Reread the email.
You trim a BOG to a working length using its DOG-mode resonance. The
former is very difficult to measure and involves helicopters. The
latter is easier than trimming a dipole, if your analyst displays
reactance and goes down to 1140 kHz.
You use a DOG, *** in the final resting place and final relationship
to actual dirt for the BOG, *** which you can measure to resonance at
1140 kHz, now in the context of it's own personal environment and
resultant velocity factor (not an "average" in a book, which will NOT
be close enough for most). When you're done, you reconnect and
insulate the middle and use the wire as a BOG, which now will do
decently at 1830 +/-. This procedure will have taken care of the
absolutely wild variation in VF found in backyards. This same
variation is likely responsible for the wild variation from success to
failure in attempted BOGs.
I would add to do this procedure when one is going through what
amounts to normal "wetter" weather if you have such. A bog tuned on
dry ground becomes a poor performer on wet and vice versa.
It is not hard to hose a bog to dampen up the ground around for a
contest, but it is the dickens to dry one out.
Remember, a BOG is a one-band antenna, and it's pattern starts to
reverse when you go past it's DOG-mode 1140 resonance length.
These are easy enough to model with your local measured constants,
once you put the DOG-mode wire low enough to ground in a model to
lower the VF to measured, and pick ground constants that show the same
DOG-mode R with zero reactance. This will be a low number of wire
diameters.
Having thus matched the DOG behavior with your own real measurements.
you can now model something like a wire alongside a curb and see what
will happen.
It is also very easy to extend and watch the pattern reversal and
currents on the antenna, which will convince one that a BOG does not
really work well cut like a regular beverage at all, and the best
pattern is obtained by UTILIZING a bit of MIS-termination.
73, Guy.
On Fri, Jul 30, 2010 at 1:22 AM, <k3bu@optimum.net> wrote:
> Uhm,
> isn't BOG - Beverage On the Ground variety?
> What you describing is DOG - Dipole On Ground.
>
> I used to have BOG run as a long Beverage wire, mostly unterminated, just
> laying on the ground, or tucked along the curb of the asphalt road.
>
> Another version was LOP - Loop On Ground. Originally intended as a electric
> dog fence around the property, about 460ft loop, burried about 1" in ground.
> By the time I put it down, dog got smart and did not need it. So I put 600
> ohm transformer on it between the ends and VO1LA - it worked and heard what
> Inv Vee could not. Seemed to be non band discriminatory.
>
> For stealth BIT Beverage In Toilet, one can flush the tennis ball with wire
> attached to it down the toilet and have the underground one.
>
> 73 Yuri K3BU.us
>
> ----- Original Message -----
> From: Guy Olinger K2AV
> Date: Friday, July 30, 2010 12:33 am
> Subject: Re: Topband: wire on the ground antenna
> To: Bruce
> Cc: Topband@contesting.com
>
>> A BOG is an antenna that suffers from incoming waves propagating at
>> the speed of light while propagation along the wire can show a
>> velocity factor from .45 to .80, sometimes varying wildly with
>> placement in a single back yard. The velocity factor varies wildly
>> with placement height above the actual radio ground (e.g. laying on
>> the grass vs. tucked into the sod) and the composition of the actual
>> radio ground. Given the low VF, at some length the incoming and
>> propagating wave are actually cancelling each other and the pattern
>> will reverse. The BOG is a SINGLE BAND antenna.
>>
>> Starting with 250 feet of insulated wire, place a BOG in it's
>> permanent placement and depth. Bend up the ends so they are not
>> touching anything. Break the center and attach an antenna analyst.
>> Shorten the BOG equally at both ends until it is resonant as a
>> dipole-on-ground (DOG) at 1140 kHz. This will be seen as either a
>> zero-crossing or minimum reactance point. The resistive reading at
>> zero reactance may be any where between 40 and 200 ohms and varying
>> significantly as zero reactance is passed, so ***SWR will NOT be a
>> good indicator for tuning***. You must have an analyst that can go
>> down to 1140 and measure reactance separately. It usually helps to
>> note the frequency above and below resonance at the first meter scale
>> mark and average them, which will be more accurate than the bottom,
>> which will be a "visually wide" indication.
>>
>> It is common for a graph of the DOG impedance to NOT be symetrical
>> above and below resonance.
>>
>> Reattach and insulate the wires at center.
>>
>> Terminate the far end with two 450 ohm beverage rated resistors in
>> parallel to a ground consisting of a pair of right angle 25 foot
>> buried bare copper radials (length not critical, but keep both sides
>> the same). At the feed end use the same method except a 4:1 isolated
>> winding transformer to flooded, ungrounded (in the vicinity) 75 ohm
>> satellite cable.
>>
>> You will need a preamp, if one is not provided in the rig.
>>
>> The mutual coupling between two BOGs is very low, so you can phase
>> them with good effect.
>>
>> BOGS of the type above can be entirely buried in a front yard lawn
>> with some care to waterproofing, making them completely stealth.
>>
>> 73, Guy.
>>
>> On Thu, Jul 29, 2010 at 1:37 PM, Bruce wrote:
>> > Have been experimenting with BOG antennas. They are cranky to
>> get going.
>> > They have a velocity factor of +- .5
>> > When mine was too long, I was hearing an LU station and
>> everything else was
>> > 30 db down. I shortened it twice ending up at .5 it started acting
>> > somewhat like a Beverage. If "way too long" the antenna can reverse
>> > direction.
>> > It had a strange reactance bump at 4.5 MHZ and found it was
>> caused by an
>> > old, in ground, iron water pipe from some bygone era.
>> Sweeping frequencies
>> > to get the correct termination, I found that the dew on the
>> grass caused a
>> > some shift.
>> > Ground conductivity may be a known value, but in some
>> locations it can vary
>> > along the length of an antenna.
>> >
>> > A preamp is a must as the gain is low.
>> >
>> > A standard Beverage antenna is a poor transmitting antenna.
>> The on ground
>> > Beverage would be very poor for transmitting. Talk about
>> ground losses.
>> >
>> > Anyone can not have too many receive antennas. Found I could
>> copy a DX
>> > station on the BOG with an approaching thunderstorm when there
>> was no copy
>> > on other antennas that included standard Beverages.
>> >
>> > Bruce-K1FZ
>> >
>> >
>> >
>> > Does the panel think hocus pocus,or is there some truth in
>> the design.
>> >
>> >
>> >
>> > _______________________________________________
>> > UR RST IS ... ... ..9 QSB QSB - hw? BK
>> >
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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