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Antenna Tuner loss questions

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K4HYJ, Sep 4, 2013.

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  1. K4HYJ

    K4HYJ Premium Subscriber QRZ Page

    I borrowed an LP-100A SWR/Wattmeter analyzer to double check some SWR readings on my old (really old) MFJ-986 "differential" tuner. Going through this process I noticed that my HF rig was seemingly not putting out full power - up to 2db down into a dummy load. Just for fun I started removing pieces of gear in the antenna path. I regained 1/2db until I removed the tuner and then I was back at 100%. I swap in a MFJ 941 tuner and the loss was almost 1/2db.

    After searching the web, I find some info stating that the MFJ-986 is very lossy - even a QST lab test http://www.rv3apm.com/tuner.pdf. The ARRL lab mentioned in several instances the losses were 21% or 1db. That same article showed the Ameritron ATR-30 to have the least losses compared to a Ten-Tec unit, and a Palstar unit!! I guess the frustrating thing to me is that even not going through the tuner's capacitor/inductor there is still a fair amount of loss. I guess that loss is heat - wasted. I realize there is always some losses, but minimizing those should be a priority if it can be changed.

    The 986 has worked fine for up to 1300 watts - no arcing or weirdness (after initially cleaning the inductor) in tuning. To paraphrase - but decibels are decibels. I only have the tuner in line with my amp on the second antenna output on my radio - otherwise I use the 1st output straight to the antenna. 21%+ is almost 300 watts when using the amp.

    Any suggestions? Maybe round up an ATR-30? Anything else to check?

    (BTW - The SWR reading was good on the 986 :) )
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Get rid of the tuner is My suggestion.


    Have Fun.
     
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I think if the tuner was really dissipating 300W a lot of stuff in there would start melting.

    Plug in a 300W soldering iron and see what happens.:eek:

    I do have an ATR-30 (for about 12-13 years now) and it's a very good tuner; really the only one I've ever used that handles 1500W on 160m with some badly mismatched antenna systems. My previous Palstar AT3K (or something like that -- it's been years and I don't have it anymore) failed under identical conditions and they didn't want to take it back. I fixed it and sold it.

    Almost all the loss in a typical tuner (most are "T" matches, with two caps and an inductor) is in the inductor, so the bigger, fatter and heavier that is, the lower the loss will generally be. But "layout" is influential also. My first tuners were homebrew and "open," built on a thick board (wood) with no enclosure. They were very efficient, but really ugly and a bit dangerous.
     
  4. KH6AQ

    KH6AQ Ham Member QRZ Page

    You are thinking that 300 watts is a lot of power to go missing. But it's only half a dB, it's only 1/12 an S-unit. To put it in perspective, at 28 MHz 40' of RG-214 has that much loss.
     
  5. KL7AJ

    KL7AJ Ham Member QRZ Page

    As with any other aspect of engineering, life is full of compromises. Even with the losses, if the tuner allows you to deliver more power to the antenna than without it, you're still ahead of the game, right? :)

    Eric
     
  6. K4HYJ

    K4HYJ Premium Subscriber QRZ Page

    Good thoughts. I have a buddy in the local radio club that has had issues with a Palstar tuner on 160 meters at 1200 watts into a decent antenna (SWR is 3.5:1) and in the clear. He is using an old Drake tuner without issue.

    I understand that the losses may be insignificant, but dealing with feedline losses etc, they start to add up. The tuner may be an easy (not necessarily cheap) part of the chain to improve. I saw a real "seat of the pants" difference upgrading coax jumpers and using good connectors - especially on 10 meters. My friend that loaned me the LP-100a, has an old MFJ - 989b or c tuner that he uses with a PW-1, I may borrow it to see what happens to the signal. He claims it has a larger inductor.

    Quoting an old timer - "When you're throwing wattage out your cottage, don't pinch the wire or you'll catch on fire".
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page


    Watt ?.....
     
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    Steve ,
    " really ugly and a bit dangerous."
    Which bit was dangerous and did that bit bite ya :)
     
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    No, I just tossed all the loose bits into my bit bucket.
     
  10. K8JD

    K8JD Ham Member QRZ Page

    Sticking RF gear in a metal shield box is safer than on a breadboard, but lossy. The extra capacitance to ground in a metal box is going to cause losses somewhere.
     
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