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Remote tuners, random length wire matter? and what about MFJ-998RT?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by NZ9Y, Dec 18, 2011.

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  1. NZ9Y

    NZ9Y Ham Member QRZ Page

    I'm curious about remote feed point tuners. Does it even matter if an antenna attached to one is resonant? Would not a randon length wire at least 1/4 wave work just as well as a 1/4 wave tuned wire on the frequency of interest? For example, at 7.2 mHz, would a wire 32.5 feet long work any differently than one 35 or 40 feet long?

    Also I'm curious about the MFJ-998RT tuner. Anyone have experience with this? Any reason it shouldn't work as advertized? I'd like to use it at the top of a tuned shortened multi-band sloper to get full bandwidth without feedline loss.

    My concern is that when installed it will be in an location that will cost a bucket lift rental anytime I need to access it, so I want to know it will work pretty well. Another tuner would be considered if it can handle at least as much power (legal limit) and isn't way more expensive.

  2. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    Your understanding is perfectly correct. There is nothing sacred about a self-resonant antenna. The prime example is the extended double Zepp, which has considerable gain over a dipole, yet is non resonant. Depending on the tuner design, some types are better at tuning out large reactances, but it doesn't matter really where you do the resonating. Read the classic article by Byron Goodman, W1DX, called "My Feedline Tunes My Antenna." It was a classic in 1956, and should be required ready by every ham now.

  3. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Some tuners can handle a wider range of impedances some can handle less. Same with power ranges.

    Random length antennas are chosen for the convenience in placement. It can be difficult to predict their characteristics even with some modeling. And modeling is really the only way to estimate if a given tuner can match it.
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I've never used the 998RT and I think it's a pretty new product, so offhand I don't know anybody who has one.

    However, matching and performance aren't well related.

    If it could match a paperclip, that wouldn't make it a good antenna system.

    The thinking that matching at the feedpoint is better has some merit, with respect to overcoming transmission line losses; no doubt about that. But on HF, line losses can be held pretty low even if the line is long, and you know what you're doing.

    In lieu of a nearly $800 remote tuner, I'd probably opt for adjusting the antenna itself, or using a lower loss transmission line and a tuner in the shack.
  5. N0AZZ

    N0AZZ Ham Member QRZ Page

    Have a look at DXengineering's remote tuner they sell with there multi-band vertical that whole setup is sold in pieces or the whole kit.
  6. NZ9Y

    NZ9Y Ham Member QRZ Page

    If its the one I saw, it doesn't handle enough power. In fact the only remote tuner I can find in production that handles legal limit is the MFJ-998RT.
  7. NZ9Y

    NZ9Y Ham Member QRZ Page

    This much I've done as far as I can. There are, however limitations in doing this. Bandwidth is the biggest problem. I know on 80-160 meters my antenna is near resonant on part of these bands, and losses are minimized with good feedline and a low loss L tuner in the shack, but there ARE losses.

    I figured with an autotuner at the feedpoint losses could be reduced furthur, AND convenience would be great. I suspect having an antenna that is "in the ballpark" self resonant is still useful as its more likely an autotuner will match.

    Thanks everyone.
  8. W4FO

    W4FO Premium Subscriber QRZ Page

    I just received the 998rt for early Christmas gift from Wife and Son.
    It tunes my 84 foot inverted L on 80 -10 and handles 1300 to 1400 watts no problem.
    I have used the 998 on the same antenna for about 2 years with no problems.
    It is same tuner as 998rt just not in waterproof case.
  9. N0AZZ

    N0AZZ Ham Member QRZ Page

    What are your early thoughts on this tuner? I have had very bad luck with anything MFJ and have sold off all that I owned and swore off them. But a legal limit remote tuner hum I have one end fed inverted L for 160m that is about 75' away from the shack it would be nice to feed it with LMR-400.
  10. W4FO

    W4FO Premium Subscriber QRZ Page

    Fred I just took the case off the 998,after two years of everyday use,it looks like new.
    I have had zero problems with this unit,all components,solder joints,first class.
    As noted the RT is basically the same tuner as the 998.
    Also it will let you no if you try to run 1500 plus.
    I keep the amp at 1300/1400 and no problems.
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