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On 2025-12-24 15:23, The Natural Philosopher wrote:
> 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.ÿ 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.

I just say that once I built a Pringles antenna at a training course, 
and it does work. Inside the tube there is a threaded metal rod with a 
number of nuts and washers that had to be put at precise distances 
according to the instructions we followed.

Black magic.

We did not have any tool to measure gain, but indeed the router read a 
higher signal that with its manufacturer antena. And it was directional. 
I can not give any number because I don't remember where my notes are.


Back to the original subject of the thread and to topic; Some of the 
designs out there just put an USB dongle inside the tube, and they work, 
somehow. No need to actually have a wifi card with socket for the 
antenna. If the Pi is small enough (I have no idea) there will be 
designs out there using it.

-- 
Cheers, Carlos.
ES??, EU??;

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