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antenna build

Discussion in 'HAM Radio' started by daveyburt, Dec 10, 2018.

  1. daveyburt

    daveyburt NES Member

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    Before I go too far down the road for this plan, I wanted to run it by you guys.

    I came up with an old CB and had a couple SS whips hanging around so, time to play.
    I'm a total Newb but, have been reading a bit and came up with this hair brained plan.

    1/2 wave, center fed, vertical dipole w/ feedline @ 90deg.
    My space is constrained and a high mast is not an option. In reading about the radiation patterns, the straight vertical may not produce optimal [email protected] my location but, would surely be 'acceptable'. Then I read more and found some 'bent' designs so, I came up with a possible a mount.
    The initial design was for the straight vertical (as evidenced by the two opposing mounts on the top flat of the bracket). Then, I added the 'swinger' bottom - crudely marked for 90, 60, 45, and 30 deg angles. (will add a second screw hole to 'lock' it into the various positions and test for strength)
    [​IMG]

    So - this is an article that i'm currently a bit interested in (qsl link below).
    With the angle change of the elements comes a change in the length. I plan to accommodate for that by using some 3/8 x 24 threaded rod to lengthen as necessary based on the angle.

    Link - Center-fed Vertical L-dipoles

    Does this overall mount plan seem sound?? I could use the change in radiation pattern, utilizing the more 'tailored' radiation pattern as my antenna location isn't perfectly suited to a straight vertical.

    I'd also assume that the length offset produced by the 'swinging' leg (rough offset from the pivot bolt to the mount [empty hole in pic]) would have to be figured into the length of that leg. True??

    Am I going down the right path?

    Thanks - I'm hoping to only have to get on the roof 1/2 a dozen times to tune it.
    ;)

    ETA: found a better link - cleaned up post based on new info.
     
    Last edited: Dec 10, 2018

  2. AHM

    AHM NES Member

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    Ya got me.

    I look around NES and I see nothing but untapped potential.
    (Sort of like a capacitor you charge to 100V
    and leave on the workbench for some fool to pick up).

    But if no one comes back,
    maybe this is a question for some forum like EHam.Net or QRZ.Com.

    Could be worse -
    you could try and ask them a gun question.

    73's/AHM
     
  3. w1ujay

    w1ujay NES Member

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    Right here
    Awesome! Bitten by the bug. It doesn't get better.

    What frequencies are you thinking to operate on? Is this for VHF? Antennas get impractically large for threaded rod to be practical in the HF spectrum.

    The angle of the counterpoise may help slightly, but getting a working antenna would be the first step- ahead of the radiation pattern.

    So if you have 2 whips, the center conductor of the feedline would go to one of them, and the outer shield would go to the other whip for a dipole. These would need to be electrically isolated from eachother, the shield can connect to the mounting hardware. (This may be obvious, but it looks like everything on your picture is bolted together?)

    The formula is simple no matter what the frequency- 468/f in MHz = length of 1/2 wave dipole so for 10m 468 / 28.4 = ~16.5 feet so each leg would be just over 8 feet of threaded rod (hint - just use 12awg insulated wire for HF) (hint2 - for VHF the radiator should be vertical and the counterpoise, or connection to the coax shield need only be a hunk of metal - think mag mount antenna)

    BUDWIG HQ-1 Antenna Accessories Insulators, HQ1

    So bounce some stuff around here and will keep an eye see if we can help.
     
  4. daveyburt

    daveyburt NES Member

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    Thanks guys!

    Here's a little more info cuz I have no real idea of what I'm creating here.
    hahaha

    I'll be putting CB behind this so, 11m would be it's operating band. The threaded rod would only be used to extend the angled lower element. IE: @ 45deg, my ground leg would have to grow by a couple inches. I'd just use ~2" of the rod coupled behind the ground whip to increase its length. The stainless whips are a little long @ 108" so, I may trim in a way to not have to use the rod. But, my intent was to do a pure vertical to start off. Then, play with angles.

    The more I read, and think about it, I may just do the 45deg right off the start (if my space allows - will be in some small branches if I do). But, this may also help me get my bottom leg a little higher off the ground. Not sure which is more critical; clean air space or bottom leg being higher. My feed point will have to be a little more than the 1/4 wave height off the ground based on structural constraints.

    There is an insulator under the positive leg mount (top vertical mount - just can't see it in the pic).

    Thanks for the formula! - I was playing with that a bit.
    Good stuff here - thanks guys!

    So - Balun/choke....?

