[TowerTalk] Dipole resonates lower than expected.

[Robert Chudek]

Terry,

Thanks for running the numbers! It confirms the insulation does lower the F.

Follow-up...

Well today I called AEA Technology and got the sad news that my HF Analyst 
needs to be looked at. The engineer I talked to knew this unit (an original 
AEA SWR-121, about 15 years old) and we walked through a number of tests. 
The self test revealed a specific issue which is not field repairable.

I see AEA has a new device (one of several) called the VIA Analyst for $700. 
It provides more statistics than this original model. Has anyone seen or 
used one of these devices? During my research, I see Bird also has a similar 
unit but their price is about double.

I like the idea of the portability in these handhelds.

73 de Bob - K0RC

----- Original Message ----- 
From: "Terry Conboy" <n6ry at arrl.net>
To: "Robert Chudek" <k0rc at pclink.com>
Cc: <towertalk at contesting.com>
Sent: Monday, October 17, 2005 6:56 PM
Subject: Re: [TowerTalk] Dipole resonates lower than expected.
>
> Just for fun, I put your antenna and feeder into EZNEC+ over average 
> ground.  Here's a look:
>
> At Antenna
> ==========
> Bare #12 conductor       F=3.809   R=72.8  SWR(50 ohm)=1.46   or 
> L=472.3/F
> #12 w/0.05" PVC insul    F=3.681   R=67.1  SWR(50 ohm)=1.34   or 
> L=456.4/F
>
>
> Looking into 100' of 75 ohm, VF=0.66 (lossless)
> ===============================================
> Bare #12 conductor       F=3.799   R=69.7  SWR(50 ohm)=1.39
> #12 w/0.05" PVC insul    F=3.663   R=63.0  SWR(50 ohm)=1.26
>
>
> It's worth remembering that 468/f is just a working approximation which 
> gets you in the ballpark.  It assumes that the antenna will resonate about 
> 5% lower than a free space half wavelength (due to end effects, etc.).  I 
> don't think "468" is etched on a stone tablet.
>
> Of course, your immediate environment will also impact resonance and 
> feedpoint impedance.  Further, coax impedance and velocity factor are 
> subject to normal manufacturing variations.
> And test equipment never lies. 8-)
>
> 73 Terry N6RY