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| Interesting way to mount 1/2 wave vertical... | |
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| Tweet Topic Started: Tuesday, 22. September 2015, 15:23 (597 Views) | |
| RadioDaze | Tuesday, 22. September 2015, 15:23 Post #1 |
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https://youtu.be/igggHkOQYKQ No commentary on it really. Thought it might turn into a bit of a cloud warmer. |
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| Northern Crusader | Tuesday, 22. September 2015, 15:30 Post #2 |
26 Charlie Tango 1760
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Far from it. Whilst it'll be a poor performer for local contacts it'll work well for DX. Edited by Northern Crusader, Tuesday, 22. September 2015, 15:30.
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| 26CT1760 / M0GVZ | |
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| RadioDaze | Tuesday, 22. September 2015, 16:44 Post #3 |
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I read of late 16 degrees TOA is typical for a 1/2 wave at 0.5M from the ground, but thought aiming for lower angles would be better for the really long haul ? Given the losses associated with multi hops off the F2. (all of which is actually very unpredictable of course) I am currently aiming to get 5/8th waves (GM or IMAX) at close to 1 wavelength from the ground which is harder than you might initially think as a lone bloke working a mobile base station in winter. Typically I assess the likely weather and set up appropriately, the greatest issue of course being wind speed. Rain is more of a inconvenience than a show stopper.
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| RadioDaze | Wednesday, 23. September 2015, 07:18 Post #4 |
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This guys mount method is akin to my Silver rod G Clamped on the gate. I don't recall it being as good as an antenna being 6M in the air on the DX side. I can do it but it seems like it does not cut through quite as well as when I have the poles up in my own minimal experience with it on the gate. (2.3M steel gate either side of the feed point) Then again could have just been conditions on the days. As it often can be. |
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| Farmer Richard | Wednesday, 23. September 2015, 13:24 Post #5 |
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26 Charlie Tango 986
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Was your silver rod isolated from the gate as is the set up in the vid you posted. This is how ground mounted antennas should be with radials coming off from outer braid of coax. Normally though the vertical is a quarter wave. |
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| Northern Crusader | Wednesday, 23. September 2015, 13:29 Post #6 |
26 Charlie Tango 1760
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You're not far off the ball there but to be a cloudwarmer it needs a TOA a lot more than that, typically higher than 70 degrees. My inverted L was definitely a cloud warmer on 40/80/160. 16 degrees TOA is good for a couple of thousand miles. |
| 26CT1760 / M0GVZ | |
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| RadioDaze | Wednesday, 23. September 2015, 13:33 Post #7 |
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When I use the gate I don't isolate it as my reasoning is that the support and the ground plane are one and the same in that event. I have also read that to allow current to flow in equal amounts in GP radials that the antenna should be isolated from the pole. (I noticed his looks wooden) The other odd thing with his set up is whilst he isolates the pole (which is tiny = about 12-18 inches?) he shorts it to the plate with braid (same difference I would have thought) Why use a braid when he has a small pole ? All a tad confusing. |
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| RadioDaze | Wednesday, 23. September 2015, 13:36 Post #8 |
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Sure, 16 degrees is ok, could be worse for sure. I read that with 10 degrees or less just above horizontal your max single hop would typically be 2,500 miles. The crux of the issue is lowest TOA on your lowest lobe is what you should aim for for DX (the ideal being a nice spread of TOA's from below 10 to up to 30-40 degrees without any deep nulls, if possible). Given height and therefore TOA (type of antenna as well) is all that is within our control and what happens beyond that is luck or bad luck as to the relative charge level of the exact bit of F2 gasses that your signal hits. Also subsequent hop angles are determined by your first angle of incidence so aiming low is a good plan. |
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| RadioDaze | Thursday, 24. September 2015, 07:53 Post #9 |
