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Dipoles and the rig's RF ground...

Discussion in 'Electronic Basics' started by billcalley, Jan 1, 2006.

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  1. Reg Edwards

    Reg Edwards Guest

    Single wire feed. I was a student (living off of my wife) and used
    what I
    =======================================

    A true radio amateur!

    Just get a random, bent wire into the air. A single-wire feed helps a
    lot. With a modest ground and a simple tuner you have an efficient,
    multi-band, go-anywhere antenna system you can be proud of.

    Anybody who boasts about his G5RV has never tried anything else.
     
  2. Right.....you should hear the bands open up when you launch a kite
    antenna. There's nothing like a few hundred feet of random long wire up
    in the air. ;-)
    WARNING: No one should ever do such a thing for what should be very
    obvious safety reasons.

    I'm a big fan of cubical quads, but you need allot of room for them.
    I'd take one over a yagi any day. I built a two element quad for 10
    meters using bamboo fishing poles for the spreaders. The boom was made
    from cedar. It lasted about three years before a flying tree limb took
    it out. I also made an 8 element quad for 2 meters using 1/2" poplar
    dowel rod spreaders and a wooden boom as well. Man was that thing hard
    to tune. Weird things happen after the fifth element is added for some
    reason. Might explain why most have only 4 elements. ;-) Seriously,
    it really kicked ass but the tornadic storm took it out too. I'll not
    be making another with that many elements, too fussy but extremely
    narrow beam w/incredible back side rejection.
     
  3. Cecil Moore

    Cecil Moore Guest

    Reg, I replaced my 130 ft. dipole with a G5RV so I could
    experiment with it. Given my modifications, Nobody can tell
    it from the 130 ft. dipole so there's no reason to return
    to the 130 ft. dipole. My G5RV has an SWR of less than 2:1
    on all eight HF bands.
     
  4. Reg Edwards

    Reg Edwards Guest

    "Cecil Moore" wrote
    My G5RV has an SWR of less than 2:1
    =========================================

    The CIA W.M.D. department must have told you that naughty fib.

    The SWR on your 380-ohm transmission line to the antenna is umpteen
    times greater than that!

    Isn't it time you changed the name of your SWR meter?
     
  5. Cecil Moore

    Cecil Moore Guest

    I'm not talking about SWR on the series section transformer,
    Reg, I'm talking about on the 50 feet of RG-213. And it's
    not "umpteen times", rather limited to about ten times.
    Nope, for a G5RV with the nominal 70 feet of 50 ohm coax,
    the SWR meter is indeed reading the SWR on the coax.
    Remember, I'm not using a tuner. The coax from the G5RV
    goes directly to the transceiver through the SWR meter.
    I actually use my SWR meter to display the SWR.
     
  6. Fred W4JLE

    Fred W4JLE Guest

    I have both a 130 foot dipole and a G5RV, I can switch between the two and
    the reports are exactly the same on 75. With 100 watts on the G5RV I have
    worked well over 100 countries on SSB 75 meters. The day I received the
    Olivia for my mix w, worked Russia on it with 5 watts on 20 meters.

    I use it nightly on my Navy Mars nets in the 3 Mhz area.

    Like the 130 foot dipole I vary the feed line length to tune.

    Both feedlines are fed from the rig to the ladderline with coax covered with
    ferrite beads at the junction end.
     
  7. Reg Edwards

    Reg Edwards Guest

    =======================================

    I see you are happy to change names when in a tight corner.

    The name "Transmission line" has been conveniently changed to "Series
    Section Transformer".

    But it still has standing waves on it far higher than what you claim
    for all bands. And don't standing waves increase loss on SST's just as
    much as they do on transmission lines?

    Louis is turning over in his grave - yet again.

    But what the heck? A G5RV will work even if you havn't got one.

    I once set up an 80 feet dipole without a series section transformer.
    Unsurprisingly - it worked. ;o)
     
  8. Cecil Moore

    Cecil Moore Guest

    As you know, standing waves increase loss on SST's just as much
    as they do on transmission lines *OF THE SAME LENGTH*. For instance,
    on 3.8 MHz, that 300 ohm series section transformer on a G5RV has
    an SWR of about 20:1 and a line loss of about 0.7 dB, about 12% of
    one S-unit. That's a small price to pay for multi-band operation.
    And using Wireman #554 (like I do) instead of 300 ohm twinlead will
    cut those SST losses down to 0.37 dB, about 6% of an S-unit.
    If you fed it with ladder-line, you fed it with a long series
    section transformer. :)
     
  9. Reg Edwards

    Reg Edwards Guest

    "Cecil Moore" wrote
    =========================================

    .. . . . and your SWR meter is not an SWR meter - it is a transmitter
    loading indicator. ;o)

    Go on then - call me a copy cat!
     
