Topband: BOG Beverage on Ground Help

[K4SAV]

Mikek said:
"I'd like to apply the loading to a BOG to slow the VF and make it seems 
longer.
  ie. make a 80 meter BOG length work on 160 Meters. But then make the 
reactance go away for 80 Meters
  My actual goal is to have a BOG that covers 500kHz to 4MHz. "


Mikek, I see you haven't given up on this project.  Experimentation with 
antennas is one of the things I like to do too.  Good luck with this.  I 
won't offer possible alternatives to do this  (there are several)  but 
will consider only your desired approach.

I don't see any switches in your circuit diagram to switch series 
inductors, so I assume you are trying to make them variable and have 
them operate from 500 kHz to 4 MHz.

There are some difficult tasks ahead to make this work over a frequency 
range of 8 to 1..  One is the RF choke.  EZNEC simulations show you need 
about 1mH or more to get enough impedance at 500 kHz. The problem is 
that the self resonance of the choke has to be well above 4 MHz.  A 
distributed capacitance of the choke of 1.6 pf would cause the choke to 
resonant on 4 MHz, so the distributed capacitance must be significantly 
less than that.  It may be possible to build an inductor like that but 
it will have to be an air wound coil using very small wire and well 
separated from its surroundings.  A ferrite or powder irom core won't 
work.  Accepting some degradation of the pattern at 500 kHz would 
decrease the choke requirements.  Other than that, I don't have a 
solution for this, other than something complicated, like switching 
chokes as a function of frequency.

Those values of inductance were derived from simulations and there is 
some possibility the numbers may not agree with experimental results.

Position of the wire carrying the current may affect the pattern if it 
is close.  Too close (like in the same cable) and the capacitance 
between the wires will effectively short out the inductors at RF.

The resistive component of the impedance of the series inductors is 
important.  Inductor material is important. If the resistance is too 
large, it will kill the response of the antenna.

DC blocking caps should present no problems.

I assume you have breadboarded the series variable inductor and 
determined the inductance range needed to cover this frequency range.


Mikek said:
  "I see certain measurements for the length of a BOG, such as 200ft for 
for 160 meters."

You will find various recommendations for BOG lengths from different 
people.  I didn't trust NEC to give a correct answer for this so I spent 
a month comparing a 250 ft BOG to a 366 ft one.  I posted my results here:
http://lists.contesting.com/archives/html/Topband/2018-08/msg00073.html

Jerry, K4SAV