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[TowerTalk] Determining "True" Resonance of Verticals

To: <towertalk@contesting.com>
Subject: [TowerTalk] Determining "True" Resonance of Verticals
From: n0tt1@juno.com (n0tt1@juno.com)
Date: Sat, 4 Aug 2001 17:26:13 +0100
Hi Brian,

Thanks for your reply!

The 6 or 7 ohms is only the *reactance* reading, not the
resistance reading and at this point I am only recording
reactance which as you said, should be zero at resonance.

There must be some reactance in there somewhere since
the reading is zero with a 50 ohm load on the 259-B.

73 es DX!
Charlie, N0TT

On Sat, 04 Aug 2001 17:00:20 +0000 alsopb <alsopb@gloryroad.net> writes:
> Hi Charlie,
> 
> You are quite correct.  The resonant point is that of minimum Z.  In
> theory the cap and induct components exactly cancel.  One is left 
> with
> pure resistance.
> 
> Your approach is the right one.  Tune ant to resonance, then match 
> it.
> 
> I was wondering what kind of vertical you are using which is 6 or 7
> ohms?
> Normal quarter wave verticals are about 34 ohms.  As the ant grows
> shorter and is loaded, the z drops.
> 
> I think you meant to say that x will read 50 ohms when the 259 is
> terminated in 50 ohms.  
> 
> Trying to do the above with balanced antennas (e.g. quad loops) is a
> problem.  The 259 is an unbalanced signal generator.  One has to 
> first
> run it into a 1:1 balun.  That does sometimes cause problems by
> itself!
> 
> 73 de Brian/K3KO
> 
> 73 de Brian/K3KO
> 
> n0tt1@juno.com wrote:
> > 
> > Hi Gentlemen,
> > 
> > This isn't exactly tower talk...maybe close enough...
> > 
> > I have tried several methods to measure *resonance* of a
> > vertical 20m antenna (which will become a multiband
> > trap vertical).
> > 
> > In tuning a antenna, I consider resonance and impedance
> > two separate subjects.  Lowest SWR to me doesn't mean
> > "resonance".  At this point in testing I don't really care
> > about the "input" impedance at the coax connector...the
> > antenna will be matched to the line later.
> > 
> > I have made many measurements using a GDO and a
> > MFJ 259-B analyzer and I get different readings of
> > resonance depending on what method I use to couple
> > RF to the antenna.  When I used the GDO, the frequency
> > was monitored with a frequency counter of known accuracy.
> > 
> > I'm thinking that the lowest "X" (reactance) indication
> > on the 259-B would be THE resonant frequency, and
> > that I should connect the instrument with the shortest
> > possible leads (like a double-male coax connector)
> > to the "input" of the antenna.  Is this correct?  Or what
> > IS the best way?
> > 
> > BTW, the "X" reading has been 6 to 7 ohms with the
> > 259-B and "X" will read zero when the 259-B is
> > terminated with a 50 ohm load.
> > 
> > 73,
> > Charlie, N0TT
> > 
> > ________________________________________________________________
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