[TowerTalk] The AEA VIA Analyst (long)

[Robert Chudek]

Hi Jerry,

Thanks for the message, comments, and observations!

BTW, the 160 meter Inv Vee is fed with 100' of RG-59/u coax. My understanding is an Inv Vee will present a better match to RG-58, but my roll of RG-8x shipped late. I will swap out the coax, cut it a multiple of half wavelength (electrical) at 1.830 MHz, and re-scan the antenna to see what I get.

The meter is set for 50 Ohms. But I checked the analyzer calibration with 50, 81, 100, and 560 ohm carbon resistors. I ran a sweep from 1.7 to 50 MHz. Here's the results:

With a 50 ohm load (1%), it reads a flat 1.01:1 thru this range.
With a 81 ohm load (1%), it reads between 1.62 ~ 1.64:1 thru this range.
With a 100 ohm load (10%), it reads between 2.25 ~ 2.28:1 thru this range.
With a 560 ohm load (10%), it reads 11.0:1 at the low frequencies but moves to 12:1 and down to 10:1 in a sine wave pattern as the frequency escalates.

Determining the appropriate ground conductivity has always been a challenge at this qth. The ground is relatively flat for miles in all directions. The first mile in any direction is +/- 30 feet elevation. If you look at some of the photos in my photo album, you will see I have a pond / stream running around 270 degrees of my house. This area is typical wetland, mucky, marshy, you'll sink 18" in the slime if you try to wade through it. The ground has a high concentration of clay. I got both my van and tractor stuck several times when I first moved here (city slicker moves to the country!). Boy that stuff is slippery! The closest woods is about a quarter mile away.

So by 160 meter standards, I classify the terrain as "flat". On 10 meters, that would be a different story. But I don't really know what the story is.

I'm headed outside because I need to make a 40m dipole for SS!

(Did I mention that I was have WAY TOO MUCH FUN with this stuff???)

73 de Bob - K0RC


Message: 6
Date: Sat, 05 Nov 2005 00:31:18 -0600
From: K4SAV <RadioIR at charter.net>
Subject: Re: [TowerTalk] The AEA VIA Analyst (long)
To: towertalk at contesting.com
Message-ID: <436C51B6.3080905 at charter.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Instead of tearing into your antenna tomorrow, take the day off. It 
appears that you have the AEA VIA Analyst set to 75 ohm reference 
instead of 50 ohms.  Your plots show a resistance of about 43 ohms and 
and SWR of 1.7.  This would be correct if the reference was 75 ohms. (A 
case of too many available options?)

Nice plots from that instrument.  For fun I tried to see how closely 
EZNEC would match your data.  I got R of 46 ohms at 1.79 MHz using 
average ground, (pastoral/heavy clay, .005s/m, diel=13), pretty close.  
If I change the ground to something a little better (flat marshy, 
densely wooded, .0075 s/m, diel=12), I get 43 ohms, exactly what you 
measured.

Jerry, K4SAV