    I've recently read, from a few sources, that needing a BALUN/Choke on an 11m low power rig isn't necessary at all and I can direct feed with my coax. So, this is apparently a 'balanced' antenna which will be fed by an unbalanced line. I had built an air choke from 18' of coax wrapped around a short length of 4" pvc. After reading more it seems, if needed at all, a 4" diameter loop with 4-5 wraps would be fine (which is what I have now) within a few inches from the feedpoint. Also, if the 45deg angled ground leg is used, that should bring the resistance of the antenna a bit closer to the 50ohm for a closer match. (per the link in the original post)
    All a mystery at the moment....but interesting none-the-less. - curious to your thoughts.
    :)
    Crazy science stuff!

    Fun fact - Currently, I have the CB hooked to a mag mount on a piece of tin outside my window. SWRs @ 1.5 on both ends of the band. Heard skip rolling thru yesterday. A guy in Kentucky was coming in clean on 28 so I gave him a shout. He heard me from my little junk rig up here in New England! I'm sure he had great ears but still surprised he could hear me.
    pretty amazing!

    Sound like my mount is valid. I plan to finish that up today with some more drilling/bolting.

    Thanks again guys! I feel like i'm geeking out - cuz I am - hahaha.
    Please share whatever thoughts you have - learning a lot here.
    -appreciated
     
    Last edited: Dec 13, 2018
  5. daveyburt

    daveyburt NES Member

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    Yup - want me to grab that for you?
    :)
     
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  6. AHM

    AHM NES Member

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    Here - catch!
     
  7. daveyburt

    daveyburt NES Member

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    :)
    Well, it's up. I went straight vertical for now.

    I had a buddy stop by with his multiband with a frequency counter and it looks like I'm SWR 1.5 or better across 1.1Mhz. It bottoms ~1.4.
    I guess it works ok. Haven't had too much time to play and haven't heard many ppl out there so, we'll see.

    I did end up cutting the whips a bit too short so, I coupled in 2" of the threaded rod to come back to where I needed to be. All in all, the 108" whips are about 4" shorter. I'd assume having those stumps of rod under there has some effect on resonance?...as opposed to the thin wire whip for the full height?

    Thanks for confirming I was on the right track. Curious to see what raising a leg will do but, I think that's for spring.

    What do I say - 73s?
    "Good Buddy" has a different connotation now-a-day's I guess.
     
  8. drgrant

    drgrant Moderator NES Member

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    So how does it work on the air? Nice homebrew mount!

    -Mike
     
  9. daveyburt

    daveyburt NES Member

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    interesting you chimed in just a bit ago...was coming out for a follow-up observation.

    It seems to work nice. My cheapo Diamond SX200 SWR meter is telling me under 1.5:1 over 1Mhz span.
    Local on-air reports seem decent. I'm a geek with a topo map app, and I've gotten repeatable hits within a ~5 mile range over the rolling Worcester hills. Having it set-up full vertical, I'm surprised. I'm in a hole (generally and acutely), and that configuration should send a low wave. I guess it's got enough resonance to push thru, and/or I'm just lucky?

    Distance comms - of course - varies but I've gotten hits down to GA and over to Illinois.

    I'm calling it success I guess. It's tough to tell as you never know what kinda rig you're talking to (to gauge receive performance). But it seems to get out ok.

    So - onto my observation.
    :)

    In an attempt to reconfigure a coax patch cord - swapping a 9' patch and a 6' patch on the back side of the SWR meter, I had a decent little bump in SWR. I swapped back and forth, ensuring good connection, and that result was repeatable. Some argue that (reasonable) COAX length should have no measurable effect but, I wasn't changing length, just the order in which they appear.
    -thought that was odd. -don't know if there's a reason. But, it's not bothering me either, besides in principal.
    Slightly different resistance between the two cables?

    It's held up thru the wind so that's a plus.
    I filled a length of 3/4" PVC with fiberglass resin as a small (12ish") mast to hold what you see pictured, and Ubolted that to a board screwed to the house.
    -cuz I like screwing things to the house!
    :)
     
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  10. drgrant

    drgrant Moderator NES Member

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    Sometimes adding length to coax can come into play if your grounding etc sucks.... That's pretty short. too, for a typical base install.

    -Mike
     
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  11. daveyburt

    daveyburt NES Member

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    Nothing's grounded except thru the AC circuit right now.
    I know - bad/bad!

    I've got a ground stud on the antenna mount to accept a solid copper run (need to hammer a rod in) to be added in the spring.
    Otherwise, for interior stuff, I'd have to run a wire down to some plumbing - another project for the list. - OR can I somehow add chassis grounds to the house electrical?

    Anything else I can do to solidify my hook-up?

    The SWR meter is on the third length of coax run. An 18 footer from the Ant, to a 12 footer down inside the wall, to the 6 footer into the SWR meter, the 9 footer to the radio (or vice-versey). <-just to supply the total length/patch count.

    Thx!
     
    Last edited: Jan 9, 2019
  12. drgrant

    drgrant Moderator NES Member

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    I like a lot of stuff posted, frankly...
     
