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|gsparks||Posted - 20 October 2012 18:30 |
The elmer I had always drew pictures with the end of the wire being the voltage node and then draw the sine wave for the frequency. On a dipole he would start at each end. He would draw the sine wave down the twinlead or ladderline to the impedance match, he wouldn't use the word tuner. Then he would calculate the different feedlines to make the sine waves on the dipole to be 180 degrees out of phase for each side of the dipole, claiming one side was positive and the other negative relative to the feedpoint. he often would hang a loop of wire on one side or another of feedpoint to get his tuning. He used this for listening to Hf, LF, beacons and hoping for submarines, not sure if he ever got a sub, but lots of beacons. Also used it for receiving 160 meter. He said if tuned right directivity didn't matter and ground didn't matter, since he was picking up phase difference between the antenna elements.
I never paid much attention to him , just yes, I see, oh, answers. I just cut my dipoles and used a balun or twin lead and a tuner, so no real world validation. Sure wish he was still around and I would have paid more attention
|_J_||Posted - 20 October 2012 19:18 |
I know about the Regan quote, but the context wasn't clear.
Anyway, not sure what to say. This is nothing I invented, its not rocket science either, not sure why you haven't heard it, it is fairly common knowledge. It is not beyond reason.
Reflected waves cant just disappear, in a collision with opposite waves. Their energy has to either be (all) dissipated in dirt (requiring a phenomenal unlikely match), or "reflected." Reflection is a misnomer, they really cause currents in the conducting boundary which re-radiates new waves.
And, do you agree there can be no electric field inside a conductor? (charges will flow and neutralize it.) Can there be an electric field on the surface of a conductor? Very near it?
If no, then what happens to the EM energy approaching the conducting boundary?
Heres a kinda simple minded analogy. Consider 2 charges, + and -. There is a field from + to -. Bring a conducting boundary near and parallel to that field. Then the field changes direction and becomes + to conductor and conductor to -, therefore rotating to perpendicular to the conductor. This is not EXACTLY analogous because it is not dynamic, but roughly.
|Mike Knowlton||Posted - 22 October 2012 10:11 |
I'd like to see this put into numbers.
To do this, someone needs to model it in EZNEC. We need the height and length of gzimmers dipole.
I would like to see R and C of gzimmers dipole at 540khz, 1Mhz and 1.7Mhz.
Then we need to see how gzimmers feedline transforms the R and C of the dipole at these three frequencies.
To start the Eznec modeler needs gzimmers dipole height and length and the feedline impedance and length. ( the impedance may be difficult if he has split the 300 ohm twin lead)
This would solve any disagreement here.
Let the modeling begin.
|Garry Nichols||Posted - 22 October 2012 12:0 |
Interesting reply! With your thought experiment of two charges and a conducting boundary, are we winding up with two fields each rotated from the original by 90 deg? That is, one field from each charge, each field going to the conducting boundary. I'm trying to get your verbal description straight in my mind!
If I am picturing it correctly, then it illustrates your prior statement, doesn't it? :
"Reflection is a misnomer, they really cause currents in the conducting boundary which re-radiates new waves."
And the two "new" fields, perpendicular to the original one, would be radiating with a polarization rotated 90 deg from the original field. (And I do understand that this is an instantaneous snapshot.)
If my picture is correct, the two new fields would be out of phase with one another. (But this point may be insignificant to your illustration.) They would make up a kind of W8JK beam changing the pattern by 90 deg also, I'm thinking.
I don't follow the "loop of wire on one side or another" to get tuning. Can you expand on the size of this loop? He appeared to be changing the length of only one side of the antenna/feedline combination.
And, how was he matching a rig to the shack end of the balanced feedline?
Edited by - Garry Nichols on 10/22/2012 12:04:17 PM
|_J_||Posted - 22 October 2012 18:34 |
Just pay attention to the field from one of the 2 charges. Pretend the other charge is too far away to see, not in the picture. I had to use 2 to keep it static, avoid electrodynamics.
I was trying to make an analogy to sort of visualize why as a horizontal field approaches a horizontal conducting plane, the field gradually rotates vertical. Approaching from EXACTLY horizontal is problematic since it has NO vertical component, but if it is slightly inclined it already has a small vertical component that it can dump energy into, works better. The more I think about it, the less fidelity it seems to have, but oh well... I tried.
Unfortunately, electrodynamics is just gets a lot more involved than electrostatics.
Edited by - _J_ on 10/23/2012 12:59:11 AM
|gsparks||Posted - 23 October 2012 7:35 |
The loop on one side or the other was to get the phases aligned, or in this case out of phase. He didn't believe in balanced feedline, only between the impedance matcher (what we call an antenna tuner) and the transmitter. that was the only balanced anything in his shack, his wife included people in that statement as well.
|Garry Nichols||Posted - 23 October 2012 10:14 |
So, why did he use a balanced line? And I realize that you may not have an answer or a sensible answer to that question!
