True Ladder Line 10-80 Antenna with Balun/tuner?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB1QYH, Dec 31, 2018.

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  1. WA7ARK

    WA7ARK Ham Member QRZ Page

    No, it is not the problem. I tried all turns ratios from 2:1 to 1:4 (impedance ratios from 50:12.5 Ohms to 50:800 Ohms) and 1:3 turns ratio (50 to 450 Ohms) is the best overall!

    Dave modeled a 1:2 turns ratio (50:200 Ohm) transformer. He used a Mininec crummy ground and I used a high accuracy average ground. He used some little wire segments as connection nodes, while I used virtual segments.

    Dave, your SWR plot agrees with mine within the modeling differences, but it it is R term that concerns me; not the SWR plot.
     
  2. KI4IO

    KI4IO Ham Member QRZ Page

    That June 2015 QST article ("Don't Blow Up Your Balun", by Dean Straw) also portrays an unbalanced tuner (a simple L-network) floating from ground, and using a simple choke on the transmitter side for use with open wire line. I built a simple L-network and along with a choke on the transmitter side (about dozen turns small diameter coax on FT240-43 core) and my 40 meter dipole, with 4" spacing OWL works fine on ALL bands (1:1 match). it will also load on 80 meters with the L-network "reversed" (I use a jumper plug to do this).

    This concept (unbalanced coupler floating from ground to a choke on the TX side) was also described by Zak Lau from the ARRL in some of their publications.

    The OWL is just slammed under the window.

    I have used a zillion different antenna couplers, including the Johnson Matchbox.

    A neat coupler for balanced lines is described by VU2ESE. You can see my version of this on my QRZ page.

    Good luck

    jerry
    KI4IO




     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I get your point and yes low real feed point impedances can create matching troubles, particularly when coupled with large capacitive reactance. But IME if you keep the SWR below about 20:1 a decent wide range T section tuner typically doesn't have trouble matching the load and if you keep the SWR below 10:1 it really isn't a problem even into low resistance loads. That's based on building an awful lot of open wire fed antennas over the years.

    About the only band that might present a matching challenge here is 40m where the feedpoint impedance is fairly low and capacitive but even this isn't a terribly hard matching challenge. A simple 440nH shunt inductor would create a very good 50 ohm match and a decent T section tuner would match it easily as well. The next most challenging band is 20m (starting at the 0.2 +j0.2 intersection) but the 7 +j7 ohms it shows at a 6.6:1 SWR isn't a difficult match for just about any external antenna tuner.

    Here's the Smith Chart view of the 125' Doublet described above with a 4:1 balun between the 20' coax feeder and the 100' of OWL. These aren't difficult matching challenges:
    upload_2018-12-31_15-34-8.png
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Bigger and higher.

    Oops. almost forgot the other "law:"

    Transmission lines that run vertically have no loss.:)
     
  5. AG5CK

    AG5CK Ham Member QRZ Page

  6. WB2JIX

    WB2JIX Ham Member QRZ Page

    Hi Jason, this is Brian from True Ladderline.
    What power level are you planning to run?
    You don't say if you currently own a tuner or not?
    I've played with many tuners for this antenna and currently, I am using the MFJ-993B, which will tune this antenna on 6-160M without a hiccup.
    Yes, performance on 160 will be poor however, it's just an example of how much I like that tuner. I've really recommended it to hundreds of customers that have ALL given me feedback on how well that model works.
    I feed it directly to the balanced terminals. It's been flawless.
    For best results with a balanced feed antenna, I do not recommend the LDG brand. I have talked to dozens and dozens of hams that just want to make them work, to no avail.Their full color, two page spread in QST works!
    I also use the MFJ-998 legal limit tuner with the Balun Designs, 4114T, which gives me all bands easily as well as the power handling capability for my KW amp.
    I also use the old Heath SA-2060, which is a great tuner.
    I have a few customers that had to get the balun away from their shack and run 50' of LMR400 from that to their tuner. Since they primarily use the lower bands, losses are quite limited.
    I'm sure the proverbial can of worms will open shortly, as it always does with open wire line. We have haters and lovers. If you want to discuss it with me, we'll speak directly.
    Happy New Year!
    Brian
     
  7. N4FFL

    N4FFL Ham Member QRZ Page

    Are you sure it is fed with 600 ohm ladderline? When I got the same doublet earlier this year it was 450 ohm. I’m wondering if that is the difference?
     
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    Back to the 125ft #16 wire 80ft agl fed with 100ft of 0.98vf 600Ohm OWL, with a 1:4 balun between 20ft of 0.87vf 50 Ohm coax.

    So here is a detailed tabulation of the SWR, R and jX at useful frequencies between 3.5 and 28.8 MHz:
    bal.png

    Taking 3.7MHz for an example, I feed that case to W9CF's T-network simulator (which uses realistic estimates of the Q of the capacitors and inductor in the T-network). It predicts that 31% of the applied power (1.6db) is lost inside the tuner.
    The 20ft of foam RG8 loses 22% (1db). Based on a conservative estimate, I believe the balun will lose another 10% (0.45db), so the total loss just getting to the ladder line is 3db, or half the power fed to the tuner...
     
  9. W9CYS

    W9CYS Ham Member QRZ Page

    Jay,


    I put up the same doublet at my QTH this summer as a bent Vee. Apex at 48’ with the N leg at 110 degrees and the S leg drooping at abt 30 degrees. (Tall tree in the wrong spot!)


    After several feedline cuts (and resolder) ended up with abt 93’ of feedline bent inside the yard. Terminated into a BD 4117 1:1 with about 15’ of 213 into the shack to a KAT500/KPA500. (Tried a Centaur 4:1 which the tuner AMP could not find a happy match < 3:1) on 40m.


    I read about a dozen articles on feedline length – there are sweet spots. Here are a few of my bookmarked pages.

    http://www.hamuniverse.com/feedlinelengths.html

    http://kv5r.com/ham-radio/ladder-line/ladder-line-page-3/

    http://webclass.org/k5ijb/antennas/All-Band-Doublet.htm


    I confess I cut and resoldered several times and tried several routes around the yard (no sharp angles < 90). It’s not perfect, but the amp doesn’t fault anymore and it works. I’ll play with it more when the weather warms up. I was first licensed in ’71 and I’ve tweaked this antenna a LOT. But it plays nice on all bands so I can be active on whatever band that has even a little activity. I’m glad I got it up and it’s held up fine in two ice storms. And it’s nice to reduce the airborne metal to just two antennas. It plays better than the OCF it replaced – and fits on the property better!


    Below are installed impendences before the tuner measured on a RE55:

    80m – 60

    75m – 45

    40m – 40

    20m – 45

    17m- 210

    15m- 70

    10m -15


    Doublet plays well on all bands except 17m – the KAT500 couldn’t make the amp happy. I have Mosley tribander for 20-15-10, so I haven’t run the doublet at power on 10m


    Recently picked up a real tuner – SA-2060A. Amp is now happy on17m and I can drive to power. In the spring, I’ll drop the balun and connect directly to the 2060A balanced connection.


    Do your research, take your measurements, assess QSO performance and be patient. You’ll be happy when you get it dialed in.


    73,

    Jim
     
  10. WB2JIX

    WB2JIX Ham Member QRZ Page

    Jim, it's so refreshing to see your post! FINALLY, someone that uses common sense and sticks with it, knowing that you'll appreciate the outcome.
    The Heath SA-2060 is one of my favorite tuners, among the dozen or so that I own and play with.


    Brian

    http://www.trueladderline.com
     

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