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[TowerTalk] 80/160 ANTENNA IS SHORT

To: towertalk <towertalk@contesting.com>
Subject: [TowerTalk] 80/160 ANTENNA IS SHORT
From: Dennis OConnor <ad4hk2004@yahoo.com>
Date: Wed, 15 Dec 2010 18:25:08 -0800 (PST)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Paul, let me be the christmas grinch here and allow as how I feel your 
bandwidth is a bit too much for the antenna you describe - not too little as 
you seem to think...
You seem to have a reasonable radial field, which should drop your feedpoint 
impedance enough to make the 160 2:1 bandwidth more 'peaky' than what you 
see...  Your report looks like you have about 20 ohms of ground loss...

I question if your 259B is getting RFI from AM sports talk radio that is 
polluting your readings - the inane chatter of sports talk radio will pollute 
anything...

I would suggest a noise bridge in place of the 259B... Since the advent of the 
259 series of antenna analyzers, the noise bridge has become almost extinct, 
which is a shame because it is a most powerful tool for measuring antenna 
resonance and impedance and J - and is not confused by sports talk radio 
insanity...  MFJ makes a perfectly serviceable noise bridge...

Lacking the noise bridge, I would suggest a 4:1 step down balun/xfmr at the 
feed point and use your radio with a few watts of drive and a SWR bridge to 
explore the resonant frequency and the feed point impedance on 160...  It is 
certainly going to be less than 52 ohms and on 160 with 72 radials, 12-16 ohms 
is in the ball park - as was commented on by others...

denny / k8do


      
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