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Author Topic: buried in noise  (Read 390 times)

KA4WJA

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Re: buried in noise
« Reply #15 on: January 06, 2023, 01:00:29 PM »

Dale,
Truer words may not have been written here on eham.  :)
Yes, it isn't always simple.
And, thank you for the discussion here!



This sounds like a great project....and a super idea!
Please post a link to this when you're done....I'd love to see this!
That's why I'm working on plotting relative gain of different
antennas as contour lines on a map that can be rotated to
account for the antenna orientation.  Especially over longer
distances, I want folks to see how different antennas can
work better (or worse) to specific locations.  And the first
application of those plots will be for gain NVIS antennas,
where there are the most trade-offs between gain and
coverage area.
(That article is in work, but Real Life has
made progress slow for the last few months.)

BTW, I'm sure you're aware of L.B. Cebik's initial work on this (~ 20 some years ago?), without the plotting patterns on a map, of course.
I learned a good deal from him over the years....he, and Walt Maxwell (a neighbor here for quite a few years before his passing) are some SK's that are sorely missed!  :(


And, for those curious....if you really want a killer NVIS signal, and don't care about coverage beyond ~ 250 - 300 miles....there are antennas that can give you about as much gain over the typical inverted-v, as you get from a KW amp!

Here's L.B.'s paper covering some of this (my fav is the "Jamaica Array" / horz Lazy-H, over a ground screen, which you'll see described/modeled on page 13....but, if you have the room and can accept an even narrower coverage area, the extended Lazy-H is the winner!)

  on5au.be/content/a10/wire/n6.pdf

In case anyone thinks I'm exaggerating....have a look at all of L.B.'s papers...

You'll see that while the common 75m dipole at typical heights of ~ 35 - 40', has ~ 6dbi to 6.3dbi of zenith gain (over "average soil")...maxing out at ~ 6.4dbi at ~ 46' high....
(and, some may wish to more "circularize" their pattern, and/or get a tiny bit more gain, with a full-wave horz 75m loop, at typical heights of 35' - 40', having 6.6 to 6.9dbi of zenith gain....maxing out at ~ 7dbi at 46' high...)

But, when looking at even the shallow 120-degree inverted-v, at the typical heights of 39' - 45', has ~ 3.6dbi to 4.5dbi of zenith gain (over "average soil")....

And, if you compare those to the 10.9 to 11.6dbi of zenith gain (over "average soil") of the Jamaica Array / horz Lazy-H (at ~ 46' high)....
Or to the 12.7 to 13.7dbi of zenith gain (over "average soil") of the extended-Lazy-H (up at ~ 56' high)....
You'll see just how much "gain" you could attain on 75m.
  :)

So, you could run barefoot (~ 100 watts) into a killer NVIS antenna (such as the extended Lazy-H),  and be just as strong (or stronger) to stations within 200 - 250 miles of you, as a neighbor of yours running 900 to 1000 watts into his full-size inverted-v with apex at ~ 40'!
(and, certainly a LOT stronger than the other guys with lossy-transformer fed EFHW's!)
 
Myself?
I don't have the room for an extended-Lazy-H!  :(
And, while I do have the length for a Jamaica Array, I don't have the lot width to accommodate the ~ 133' width needed for this array, but I might be able to fit in a 100' wide array someday...and, while I'm not an antenna modeler, I suspect that if I also rigged a ground screen, I'd only lose 1db?
So, I could still have 4+ db of gain over my full-wave loop...but...

But, these days, since I don't need more zenith gain (rather am looking for more low-angle gain), I'm not likely to go thru the effort.
But, those that desire this close-in / NVIS advantage....Go For It!  :)


BTW, just an old anecdote....many decades ago, while the good ole' boys from Mississippi Valley area / SE US, on 3895 decades ago (PUC, TNY, etc.), did have some strong signals from their multi-KW amps, and decent antennas (heck they were 40-50 over S-9 into Mass. back in the day when I was in college up there)....but the strongest 75m signal I ever heard was from a guy ~ 120 miles south of me, running a TR-7, driving an Alpha 77 (or Henry 4K ?), into a Jamaica Array (horz Lazy-H)....not sure if he had a ground screen under it, but maybe.