  10. Guest

    I have both a 130 foot dipole and a G5RV, I can switch between the two and
    the reports are exactly the same on 75. With 100 watts on the G5RV I
    have
    worked well over 100 countries on SSB 75 meters. The day I received the
    Hummmmm.......... :/

    Both feedlines are fed from the rig to the ladderline with coax covered
    with
    ferrite beads at the junction end.

    Try the 130 ft dipole fed with straight coax and see if you don't
    see a difference then. Sure, it won't be huge, but it should be
    there, and be quite noticable too on a receiver. I think this why you
    are seeing no difference. .
    You are "clutter" feeding both antennas. :/ Seriously.
    Coax to ladderline...yuk...:/
    But saying that, it's obvious it works well nuff I suppose..
    I just like to stir it. It's been too slow around here lately.
    But...I am serious about what I say.. If you want the vurry
    best 80m dipole, feed it with nuttin but coax.
    MK
     
  11. Pig Bladder

    Pig Bladder Guest

    [snip]

    Broken shift key, huh?
     
  12. Well, I'll put the system I started to design last night up against most
    other 80m antennas. But it won't be cheap to build. Needs 8 165-foot
    towers, and a bunch of phase delay networks and some power dividers. :p

    But the gain over ordinary ground works to between 9.5 and 10.5 dbi
    depending on the direction favoured by the phasing networks.
     
  13. I swear OH8OS used to MAKE his own band openings or 15 back in 65 when I
    used to work him from VE8ML. He had a huge quad, 15 elements, I think,
    pointed right in my direction.
     
  14. There's nothing wrong with a G5RV if you couple power to its radiating
    element efficiently. I usually just don't bother with the coax part of
    the feed system and prefer to just run 300 ohm (or better yet 450 ohm)
    line right to the shack and feed it through a tuner.
     
  15. Cecil Moore

    Cecil Moore Guest

    Well, as a data point, Owen's transmission line loss
    calculator says there's 0.362 dB loss in 100 ft. of
    RG-213 feeding a 50 ohm antenna on 75m. The loss using
    100 ft. of open-wire feedline feeding a 50 ohm antenna
    on 75m is 0.169 dB, less than half the loss in the coax.
    Even the Wireman #554 "450" ohm line is better than
    the coax at 0.269 dB. Where are the losses in a Ladder-
    Line fed system?
     
  16. You just about can. Even with just two elements on 10, I worked several
    contacts from Houston that couldn't hear anyone else in the US. I
    really loved that antenna.
     
  17. Fred W4JLE

    Fred W4JLE Guest

    Tell me how to coax feed a dipole that works from 3.3 to 4.1 MHz and you
    have my attention.

    ..
     
  18. Guest

    Where are the losses in a Ladder-
    The tuner that is usually used offsets the advantage
    of the line itself. Sure, on paper you shouldn't really
    be able to notice it. But I do when I test it. It's actually
    measureable on an S meter when doing A/B comparisons.
    Or at least it was for me when using a 989c tuner
    and minimum inductance vs coax fed.
    That tells me the tuner loss can often be a bit more
    than it's cracked up to be. But I also found if you don't
    use the minimum inductance when tuning the tuner,
    you can lose quite a bit. I saw easy 20 % losses when
    testing that one time. If I used the very least inductance,
    I could get it down to an almost unmeasureable level.
    If I get on 80m and want the very best efficiency I can get
    feeding a dipole, I use coax.
    Of course, the line is never more than 100 ft.
    Usually more like 50 ft. I have a 50 ohm radio feeding a
    low loss 50 ohm line, to a 50 ohm antenna feedpoint. You
    have uncluttered perfection. :) And in the real world
    the most efficient that I've seen so far. If there was better,
    I'd be using it. I could see using the ladder line on real
    long distances. On the higher bands, it could be noticable.
    But like I say, my run is about 50 ft. Considering efficiency
    vs ease of use, wx resistance, ease of lightning protection,
    coax is a no brainer for me. Of course, I ain't everyone.. :/
    MK
     
  19. Guest

    Tell me how to coax feed a dipole that works from 3.3 to 4.1 MHz and you
    Probably wouldn't be practical for you.. Just offhand, I can think
    of a way, but you'd have to run at least two set of dipoles, and
    maybe even three, tied together in parallel. You would stagger
    tune them one low, one middle, one high, and the SWR
    plot should look about like a \/\/\/ . I've never tried using
    three dipoles, but I've done it with two and having a W SWR
    plot. That is one way you could have that range and use
    coax feed. But like I say, probably would be a PIA with
    it needing at least one center support and six tie off
    points.
    MK
     
  20. Cecil Moore

    Cecil Moore Guest

    Fred and I don't use a tuner.
     
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