[TowerTalk] Tower and antenna decisions

[Joe Subich, W4TV]

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.
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> Chris
> KF7P
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> On Oct 25, 2013, at 11:03 AM, Joe Subich, W4TV wrote:
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>>
>> 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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