making a g5rv mini

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD8DES, Jun 11, 2012.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: MessiPaoloni-1
ad: Left-2
ad: Subscribe
ad: L-MFJ
ad: K5AB-Elect-1
  1. KD8DES

    KD8DES Ham Member QRZ Page

    I have a tiny city lot ( less than 50' wide) and I want to make a miniG5RV type of dipole, for 10 to 20 meter bands.
    I have dipole legs of 12' 9'' of hard drawn copper #14, and am making 8' of ladder line. I am using insulated
    #14 stranded for ladderline, and am making spacers of acrylic. I am using about 9-10 spacers 9-11 inches apart.
    I am considering building a balun so I can feed coax from the shack out to the antenna.

    Any suggestions as to how I might make this better ?
     
  2. W5DXP

    W5DXP Ham Member QRZ Page

    EZNEC sez if you increase your 300 ohm matching section to 9 feet, you will get better results on 20m and 10m where it will perform reasonably well. Unfortunately, on all the bands in between, the SWR on the coax will be ~13:1 on 12m, ~22:1 on 15m, and ~19:1 on 17m so it will not perform nearly as well on those three bands.

    A G5RV type antenna has design frequency specifications: 1.5WL dipole fed with 1/2WL of parallel feedline. The G5RV type antenna will work well on the design frequency, f, and on 1/2(f), 1/4(f), and not many others. That's about all one can expect. For the G5RV type ham band antennas, the following bands perform reasonably well:

    dipole
    204': 160m, 80m, 40m, and the WARC bands (design frequency = 7.2 MHz)

    102': 80m, 40m, 20m, and 12m (design frequency = 14.2 MHz)

    51': 40m, 20m, and 10m (design frequency = 28.4 MHz)

    Your 25.5' G5RVmini: 20m and 10m (design frequancy = 56 MHz)

    What I have done to solve that same problem is put up a 33' 20m rotatable dipole fed with ~64' of 300 ohm line. It works well on 20m, 17m, 12m, and 10m with the internal autotuner on my IC-756PRO and with an external MFJ tuner on 15m.

    Here are the "magic" 300 ohm twinlead no-tuner lengths for a 1" diameter, 33' dipole at 40', according to EZNEC:

    20m = 62.4', 17m = 66.3', 15m = 54.2', 12m = 62.7', 10m = 54.1' or 69.7'

    Note that a 33' dipole with a 54.2' 300 ohm feedline works well with no tuner on 15m and 10m with gain over a 1/2WL dipole on those bands.
     
    Last edited: Jun 11, 2012
  3. KD8DES

    KD8DES Ham Member QRZ Page

    That's a LOT of ladderline to manufacture! Any suggestions as to the best distance between feedline spacers?
     
  4. W5DXP

    W5DXP Ham Member QRZ Page

    It is admirable to want to roll your own ladder-line but I have had excellent results with 300 ohm transmitting line, available from www.TheWireman.com #562 and is actually a few ohms less than Z0=300. Your #14 wires seem to be somewhat of an overkill. How much power are you going to run?
     
  5. KD8DES

    KD8DES Ham Member QRZ Page

    I am running 100 watts. I am using #14 only because I have tons of it, obtained cheap at an estate sale.
    At the prices advertised, it makes sense to buy the ladderline, even though I have always wanted to manufacture my own.
     
  6. N5MDT

    N5MDT Ham Member QRZ Page

    If you have tons of cheap wire and are willing to home brew ladder line, then consider a fan dipole instead. Probably wouldn't need ladder line or a balun. You can go coax all the way to the feed point.

    Probably wouldn't need a tuner either.
     
  7. W5DXP

    W5DXP Ham Member QRZ Page

    Cheap and tons are good. I once "manufactured" ~300 ohm line by using popsicle sticks as spacers using the width (not length) as the spacer for insulated wire. (We used to boil wooden spacers in wax.) Nowadays, I would use a piece of a plastic coat-hanger for a spacer. About 1/3" is about right for 300 ohm feedline.
     
  8. WA9SVD

    WA9SVD Ham Member QRZ Page

    Also check the "Yellow Pages" for a "Plastics" shop. If there's one local, they often have an "odds and ends" bin where you can get Lexan, Plexiglass, Delrin, and other remnants, many of which are weather-resistant.. The local shop here had 30" x 0.5" fiberglass rod remnants by the hundreds, and easily cut with a hacksaw.
     
  9. KD8DES

    KD8DES Ham Member QRZ Page

    I have never considered a fan dipole-- that may be the best way for me to have resonant antennae on eace band without needing a tuner.
    Any ideas on how much space I need to leave between elements?
    Will the close proximity of elements affect the lenght I need to cut for resonance on each band?
     
  10. N5MDT

    N5MDT Ham Member QRZ Page

    I would use a center insulator that could start the elements 6" apart. The elements do not need to remain parallel. They could be much farther apart at the end of the higher frequency element. Or you could keep them 6" apart all along the length of the high freq element.

    I guess the real answer is, as much as you can. The closer they are the more coupling you will have and the shorter the elements will have to be to be tuned.

    Put a 1:1 balun at the feed point or coil the coax into an air choke using the first 18 feet or so coiled around a 6"-8" form.

    An antenna analyzer is your friend.
     
Thread Status:
Not open for further replies.

Share This Page

ad: M2Ant-1