[amsat-bb] Re: quadrafilar helix for 70cm- ambiguous design specs

[Franklyn A. Ballentine, jr]

I have a question along the same line.  Is the QHA in the ARRL
Satellite Handbook \ Antenna handbook, a good starting place?

Thanks,
Frank B.
KB1QZH

On Tue, Sep 29, 2009 at 11:17 AM, i8cvs <domenico.i8cvs at tin.it> wrote:
> ----- Original Message -----
> From: "Tim Goodrich" <tim at timgoodrich.net>
> To: <amsat-bb at amsat.org>
> Sent: Monday, September 28, 2009 9:45 PM
> Subject: [amsat-bb] quadrafilar helix for 70cm- ambiguous design specs
>
>> Hi All,
>>
>> The house I just bought precludes me from even using my arrow inside as
>> there must be something un-RF friendly in the walls. Therefore, I was
>> looking for a roof antenna and the October QST article on the QFH inspired
>> me to build one. However, after doing some research, I have come up with
> two
>> sets of design specs and I'm unsure which one is correct.
>>
>>
>>
>>  I converted everything from you're the 146Mhz QST model to 436Mhz.
> However,
>> when I plug that info into http://www.jcoppens.com/ant/qfh/calc.en.php
>>
>> The values it puts out are different in the "compensated length" field.
> The
>> only difference is this model calculates for a full turn as opposed to a
>> half turn, but the lengths shouldn't be as different as it says. Under the
>> QST model, I get a wavelength of 688mm, but under the website's model, it
>> gives me a "compensated wavelength" of 729mm.
>>
>>
>>
>> The values I used to calculate are:
>>
>> 436
>>
>> 1
>>
>> 1
>>
>> 15
>>
>> 2
>>
>> .23
>>
>>
>>
>> Can anyone tell me which specs to use and/or explain this compensated
>> wavelength issue?
>>
>>
>>
>> Thank you,
>>
>> Tim
>>
>> KI6VBY
>>
> Hi Tim, KI6VBY
>
> Read please the book "REFLECTION" Transmission Lines and Antennas by
> M. Walter Maxwell, W2DU Chapter 22 The Quadrifilar Helix Antenna pages
> 22-1 to 22-23 and also
> "Experimental Investigation of Quadrifilar Helix Antennas for 2400 MHz" The
> AMSAT Journal May/June 2004
> In a separate email I have sent to you both articles as an attachement.
>
> 73" de
>
> i8CVS Domenico
>
>
>
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