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Wa2nan - True-talk 102' G5rv Antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N7SGM, Jul 7, 2008.

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  1. N7SGM

    N7SGM Ham Member

    I have a few questions about the WA2NAN True-Talk 102' G5RV antenna. I have a Kenwood TS-450SAT and am wondering if the radio's built-in antenna tuner will work for this antenna? I would mount it about 40' high as an inverted "V" in a North/South manner. Also, would the steel mast have a bad effect on the antenna? I would like to operate on 80, 40, and 20 meters. Thanks very much!!

    Best 73's
    Bob
     
  2. AG3Y

    AG3Y Ham Member

    I can't answer your question about the auto-tuner, as I have no experience with it, but as for the steel mast; no, there should be no adverse effect! Hams and commercial SWBC sites have been using steel masts and towers for antenna supports for years!

    In fact, half slopers use the mast as part of the radiating system, and of course, there are always verticals which used the tower AS the radiator !

    String it up and enjoy! If your auto-tuner will not match all the frequencies, get an external tuner with additional matching range. You might want to consider getting a balanced tuner and feeding the antenna as a convention balance-fed doublet rather than a "G5RV" design. You will probably find that it works much better that way !

    73, Jim
     
  3. KR2D

    KR2D Ham Member

    The ladder line needs to be kept a few inches away from the steel mast.

    You internal tuner might be able to match the G5RV, and it might not. No way to tell until you try it. The internal tuner on my IC-746Pro matched my G5RV on all bands from 160m to 6m.
     
  4. G0GQK

    G0GQK Ham Member

    To answer your question, No. The tuners in tranceivers are to be regarded as trimmers, if an antenna is almost resonant at the frequency you wish to use then the in- built tuner will do it. A G5RV requires an external ATU and very often these will not allow the use of 15 metres and sometimes 10 metres.

    G0GQK
     
  5. K1FBI

    K1FBI Ham Member

    Then Again

    My WA2NAN 102 ft G5RV tunes perfect on 15 meters as a flat-top. 40 meters is 2:1 without a tuner and 20 Meters is 3:1 without a tuner and the same for 80 Meters. Don't even think about 10 Meters it's at least 5-6 S units down from my AR-10 Vert.
     
  6. K8JD

    K8JD Ham Member

    My USED TS440s Came with the built-in Tuner but it does not have much range but I never use my antennas out of the bands I designed them for anyway. Well....I used my 160 M dipole for 60 M a few timesw but it was only about 2.5:1 and the tuner did handle that mismatch ok.
     
  7. WA8RTI

    WA8RTI Ham Member

    I can't say for your Kenwood, but my ICOM 746 Pro tuner had no problem finding a match 80 to 10 meters with my homebrew 102' G5RV.
     
  8. W5DXP

    W5DXP Ham Member

    If you install an SWR meter between the tuner and the G5RV to measure the actual SWR on the coax, you might change your mind. EZNEC says the SWR is 30:1 resulting in 6.7 dB loss in 80 feet of RG-8x used on 15m. That's about 80% of your power wasted heating the coax on 15m. A G5RV is NOT a good 15m antenna. Probably the only reason your autotuner can match it is because the transmission line is acting as a dummy load.
     
  9. N8YX

    N8YX Ham Member

    Additionally:

    The G5RV was meant by design to be a 3/2w 20M antenna.

    Mine is a 102' version and is fed with 450-ohm "window line". It'll cover the lower end of 20M with a VSWR of less than 1.4:1.

    If your particular full-size G5RV will not resonate with a fairly "close" match on 20M, something's amiss with its feedline...and as 'DXP points out, the coax is likely being used as a dummy load.
     
  10. W7WAC

    W7WAC Ham Member

    Hello,
    I have the 204' version and with a Yaesu 920 driving and think it best to use a external tuner, but to be honest I have never tried it with just the radio tuner. Also I would strongly advise contacting Kerry, the builder of the True- Talk, he is very helpful and always willing to listen. Kerry
    E-mail Address(es):
    kerry@northnet.org

    I have my 204' up 55' on a tower and Kerry said to use at least 12 inches stand off for the ladder line.

    Great antenna by the way..

    Good Luck!
     
