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5/8 wave with close to vertical (drooping) radials

Discussion in 'Amateur Radio Antennas' started by TheBlaster, Mar 19, 2021.

  1. TheBlaster

    TheBlaster Active Member

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    I am going through a few things in my mind here.. I am making a fast deploy (wire) 5/8 wave antenna.. coil loaded for 10m band. I am trying to work out what the compromises might be from having either 32 very thin wire x 1/4 wave radials laying on the ground versus elevating the feed point by 4-5m on a fibre glass pole and dangling said thin wire radials downwards randomly from the feedpoint.

    I am thinking this is a ground losses versus elevation, versus radiation angle compromise.

    Ultimately a try it and see situation (assuming it tunes ok both on ground and elevated some 4-5 meters up to feed point)

    Anyone have any experience with ground mounting vs elevating such an antenna ?

    If someone says either one will be better than the other it may influence what I do with the radials.. i.e. possibly shortening them and doubling number (64 x .125 lamda elevated vs 32 x .25 lamda radials ground mounted) I assume this will mean I need to tune the antenna slightly differently and before I commit wondered if anyone had any experiences.

    Of course we know radiation angle lowers with height above earth .. but will the dangling radials compromise that "gain" given the are not at the ideal of right angles ?

    I guess in short... elevated or ground mounted? (with 64 x 0.125 or 32 x 0.25 wave radials respectively)

    Thanks for your thoughts in advance.


     
    #1 TheBlaster, Mar 19, 2021
    Last edited: Mar 19, 2021

  2. sp5it

    sp5it Master of puppets

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    Long story short: 4 elevated radials.
    Mike
     
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  3. TheBlaster

    TheBlaster Active Member

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    lol thanks...

    To elaborate though... this is portable.. so 4 x 1/4 wave elevated radials are a practical impossibility.

    My goal maximum performance, maximum convenience, this my shortened radials approach (which if I understand correctly are not much of a compromise compared to 4 x 1/4 wave radials - i.e. cannot do 4 long ones... them add more radials.)
     
  4. sp5it

    sp5it Master of puppets

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    5/8 wave don't need such long radials. Even 80cm each would do.
    Mike
     
  5. TheBlaster

    TheBlaster Active Member

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    That bodes well.. and it actually feeds into a happy accident.. I was delivered solid core thin wire which will in fact hold themselves up better.(y)

    I sawed down the mount section of a cheap aluminium 5/8 silver rod, removed the aluminium driven element... attached a 6.5m (roughly) 1.5mm copper wire and I plan a bunch of thin copper radials attached to the 3 screws at the bottom. Soldered onto eyelets/tags. The wire may make it a bit narrow band but good enough for the 1MHz of interest.

    The goal here is a fast deploy 10m band 5/8 wave with as few compromises as possible. With short GP's I can get the benefits of some elevation (close to 1/2 wave above earth and keep some radials) hopefully this compromise will be the best one.

    This looks like it will work out nicely. The tricky bit is taken care of.. the loading coil, already nicely housed and built in.

    Once the chosen radials (probably 0.125 x 64) are on... tune up will be a snip, snip, snip job. I just want something I can throw up a fibre glass pole on the off chance 10m becomes open when I am playing on lower bands.

    I want to make sure it sh*ts all over a T2LT for DX.. which won't be difficult.
     
    #5 TheBlaster, Mar 19, 2021
    Last edited: Mar 19, 2021
  6. TheBlaster

    TheBlaster Active Member

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    Well what I visualized has not quite transpired. The GP's are a mess ! So a bit of a gamble this antenna.. 36 x 0.125 lamda radials randomly hanging down.. first I will have to see if it tunes up.. and the wait 4 years for 10m to be open.:LOL:

    No doubt the 6.5m driven element will need chopping to more like 6.3m but best to start long of course.

    I will let you know how it tunes up... bit of an experiment really.
     
