DIPOLE WITH PAWSEY STUB BALUN

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darren123
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DIPOLE WITH PAWSEY STUB BALUN

Post by darren123 » Tue Feb 21, 2017 7:16 pm

hi there has anyone got any knowledge of a dipole with a pawsey stub , ive made one with the pawsey stub balun and it has a very low swr level.....
my question is ..
is the pawsey stub wasting my radiated power , would the dipole do better without it and with a higher swr.

I wasn't able to get a low swr at all without the balun as I thought that I would.

pirateaddict
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Re: DIPOLE WITH PAWSEY STUB BALUN

Post by pirateaddict » Tue Feb 21, 2017 8:33 pm

From what I've learnt on here you need the balun to stop the signal going back down to the coax and radiating from it coz the signal isn't balanced... It shouldn't affect the power of the signal though.. Someone with waaaay more knowledge on the subject will probably be along a little later... But that's my understanding on the balun.. But please don't take my word as Gospel tho as i could've misunderstood the concept..

radio-berlin
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Re: DIPOLE WITH PAWSEY STUB BALUN

Post by radio-berlin » Tue Feb 21, 2017 10:15 pm

That doesnt add up.. What are you using to measure the swr?
From expereince of making dipoles for my own use the balun only brings down the swr ever so slightly, maybe from a 1.5 to a 1.2 and so on.
You shouldnt be getting high swr without it and low swr with it, something is wrong there. post up some pics so we can help.

I personally tune up my dipoles without a balun then add it after, i make the stub slightly longer and add solder to shorten it on my feeder until i get 50ohm on my meter or as best as i can get, however my new analyzer has a great feature for measuring 1/4 or 1/2 wavelengths of coax which makes this task much easier now.

In the real world you probably wont notice much difference on air with or without a balun as its only a matter of a few watts lost without the balun if your running say 100 - 150 watts, however it will match much nicer with the balun and hopefully stop your coax from radiating which will help with immediate interferance on your roof to tv amps and other sensitive equipment. A dipole is balanced and your feeder is unbalanced, so we use a balun in this situation.

If i was you then id concentrate on getting a low swr without balun, once you achieve this then add the balun after.
Use this formula to get you in the right area, (300/freq) x 0.935 x 0.5 = 1/2wave length of your dipole end to end.
If your using thicker aluminium ive found that the velocity factor of 0.935 can be ommitted from this formula, 1" 16awg tube always seems bang on half wave length for me. If using normal 1/2" or 12mm tube then keep the 0.935 bit in there.
Hope this helps

Albert H
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Re: DIPOLE WITH PAWSEY STUB BALUN

Post by Albert H » Wed Feb 22, 2017 11:46 pm

Berlin's pretty much bang on with his advice. You don't lose any power at all with a Pawsey stub - in fact if it's all correctly matched, you'll radiate a higher proportion of the energy coming out of your rig! In raw terms, connecting the coax straight to the dipole will give you an SWR - at very best - of 1.5 : 1. The coax outer will also radiate.
"Why is my rig humming?"
"Because it doesn't know the words!"
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