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Thread: Tuning

  1. #1

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    Default Tuning

    Easy question: Let's say I use the tuner in my FT-450D to tune to a 50 Ohm dummy load and I'm set somewhere in the phone band on 40m, for example, and then I use an external tuner to optimize my reception and transmission near a frequency I want to use, do I need to tune with the dummy load again if I change bands like to 20m or something. That is, do I lose what I did with the dummy load if I change bands?

  2. #2

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    Default

    You don't tune a dummy load. If the impedance of the load is the same as the radio's impedance, in this case 50 phms, then you don't need a tuner between the radio and the load.
    A tuner is only needed when the aerial is not a suitable harmonic of the frequency that you want to TX/RX on.

  3. #3

    Default

    I thought that was a bit odd too - I suspect just a misunderstanding of what dummy loads are for - which of course is simply to replace a radiating antenna with a device that doesn't, for testing. ATU's as said above just control capacitance and inductance components, which impact on impedance - and you're changing a less efficient impedance from an antenna not completely resonant into something the radio believes IS! Adding some inductance to a physically too short antenna is commonly done by a coil at the bottom of the antenna, but an adjustable inductor in the ATU, indoors is much easier to adjust.

  4. #4

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    Default

    Hmmm... I need to think a bit and perhaps ask my question differently. I have something on my mind about this and my internet quests and a thorough search through the ARRL handbook have not been able to properly address the issue. I'll be back.

  5. #5

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    Don't worry about the question at all - what process do you want to carry out that actually needs a dummy load? Loads of people live a long life without ever having one?

  6. #6

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    Default

    I don't use the on-board tuner in my FT-450D; I use a stand-alone tuner. So I want to insure that my FT-450D is set up to see a 50 Ohm load. That's what the dummy load is for.

    As far as my question, I think I've answered it already as all tuning is carried out at a particular frequency. So, change the frequency and the SWR follows the curve away from its minimum value until re-tuning again.

    At least I think I understand this. I'll probably put myself into a state of confusion by tomorrow though!

  7. #7

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    when you put the dummy load in line, your tuner is not doing anything...the dummy load is already a "perfect" match...
    your tuner should come with "best guess" suggested starting points list for each band.
    Your antenna if not a perfect match is where the tuner will do it's work.
    Set the tuner at the suggested start points for each band and put the radio in a low power setting, using cw or AM, find an open spot on the band and key up, set your tuner to the lowest SWR reading and then run your power up to the level you need to make the contacts you want and have fun.
    Once you have the best setting in each band, write them down and next time just preset the tuner...
    If you add an amp to your system later on... follow the same procedure, except when you tune the amp, do that into the dummy load, then since your tuner is already adjusted for the band when you put the amp on line you are good to go.
    I hate it when folks do their amp tune ups on the air.

  8. #8

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    "...when you put the dummy load in line, your tuner is not doing anything...the dummy load is already a "perfect" match..."

    So if I understand what you are suggesting, my FT-450D with its built-in tuner, will always present a 50 Ohm impedance at the output of the transceiver.

    So even if I connect an antenna system to the transceiver that will resonate at 45 Ohms and I have this built-in tuner tune to this antenna system, instead of matching impedance at 45 Ohms it will stay at 50 Ohms.

    I would think that it would match the 45 Ohms of the antenna system as that's its job.

    So what do I do if I want to return it to 50 Ohms, for whatever reason? Reset the rig to its factory settings? That would do it, of course, but at the cost of losing whatever other settings I've changed, so that is not a desirable solution.

    My solution would be to tune it to a 50 Ohm dummy load, because as it sits, having been matched to a 45 Ohm load, is not already a "perfect match" to the dummy load.

  9. #9

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    I think this all goes back to what you should have learned when you obtained your
    technician class license, but did not learn, because there is no minimum requirement
    of what you should know when you were first licensed.
    In electronics / communications 101 - you would learn that in a perfect world a
    antenna tuner doesn't really tune a antenna system, it just tricks the transceiver
    into applying all or most of its power into the tuner..
    The dummy load - in theory, if you apply power into a resonant load, all the power
    applied is absorbed by the load - hence if you think your radio produces 100w, most
    all of the 100w is applied to the dummy load.
    However, when you connect jumper cables between the transmitter and the tuner and the dummy load
    those cables changes the line impedance resistive / reactive - all goes back to good theory -
    Nodes and junctions and Smith chart equations - what happens when you use coax of X length.

