[OKDXA] Shunt-Feed Tower for 160 m

[Bert Aaron]

Kim,

I think is just XL = 2piFL and XC = 1/(2piFC)

73,
Bert  K2BA

-----Original Message-----
From: okdxa-bounces at mailman.qth.net [mailto:okdxa-bounces at mailman.qth.net]
On Behalf Of Kim Elmore
Sent: Saturday, March 01, 2008 11:18 AM
To: Discussion of OKDXA
Subject: RE: [OKDXA] Shunt-Feed Tower for 160 m

I tried that, too. I found that as I increase frequency, the 
impedance rose, which would indicate an inductive reactance. So, so 
far, things are consistent. As an aside, I've read that some 
commercial units do this, but that under some circumstances this can 
lead to errors (I've forgotten now what those circumstances are).

Kim N5OP


At 11:12 AM 3/1/2008, you wrote:
>Kim,
>
>You can usually determine the type of reactance by adjusting frequency. If
>frequency is increased and reactance (X on the display or Impedance on the
>meter) decreases, the load is capacitive at the measurement frequency. If
>frequency is reduced and reactance decreases, the load is inductive at the
>measurement frequency.
>
>73,
>Bert  K2BA
>
>-----Original Message-----
>From: okdxa-bounces at mailman.qth.net [mailto:okdxa-bounces at mailman.qth.net]
>On Behalf Of Kim Elmore
>Sent: Saturday, March 01, 2008 10:39 AM
>To: okdxa at mailman.qth.net>
>Subject: [OKDXA] Shunt-Feed Tower for 160 m
>
>I borrowed a friend's MFJ-259B analyzer to supplement my readings
>from my noise bridge, as I didn't think those made sense. I kept
>getting an inductive reactance well below what I knew to be the
>system's resonant frequency.
>
>The MFJ-259B showed a reactance of about 360 ohms, but without sign
>information. To remedy that, I put a T-connector on the port, put the
>load on one side and piece of RG-8 coax about 19" long on the other
>side. A 19" long piece of RG-8 should have about 48 pF of
>capacitance. The 259B said about 60 pF, so that seemed close enough,
>counting the connectors. Thus, I added about 60 pF in parallel with
>the unknown reactance.
>
>I figure that if the impedance is inductive, adding a capacitor will
>increase the reactive component by cancelling out the inductive
>impedance since I'm essentially approaching parallel resonance.
>Alternatively, if the reactance decreases, then the load reactance
>must be capacitive.
>
>The added capacitance increased the reactance, so I conclude the
>antenna impedance must be inductive. Does this sound right?
>
>Kim N5OP
>
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