Hi Mike,
Congratulations on your first post regarding BOGs. They're a great
antenna when stealth is the driving requirement, but here are better
choices when stealth isn't so important.
The front-to-back ratio of a BOG results mainly from its laying on the
ground. A signal arriving from the back of the BOG is already greatly
attenuated before it arrives the termination, the value of the termination
resistor isn't as important as it is for an elevated Beverage. You can
clearly see this affect with a TDR or an antenna analyzer as you
install/remove the termination resistor on a BOG vs. an elevated Beverage.
Do you have enough space to install another BOG at least a few feet away
from your existing BOG? That would give you a reference to compare
attempted improvements made to one of your BOGs.
The RF resistance of a ground rod used with a Beverage or BOG isn't very
important, more important is the stability of the RF resistance during
varying wet/dry weather conditions. Stability can be improved by using
multiple spaced ground rods or by adding radials or a ground screen
such as chicken wire. Lowering the resistance isn't important because
you lower the resistance you'll need to increase the value of the
termination resistor to compensate for the lower resistance of the ground
rod.
73
Frank
W3LPL
----- Original Message -----
From: "Mikek" <amdx@knology.net>
To: topband@contesting.com
Sent: Monday, August 6, 2018 5:06:12 PM
Subject: Topband: Several BOG questions
I have installed a 253ft Bog,
I used WD-1A a pair and just twisted the two wires together.
Any reason I should separate the pair and just use a single wire?
Can the WD-1A be used for a Bi-directional BOG, or is the spacing too close?
I have installed a variable termination on the North end of the BOG and
a matching transformer
on the South end, for receiving from the north. I'm in the Florida
panhandle about 1 mile from the gulf.
I'm a little disappointed that the Variable termination does not have
much effect between 200 ohms and 1300 ohms.
I use AM Band stations as a guide to the directionality of the BOG and
it does seem to have good directionality,
just no noticeable difference while adjusting the termination. It is
also quiet when compared to a 150ft long wire.
In an effort to make the antenna seem 'apparently' longer I have loaded
the BOG with 9 ferrite binocular cores.
Using info from W8JI's page,
> https://www.w8ji.com/slinky_and_loaded_beverages.htm
I originally measured my Velocity Factor as .78 and by installing the
cores I was shooting for a VF of .55
I made a single pass through a single hole in the binocular core.
A single pass through a single hole in the binocular core is about
8.9uh. My calculation said I needed
11.8uh, but I installed all the cores I had and ended up with a VF of
.67, lower but... when I get more cores
I'll install them and test VF again.
Your thoughts?
I have measured my ground rod resistance using the method on page 24 of
the this pdf.
> www.weschler.com/_upload/sitepdfs/techref/gettingdowntoearth.pdf
I got 117 ohms on both ends, I bought some calcium chloride and put
2.5 lbs into and
around my 3 copper pipe rods. I pre-drilled the rods every 3" to allow
the solution to
distribute more evenly around the pipes. (5ft rods/pipes) I did this at
one end.
A day later I retested the ground rod resistance, and it was 73 ohms,
some improvement,
and another couple days I remeasured and it was down to 60 ohms.
A week later I added more Calcium chloride and I'm at 34 ohms now.
I just finished retesting ground resistance, North end 34 ohms, South
end 23 ohms.
Is the method in the pdf article a reasonable way to measure ground
resistance?
I used 60 hz, because it's available. My last test used ~ 25V and
supplied 600 mA.
I have no other AC source at a different frequency that would apply
that much power.
I bought a 74AC14 TDR and used it to measure the characteristic
impedance and VF.
I measured the Characteristic Impedance, which I then use to calculate
the matching transformer.
Does the ground resistance show as part of the Characteristic Impedance?
ie. If my ground was 117 ohms and I treated it and it is now 23 ohms,
will my Characteristic Impedance,
impedance drop by 94 ohms?
I measured my Characteristic Impedance as 358 ohms before Binocular core
installation,
and measured 501 ohms after Binocular core installation.
OK guys, this is my first post, there are a few questions, I hope to
get some help on this project.
btw, I did make a video showing how it compares to my long wire antenna
using AM band stations.
> https://www.youtube.com/watch?v=QuMwGDK6IhQ&t=51s
Thanks, Mike Knowlton
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