Many thanks Guy for this and previous posts about BOG antennas.
Two or three seasons ago I watched and listened to a You Tube video of a
Canadian station listening to EU signals in mid afternoon on a BOG. Now, this
was NE Canada, and I knew the prop would never be like that in WV but still, I
was impressed that a BOG would do this.
I have a Hi Z Triangle array with 50’ spacing and it works great, very
directive, and a lot of DX has been worked with it. However, there are noisy
powerlines around and below my elevated location and my verticals were prone
to noise pickup. A standard 600’ beverage on EU was less susceptible to the
noise, but was located on a STEEP hillside that a mountain goat would have a
problem traversing. At least 3 times per year, trees fall on the beverage and
take it out. I decided to pursue the BOG idea.
I ordered several of the KD9SV single direction feed transformers from DXE,
which came with termination resistors. Ground rods and wire came from Home
Depot. Before beginning installation, I did the DOG tests described by Guy.
The VF varied quite a bit on my hilltop/hillside location, but a length of 220’
to 250’ seemed to work.
I have had as many as 5 BOGs deployed in various directions, along with the
standard beverage, a JK Bevflex 4 deployed as a standard bi-directional
beverage, and the Hi Z Triangle. All of these antennas were brought to a Hi Z
antenna relay switch here in the shack, so instant comparison could be made.
The BOG’s have worked good for me. In fact, my east BOG is the go to antenna
for Africa DX. I am convinced if the DX can’t be heard on my Africa BOG,
there is no propagation. Since deployment, this 220’ BOG on 160 meters has
not let me down. Since we started deploying these BOG wires, my receiving
capability on 160 and 80 meters has improved dramatically. The BOG’s are much
less prone to picking up the local power line noise, a problem that has plagued
me since getting on Topband in 2008. They can hear the signals many times when
the other antennas won’t due to local noise.
I was busy last fall building other antennas, but as soon as the 6M E skip
season is over my current plan is to install several BOG pairs for phasing
through my DXE NCC-1 phasing controller. The antenna switches have been
acquired to set this up, and I am anxious to see how it plays this coming
season.
Nothing will beat good long beverages and the currently available arrays of
short verticals, except perhaps a horizontal Waller flag, which is not
practical here. There are too many other towers and antennas in the available
space on my hilltop. My property does not lend itself to the deployment of
more than one or two beverages, due to the terrain, and I can’t keep beverages
up. So far these BOG antennas have helped me in my situation. Your mileage
may vary, but they are worth a serious deployment effort if you have issues
preventing installation of beverages or vertical arrays.
I have tried EWE antennas, single large vertical flags, and dual phased flags,
fixed in a direction. Like with the beverages, I could not keep my tree
supported dual phased flags up. I had one for 4 or 5 years, and it seemed to
work, but it was too much hassle to keep up in my woods. The BOG’s have
exceeded my expectations and now I am going to try and refine the installation
of them.
To work the KH1, a temporary 220’ BOG was stretched across two driveways and
through the middle of my yard. The antenna worked well, knocked down the
summer static, and produced a very solid, workable copy on the DX. Laid the
antenna down one day, worked KH1 on 160 the next day and on 80 the day after
that, then took up the wire and went back to mowing!
73 Charlie N8RR
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10
________________________________
From: Topband <topband-bounces@contesting.com> on behalf of Guy Olinger K2AV
<k2av.guy@gmail.com>
Sent: Monday, August 6, 2018 7:34:19 PM
To: Mikek
Cc: TopBand List
Subject: Re: Topband: Several BOG questions
Hi Mike et al,
BOGs have a well deserved reputation for being cantankerous, with great
results for K4ABCD over here and awful results for K3WXYZ over there. There
is a part of the explanation for that variation that really isn't fixable.
But better outcomes are possible with a more detailed explanation of how a
BOG works, and understanding its significant differences with a standard
beverage RX antenna.
First off, a normal beverage will have a velocity factor (VF) of ~ 95%,
maybe a little more if it is high. That means that the VF can be ignored,
and all the well-documented regular beverage understandings and procedures
apply. However...
When you put the wire on/in the ground, notched below the grass, etc,
**measured** VFs in my area have ranged anywhere between 45% and 85%. This
means a lot we understand about a beverage antenna does not apply. We
measured VF by finding the resonance of a 151 foot (46 meter) dipole on
ground (DOG), laid in the same place and manner as an intended BOG.
The most common VF's were in the high 50% range. The values did not seem
related to any local factor easily exposed. There were times when rotating
the DOG around the center 90 degrees made a large change in VF, even though
the owner of the property insisted there was no piping, cable or drainage
fields beneath and nothing overhead. Presumably exact composition of dirt,
rocks, and varying water table or water presence, were responsible. This in
turn varies the response to the specifics from site to site.