  13. AHM

    AHM NES Member

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    If you just assume the other station is running 100W on HF,
    you'll seldom be wrong. There are 200W and 400W rigs (and 5W, too),
    and you can turn down the power, and there are amps,
    but that seemed more the exception than the rule for rag-chewing.

    OTOH, for rag-chewing or just making casual contacts,
    you're totally missing out on how to pad your QSO
    to simulate an actual human conversation by describing your rig,
    and asking the other guy about his. As someone once lampooned, in part:

    So. Fine copy. What's your receiver? The weather is nice here. Antenna DA100E.
    Receiver here is Drake R8B. How copy?​

    It's de rigueur; the radio equivalent of a post card with a handwritten note:

    Weather is here.
    Wish you were fine.​

    Even (non-contest) CW contacts that are painful for at least one operator to pound out the basics
    (because they're learning, or because conditions suck) tend to include the rig/antenna stuff; even if they can barely spell out their name and the weather.

    Besides, if the other guy realizes he's helping you evaluate a homebrew antenna design,
    he'll even be willing to offer an opinion about whether your azimuth is in a lobe vs a gap in his antenna pattern. ("I get out to New England OK" or "wow, I haven't worked your state in months on this band").

    No (and I had to look this up because I just never commit the coax vs. twinlead
    differences to memory), coax length (except for ohmic losses) only doesn't matter
    when its impedance matches both the antenna at one end and the black box
    at the other end. Your actual antenna isn't perfectly resonant everywhere
    (even if it's resonant somewhere in any ham band - didn't look to see).

    Also, it probably doesn't match the coax (what does an antenna analyzer
    plugged directly in to the antenna say?).

    So changing the lead-in length changes the losses (at every frequency).

    Again, I know plenty of guys who can rattle this off in their sleep,
    and I dishonor them by not having memorized their club talks.

    Which (for me) highlights that if the antenna itself isn't balanced,
    there will be current on the outside of the braid (and probably RF in the shack).

    I can't even deliver the real party line on that.
    Oh wait, I can link to something that sounds good:

    Radioworks.Com: Ground Problems

    Note that:
    1. I can't personally testify to the effectiveness (or cost effectiveness) of the MFJ-931 Artificial Ground. Actually, I've not ever had anyone else discuss that black box within earshot. And I've never seen anyone sell a competing product - not even in kit form. So I'm not looking to scare you into pissing away $110 on one, sight unseen. But if you're getting RF burns from metal objects in the shack, or your PC crashes every time you transmit, you probably need something. But see below.
    2. The "use several parallel ground wires, at least one of which is not an odd quarter wavelength for each band" method seems cheap and fast. And I frankly don't understand why the article says they should all go to separate ground rods.
    On a related note, here's some old discussions about lightning
    (speling erors not mine):


    At the very least, be sure you disconnect the lead-in(s) from gear whenever you're not using the shack (ideally, ground them). Don't leave them connected except when you happen to notice a thunderstorm forecast.

    Connecting the coax only when in use
    may not keep your antenna from burning your house down,
    but it will at least keep more lightweight static build-up from roaching your rig,
    even if it didn't have enough energy to start a fire.

    (And of course remember to re-connect it before you transmit).

    The half-assitude of this technique is discussed in the above web page -
    look for "mayonaise jar" (sic). Not "olive", not "pickle", not "caper" -
    only a mayonnaise jar provides the proper insulation for small storms.
    (No jar protects against Thundersnow).
     
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  14. Uzi2

    Uzi2 NES Member

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    Good setup, how are you mounting it and what are you mounting it to?

    If they are full length 102 inch whips, you shouldn't have to tune anything for full coverage of the CB band.
     
  15. daveyburt

    daveyburt NES Member

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    Thanks AHM! A lot to decipher there for me but, good info and links. <-will review thoroughly
    As far as my coax observation. I didn't change the overall length - just swapped the 6 and 9 footers amongst themselves.

    Uzi - I used 108" ss whips. Without cutting they were very long for 11m. The best SWR reading was WAY into the 12m band. I trimmed them down to a little over 102, and was then too short. GRRRR. There was a formula I found for figuring out how much to chop, which didn't work out as easily as is seemed. I prolly screwed up in the math though...
    Building and Tuning A Dipole The Easier Way - A Faster Way To Tune A Dipole Antenna Project

    But, alas, I lengthened the radiators by patching in a couple inches of 3/8 fine thread SS rod, with additional couplers, which got me to where I needed to be. ~104 is where I ended up.
    -Not sure if the girth of those rod patches affects resonance but, I believe it would.

    Anywho - I'm under 1.5:1 over a full Mhz of bandwidth so, I've got 11m covered for sure. 1.3:1 is my lowest reading.
    Designs for this type of vertical seems to indicate a 1.4:1 is about what to expect so, a little reading, lots of luck, and input from others did me well, I think.

