MFJ ANTENNA ANALYZER AND AMERITRON AL-811H AMP = TUNING ISSUES

Discussion in 'Ham Radio Discussions' started by K5FRH, Apr 9, 2019.

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  1. K5FRH

    K5FRH Ham Member QRZ Page

    Thanks to all who gave me excellent advice on constructing my horizontal loop antenna. I have been going thru everything and tweaking where necessary as I prepare to add my Ameritron 811H amplifer in line.

    Here is my question. I have tested the antenna by itself with a MFJ analyzer and gotten excellent readings of 2.5 or less and resistance of 50 or less on all bands. Adding in my Dentron Super Super Tuner I am able to flatten the SWR down to 1.25 with resistance 30-50 on all bands.

    However, when I add the amp inline WITHOUT powering it up, the MFJ tuner just reads maximum on SWR and Resistance. Is this normal or do I have a problem with the amp. I dont want to power up the amp till I understand why this is happening.

    (A brief overvew of the antenna: 14 gauge stranded insulated copper wire, 278 feet length, 25 feet elevation, eventually to be raised to 50. DX Engineering/Jerry Sevick 4:1 Current Balun fed by appx 30 feet of 300 ohm ladder line. Transmitter is fed by 15 foot length of RG213U. Everything Grounded with 6 Gauge solid copper wire going to an 8 foot ground rod appx 10 feet away out side of the shack)

    Thank You.
    Rod, K5FRH
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The amp when powered OFF or in STBY shouldn't change anything, as all it does is add another few inches of 50 Ohm transmission line inside the amplifier, in series with what you already have. Your coax "patch" cable from the rig to the amplifier is undoubtedly much longer than that.

    The analyzer should be installed where the "rig" would normally attach, of course -- and not directly to the antenna transmission line!

    If the analyzer is connected in place of the rig, so the setup is ANALYZER -> AMPLIFIER -> TUNER -> ANTENNA and you've already set the tuner for min SWR before you added the amplifier in line, absolutely nothing should change at all when you insert the amp in line. If it does, it sounds like you have a bad patch cable between the analyzer and the amplifier (or possibly between the amplifier and the tuner).
     
  3. AA5CT

    AA5CT Ham Member QRZ Page

    Sounds like the contacts on the receive side of the T/R relay are dirty (or a cable is bad?) .... no RF is getting through the amp ...
     
  4. K0MB

    K0MB Ham Member QRZ Page

    SWR
    of 1:2 should not produce 50 ohms on the analyzer.
     
  5. K5FRH

    K5FRH Ham Member QRZ Page

    I think I may have discovered the culprit. One jumper cable tested OK with the VOM, but was showing "open" with the MFJ. Wiggling the cable made the MFJ meters fluctuate wildly. Ran out of time to rebuild the errant cable, but will do so tomorrow.

    Thanks to all for help.
     
    KA9JLM likes this.

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