EZNEC doesn't tell the whole story.
VOACAP says the optimum takeoff angle on 40m for crossing roughly half
the U.S. (I used from my Arizona QTH to Chicago), such as for
Sweepstakes, is about 20 degrees plus or minus a few degrees depending
upon whether the opening is just beginning or is in full bloom.
VOACAP says the optimum angle from the west coast to Europe on 40m is 10
degrees or less (usually less).
HFTA gives the following figures for takeoff angle for a 2 element 40m
yagi over flat ground (per the original posting from NY6DX) at different
heights:
10 degrees 20 degrees
45 ft 2 dbi 7 dbi
60 ft 4 dbi 9 dbi
90 ft 7.5 dbi 11 dbi
120 ft 12.5 dbi 14 dbi
Putting the 40m yagi at 90 feet instead of 45 feet gives NY6DX a 4 db
improvement for domestic contacts and at least 5.5 db gain for DX. For
all practical purposes that's an entire S-unit. You'd need a stack to
get that kind of additional gain.
Like the man said, 45 feet is too low for a 40m yagi.
And like the other man said, 89 feet is too high for 15m and 10m.
Dave AB7E
Al Williams wrote:
> EZNEC DISAGREES??
> It seems that most often an assumption is made that "effectively" for
> antenna height refers to dx propagation. My modeling of a 3 element 40m
> Yagi shows that the maximum gain of the antenna is within a db for heights
> between 70' to 130' and falls off only ~3 db when lowered to around 45'.
> However the elevation angle of the maximum gain lobe does benefit dx
> propagation as the height is increased.
>
> This lowering of the elevation angle is of "effectively" benefit for dx but
> instead may be detrimental, depending on the distance desired--e.g.
> Sweepstakes contesting.
> k7puc
>
>
>
>> ----- Original Message -----
>> From: <donovanf@starpower.net>
>> To: <towertalk@contesting.com>
>> Sent: Monday, November 27, 2006 4:24 PM
>>
>>> 60 feet is too low for a 40 meter Yagi to perform effectively.
>>>
>>>>> W3LPL
>>>>>
>>> ---- Original message ----
>>>
>>>> Date: Mon, 27 Nov 2006 14:57:48 -0500
>>>> From: ny6dx@aim.com
>>>>
>>>> am putting up 2 towers with 2 bay stacks for 10 15 20 and 40 wonder the
>>>> best way to do this. Am thinking of 20 and 15 on the 89ft tower and 2 10
>>>> m anttens and a 2 el 40 on the 60ft. any advice?
>>>>
>
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