Balun or Antenna Tuner?

Discussion in 'General Technical Questions and Answers' started by K1HON, Nov 3, 2009.

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  1. K1HON

    K1HON Ham Member QRZ Page

    Just got my first HF rig, a used Yaesu FT-450AT. I hooked it up tonight to a G5RV jr (From, 25 feet of RG8U sits between the radio and the ladder line connector.

    From reading around I was pretty sure I wasn't going to be able to get a tune on every band with the built in tuner, but I was at least hoping to be able to get a tune on some bands. It won't tune on any of them. (well, it does tune on 6m AM, but that's not too helpful as I think most 6m stuff is FM)

    I guess i'd like to avoid tossing another $200 at an external tuner right now, can I just add a 4:1 balun to get a better match that the internal tuner will be able to deal with? What kind of balun and I looking for? I'm real close to HRO's store and can run by there in the morning. I am very new to this HF stuff...

    Thanks for any advice...
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Describe how you have it installed.

    Include how long the end support ropes are, what the end supports are, and how the ladder line is falling from the antenna to your coax splice point.

    If all is installed properly, probably the only thing you need to do is use more coax instead of 25 feet, to make the internal tuner work for you.

    But the end supports and the routing of the ladder line are important. Preferably, the ladder line should fall straight down vertically from the G5RV feedpoint towards the ground. The coax should fall from the splice point, more down towards the ground, until it hits the ground and then runs towards the rig from that point.
  3. K1HON

    K1HON Ham Member QRZ Page

    Ok, lets see if I can paint a complicated picture here...

    Antenna is installed in the attic. The attic is 29 feet by 15 feet. its a typical attic with a peak height in the center of 7 feet. The peak ridge runs across the 15 foot span.

    The antenna center section (the PCV Tee) is installed at the peak and the side legs run down the ceiling towards the floor and then the rest of the line runs along the floor back towards the center. basically forming almost a triangle, the end points don't meet in the center but are about 6 feet apart. everything is suspended about 6 inches away from the ceiling and floor so nothing is touching anything. the ladder line runs away from the center tee along the roof peak at a 90 degree angle from the triangle for about 8 feet and then back towards a wall at about 35 degrees, the coax connector is about 4 feet off the ground..

  4. KE5KTU

    KE5KTU Ham Member QRZ Page

    Just a helpful hint. A G5RV should have a SWR of 2.1 on 20 meters. If it does not, then you may want to look at the way it is installed. Your internal tuner should be tunning it. The G5RV is a compromise antenna, and the compromise is that it is relatively easy to tune. I would move the legs around in the attic and try to get the swr on 20 meters close to 2.1.
    Hope you have good luck !
  5. AG3Y

    AG3Y Guest

    Well, shoot, you sure don't have a "G5RV Jr." there! No wonder it isn't working as you would expect it to! I am referring to how you are trying to use the antenna, of course.

    I doubt seriously that adding a 4:1 balun is going to improve the situation, either. In fact, it will probably make it worse !

    What you are experiencing is the negative consequences of folding the antenna back on itself. You also have the antenna inside a structure, and you have not told us whether the structure has a conducting roof ( copper, galvanized sheets, or whatever ) and what material the walls are made of. Anything remotely like this is bound to affect the resonant frequency of the installation, which is really designed to be used as a flat top or at the least as an inverted VEE. Anything else is going to severely compromise the performance and where you will see the best performance, if even close to an actual ham band !

    Is there ANY way you can get that antenna out of those cramped quarters? Even if you do buy an external antenna tuner ( and no, you don't have to put out $200 for one ) you are NOT going to get the performance out of that antenna that you could if it were mounted outside the house. And be aware that a G5RV is going to be a compromise on any band but 20, in any regard!

    Sorry, that's just the way it is right now. 73, Jim
  6. K1HON

    K1HON Ham Member QRZ Page

    Would the same be true on a G5RV JR? Would 20 meters be the easiest band to tune and test with while moving the legs around?

  7. K1HON

    K1HON Ham Member QRZ Page

    Its is the G5RV JR. 54 feet long with 18 feet of ladder line.

    I am in a condo and outside antennas are a no-no. I can try rerouting the legs so they don't fold back on themselves as much, but there is only so much room up in the attic. the attic construction is wood with standard shingles, no metal on the roof except for nails...

  8. K8JD

    K8JD Ham Member QRZ Page

    tRYING TO FIT A HF antenna into a small attic is a big challange ! You may be able to straighten out the legs a bit but you will probably need an external tuner and still not get much signal out. I would try a 20M halfwave dipole (33 ft total length) , fed with coax cable. It's hard to run ladderline in that kind of space without getting close to metal heating pipes or electrical wiring and mess it up. If that works ok you could add wires to the dipole for 17 and 15 meters. Forget 40, 80, 60 or 160 M until you move to a house with a big yard.
    Last edited: Nov 3, 2009
  9. KE5KTU

    KE5KTU Ham Member QRZ Page

    Yes, the same would be true for a G5RV JR. To be honest, you may want to look at making a 20 meter dipole (end to end it should be around 32 feet long). You can try to tune it up on 40 meters and you may be able to, or may not, but at least you would have a lot less antenna to try to squeeze in there. Another thing to think about is if you have a balcony there are several vertical antennas you can try like a screwdriver or something with a coil. If you are creative you can usually hide them.
  10. W9GB

    W9GB Ham Member QRZ Page

    I had that exact setup in graduate school but with a half-wave dipole.
    I lived on third floor of building and had access door to attic space.

    I was never satisfied with the setup (I used a 40 meter dipole with legs zig zagged to fit space) -- it was like adding a 10 dB attenuator to the transceiver! My home 80-40-15 meter Novice antenna performed far better, and it was only 3 inches above the shingles (well hidden).

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