    The mount seen above was through bolted to a 3/4", epoxy filled, length of PVC (about 12"), and that was ubolted to a board which is screwed to the house.
    The solid copper ground will be the first thing that happens once the soil thaws. - need to hammer in a rod.

    I'm getting a kick out of the Big Talking Rag Chewing skip shooters. It's a new dialect that's fun to figure out.
    :)
     
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  16. AHM

    AHM NES Member

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    De nada. Feel empowered to Google any ideas that you are considering implementing.
    (Well, at least anything that takes a lot of your money or time).
    You owe yourself a sanity check on anything that's single-sourced.

    It still means that meter's measuring the SWR at the shack end of a different length of coax
    (that's still plugged into a mismatch at the far end).

    So the number you get out of the inline SWR meter would change...

    BTW, I'm not trying to claim that 1.5:1 is a pant-<bleeping> horror situation.

    But you might not have observed that SWR measurement shift while swapping coax segments
    if you played the same game with, say, a monoband antenna that's close to perfect.

    If it's like the rod from Lowe's that I had our well pump dudes drive in,
    it's copper-plated steel.

    eHam: When do I need a Balun for a Dipole?

    The caveats about sanity-checking apply even more,
    since it's a debate on a discussion forum rather than
    a monograph by a single alleged expert.
     
  17. daveyburt

    daveyburt NES Member

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    now i get it. the length to the radio was the same but not the SWR meter. -duh
    thx!

    Yes - from what I've read, the straight vertical dipole is closer to 70ohm than the 50 i'm looking for. It was also mentioned that impedance will begin to drop as I start to angle the counterpoise leg to - 30, 45, 60 etc. ...Seeing the closest match between 45 and 60deg.
    Haven't messed with that yet.

    -Just somewhat thrilled that the thing works decently for now (sans being not earth grounded).

    ...and thanks for more good info!
     
  18. AHM

    AHM NES Member

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    Glad the explanation's plausible.

    No sweat. Note that it's not that I have answers -
    it's just that your situation reminds me of stories where there are issues.
     
  19. daveyburt

    daveyburt NES Member

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    as always, I appreciate the thought provoking input.

    Here's one for you.
    I seem to get strange harmonics, for a limited time, certain times of the day. It almost seems like someone is broadcasting a tone but, it happens on every 4th channel across the 11m band.
    Many times a day channels 1, 5, 9, 13, 17, 21, etc - Most prominent on CH13 - give off a tone which increase/decrease in audible frequency (changes in pitch) as you move away from CH13 - higher pitched if you go to a higher channel, lower pitched if you go to a lower channel than 13. Always on those particular channels. Then they go nice and quiet for a while but, it re-occurs with regularity.

    strange....

    ....and I don't doubt there are issues - thanks for helping me find them!
    :)
     
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  20. AHM

    AHM NES Member

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    One of these days you'll be waiting at a stoplight near your house and realize it's the stoplight.
     
  21. daveyburt

    daveyburt NES Member

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    :)
    ...or the transformer on the street at about the same height as my top whip?
    -need to get some chainsaw fuel.

    Another HAM mentioned there's some sort of magnetic resonance cycle that moved through the bands? - comes and goes.
    I was chatting with him (he's a few miles away) and he hears it as well on those same channels.
    It gradually rises in intensity, holds for a bit, then fades more quickly.

    >off topic
    I hear that filling a hole with water and 'butter churning' the ground rod in is the best/easiest way?
     
  22. AHM

    AHM NES Member

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    Do a Google search to try and infer best practices.
    I've no experience because I jumped on the opportunities to get the well guys to do it.

    Turns out it's so close to the foundation that it may have gone in easily with the electric
    impact tool because the actual dirt may be clean post-foundation backfill instead of
    gen-u-wine New England undifferentiated glacial till, full of cobblestones and crap.
     
  23. drgrant

    drgrant Moderator NES Member

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    Best thing is to have a machinist make you a ground rod pounder thingy. Basically its n iron bar with a pipe mounted on the end just big enough to fit over the
    bar and slide up and down... it works like a a slide hammer. You might have to get on a ladder to use it. Unless you hit a giant boulder, this will drive it through pretty much anything. Then when it gets close to the ground you can just revert to a sledgehammer, lmao... other hams or tech-oriented CB guys may have these laying around.

    If you give me some time (a couple weeks) I might still have mine. I have to go to my parents house and look for it though. Mine was ghetto compared to one of the much better ones that existed but it worked.

    Another trick is multiple rods. You can get multiple 4 ft rods and wire them together if you space them apart, etc. drive 2 or 3 of those pups in the ground and it
    will work. They are skinnier and 4 feet is a lot simpler than 8 feet. I don't know if anyone still sells these anymore, radio shack used to for short money.

    -Mike
     

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