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@arrl.net>
To: "Robert Chudek" <k0rc@pclink.com>
Cc: <towertalk@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
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