Ah....the variables of latitude.  :)
I've heard of you guys in the frigid north having issues with the critical freq in winter months and/or at solar minimums, but down here we really don't have much of an issue
Here at 27* to 29* latitude, I've only heard 75m lose our NVIS coverage (critical freq falling below 3.6mhz) a few times!
Seriously, in > 40 years, I can count these instances on one hand!

Here at 45 degrees north, we can go years without
40m opening up for NVIS, and much of the time 80m goes
out about sunset.  I've been advocating the use of 160m
as an alternative for about 3 sunspot cycles now, and those
who did use it were amazed how well it worked, even with
low dipoles and portable operation.  (Yep, we strung a
portable 160m dipole across the lawn in front of the county
EOC.  If folks tell you it can't be done, they just aren't
being very creative.)

So, yes, I agree that there is a lot of variation in
coverage distance at a particular angle.  And any
single number will be wrong much of the time,
because conditions change.



Dale, thanks again for the discussion!
It's fun to talk to someone that "get's it"... hi hi

73,
John,  KA4WJA
« Last Edit: January 06, 2023, 01:02:49 PM by KA4WJA »
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WB6BYU

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  • Posts: 20896
    • Practical Antennas
Re: buried in noise
« Reply #16 on: January 06, 2023, 02:00:03 PM »

Quote from: KA4WJA

This sounds like a great project....and a super idea!
Please post a link to this when you're done....I'd love to see this!



I’ll be adding it to the website once I get
enough of it done to be useful.

I keep finding interesting “little” projects that
continue growing once I start on them.  It
turns out that the plots can get rather messy,
with irregular shapes.  I’m in the process of
trying to automate as much of the data
collection process as possible, but it is still
slow.  And I have a lot of different models
I’d like to do, although I expect I’ll publish
it with a small number of patterns and add
to it as there is interest and/or I have time.


Quote

BTW, I'm sure you're aware of L.B. Cebik's initial work on this...



Yes, I am linking to his various articles.

While I have great respect for his work, we do
come to different conclusions on occasion.  Not
because we use different models, but because
we have different operating assumptions.

For example, he makes a big deal of having a
nearly circular radiation pattern, but that
isn’t necessarily optimum to cover a long,
skinny state (like Tennessee, for example).
And while he focused on squeezing every
possible fraction of a dB out of an antenna,
I tend to emphasize having an adequate
signal.  When conditions are poor, being able
to switch to a better band gives far better
results than trying to increase gain to
get through when the ionosphere isn’t
cooperating.  So, for example, up here I’d add
an antenna for 160m before trying to
increase gain on 80m (unless I was using
a really poor antenna - there are several
on the market).

That’s not to say that either of us is “right”
or “wrong”, just to understand the context
and underlying assumptions of the author
when reading articles, to see how well they
apply to our own circumstances.


Quote

...there are antennas that can give you about as much gain over the typical inverted-v, as you get from a KW amp!




So far, for 75m antennas at ~30’ without a
ground screen, over somewhat poor soil
(typical of much of Oregon) none of my
models have shown more than about
6 dB over a half wave dipole in the same
conditions.  Of course, the results will vary
depending on the specific antennas chosen,

(But I guess some of the older “1 kW” amps
we’re rated by DC input, rather than PEP
output, so they might not be that far off...)

And again, that comes down to personal
operating preferences and trade-offs.


So the important message is that
personal preferences and operating style
play an important part in determining
what antennas are preferred for each
operator. 

KJ4SKP

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  • Posts: 106
Re: buried in noise
« Reply #17 on: January 07, 2023, 07:37:13 AM »

reading through all these excellent replies. Thanks so much to the operators that took time and energy to help me come up w/ a solution for my propagation issue.
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N4KZ

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Re: buried in noise
« Reply #18 on: January 14, 2023, 10:18:30 PM »

For the distance you want covered, try the 80 meter band at night. You will find that at times on 40 meters you’re too close. Ditto for 20 meters. When I say too close that means your signals are skipping over each other. The results are weak signals that are hard to copy. 73, N4KZ
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WA3SKN

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Re: buried in noise
« Reply #19 on: January 15, 2023, 09:23:21 AM »

I find a large loop about 1/4 wavelength high works well with NVIS. Of course, NVIS does not really work for frequencies above 10MHz so plan accordingly.  Just add ladder line and a tuner!

-Mike.

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