The comments in your first paragraph are very confusing, mixing up
information on different antennas, old or proposed, and parts data,
without clearly distinguishing what each comment refers to. I doubt
that anyone will be able to sort that out unless they went thru the
thread on QRZ.
https://forums.qrz.com/index.php?threads/feedback-on-building-a-bog-antenna.669192/
Take a little more care in describing things so that you don't mislead
people. There are some knowledgeable people on this forum, and I would
like to hear what they have to say.
The main problem with your first attempt was that the beads you added
had little inductance and a lot of resistance, a total of 238 ohms on 1
MHz and 895 ohms on 4 MHz. That pretty much kills the antenna.
Although I am skeptical of NEC's ability to accurately model a long BOG,
a 250 foot BOG on 500 kHz isn't a long antenna. I think NEC data should
be usable for that, although performance of a BOG can vary a lot in
actual implementation because of variations in ground characteristics
and actual height above the dirt. Performance of low gain antennas are
also very sensitive to circuit implementation and taking care of common
mode current. And don't point them at noise sources.
500 kHz to 4 MHz is an ambitious goal for a 250 ft long BOG. W8JI's
discussion on adding beads and inductors to Beverages is very good, but
I don't think you will have to worry about a 250 ft BOG reversing
directions on 500 kHz because you added too much inductance. You will
be worrying more about getting enough inductance to produce some front
to back in the pattern. And of course the required inductance will vary
with frequency, so you have to figure out how to do that if you want it
to cover a wide bandwidth.
Jerry, K4SAV
On 8/25/2019 12:31 PM, Mikek wrote:
I have never modelled an inductively-loaded Beverage, but my intuition
is that it will not perform any better than an unloaded wire of the same
physical length.
I haven't modeled for 10 years and even then I was in the dark.
I started on this quest when I saw this W8JI page about inductively
loaded beverages, I thought why can't that work on a BOG.
http://www.w8ji.com/slinky_and_loaded_beverages.htm
There is discussion about having to much inductance which causes a
reversal of the receive direction. I also have some idea that the BOG
already
has a slowed VF because it is on the ground. So I don't how much more
inductance we could add.
On a forum, someone modeled my first BOG that I used #73 binocular
cores on, using one pass through one hole. This was about 1/2 of the
suggested value
that the model showed at 1MHz. Also the cores had a Q of less than 2!
It was suggested that the losses did more for the pattern than the
inductance.
The modeler also said that you need 70uH at 500kHz. The modeler did
say the inductors altered the pattern to some degree (I don't think he
was impressed),
He said, "At 1 MHz, front to back at 20 degrees elevation improves by
1.5 dB and gain drops by 6.6. dB. Elevation beamwidth drops by 9.6
degrees."
*However, *those numbers were with the values *I* used, they were not
optimized values.
I have no idea how much iteration the modeler did, I'm thinking not a
lot, he didn't concentrate on just my BOG, but I don't know that for
sure.
It needs to be modeled. In the model. I don't know if it would best to
optimize the length for 4MHz and then load and terminate
for best 550kHz or, just make it as long as I can, 250ft in my case
and go from there. It may be a compromise in my case.(550kHz to 4MHz)
For you guys wanting 160M and as side benefit 80M, you might be able
to optimize on 80M and then load it for 160M and still get good results.
In the model as frequency goes down the size of the inductors must
increase to optimize, I expect the termination resistance also would
change.
I envision two knobs, one adjusts termination value and one alters
the inductance of the nine inductors. Probably some interaction, so
just adjust
them until you have the best S/N. Inductance may have a narrow range
so you could mark your adjustment on the scale for the frequency of
interest.
I'd love some response to this, but if you don't have any, can you
help me with this.
How do you respond to a specific post?
I'm just clicking topband@contesting.com and then copy and pasting in
what I want. Is that the way it is done here?
I'm used to forums and newsgroups where you can quote at the push of a
button.
Thanks, Mike
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