Rich
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RF Systems Engr (retired)
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Post by Rich on Mar 8, 2019 17:32:24 GMT
... If the primary length of the antenna system is below the transmitter it should work as well if not better than with it at the top. ... The 3D graphic I posted earlier today shows that equal power is supplied to both sides of that center-fed dipole. It would not matter to its total radiation pattern if the antenna output connector on the transmitter was pointing up, or down. It still wouldn't matter to the pattern it would radiate if the two sides of the dipole had unequal lengths.
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Post by End80 on Mar 8, 2019 20:57:17 GMT
... If the primary length of the antenna system is below the transmitter it should work as well if not better than with it at the top. ... The 3D graphic I posted earlier today shows that equal power is supplied to both sides of that center-fed dipole. It would not matter to its total radiation pattern if the antenna output connector on the transmitter was pointing up, or down. It still wouldn't matter to the pattern it would radiate if the two sides of the dipole had unequal lengths. Would a steel pole acting as the ground rod, and primary antenna/lead, and the mast itself alter the conclusions in any way?
By the way, your post earlier in this thread that answered the multiple questions which Mram posed was particularly good.
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Rich
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RF Systems Engr (retired)
Posts: 112
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Post by Rich on Mar 8, 2019 22:05:37 GMT
Thanks for your good comments, End80.
Could you please post a sketch of the configuration you last described? I can't quite picture it in my mind.
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Post by End80 on Mar 9, 2019 1:52:51 GMT
Already been asked that.. I guess I don't explain things clearly.. It's a pole in the ground with a transmitter at the top! Ok, I modified a diagram of the ISS vertical profile antenna system to represent what I'm considering for a 3 meter part 15 system:
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Rich
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RF Systems Engr (retired)
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Post by Rich on Mar 9, 2019 13:41:14 GMT
Thanks for the pic.
If that little wire shown near the elevated transmitter connects its chassis common bus or its "ground" terminal to the supporting pole, and that pole is a good conductor at radio frequencies, then the entire length/height of that pole that is not buried in the earth will radiate.
From the visual scale suggested by the drawing, that "ground lead" path from the transmitter to the buried part of the pole likely means that installation does not comply with FCC §15.219(b).
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Post by End80 on Mar 9, 2019 23:54:48 GMT
It's not scale, I just modified an existing diagram to represent the configuration. The pole above ground would be approximately 8 feet and the short antenna on top the transmitter would take up whatever the difference leading to 3 meters.
As for the pole material itself, not sure. I was thinking a galvanized steel pole, which is supposed to be a good radiator so far as ground rods go.. or possibly use a steel water pipe if the radiation characteristics are good which would easily enable a threaded connection a few inches under ground, making an easier removal later if the need arose.
It just seems a more reasonable approach than installing a transmitter just above the dirt, because such would invite a whole slew of potential problems. A ground mount I think is an act of desperation to insure 3 meters, and is really borderline ridiculous to me.
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Rich
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RF Systems Engr (retired)
Posts: 112
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Post by Rich on Mar 10, 2019 1:02:52 GMT
It's not scale, I just modified an existing diagram to represent the configuration. The pole above ground would be approximately 8 feet and the short antenna on top the transmitter would take up whatever the difference leading to 3 meters ...
That clears it up, thanks.
I haven't modeled it (yet), but I expect that system would radiate OK, at the expense of the high inductive reactance it would take to resonate it, its relatively narrow r-f bandwidth, the difficulty in tuning it to resonance, and the stability of that tuning with changing temperature and precipitation.
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Post by End80 on Mar 10, 2019 6:37:55 GMT
I expect that system would radiate OK, at the expense of the high inductive reactance it would take to resonate it, its relatively narrow r-f bandwidth, the difficulty in tuning it to resonance, and the stability of that tuning... Huh?..., So you're saying it would not perform equally in performance to a ground mount install of the transmitter?
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Rich
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RF Systems Engr (retired)
Posts: 112
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Post by Rich on Mar 10, 2019 12:35:16 GMT
I expect that system would radiate OK, at the expense of the high inductive reactance it would take to resonate it, its relatively narrow r-f bandwidth, the difficulty in tuning it to resonance, and the stability of that tuning... Huh?..., So you're saying it would not perform equally in performance to a ground mount install of the transmitter? In addition to what I posted earlier about this — below is a model of what you proposed, showing its calculated components and performance.
Observation: The internally-mounted loading coil supplied in some transmitters may not have enough inductance to resonate this antenna system.
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Post by End80 on Mar 10, 2019 14:55:53 GMT
Observation: The internally-mounted loading coil supplied in some transmitters may not have enough inductance to resonate this antenna system. Ok, now I've been thrown for a loop.. All through this thread you repeatedly emphasized it should perform equal or in excess of a ground mounted install of the transmitter.. but now you seem to be indicating the exact opposite.. the only thing different is that I provided a diagram which corresponded directly to my prior description.
So what's different? Why suddenly does the inverted antenna system scenario now suggest it would not perform equally to a ground mount install?
So then.. which is correct? It will perform better or it won't?
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Rich
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Posts: 112
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Post by Rich on Mar 10, 2019 15:28:28 GMT
So then.. which is correct? It will perform better or it won't? Once you adequately defined what you were thinking about, "the chips fell where they may." A ground-mounted, 3-m, base-fed, resonated monopole driven against an 8-ft vertical, buried ground rod would be a more efficient radiator (by several times), and likely the loading coil in a stock transmitter would have the tuning range needed to resonate that system.
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Post by End80 on Mar 10, 2019 23:29:31 GMT
I don't understand. OK, so my diagram changed something.. Let's rewind 4 post, step back to right before I even posted the illustration drawing..