  7. The DB

    The DB Sr. Member

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    If your looking for a quick deploy antenna, go elevated. I would use a 5/8 design that doesn't require radials, and choke the coax both at about a foot below the feed point and about 9 feet below the feed line. Yep, I said it, two chokes. Also, if you have a mast, make the part the antenna it attaches to non-conductive.

    Elevated horizontal radials essentially do two things, they help lower the feed point impedance, making it easier to match, and if they are near 1/4 wavelength they also act like an RF trap, having an effect much like a choke. Shorter radials will only have an effect on the feed point impedance, and even with that it will be less of an effect than full size 1/4 wavelength radials, even if you have more of them. All 5/8 wavelength antennas require some form of matching, they do not have a naturally low feed point impedance. You could use 3/8 wavelength radials to counter the 5/8 wavelength element's reactance, but even then your going to need something to raise the impedance to between 200 and 400 ohms, a matching circuit, or perhaps a 4:1 unun?

    Angling elevated radials down on a 5/8 wavelength antenna is also not a good thing. If they are horizontal the RF from the radials will cancel. However if they are angled down, some of the RF on the radials will radiate, and that radiated RF will be out of phase with the part of the antenna that benefits you the most, which will raise you angle of radiation. As 5/8 wavelength is already near the upper length limit when it comes to maintaining a low angle of radiation, any radiation from radials that are angled down will not be beneficial to the antenna.

    When it comes to ground mounting the antenna, the radials act very differently than elevated radials. You already have a ground present in the earth, although it is a crappy ground, it does exist. In this case, the radials directly affect the efficiency of the antenna by increasing the quality of the earth in the vicinity of the antenna. The radials are not the entire ground system as RF currents exist beyond the radials in said earth. Essentially the more radials in this case the better. Twice as many 1/8 wavelength radials is better than half as many 1/4 wavelength radials. You could also put down a "ground screen" or a roll of chicken wire or something and attach the ground side of the feed line to it and still get a very good results. Any which way, to maintain a good efficiency, you would need a lot of radials, which will take time to set up and take down. Also, many people will add radials to a ground mounted antenna until the SWR stops going down, then they will stop as SWR then starts going up again. If this were a permanent mounted antenna I would say don't make this mistake. If adding more radials is still affecting SWR, then adding more radials is making the antenna more and more efficient. SWR is not a measure of how efficient an antenna is, just how well it is matched to the feed line. A lot of people will use about 20 radials, and others will insist on using 32, or even 64 or more (or double those numbers if you are using 1/8 wavelength radials). Long story short, the number of radials used on this type of antenna directly affects how well it will perform, which means you will need to take the time and set up all and take down of those radials every time, which imho, kills the idea of a quick deploy antenna. When mounted on the earth, 4 radials is simply not enough.

    When it comes to antenna performance, a t2lt mounted at the same tip height as a 5/8 wavelength antenna will perform about the same as said 5/8 wavelength antenna. If the 5/8 "sh*ts all over* any other antenna antenna mounted at the same tip height, then the other antenna has a problem that needs to be fixed. The great secret to antenna performance isn't in the antenna's length, it is in the height of the antenna's current node, which in a vertical is electrically 1/4 wavelength down from the antenna's tip. All the length of a longer antenna does is raise this current node higher than on a shorter antenna (assuming the same mounting height), and it actually does it at a cost. In this case, the t2lt mounted at the same tip height will have a *slight* advantage when it comes to local contacts and the 5/8 will have a *slight* advantage when it comes to DX contacts. You will not I put astrics around the word "slight". If its so much that you notice much of a difference then you have a problem with one of the antennas being tested.


    The DB
     
    #7 The DB, Mar 19, 2021
    Last edited: Mar 19, 2021
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  8. TheBlaster

    TheBlaster Active Member

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    Many thanks for that extensive reply.. The choke idea is interesting and something to be seriously considered (if no radials 5/8 has to be the choice). I can see there are some real performance drawbacks here with the "danglies" then which may mean there is no advantage, depending on what the definition of a portable, fast and high performance antenna ends up being..