What was he accomplishing with the loop on one side of the line? Was it the same thing as lengthening or shortening the balanced feeder to alter the complex load at the shack end? Seems like that would have been easier and more sensible.
I enjoyed the humor also !
|Garry Nichols||Posted - 23 October 2012 10:28 |
OK, John, thanks! I'm starting to see the light (I think!).
My comment about low angle horizontally polarized waves simply canceling out with a horizontal dipole is based on thinking reciprocally about the antenna and about radiation patterns that I have seen.
My usual way of thinking about this is that the direct wave coming off the antenna at say 5 deg above horizontal arrives at the receiving antenna approximately out of phase with the wave that was reflected off the ground and then arrived at the receiving antenna. (If I recall correctly, a ground reflection of a horizontally polarized sig undergoes a phase reversal.) So most of us hams would say it was destructive interference, creating a null in the pattern.
And I guess the energy is not lost, but added to higher wave angles where the direct and reflected waves arrive at the receiving antenna approximately in phase creating constructive interference and what we would term a lobe in the pattern at that wave angle.
Edited by - Garry Nichols on 10/23/2012 10:30:19 AM
|gsparks||Posted - 26 October 2012 7:52 |
Most of his stuff was trying and what worked, sheds full of junk for future projects or ones that didn't work, great fun to get into and listen to his view of the world.
The loops next to house was for convenience, the far ends were on guyed poles, using the pipe for the top rail of chain link fence, another thing I learned from him, between 1 and 2 dollar per foot, and swedged to make it easy to put them together. He used porcelain electric fence wire insulators nailed to the house.
My own experience on under 5 Mhz experience with dipoles verses longwire, verses balance or unbalanced feed led me to one conclusion, the more wire the higher for receiving, with horizontal rectangle loops being the best but most difficult to make and keep up. Their performance makes no sense to me, but one off the few configurations I tried that made a noticeable (on you could hear) difference.
|Garry Nichols||Posted - 26 October 2012 11:55 |
Thanks sparky. If one is able to put it up, a good multiband ham antenna (they say) is a loop that is a full wave at the lowest frequency of interest. Other higher bands are often (but not always!) close in resonance, so the mismatch is not too bad. Coax feed is not even prohibitive in many cases. They are put up just about any way you can get a "loop" -- square, triangle, polygon. But for square ones you can often find some pattern modeling in books and online.
I've never had the right supports.
How close to a full wave were you on your frequencies of interest?
|gsparks||Posted - 27 October 2012 19:44 |
For the loops, I cut the wire using the 1005 divided by mhz formula. I ran some pvc from peak of roof and dormers, about 25 foot up, and attached the wire, then any extra length to some other high place, usually pvc attached to vent pipes. by no means exact square, but typically fairly close. The base frequency was for 80m. On one of the projects I put a 40 m inside. I used 450 ladder line to a homebrew tuner. The tuner had a coil with taps on either side of a swinging link coil between them, and the a butterfly variable and two other variables, a crude copy of a Johnson matchbox, would load about any frequency, performance good on receive, transmit not so good.
|_J_||Posted - 27 October 2012 20:5 |
Re: "...most of us hams would say ..."
Hey, I am one of "us hams," since I was 7.
|Garry Nichols||Posted - 28 October 2012 8:34 |
I wasn't sure about you (being a ham!). A Novice at age 7 ? Is that what I'm hearing? Was there a ham in the family to foster this rather remarkable accomplishment?
Guess you got distracted from it by "life" afterwards. I was 15 went I got my Novice license, then late teens to mid-twenties did not practice the art. Then got back into it. Am active on and off, mostly QRP CW with wires in trees.
Do you still own any gear?
|_J_||Posted - 28 October 2012 15:5 |
Maybe not so remarkable... I think I figured that wrong. I was in the 4th grade, couldn't have been 7? Must have been age 9 or 10 or something? No one else. I was so interested in electricity, loved that stuff, a nerd from the get go.
I was active in waves, or phases, on and off. I had other burning interests too. I don't have any real 'ham' gear now.
Edited by - _J_ on 10/29/2012 10:09:56 AM
|gsparks||Posted - 1 November 2012 17:7 |
I took an electronics class as a Freshman in high school that the semester exam was the Novice test I was, 15, WN0HWI. I was very involved for the 2 years, but didn't upgrade, seems I got distracted by girls and cars. I do still have the Heath HW16 and VF1 -both in bad shape, I did inherit a Colins S-line and Drake TR3 from my old elmer. The Drake I think has lightning strike, and I haven't used the Collins for a couple of years
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