    Can you tune the receive antenna with an antenna tuner? answer is no - not really..
    The only thing that will happen is that the signal strength will increase when you approach resonance.
    The old Pre Selector on the old tube type radios did basically the same function..

    Your best bet is to find yourself an Elmer, someone knowledgeable about these things and get
    them to teach you how to operate properly.
    Get rid of the non resonant antenna, don't use a G5RV and don't worry about SWR or tuners..

    A 40M DIPOLE IS NOT A VERY LARGE ANTENNA, NOT OUT OF REACH OF MOST AMATEURS WITH A LIMITED SIZE LOT.

    IF YOU CAN ONLY AFFORD ONE ANTENNA, BUY A GOOD RESONANT 80M OFF CENTER FED ANTENNA LIKE THE ONE OFFERED BY THE HY POWER ANTENNA COMPANY WITH A GUANELLA BALUN..
    THIS WILL GET YOU 2M, 6M, 10M, 20M, 40M, 75/80M - WITHOUT A ANTENNA TUNER!

    I don't waste my time playing around with antenna tuners, amplifiers or non resonant antennas, life is too short....

  10. #10

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    Default

    I'm getting the feeling that we are addressing separate issues.

    But that's OK - I think it's time to drop this.

    Thanks for the responses.

  11. #11

    Default

    well sixmeters made a technical error in his statement... he said in a perfect world the tuner does not tune the "antenna system" it just tricks the radio...
    that is not correct... the radio does not know what is out there, it does not know what type or how long the coax, transmission line etc is, it does not know what the antenna is... it only know what it sees at its output... the tuner actually does tune the LOAD to an impedance match...it does not affect the efficiency of the antenna...
    lots of folks like to use the old wives tale of just "fooling" the radio... it does not do that... it does impedance match the load...lots of radios do have a built in function to reduce the power out if it does not see a good impedance match..l which is the whole load, not just the antenna.

  12. #12

    Default

    your radio should be able to turn the built in tuner off...

  13. #13

    Default

    Well Obed, not to be combative, but unless you can bend the laws of physics, you cannot make a non resonant antenna resonant by just cancelling out the reactive or resistivity component. As you claimed, all you are doing is tricking the radio to accept what ever is connected to the feed line...

    As you claimed, all you are doing is changing the impedance of the line at the radio end.

    Anything not adsorbed by the load or the line is reflected back towards the source, turned into heat. Good for keeping your coffee warm, but not good if you want that power to be used efficiently. How many times have you heard someone brag that they are running 100w.. When in fact what they are radiating is much less than the 100w the transmitter could produce - had the antenna been resonant...

    Point in case someone misses it is the G5RV. Which is semi resonant on 20 meters, not resonant at all on 10 or 40 meters..

    Wanna buy a burned up MFJ antenna tuner, just ask everyone that ever tried tuning their G5RV what happened with they hooked up their 949 antenna tuner to it, even with the ladder line strung directly from the antenna to the tuner.

    Result is heating or arcing that damages the tuner and people on 40 meters telling you to get the heck off that G5RV!

    Also the reason why so many LIDS hangs out on 80m - since it is not the 1st harmonic of 20 meters... When you ask them to QSY to 40m - they run like skeered cats, because they know the jig is up as soon as they try to tune up and can't - because it is physically impossible..........

    The best thing an Elmer can do for a new ham or a old ham that doesn't know anything is to steer them away from G5RV and non resonant antennas...
    Last edited by Sixmeters; Mon 13th Aug 2018 at 16:43.

  14. #14

    Default

    Seems odd to ask a question, get decent answers that clearly have been a bit misunderstood then walk away, with the wrong explanation in your head.

    The radio never presents a 50 ohm source to the outside world if that antenna is anything other than 50 Ohms - it does it's job by converting one impedance into another, maximising efficiency. one end of an antenna tuner is designed to be 50Ohms, and the other can be whatever is needed.

  15. #15

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    Default

    Quote Originally Posted by paulears View Post
    Seems odd to ask a question, get decent answers that clearly have been a bit misunderstood then walk away, with the wrong explanation in your head.
    I'm not new to forums and there's a recognizable trend taking place so I've politely bowed out. I thanked everyone for their responses.

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