Modeling a BOG in NEC4 exposes the issue: the incident incoming RF is
traveling at almost speed of light, and the RF already collected at a given
point has traveled on the wire at only half that. A physical quarter wave
of wire on ground appears roughly like a slowed down half wave. This causes
RF energy on the wire from the far end to be nearly out of phase with
incident RF near the feedpoint. BOG lengths beyond 250 feet can actually
start to reverse their pattern at higher frequencies. This makes a BOG a
one band antenna for front-to-back.
220 feet terminated by a pair of those 450 ohm beverage termination
resistors in parallel usually seems to do "passable" for a quick
slam-it-down-and-go-operate-in-a-contest five minutes later. But neither
length or termination is predictable to anything like the same degree as a
normal beverage.
A BOG is lossy. Frequently a BOG will work better with a
properly-feedline-isolated remote preamp.
A decently-centered BOG with a modicum of F/B can be had by first
installing it as a DOG. If you live in a primarily arid area then do this
exercise when it is dry. If wet or damp is common in the 160 "season", do
it in a wet time, so the ground is NOT dry.
Operating later, if things have gone dry, if you installed it in the wet
you can always go "water the BOG" before an important operating event.
W0UCE referred to this ritual as "water the boggies".
To create a location specific BOG, using 1.825 MHz as center:
Starting with a 250 feet length of PE or teflon insulated wire, lay the
wire out in the exact line and manner as you intend for the BOG. Bend the
end tips of the wire up an inch in the air so they don't short to the
ground. Break the center of the wire and temporarily attach an SO239. You
have created a DOG which you will now prune to vagaries specific to your
location and placement.
Use your RF analyzer at the center to find the lowest frequency resonance,
which will be well down in the AM broadcast band somewhere. The R where X=0
will usually be anything from 100 to 250 ohms. This is not critical.
***Trim equal lengths from the ends*** to move the resonance (X = 0) up to
1140 kHz (one point one four zero MHz). R is immaterial. Don't get in a
hurry, the effect of cutting off a foot (6 inches both ends) is often not
linear because the instant VF at a point on the wire most often is NOT
uniform across the wire. Only when you have trimmed the DOG to 1140 kHz in
this manner, reconnect and re-insulate the center, and only then place feed
transformer, termination and run feedline. A BOG done in this fashion will
have a predictable pattern (for a BOG) which makes best use of the fast vs.
slow RF velocities involved.
A ground of two equal length 40, 50 foot bare wires notched 2, 3, 4 inches
into the ground at right angles to the main wire will do as well as needed.
50 feet either way seems to be enough, though this is a very fuzzy length,
and will never be precise. Terminate the far end with 225 ohms (two 450's
in parallel) to ground. Less than 40 feet may start to lose signal transfer
to the feed transformer increasing an R in series with the primary winding.
But do what you can
In poor ground, a short ground rod by itself might be an adequate
termination. This provides a termination by providing a very resistive
ground, quite unsatisfactory for other applications. You need SOME
termination R, but the value is not critical. Any precise F/B with variable
R listening to a back side signal will **vary significantly** in the
weather with how damp your ground is, how far down in the lawn or leaves
your wire is TODAY vs. when it was set up, etc, etc. It's just not worth
it. You can set it right now, but an hour with sunshine, or an hour with
settling dew, will UN-set it for you. Soaking rain could throw it off the
cliff. Luckily the pattern does not depend so much on termination as the
VF.
For far end termination, use 225 ohms made from commonly available 450 ohm
resistors made for the application, or try poorly grounding it. Note that
this poor ground does not work so good at the feed end, where you really
need the wires.
The regular *beverage* procedure (looking at SWR through the feed
transformer to the far end to set termination value) does not work well on
a BOG. This is quite obvious in NEC4 analysis of the issues. The best
solution involves a devil's balance of the reflected power *and* the
incident VF *and* the along-the-wire VFs. It will not be found with SWR,
quite contrary to a standard beverage.
The lack of cutting BOG as DOG to 1140 kHz, thereby not incorporating local
conditions and VF, is probably most responsible for poor initial
performance. In a close second for screwing up results, varying wetness and
varying "buried-ness" are most responsible for changes for the worse across
time.
The NEC4 modeled BOG incoming pattern at best does not improve over a
well-done K9AY. But if you get it to work, it's "invisibility factor" could
be priceless. Further, the BOG seems excellent at rejecting very low angle
vertically polarized local noise sources off its sides to a degree I've not
seen with a K9AY.
W0UCE, out in the woods at an earlier QTH, utilized a pair of phased
side-by-side 220 foot BOGS spaced 200 feet for NE and a similar pair for
NW. I operated with those and found them excellent RX antennas, far better
than listening on any of his TX antennas. But more than once we had to go
out with a hose and soak them in very dry spells. Performance did suffer
with leaf buildup and when we finally figured that out, we had to pull the
wires up to get them on top of the leaves. The BOGs DID need a preamp, my
opinion, a conclusion not shared by all those who operated out there.
73 and good luck with yours,
Guy K2AV
On Mon, Aug 6, 2018 at 1:06 PM, Mikek <amdx@knology.net> wrote:
> 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<http://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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