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Discussion in 'QRP Corner' started by AA4OO, Mar 25, 2016.

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  1. AA4OO

    AA4OO XML Subscriber QRZ Page

    Bacon Lettuce and Tomato... or is that Balanced Line Tuner?
    • Matches balanced loads without the use of lossy baluns.
    • Being a parallel resonant circuit, the Z-match can provide some band-pass filtering for your receiver and harmonic attenuation for your transmitter.
    • A well-designed Z-match tuner has a high Q and is more efficient (less lossy) than other types of tuners.
    • The fixed inductor simplifies construction (no taps or rollers needed).

    KC8VWM likes this.
  2. KB4MNG

    KB4MNG Ham Member QRZ Page

    Very interesting. Would this perform better than the kx3 on board tuner?
  3. AA4OO

    AA4OO XML Subscriber QRZ Page

    I prefix all this with the fact that I am still learning about this stuff and I'm conveying what I've learned from QRP hams I trust rather than "internet wisdom".

    The BLT+ tuner doesn't have the tuning range of the KX3. So don't expect it to tune an iron skillet like a KX3 will.

    The issue is the use of a balun with a Doublet as a multi-band antenna.

    When you use a balun with a Doublet antenna ahead of the tuner there can be a lot of loss due to the large impedances present. I don't know how much loss, but I've measured my own Elecraft balun heating up more than 10 deg F over ambient when used with a Doublet at QRP output levels.

    The BLT doesn't use a balun but rather a center tapped coil inductor. For reasons I don't understand (I'm still learning) that tapped coil inductor has far less loss than a balun but due to the center tap it expects a balanced input.

    So for use with a doublet the BLT is likely to be more efficient than the KX3's internal tuner used with a balun. I haven't A/B compared back to back RBN tests using the KX3 with the BLT and without. But QRPers have raved about the design and the efficiency of Z-match tuners for years so there may be something quantifiable to their claims.

    My primary planned use for the BLT will be with the 1Watter radio I just completed.

    Rich, AA4OO
  4. K8JD

    K8JD Ham Member QRZ Page

    Balanced Line Tuner
    When I decided to make a non resonant gain antenna (extended double Zepp) I got the big MFJ 974 balanced line tuner to use with 450 Ohm feedline.. I am glad I did now.
    It's a bit large to take camping but I have run QRP thru it and it performs very well even with a few watts.
    This tuner makes my 20M EDZ work on everything from 5 to 18 MHz !
    This one has ganged capacitors to form a double sided T network and has no need for a balun.
  5. AA4OO

    AA4OO XML Subscriber QRZ Page

    That looks like a very nice balanced line tuner but the SWR meter doesn't seem to offer much resolution under 5w. How do you use it to tune at 5w or less?

    I was using the BLT today out in a field with my 1 watter QRPp radio. The SWR bridge worked fine with the 900 milli-watt output from the radio and everything easily fit in my backpack with room to spare.
  6. K8JD

    K8JD Ham Member QRZ Page

    5 and 10W are nearly a third and half scale on the low watts range of the meter in the MFJ974. The Wattmeter spec is 30 and 300 W fullscale.
    Tuning up is easy, just adjust until the refl pwr meter is at ZERO.
  7. VK3YE

    VK3YE Ham Member QRZ Page

    I recently built VU2ESE's balanced tuner

    Only had room for 5 switches so omitted the 0.1uH and 6.4uH coils. Also left out the meter circuitry. But I did insert a switch that shorts out the balun for use with an unbalanced antenna. Worked first time. Recommended.

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