  11. K1FBI

    K1FBI Ham Member

    RE: "Dummy Load"

    10/12/2008, 4:58 UTC, 21.305 MHz, Contact with VP2E Anguilla...1700 miles! I really like my "dummy load"!:)
     
    Last edited: Oct 13, 2008
  12. K1FBI

    K1FBI Ham Member

    Oh Really

    I trimmed 16 inches off my G5RV after reading your post and SWR is now 1.5 to 1 on 20 meters without my tuner (Palstar AT2K). On 40 meters 1.7 and and 3.875 MHz I have 2.0 to 1 without the tuner. Glad I had today off! Thank you for that advice. As for you supporting the "dummy load" comment; Multiple contacts with 27 Countries and 9 Islands on this "dummy load"! I should do even better with the lower SWR.
     
  13. K1FBI

    K1FBI Ham Member

    15 Meter "Dummy Load" Update

    21.290 Mhz/13:02 UTC/contact with TM6VG(France)...not bad for 15 Meters on a "Dummy Load".
     
  14. W5DXP

    W5DXP Ham Member

    What is the SWR on 15m without the tuner?

    The "Dummy Load" remark was meant to imply a dummy load in parallel with the system load, not a dummy load used by itself. Resistors in antenna systems are generally not a good idea and the loss in the RG8x is mimicking a resistor.

    If you are running 100 watts on 15m, you may be radiating 20 watts on that G5RV. One can certainly talk all over the world with 20 watts on 15m but wouldn't you rather be radiating 80 watts instead of wasting 80 watts as heat in the RG8x coax?

    An internal autotuner is not likely to match an impedance on the 30:1 SWR circle. The coax loss seems to be lowering the 15m SWR at the tuner to a more manageable value. But if you are happy with 20% efficiency, I guess that's all that matters. Just remember you could be radiating 6 dB more power on 15m thus increasing your signal reports by at least an S-unit.

    Incidentally, here is a graph of the optimum lengths of twinlead matching sections for a G5RV for all the HF bands. [​IMG]

    You can see the mismatch problem is not as bad on 15m as it is on 30m, 17m, and 10m.
     
    Last edited: Nov 15, 2008
  15. K1FBI

    K1FBI Ham Member

    Not So

    Look at your own chart for 12,15 and 75 Meters..if what you propose is at all true then the antenna design should also be down about 80% of power on 12 and 75 meters. With 4 feet or less wire compared to 20 Meters using your chart, it is highly doubtful. If you want to see someone who actually tested things, look at this link which lines up with my actual results. http://www.w8ji.com/g5rv_facts.htm

    73
     
    Last edited: Nov 17, 2008
  16. W5DXP

    W5DXP Ham Member

    On 75m, being off by two feet is equal to less than 1% of a wavelength, i.e. mostly negligible. On 15m, being off by four feet is equal to 9% of a wavelength, i.e. not negligible.

    It is entirely possible that the dimensions of your "G5RV" differ from the G5RV design specifications in which case, it may not have 80% loss on 15m. If you will tell me what is your SWR on 15m and what kind of coax you are using, I can be more accurate about your coax losses.
     
  17. K1FBI

    K1FBI Ham Member

    Here you go

    Without the tuner my SWR is 3.2:1 and I can tune 1:1
    The coax is 31 FT of HD 300 Ohm window line into 70 FT of RG8X.
    Don't forget I trimmed 16" off the total original overall length of the 102 FT antenna section.

    Should be interesting. Thanks and 73 K1FBI John.
     
  18. W5DXP

    W5DXP Ham Member

    Well, everything is clear now. Your antenna doesn't meet the G5RV specifications as it is now resonant on approximately 14.5 MHz. Your dipole is shorter than 1.5WL on 20m and your parallel matching section is shorter than 1/2WL on 20m. EZNEC says the SWR at the coax/twinlead junction on 15m is now 6:1 instead of the 30:1 reported for the standard G5RV. I also checked 80m, 40m, 20m, and 12m. The changes don't seem to have bothered the performance much on those other bands. Looks like an excellent modification. Congratulations.
     
  19. K1FBI

    K1FBI Ham Member

    Thanks for running those calculations for me Cecil. That is good news.
    73, John
     
  20. W3JN

    W3JN Ham Member

    Outstanding advice. Why the so called "G5RV" antennas are so popular is beyond me.

    A fan dipole fed with W7FG ladderline and a homebrew balanced tuner was the best investment I ever made to my station.
     
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