Yes, this was posted a couple weeks ago. Excellent article, excellent
antenna, model file is on this site as well:
http://www.realhamradio.com/Log_Periodic.htm
-Scott, WU2X
On Sun, Jan 24, 2010 at 3:20 PM, Jack KZ4USA <videorov@verizon.net> wrote:
>
> Any one have a good large LPDA model that would work in NEC- WIN Plus+ ?
>
>
> Jack
> KZ4USA
> Bradenton, Florida
>
>
> ----- Original Message -----
> From: "Steve, W3AHL" <w3ahl@att.net>
> To: "Tower and HF antenna construction topics." <towertalk@contesting.com>
> Sent: Sunday, January 24, 2010 3:05 PM
> Subject: Re: [TowerTalk] stacking logs
>
>
>> There are two reasons to stack yagis or LPDA's:
>>
>> 1. To increase gain by using a phased array. Maintaining a specific
>> wavelength spacing is important.
>>
>> 2. Taking advantage of the different take off angles that antennas at
>> different heights have, due to their interaction with the ground.
>> Depending
>> upon the ionospheric conditions, the band, the distance between stations,
>> etc. sometimes a lower antenna is better than a higher antenna. Often the
>> antennas can be switched so that all, any two or only one antenna is
>> active.
>> This is commonly called "space diversity". Spending an hour with a
>> program
>> such as HFTA will provide some insight into why stacked antennas are the
>> mainstay of contesters.
>>
>> Steve, W3AHL
>> ----- Original Message -----
>> From: "jim Jarvis" <jimjarvis@optonline.net>
>> To: <towertalk@contesting.com>
>> Sent: Sunday, January 24, 2010 2:42 PM
>> Subject: Re: [TowerTalk] stacking logs
>>
>>
>>> OK, I vowed not to add further to this thread. I lied.
>>> Curiosity has the better of me.
>>>
>>> Where the logs are stacked horizontally, they would seem not
>>> to be ideally spaced for vertical angle pattern, over frequency.
>>>
>>> The installation on the DX eng'g website... N9IN or wherever it was...
>>> has the
>>> logs at 44, 74 and 116 feet. That's a 30' and 42' spacing between the
>>> pairs,
>>> and 72' between top and bottom. There may be some frequency dependent
>>> relationship in this spacing, but it isn't falling out in my feeble
>>> brain.
>>>
>>> The spacings don't work out with any of the free-space pattern spacings
>>> with which I'm familiar.
>>> Maybe modeled over ground, there's some sense there?
>>>
>>> In any case, if anyone is able to explain the concept, I'd be interested
>>> to hear it.
>>>
>>> N2EA
>>>
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
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>>> TowerTalk@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>> _______________________________________________
>>
>>
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