XPost: comp.sys.raspberry-pi   
   From: tnp@invalid.invalid   
      
   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.  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.  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.   
   >   
   > 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   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)