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On 27/12/2025 20:51, Carlos E.R. wrote:
> 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.
> 
Sounds like a primitive Yagi...

> 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.
> 
Always hard to tell anyway.

> 
> 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.
> 
As I said, I took the shortest route to success - relocated the wifi 
point to higher up with less obstructions, and added a suicide alarm to 
kill the receiving  process if the signal fails mid message...

I will have to add another wifi point to replace the one I stole, for 
next summer when that part of the garden is in use :-)

-- 
"Anyone who believes that the laws of physics are mere social 
conventions is invited to try transgressing those conventions from the 
windows of my apartment. (I live on the twenty-first floor.) "

Alan Sokal


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