BLT+

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

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  1. AA4OO

    AA4OO Ham Member 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).
    http://www.hamradioqrp.com/2016/03/blt-balanced-line-tuner-at-excalibur.html

    [​IMG]
     
    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 Ham Member 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
    http://hamradioqrp.com
     
  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 Ham Member 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 http://hfsignals.blogspot.com.au/2015/06/a-balanced-tuner.html

    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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