    I am going to have to do this.. can I see a model of a T2LT ? and not the dipole many speak of and present when speaking about this antenna.

    A coaxial antenna, because I have never seen one modeled and I have had poor experiences with T2LT with DX (with the choke of the T2LT about 5-7m high) and I have some suspicion that something is awry with its radiation pattern. (despite often drawing parallel to a "half wave dipole")

    For some reason I have done better with a 1/2 wave end fed silver rod type antenna and would choose one every time over a T2LT.. (other than when you cannot be bothered with anything better)

    Your thoughts appreciated... could there be something odd about the radiation pattern from T2LT give its unique design. It is clever I will give it that.

    Just a few thoughts on it... could the coaxial coil be extra lossy? Could the way the antenna is set up somehow mean it would not have a radiation patter like a dipole ? Could for example that coaxial choke make an antenna tune but in reality there are some CMC's under the choke which messes the pattern up (unlike a true dipole).. i.e. if there was 1/8 wave of CMC breaking through and under that choke could that mess its pattern up ? (1/8 wave just being a random example)

    I mean.... I don't know but I have found the antenna had lackluster performance when I have used it myself. I am sure in good conditions it will work DX.. but when there are poor conditions (weak ionization) ... when antennas tend to show their real value I found it lacking.
     
    #8 TheBlaster, Mar 19, 2021
    Last edited: Mar 19, 2021
  9. The DB

    The DB Sr. Member

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    A t2lt is a near center fed dipole, and should have essentially the same pattern as a center fed dipole. However, as a vertical dipole, both sides won't be perfectly in balance like a horizontal dipole as the earth below will always have more of an effect on the lower leg of said dipole than the higher leg. The t2lt also has two legs of different diameters, which will also cause some balance issues. If modeled in free space this *might* change the angle of radiation up by a degree or three.

    To put this angle in perspective, a 5/8 wavelength antenna in freespace has an angle of about 5 degrees above the horizon (pulling from memory, may be off a bit). If you are looking for dx over local contacts, in my opinion a freespace angle of around 5 degrees or even a little higher is better than a pattern where the peak is on the horizon, so its entirely possible a 5/8 wavelength end fed antenna will be the best option when it comes to dx. I want to point out again that this last part is opinion, but that opinion is based heavily on modeling, and some experience as well.

    All this being said, when it comes to antennas balance isn't a big concern to me. I know some people insist that it is all important, but I am not one of those people. For me its just getting current to flow where it is supposed to flow, and as little as possible at other locations. If balance was all important, there wouldn't be anything like an off center fed dipole, or even any vertical antenna as all vertical antennas are unbalanced antennas.

    I have made several t2lt antennas in the past, and one time I had an issue with it I made another one and it worked fine. The t2lt design seems to be very picky when it comes to some aspects, especially if you are using a coaxial choke. More recently I tend to use ferrite chokes, and since I started using said ferrite chokes I haven't had one issue with them. One thing you might try is if you have a problem, put a second choke about 9 feet down from the first choke on the feed line, if something changes, then you either have a problem with the first choke, or the feed line is a very unlucky length and is causing problem with how the choke works. Part of why I tend to use ferrite is coax chokes are reactance based, and are far more sensitive to said things than ferrite chokes, which for me tend to work better in most circumstances.

    As far as efficiency, the t2lt is about as efficient of a design you can have. There is no matching network involved, and it goes straight from coax into antenna.

    It is possible that the t2lt might not be the right antenna for you location for whatever reason. This also happens. There are plenty of examples in prior posts where one person insists that one specific antenna is always better than another specific antenna, then another person will come on and say that he had the opposite experience with these same antennas. It could be 10 to 1 against a group of people on which antenna is better all based on personal experiences, but they will sometimes even fight to the point that it becomes personal to them. In reality, both sides can be right for their own circumstances. So if you find yourself moving from, say, a heavily mountainous region to, say, an area of fertile farmlands, or vice versa, or even any other different type of location, it may be in your best interest to try out antennas that didn't work so well before. You may be surprised at the results.