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If true for verticals then it beckons the question of why we put our antennas on poles at all. The only thing is this guy talks about ground plane antennas. When I hear "Ground Plane Antenna" I think of 1/4 wave with 3 to 4 45 degree angled radials. (Then there are ground plane type antennas.. like your silver rods etc. 1/2 and 5/8 wave, the irony being the 1/2 wave is not fussy about having radial ground planes unless you count the coax ) So maybe, given his use of a true 1/4 GPA there may be better "shielding" against the effects of the earth from design.It is not clear he uses a 1/4 wave GPA he just says : "simulation of a full size groundplane antenna" and it is a shame despite his 3D plots you cannot actually quantize the angle of radiation at 0.25 and 0.5 Lambda. The lowest lobe could in fact be emitted at a lower TOA than the low antenna which would be advantageous on the long hall F2 DX. At only 0.5M maximum angle of radiation is the same as what Sirio wants us to believe for the GM i.e. 0 degrees (their plot merely says typical radiation pattern) when comparing the GM against other 5/8 waves. I often wondered if 0 degrees TOA's just get attenuated en route to the F2. Can your TOA be too low ? And your RF get attenuated by buildings and terrain before it gets where it needs to be. http://www.qsl.net/df3lp/projects/vertical/ Seems you need to be at awkward to achieve heights above earth surface before benefits are evident for DX at 11m. 1.5 wavelengths being 16.5M The bonus comes for local communications with the height most people strive for. I think experiments might be in order on a ground mount on day. Though right now I feel that for DX it is extremely difficult to interpret the results based on different daily conditions. I don't get much radio time as it is so thinking about all this leaves me just scratching my head and pondering. I bet a Gain Master would not like ground mounting for DX or otherwise. The more I read the more opposing ideas are presented along with more ifs and buts. The only reason why I question this is because I want my verticals do do the best possible for long haul F2 DX. |
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| RadioDaze | Thursday, 24. September 2015, 08:21 Post #10 |
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To clarify regards isolating the mast/pole, which this guy did by using a wooden pole. Why do that if you are going to short it with braid to the base plate, why not just use a conductive metal pole. I do not understand that. Is there some differing electrical or RF properties between braid and a short stub of aluminium pole ? |
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| The DB | Thursday, 24. September 2015, 13:00 Post #11 |
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Maybe that PVC pole (to my eye, you said it appeared to be wooden to you) is just what he had on hand, and it was already cut to size or easy to do so. There is no real difference between using a conductive pole and running a wire down a non-conductive pole. If he had an aluminum or other metal pole already cut to size there would be no need to run said ground strap. Further, cost may have been a factor, it is more expensive to get a metal pole and cut it to size than doing the same with a wood or PVC pole. The DB |
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| RadioDaze | Thursday, 24. September 2015, 14:01 Post #12 |
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Maybe. Does that not defeat the objective of isolating the antenna from the mast in such an installation ? I thought the goal was to isolate antenna from mast to ensure current flows in the counterpoise. (let's say a radial kit on an IMAX or A99) I read that one reason people often see no differences when they put a GPK on a antenna is because the antenna is electrically connected to the mast. (in effect the pole/mast acting in part as a ground plane/counterpoise)Maybe in this case the pole is so short it has virtually no effect anyway, metal or an insulator. Let's say... a normal mast 6M/20ft long and not ground mounted (average/minimum ideal height I guess) If you put a fibre glass top pole on to isolate the antenna from the aluminium mast below I read that this ensured that there was current on the radials which made the ground plane radials effective. I have to say the more I read the more "making it up as people go along" I find. Not yourself I hasten to add but it just seems people online make something up and that'll do. Either that or important details are missing from articles which make it hard to find logic between when comparing articles and likely effects of various mounting methods and heights. It is no wonder antenna systems are ill understood. And to top it with regard to DX performance every day is dependent on ionosphere conditions meaning no useful comparison to various installs can be made. I am not sure there is even much point to looking into it anymore. This is where the disconnect stems from when trying to gauge performance for DX. Seems a matter of getting an antenna as high as you can and that's it. There seems to be no other methodology to understand what height your antenna will perform best for DXing. Very unsatisfying that you cannot know the best height. Somewhere between the ground an 1.8 wavelengths seems to be the answer. Take your pick. I seem to use 1/2 - 3/4 wavelengths myself from a practical perspective and theoretical guess. I don't trust that ground mounting to allow the lowest lobe your antenna can get to not be affected by the ground with a couple of copper wires vs 99.5pct earth to absorb your signal. Something does not ring true to me. Unless something very counter intuitive is at play. A few examples: At 3M off the ground with a Gain Master I got to Indonesia. 6M off the ground with a Silver Rod to Kenya/Reunion Island. 6M off the ground with Gain Master to Australia. Brazil with a Silver Rod 0.5M from the ground bolted to gate. Chile with a Gain Master at 7.5M. Anything seems to work. It would be nice to know what height above ground would produce the greatest signal strengths at the other end in the vast majority of cases? Ground mounting or mounting at 1/2 wave and above but below 1.5 wavelength which is too high practically for most. (16.5M) I think I have beat this one out now so I will make peace with the impossible question and leave it there. |
