Week 2 Foundation licence (Ham radio, Dipole antenna)

1. 

   MyHamShack says:

   February 28, 2014 at 3:23 PM

   5:26 ”SWR meter for testing aerials”

   While it is common practice to use SWR meters to evaluate in some way
   whether or not an antenna is good or bad it is a very risky exercise that
   can lead a person into making false conclusions.

   SWR meters simply will tell you if the meter see’s a 50 Ohm match.
   New Hams (and many not so new Hams) are very pleased when they see a low
   SWR reading , however this reading is in no way a judgment on how well an
   antenna works.

   Take this example , , , , say our antenna is really screwed up for some
   reason and it has a 10 Ohm impedance.
   Consider too that our coaxial cable connectors are badly soldered and they
   now add 40 Ohms extra resistive impedance.

   This settup is going to really SUCK and you would be lucky if anyone hears
   you at all……however the SWR meters says , ¨Everythings fine buddy , we
   have a 1-1 SWR¨ – while the meter says it see’s a 50 Ohm match , the
   antenna is still garbage.

   SWR meters have very limited use in Ham shacks and are very often
   unrelaible source of usefull information , yet for some reason , every Ham
   has two or three of them hanging around somewhere., and some will even pay
   big dollars for a meter that very accurately tells him nothing much at all.

   ———–

   6:18 ”Ime hoping that won’t matter much” (hot melt glue)

   The glue can only affect the way the antena works if it affected by RF
   radiation.
   To ckeck if it is , get a hot melt glue stick and put it in the microwave
   oven for a few miniutes on high power.
   If it melts or gets hot thats not good.
   But if it stays cold and hard then it is not affected by RF radiation —
   that’s good.

   The same thing applies to your other plastic parts.

   While I haven’t tested hot melt glue in the microwave before I have checked
   PVC pipes and they are usually good.

   Thumbs UP buddy :-)

   Reply
2. 

   English Ham says:

   February 28, 2014 at 2:27 PM

   Dan, yes of course.

   My Ham Shack, what I meant to say was an antenna analyser rather than a swr
   meeter. As I understand an analyser can also measure the impedance as well
   as the swr.

   I also have had some success in ‘hacking’ my psu. So will do a video on
   that soon.

   Reply
3. 

   ColdestMoon says:

   February 28, 2014 at 1:35 PM

   Hi Ben. fab video. Can you bring your antenna to class next week ? It will
   be a perfect prop for our class. and I will be able to show you the SWR of
   your antenna quite accurately !

   Reply

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