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Antenna Tuner

Discussion in 'Home Brew' started by datsun66, Dec 13, 2011.

  1. datsun66

    datsun66 Active Member

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    I built an antenna tuner on the the wiring of the ultimate transmatch and this thing runs weird.
    I hooked it up to a 857d and tested the tuner with the swr in the radio and an swr meter external to see how it would work. It tuned up the antenna fine but the weird thing is the radio would measure high swr and the swr meter would measure low. Yep I did check the cabling.


     

  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    What frequency and how much cable between the radio and the external meter and how much cable between the external meter and the tuner?
     
  3. datsun66

    datsun66 Active Member

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    20 meters, 80 meters 4 feet on each, 100watt.
     
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Well there goes my theory. :blink: Those lengths should not have much of an impedance transformation on 20m and pretty much nothing on 80m.
     
  5. W5LZ

    W5LZ Crotchety Old Bastard

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    Just for general principals, I think I'd take another look at how things are set up or built with the home-brew tuner. That sort of difference is kind'a much. A smaller difference in meter readings really don't mean much because or how those meters are calibrated. Larger differences usually mean something isn't exactly right somewhere. There are variables in how components are marked, the indicated values may not be exactly what you think they are, just 'close'. I know I've certainly run into that before.
    About all I could do would be to try to narrow things down to specific areas/circuits where things may not be exactly what's claimed. Then go from there. And when you think about it, that's all trouble-shooting is anyway... Oh well.
    - 'Doc
     
  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Check the cable between the radio and the SWR meter. It may be bad causing everything before it to see a high SWR while everything after it would see a good SWR as tuned by the tuner.
     
  7. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    If you trust the rigs VSWR meter take the outboard meter out of line, tune the coupler for your flat VSWR, or better yet use an antenna analyzer to tune the coupler then compare it to both your VSWR meters, the one in the rig and the external.

    Bad jumpers can drive you crazy.

    I used the analyzer to tune the fan dipole. Looked great.

    Connected the feed line to the thru bulkhead connector and used a small jumper to recheck the antenna with an analyzer again. VSWR way off what they were outside. I changed bulkhead connectors, tried different jumpers, nothing worked. I rechecked the antenna with just the feed line coax and VSWR were all good.

    I cut the feed line connector and soldered on a new one, VSWR checked good direct and through the bulkhead feedthru.

    A lot of fun chasing those gremlins.
     
  8. datsun66

    datsun66 Active Member

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    Just a dumb question. It's been a week from hell and my brain box is about done it. Anyhow, I quad checked the wiring, The air caps are at 215pf and as you can see there are two split caps and I jumped the antenna cap to get the 215pf. On the transmitter cap, I would measure 220pf unhooked to the inductor and when I hook up the lead to the inductor the cap goes to 435pf. Is that normal.
     
  9. datsun66

    datsun66 Active Member

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    pic of the tuner.
     

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