[OZAPRS] Newb HF questions ;)

David and Justine Olsen davejust at bigpond.net.au
Sun May 24 12:54:56 EST 2009


Well my 1/4 wave is closer to 1/2 meter


On 24 May 2009, at 10:09, Craig Turner wrote:

> Hmm,
>
> Actually the standard VHF antennas on the aircraft I fly are about  
> the length of a knitting needle. Are the V shapped horizontal  
> antenna often found on the empennage a diploe? I had thought they  
> might be as there is one element either side of the empennage?  
> Actually those ones look more like wire coat hangers than knitting  
> needles
>
> Craig
> VK3LCT
>
>
>
> David and Justine Olsen wrote:
>> No but I did think to myself, that is a short dipole for 120 MHz-  
>> I am a pilot.
>> On 24 May 2009, at 08:10, Ray Wells wrote:
>>> Ben,
>>>
>>> Nope, not a knitter, but my wife is.
>>>
>>> Didn't anybody spot my "mistake"?
>>>
>>> If one needle when used as a quarter wave, and the frequency is  
>>> 240MHz, two of them used as a dipole will still be 240MHz, and  
>>> not 120MHz.
>>>
>>> Ray vk2tv
>>>
>>> Ben Lindner-VK5JFK wrote:
>>>> Well done Ray. Were you a knitter from way back ? having those  
>>>> needles hanging around. Not that there is any thing wrong with  
>>>> that, a lot of men knit :-)
>>>>
>>>> Ben vk5jfk
>>>>
>>>> Ray Wells wrote:
>>>>> Looks like it's time to get technical, heaven forbid!
>>>>>
>>>>> I've just measured a typical aluminium knitting needle at  
>>>>> 300mm. If we assume it is a quarter wavelength and the length  
>>>>> to diameter ratio is 0.96 we can divide 300000 by (1200/0.96)  
>>>>> to arrive at 240Mhz. This is a reasonably thin needle so an  
>>>>> appropriate adjustment needs to be made for fatter needles. The  
>>>>> metal end-cap would add slight capacitance to slightly lower  
>>>>> the resonant frequency.
>>>>>
>>>>> Since knitting needles are usually used in pairs, a dipole  
>>>>> would be resonant at about 120Mhz which is great for the  
>>>>> aircraft band.
>>>>>
>>>>> Ray vk2tv
>>>>>
>>>>>
>>>>> Tony King wrote:
>>>>>> I had to ask.... What band are knitting needles resonant on??
>>>>>>                                        Regards Tony VK3API
>>>>>>
>>>>>> Ben Lindner-VK5JFK wrote:
>>>>>>> "Have you thought about trading in your radios for knitting  
>>>>>>> needles :-) "
>>>>>>>
>>>>>>>
>>>>>>> Ray,  I believe that Scrap Booking and Quilting have taken  
>>>>>>> over from knitting now. :-)
>>>>>>>
>>>>>>> Ben
>>>>>>> VK5JFK
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