Is there a QRO, balanced line, automatic tuner?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K3RW, Nov 24, 2016.

ad: L-HROutlet
ad: l-rl
ad: OK1UUad-1
ad: Subscribe
ad: FBNews-1
ad: Left-2
ad: Left-3
ad: L-MFJ
  1. K3RW

    K3RW Ham Member QRZ Page

    I've been using the MFJ-949D that I picked up at a hamfest at a good price. For the money it seems to be a good entry-level balanced-line. But it is VERY touchy to tune--just like my MFJ loop tuner box.

    If it exists, I'd really like an auto-tuner to run balanced line. QRO-capable would be great too. So far I've checked LDG, MFJ, Ameritron, and Palstar--but I may have missed something. Unless I stay with a manual one, so far no luck.

    Only thing I can see that sort of fits the bill is a remote tuner, something like the RT-600 or SCG-230. But given the months of rain on end, and the tendency of my kids messing with antenna stuff in the yard, I'd rather not go that route.

    Am I looking for something that doesn't exist?

    Only other option is trying to hookup the MFJ legal limit tuner to a coax stub to a balun, etc. I've not had luck with that, but maybe I did something wrong.

    This question seems to come up every few years but never gets resolved. I suspect there isn't a auto-tuning balanced-line one, but maybe something has changed, or maybe there was one a few years back but isn't on the market now, etc.
    Last edited: Nov 24, 2016
  2. WW1WW

    WW1WW Ham Member QRZ Page

    What you need is a Real Balun like a Hilomast, the HF 100 should hold up.
    K3RW likes this.
  3. W6OGC

    W6OGC Ham Member QRZ Page

    I ran balanced line with an Icom AH-4 for a long time. The disadvantage is running the 4 wire control line out to the feedpoint. It is also limited to ~125 watts or so.

    MFJ has remote autotuners in different power levels but I've never used one. LDG has the RT600, which with a balun or unun might be a good choice. I have used the RT-100 with success, and it does not require a control cable. It has a more limited matching range than the AH-4, I believe.
    K3RW likes this.
  4. W1VT

    W1VT Ham Member QRZ Page

    You could build one, or if you don't want to start from scratch, just modify one for a balanced output with big beefy components.
    You have a distinct advantage over a manufacturer in that you can use one-of-a-kind surplus parts--they can't use a part unless they can get it in quantity.

    Zack W1VT
  5. K3RW

    K3RW Ham Member QRZ Page

    I was looking into that also. But how could I make it 'automatic'? I don't have that level of expertise.

    Only thing I could think of was to get an auto-tuner and modify the inside so it would have a balanced line out in lieu of a coax one. and if it was a QRO one like my legal limit tuner, its already QRO.

    Not sure if that would work the way I think it would. might not tune, catch fire, etc. :rolleyes:

    It doesn't have to be QRO. But I would like it to be automatic and a balanced line tuner.
  6. W1VT

    W1VT Ham Member QRZ Page
    He published an auto tuner design in QST.
    LDG actually published his first design in QST, but I heard that the tuning algorithm he gave away was really crude.

    Zack W1VT
    K3RW likes this.
  7. K7TRF

    K7TRF Premium Subscriber QRZ Page

    That's what I'm currently running for my Inverted-V Doublet. I've got the Doublet installed above the roof with the center supported by about 25' of guyed telescoping fiberglass masting with the base mounted in a 4' GlenMartin roof top tower. Open wire feed line runs from the Doublet feed point down the mast to a 4:1 current balun(about 22' of balanced feeder) which connects to an LDG RT-600 remote tuner via a 2' jumper of LMR-400. Coax feed line runs about 60' back to the shack(with the coax shield grounded prior to entering the house) through the bias-T and to the antenna selector switch.

    The LDG tuner itself is mounted up on the roof so it's out of harms way but it does sit out in all kinds of weather including some very wet and very snowy cold months. I usually run with 100 watts or less but have driven this up to 600 watts with my SB-200 without problems. When I first tested this configuration I used one of the mid power MFJ remote tuners, it also worked fine but I liked the way the LDG tuner was packaged and the LDG seemed to find a tuning solution faster than the MFJ plus the MFJ has a habit of not trying to tune when you switch bands unless you power it down and back up again at which point it goes through it's entire tuning cycle. The LDG seems to remember settings for each band better and quickly jumps to the stored setting after a band change.

    Anyway, the remote tuner feeding a balanced system can work if you decide to go that route.

    You mentioned having troubles using a shack tuner with a coax jumper to an outboard balun. What problems has that given you? Do you struggle to tune on all bands or just some bands and what's the overall antenna configuration including feed line type and length?

    K3RW likes this.
  8. K8JD

    K8JD Ham Member QRZ Page

    Balanced Line Tuner
    I use a MFJ974HB (made specially for balanced line systems) for my one balanced line fed antenna, It can handle 200-300 W, but I believe there is a bigger, kiloWatt version. I have had very good results with this tuner with a 450 Ohm Line to a 20M EDZ, it works fine between 5.3 and 18.1 MHz !
    NL7W and K3RW like this.
  9. K3RW

    K3RW Ham Member QRZ Page

    In the past I tried a balun, and I just realized looking it was a 9:1 voltage balun, and the stub had a ton of ferrites too. Ah, that might be why. I didn't build the system or have any understanding of it at the time. Doh!

    Somewhere I saw a guy that stuck a balun directly on the back of his autotuner. Not sure if he used an adapter (male/male?) to put it directly on the coax 1 output. If that looks promising I could always stick a 1:1 current balun there (or some other value--I can never figure out which one). It would be great to have the QRO ability of the legal limit tuner for a safety margin (and occasional fun).

    A bit of further research raised the question to me... people recommend balanced line because even with high SWR it can work well. BUT, on some balanced line antennas the SWR can be really high depending on the band--like 10:1 or greater. So, not being intimately familiar with the tuners I have, am I likely to have problems knocking down a high SWR? Skip using a tuner on a doublet/etc.?
  10. W1VT

    W1VT Ham Member QRZ Page

    W5DXP's variable line length idea is actually one of the more practical approaches to feeding a doublet with open wire.
    NL7W, NH7RO and N2EY like this.

Share This Page