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| The DB | Thursday, 24. September 2015, 15:27 Post #13 |
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Hmm, counterpoise... I hate that word, but then you already knew that... In the case in the video above there are 10 directions for the discussed current to flow. Eight of them are radials, all of which will provide a low impedance, which will attract current flow. One of them is to the base, and a note here, this path will not continue into the earth as there is no ground rod in play. Sitting a piece of metal on an earth is very different electrically than driving a ground rod into it. Because of this this connection that you are worried about will present a high impedance and thus resist current flow, it is almost like there is no connection at all. If, however, the base of the antenna was connected to a ground rod in the earth, this would switch to a low impedance, possibly even lower than the radials in the radial system, and because of this adding a ground rod to the setup could potentially have the effect you are worried about. One of them is the coax, which will have a random impedance, but almost certainly an impedance that is higher than the radials. With the setup in the video linked above, most of the current will still flow to the radials. Be it accidental or otherwise, he set this system up properly. One thing to consider is the RF in question does not act like DC, and forgive me if I am mistaken, but you seem to think it does. It is possible to make the RF see what we want it to see. Some antennas will have an RF signal at a given frequency see an open circuit, while a DC multi-meter sees a direct short. The opposite can be done as well. Its possible, depending on the circuit or lengths involved, to make an RF signal see anything we want it to see irregardless if there is a DC open or short circuits involved. It is also worth noting that a proper set of radials go a long way in minimizing currents on other possible current paths, namely the mast and coax. Unless you have an unlucky length when it comes to feedline or mast (which can happen but pretty rarely in practical use), a good set of radials are often all you need to minimize currents on said other paths. The only time you really need to isolated the mast is for an antenna is one that has no radials and no built in choke. The a99 without said GPK or home made radials for instance. Not that there aren't some other antennas that could benefit from isolating the mast as well, but it often isn't needed. I guess long story short, there isn't any one easy set of rules that works in every case, and in some cases, what works for one antenna installation will break another. The DB |
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| RadioDaze | Thursday, 24. September 2015, 18:47 Post #14 |
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I have to say that large paragraph about the braid/pole lost me a bit For the life of me I cannot see why a metal pole is different to a metal braid. I think I have grasped this ......so you only need to isolate a pole from an antenna if the pole is earthed and you want current to flow in the radial kit you installed which makes the antenna technically complete ? "One thing to consider is the RF in question does not act like DC, and forgive me if I am mistaken, but you seem to think it does." Yes and no , I know it does not because many antennas are DC shorted yet still work so I know that the RF does not see this protective short. But it is only in this context that I have come across it.Now there is a short between the mounting of the Antron99 (braid not pole). I think he could have not bothered with the braid and just used a stubby pole ? Are you saying this system of mounting does not require isolation from the pole because there is no ground spike ? Ahhh I think my head might explode lol ! |
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| The DB | Thursday, 24. September 2015, 19:38 Post #15 |
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Let me make this clear for you. There is no real difference between using a metal mast or a metal braid in the video above. You are absolutely right, they do exactly the same thing. Also, in this case, weather that braid is there or not is actually irrelevant to the operation of this antenna setup. Note, the words, "this antenna setup", that does not include all possible antenna setups. If the radials are designed properly, you don't need to force current onto them, they will attract said current on their own. Another way of saying this is if the radials are designed properly, the radials themselves is all you need to force current onto the radials. The DB |
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| RadioDaze | Thursday, 24. September 2015, 19:46 Post #16 |
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That is clear, cheers.. I think. So you could attach ground radials to the base of an antenna (metal ones) with an insulator material between and they will still attract RF current as a radial despite there being no DC conductive connection between them and the metallic base of the connector. |
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Typically I assess the likely weather and set up appropriately, the greatest issue of course being wind speed. Rain is more of a inconvenience than a show stopper.
unless you count the coax
) So maybe, given his use of a true 1/4 GPA there may be better "shielding" against the effects of the earth from design.
8:47 AM Jul 11