Topband: Topband Digest, Vol 200, Issue 28

Mon Aug 26 12:38:55 EDT 2019

  Sorry for all the extra quoting, I'll try to minimize next time.
  Hi K4SAV, You have more understanding than most, I started a similar 
thread on the QRZ forum.
I'll try to stick to only one antenna at a time. I've been hard on this 
and not sleeping well so I may not be a clear as I could be.

  My previous BOG I had #73 binocular cores.
I thought you measured a pass though on hole at "1 MHz ___ 23.8 + J 42.2 
____ 23.8 ohms plus series 6.7 uH"
so where does the "238 ohms on 1MHz " you wrote below come from? Is that 
just part of the confusion I caused?

  On the possible  inductor loaded BOG design:
On the QRZ forum you gave these values , not sure you optimized them or 
just how the came out of you model.
But they don't seem extremely high so easy to make.
Freq ____ Each L ___ Termination
500 kHz __ 70 uH ____ 230
1 MHz ____ 9 uH ____ 250
1.8 MHz __ 13 uH ___ 290
3.5 MHz __ 0 uH ------- 300
3.9 MHz ___0 uH ____ 300
And yes, I am clear about the limitations caused by being close to 
ground on the accuracy of the modeling.

  As far as the wide bandwidth, if there are limitations, that's life, 
if the idea can optimized for a 160M / 80M
antenna great, If I can optimize it for 550kHz to 1.7MHz, I'm happy, if 
it makes it up 4MHz even better.
But I won't know until I push the idea, and I need help as I really 
don't have talent to figure it out by myself.

I'll stop here before I seem to be mumbling.

                           Thanks for your help, Mikek

On 8/26/2019 11:00 AM, topband-request at contesting.com wrote:
> Message: 2
> Date: Sun, 25 Aug 2019 14:47:44 -0500
> From: K4SAV<RadioXX at charter.net>
> To:topband at contesting.com
> Subject: Re: Topband: An oddball question about a BOG.
> Message-ID:<5D62E5E0.2050505 at charter.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> 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 clickingtopband at 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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