For the entire discussion you emphasis was an elevated (8 to 10 feet) transmitter would not only perform equally to, but even potentially exceed the performance of a transmitter which was located on the ground. The reason being that the current flow would be more uniform from lead to ground than what the path of a standard whip provides.. An elevated 3 meter install is likely to outperform a ground mounted 3 meter install.
Am I correct so far?
If that be the case, and because my suggested method is flawed, then specifically what configuration would be required for an elevated xmtr 3 meter install to perform in such a manner to correspond with your expressed conclusions through most of this thread?
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Rich
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RF Systems Engr (retired)
Posts: 112
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Post by Rich on Mar 11, 2019 12:11:40 GMT
... what configuration would be required for an elevated xmtr 3 meter install to perform in such a manner to correspond with your expressed conclusions through most of this thread? Below is a graphic showing a setup that might be acceptable to you. The configuration uses an elevated transmitter installed near the bottom of an elevated, 3-meter radiator. (Note that the transmitter r-f output power shown there includes the power lost in the loading coil when tuned to system resonance.)
Using a shorter, but still non-conducting support pole wouldn't change the results much, and the system would be easier to access for tuning adjustments.
This configuration has four benefits relative to your concept:
- Radiation resistance is higher
- Capacitive reactance is lower*
- Lower r-f loss possible for the loading coil
- Improved radiation efficiency for the complete system
* Possibly within the range that a loading coil in a stock "Part 15 AM" transmitter could resonate
Two caveats (and the same is true for the elevated system you proposed):
- Radiation from wires supplying d-c power and program audio to the elevated transmitter could make that system non-compliant with FCC §15.219(b)
- Using r-f filters at the points where those wires connect to the transmitter could reduce their radiation, but their effectiveness would need to be demonstrated to the FCC if that setup was inspected by them after it was in use
Unfortunately, antenna systems we wish we could use are still subject to FCC Rules (if meeting them is a goal of the operator).
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Post by End80 on Mar 11, 2019 16:57:59 GMT
"The configuration uses an elevated transmitter installed near the bottom of an elevated, 3-meter radiator."
What the hell?? Are you calling that elevated with a straight face? The entire concept in this discussion has been about getting the transmitter off the ground, clear of snow, flooding, children, people in general, animals, vandalism or accidental damage, whatever.. Repeatably through this thread you have stated it makes no difference so far as performance if the transmitter is at the bottom or the top of a 3 meter antenna system, and now you have suddenly took and about-face.
What a waste of time.
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Post by End80 on Mar 11, 2019 17:12:44 GMT
For the sake of illustration let's review in short order this discussion that's been going on for days, by removing all the erroneous parts and focusing specifically the primary points you have made:
[me]With something like a Rangemaster, is there really any difference between the whip on top or a ground lead of equal length below it? - or if you employed about 48" antenna with a 48" ground lead, would that not perform equally to a ground mounted install with just a 96" whip?
[your response]The conducting path(s) leading from the transmitter circuit board common bus and/or its r-f ground terminal can radiate more r-f energy than the ~3-m whip attached to the transmitter that is considered to be "the antenna."
[me] That's very interesting.. not sure how to take it though.. When you say the ground lead CAN radiate more than the actual antenna whip, I'm guessing you mean only if the ground lead was longer than the antenna. But providing both were of equal length then both would have equal radiation - correct??
[your response] For practical Part 15 AM setups, …it is quite easy for the radiation from conductors connecting from the transmitter chassis/ground terminal to the buried r-f ground conductors to be significantly more than from the 3-m whip.
[me] If you have a 102 inch whip antenna and a 4 inch ground lead, would that perform equally to a 102" ground lead and a 4" antenna?
[your response] In free space it doesn't matter to the performance of that system configuration as to which of the two output terminals of the transmitter connects to a 4" wire called "the antenna" and the other to a 102" wire called "ground," or with the wires reversed.
[me]there are a select few hobbyist in the last decade who feel compelled and more secure by employing a ground mounted install… if you're going to do that then why not at least raise your transmitter to a reasonable height and have the antenna below instead above it? ... Would such an installation perform just as well as putting your transmitter on the dirt? The consensus so far seems to indicate that it would, and even possibly better. But is some factor being missed? Is something not being considered? [me]... If the primary length of the antenna system is below the transmitter it should work as well if not better than with it at the top.
[your response]It would not matter to its total radiation pattern if the antenna output connector on the transmitter was pointing up, or down. It still wouldn't matter to the pattern it would radiate if the two sides of the dipole had unequal lengths.
[me]Would a steel pole acting as the ground rod, and primary antenna/lead, and the mast itself alter the conclusions in any way?
[your response]Could you please post a sketch of the configuration you last described? I can't quite picture it in my mind.
[me](posted illustration drawing)
[your response] If that little wire shown near the elevated transmitter connects its chassis common bus or its "ground" terminal to the supporting pole, and that pole is a good conductor at radio frequencies, then the entire length/height of that pole that is not buried in the earth will radiate.
[me] The pole above ground would be approximately 8 feet and the short antenna on top the transmitter would take up whatever the difference leading to 3 meters.
[your response] I haven't modeled it (yet), but I expect that system would radiate OK, at the expense of the high inductive reactance it would take to resonate it, its relatively narrow r-f bandwidth, the difficulty in tuning it to resonance, and the stability of that tuning with changing temperature and precipitation.
[me] Huh?..., So you're saying it would not perform equally in performance to a ground mount install of the transmitter?
[your response] The internally-mounted loading coil supplied in some transmitters may not have enough inductance to resonate this antenna system.
[me] So what's different? Why suddenly does the inverted antenna system scenario now suggest it would not perform equally to a ground mount install?
[your response] Once you adequately defined what you were thinking about, "the chips fell where they may."
And that brings us to here...
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