    The DB
     
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  10. TheBlaster

    TheBlaster Active Member

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    Yes that makes sense and I started thinking about off centre dipoles in fact (which I know little about so off to check their patterns out if I can find some) I had a wacky idea that they are rather more like the pattern of a 1/4 wave with a high take off. (which also has I-max at feed point)

    Bit of wire on a tuner work skip when the conditions are there but that is not the mark of a high performance antenna. And I notice these difference as I tend to be a like to chase this really quiet stuff and try and get a contact on the edge of possibility but just found whenever I was using it the T2LT just seemed to fall out of favour with the various antennas I have cycled through. Usually the bottom of the T2LT is pretty high up above ground, always minimum 1/2 wave and often a bit more than that so I would have thought that would give it less chance for the bottom half to be influenced.

    It could just be stray CM on that coax under said choke in conjunction with the slightly unbalanced thing is affecting take off angle somehow.

    Anyway I loathe to use one again so will carry on thinking this through. It is also more interesting to experiment... an ultimately more satisfying to use something a little more out of the ordinary.

    Does a "no radial" dual choked 5/8 start increasing its lowest radiation angle or reducing gain at said angle ? If not that could be the one for me. I could always have "minimal radials" 64 x 2 feet stubby ones just for the hell of it, it may help the match, I'd better get my soldering iron out. That may well be the ultimate compromise.

    I am going to guess that the feed line is radiating and messing the pattern up a bit with some T2LT's.. maybe I was just unlucky both times.. twice is enough to have given them a chance.
     
    #10 TheBlaster, Mar 20, 2021
    Last edited: Mar 20, 2021
  11. TheBlaster

    TheBlaster Active Member

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    I am not a fan of compromise and I start to think the negatives of fast deploy (long fishing rod) elevated portable verticals for 10M are greater than I want to accept. That is fine though... you have to go through these things in the mind to see where your comfort/enjoyment lies with what you operate with.

    You cannot have it all... convenience (fast/easy/practical to set up) and the best radiation pattern. Similar for a multi-band option (some the patterns suck ! ) verses top level single band performance.

    I will have to go with a higher effort based solution to enjoy 10m...even if that means committing to the band before I go out on any mini expedition... no rush for that unless you enjoy E layer summer skip.
     
    #11 TheBlaster, Mar 20, 2021
    Last edited: Mar 20, 2021
  12. HomerBB

    HomerBB Sr. Member

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    For fast deploy horizontal radials get a pvc coupler and put ar t least 8 holes around its circumference.
    Put short 1/4-20 screws in them from the inside so threads face outward. Put "coupling nuts" on the screw threads. Get 1/8ƛ long all thread rods and screw them into them. Connect the radials to each other, to the braid side of the coax, and to the bottom of your matching coil.
    The pvc coupling can be fastened to the antenna by whatever means you wish. You can screw and unscrew those radials rather quickly.
    Screenshot_20210412-154553_DuckDuckGo-01.jpeg Screenshot_20210412-154859_DuckDuckGo-01.jpeg Screenshot_20210412-154612_DuckDuckGo-01.jpeg Screenshot_20210412-154950_DuckDuckGo-01.jpeg
     
  13. TheBlaster

    TheBlaster Active Member

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    Thanks for sharing your idea.
     
  14. Boat Anchor 63

    Boat Anchor 63 Active Member

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  15. Boat Anchor 63

    Boat Anchor 63 Active Member

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    DB,
    With all of your knowledge and experience which antenna will work best in a desert area surrounded by mountains ⛰ the t2lt or the sirio 5/8 gain master ?
     

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