
except for 10 Meters (C3e has three active elements on 10) so your
comparison, which is generous based on my studies, is to a two element
antenna with a maximum effective (active) boom length of around 8 feet.
I doubt there is more than a fraction of a dB difference between the
Cushcraft and Tennadyne designs as LP parameters are fixed based on boom
length and number of elements with only minor differences based on exact
design bandwidth and phasing line impedance.
When the 8 element LP is compared to a real three element yagi (the
SteppIR), the LP loses by an average of 3.1 dB per band with as much as 12
dB poorer F/R.
73,
... Joe, W4TV
On 10/25/2013 1:08 PM, Chris wrote:
I did some EZnec model comparing an 18 ft. boom T8 to an 18 ft. boom C3.
The gain is down about half to 3/4 dB on the T8, if I remember correctly.
And it covers more bands and is $400 less. I haven't compared anything
larger yet.
Chris
KF7P
On Oct 25, 2013, at 11:03 AM, Joe Subich, W4TV wrote:
Only a small portion of the LP elements carry significant current on
a given frequency - only a "few" elements are "active". This means
that the gain of an LP is generally equivalent to a non-optimum two
element or short boom three element antenna at best. Given the
limited number of active elements and the sub-optimal currents, side
and back rejection are generally significantly poorer than a well
designed Yagi.
Log Periodic antennas provide coverage of a lot of "useless" spectrum
at the cost of efficiency, reduced performance in the narrow amateur
allocations and substantial mechanical complexity.
73,
... Joe, W4TV
On 10/25/2013 12:45 PM, Jim Brown wrote:
On 10/25/2013 9:38 AM, Gene Fuller wrote:
Would you like to add any comments regarding LP's.
I don't know enough about them to comment. I've only heard that
their gain is relatively low compared to a Yagi with the same boom
length. It has long been well known that the gain of a Yagi is related
to boom length.
73, Jim K9YC
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