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On 24/12/2025 14:04, John R Walliker wrote:
> On 24/12/2025 12:16, The Natural Philosopher wrote:
>> On 24/12/2025 07:58, mm0fmf wrote:
>>> On 11/12/2025 21:18, Carlos E.R. wrote:
>>>> Home made with a box of Pringles. just google for "pringles wifi 
>>>> antenna".
>>>
>>> Also Google cutoff frequency and see that the Pringle tube is too 
>>> small in diameter to be effective at 2.4GHz.
>>>
>> Assuming that is a relevant issue.
>>
>> Shouting down a pipe whose diameter is way less than the wavlength of 
>> voice frequencies, still works....
>>
>>> Of course, designs on the internet do not have to follow the laws of 
>>> physics! :-)
>>>
>>
>> ..especially for people who don't fully understand them...
> 
> Indeed.ÿ And I'm sure you are perfectly well aware of the difference
> between longitudinal sound waves propagating down a narrow pipe and
> transverse electromagnetic waves in a waveguide.

An antenna is not a waveguide.



> If a Pringles can were highly conductive it would have a cutoff
> frequency of close to 2.4GHz so the attenuation would be very high.
> However, a very thin layer of aluminium on the inside of a cardboard
> tube will be so resistive that it will not make a lot of difference.
A statement which clearly contradicts the well known skin effect of 
conductirs at high frequencies.

> For many purposes a well made half-wave dipole or quarter-wave
> monopole gives excellent results which are far better than anything
> that can be achieved with small pcb antennas.
> 
Sure. Most routers come with wavelength sized wobbly penises that give 
you a few dB.

> A quarter wave monopole made from relatively thick wire or rod can
> be an excellent match to 50 ohm coax so long as the ground plane
> is at least a few wavelengths across.
> 
> A half-wave dipole combined with a coaxial balun can also be a very
> good match but has a slightly narrower bandwidth due to the
> frequency dependency of the coax balun.ÿ The choice of which one to
> use depends mostly on how the antenna is to be mounted.
> 
> An almost omnidirectional antenna with very low losses can be
> more effective than a lossy directional one.
> 

> John
> 

Nevertheless I have seem that sort of design work.
I worked around radar antennae briefly in the 1960s.

What I learned was that theory is too simplified to actually be able to 
design a real antenna: All our designs were field tested and adjusted.

I am not advocating Pringle cans.  I wouldnt use one myself. But I am 
not so quick to rubbish them as you are.

RF propagation is tricky, and real world objects of no apparent value 
often have enormous effects.


-- 
The lifetime of any political organisation is about three years before 
its been subverted by the people it tried to warn you about.

Anon.


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