The saying "A picture is worth a thousand words" holds merit when discussing
antenna characteristics.
The Beverage antenna discussion a few weeks ago prompted me to run some graphs
on my Beverage I recently installed. This is the first Beverage antenna I have
ever used. It's 410 feet long, headed NE/SW, up about 8 feet, on 4 feet of T
fence posts, with 4 feet of fiberglass rods, using #12 gauge insulated copper
house wire, held with electric fence insulators, and terminated with I.C.E.
Beverage devices on top of 8 foot copperclad steel ground rods, driven 7 feet
into the ground, at both ends. (Boy, that was a mouthful!)
The discussion about matching the antenna for minimum variation in vswr and not
absolute minimum vswr made me curious. My I.C.E. units provide a terminal block
to select 300, 450, 600, and 900 Ohms. I had set both ends to 450 ohms as this
seemed to be the default value all the literature suggested would work "OK".
So, having my new AEA VIA Analyst and VIA-Director program available, a warm 30
degree (F) night, itching to learn something new, I decided to "walk the wire"
and chart my new Beverage antenna characteristics.
I posted a new pdf file to http://chudek.aberon.net in the AEA Analyzer folder.
Originally I swept from 1.0 to 5.0 mHz at 300, 450, and 600 Ohm settings. The
300 and 600 settings proved to be nearly identical so I omitted the 300 setting
to keep the final graph "less busy".
Results: The BLUE trace shows the varying vswr at the 600 Ohm setting. The RED
trace shows the vswr at the 450 Ohm setting. This chart clearly shows what Tom
and others have been saying about "tune for flattest vswr". You will notice the
600 Ohm setting actually has lower vswr values in several spots.
Out of curiosity I also swept the Beverage from 1 mHz to 50 mHz with the 450
Ohm terminations. This is the second pdf file in the AEA folder. The vswr
remains under 3:1 across the entire spectrum. This scan was done at the end of
124 ft of rg-8x coax so the values are probably dampened somewhat as the
frequency goes up, but I think the results are valid for a trend analysis. The
original 1 ~ 5 mHz scans were done at the receiving post using a double male
PL-259 on the Analyzer so this chart should be pretty accurate.
My next task is to see whether this new antenna helps pull DX signals out from
the noise. So far, I have had mixed results. The s/n ratio between the Beverage
and my 160m Inverted Vee appears to be about the same. Also, on 80m, my sloping
dipole broadside to EU hears better too. I probably need more time and practice
to hear the difference. By all reports, the low bands have been exceptionally
good recently. I am in a rural location so there is less noise in the first
place. I did have success with one stateside contact during the 160 cw contest
that would not have been in the log otherwise!
73 de Bob - K0RC
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