Using an antenna analyzer with OWL

Discussion in 'Technical' started by K4TQF, Jun 29, 2016.

  1. K4TQF

    K4TQF Member

    I have one of these and use it to tune up before I connect a transmitter. It has a unbalanced N connector for antenna input. It does a great job with coaxial fed antennas. It also does a good job with the 50 ohm input to my Stoner 600 ohm OWL tuner.
    Question is, if I make a bal-un for the input and do some sort of testing or calibration thru the bal-un, will I be getting a true reading when testing an OWL? Or, will just "fooling" the analyser?
     
  2. W5HRO

    W5HRO Administrator

    That usually never works very well. I've tried using baluns between MFJ analyzers and OWL fed antennas for example and it never works right. You can sometimes find the resonate spots, but it won't be anywhere close to 50-ohms. You won't even see a good match using one into a directly coax fed dipole either because the antenna will always be closer to 72-ohms at it’s resonate spot. It will never yeild a 1:1 match using a 50-ohm analyzer. It will just be a lot worse trying to use one into OWL even with a balun.
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  3. W5HRO

    W5HRO Administrator

    I pulled out my old MFJ analyzer and connected it to my coax fed dipole and below are the results.

    MFJ_SWR.jpg

    It can find the antenna's self resonate point, 3.6198Mc, but it cannot get a 50-ohm match. It shows 38-ohms with a 1.8:1 VSWR, but it would rise up closer to 72-ohms if would drop all the way down to 1:1, but it cannot.

    Anyway, that's the problem with 50-ohm analyzers, they are limited and not very accurate unless the load is exactly 50-ohms.
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  4. K4TQF

    K4TQF Member

    I can get this on my OWL fed dipole cut for 3.885

    image.jpg

    Thru this tuner
    image.jpg

    But, that's all tuner... 50 ohm input 600 ohm out. There is another screen that gives a bunch of other info, i.e. Impedance, Inductance, C, etc.... But I don' have a screenshot.

    image.jpeg
     
  5. W5HRO

    W5HRO Administrator

    Yep, that's all tuner and has nothing to do with the antenna. The 600-ohms on the output side of the tuner isn't really 600-ohms. That impedance varies dramatically depending on what band you are on and even on the antenna's self resonate frequency. Unlike using coax OWL becomes part of your actual antenna.
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  6. K4TQF

    K4TQF Member

    I would really like to hook up my analyser ( I think it's 500 milliwatts ) and walk or drive around and see what I can see on the KX3. It has a dbV scale, but I think it's measuring audio, not RF.
     
  7. K4TQF

    K4TQF Member

    Here's a shot of the other screen...
    image.jpeg image.jpeg
     
  8. K4TQF

    K4TQF Member

    I'm presently using a delta loop for an antenna. It started out as an inverted V. I then put up a low hanging 1/2 wave 80 M dipole. Neither one worked very well, so, I tied the ends together, shorted the apex of the inverted V and am feeding the whole thing at the middle of what was the 80M dipole with 600 ohm OWL. Here's where it gets interesting... I was looking at the DCR and just for grins I flipped my polarity reversing switch on the OWL. The reading went from 16 ohms DCR to about 8 ohms DCR when reversed ! :icon_wtf:

    In total, there is about 280ft of wire in the air.

    Also, it is directly wired, no baluns.
     
  9. K4TQF

    K4TQF Member

    I have an AEA VIA analyzer. It has a N type connector and is designed for use with 50 ohm coax. Is it possible to get any meaningful reading from this thing by using a balun for my balanced feed line? The factory engineer hemmed and hawed when I asked him and would not commit to a straight answer.
     
  10. W5HRO

    W5HRO Administrator

    Since this is basically the same topic from last June I merged them. Is the knee medication starting to affect your memory? :mrgreen:
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  11. K4TQF

    K4TQF Member

    My memory has been shot for a while. This was a little different in that I wasn't using the tuner. Just trying to go directly to the 600 ohm OWL. I would think using a balun with the correct ratio & calibrated would be much different than going thru a tuner. No?

    Then, again, trying to wind & calibrate a balun with a resistive load, then using it to measure an antenna would be all out of whack...
     
  12. K4TQF

    K4TQF Member

    Here's where it gets interesting... I was looking at the DCR with a Simpson 260 just to see if the wind had broken any connections. Just for grins I flipped my polarity reversing switch on the OWL. The reading went from 16 ohms DCR to about 8 ohms DCR when reversed ! :icon_wtf:
     
  13. W5HRO

    W5HRO Administrator

    The analyzer will never work with that antenna even when using a balun. When you use the tuner you are just getting resonance at 50-ohms for the analyzer, but that’s different. Without the tuner it will never work and even with the tuner it’s not really telling you anything about the antenna anyway.
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  14. NewWave

    NewWave Member

    interesting subject !!
    But so I can see, there is more snow as we have here on this moment 8)
    But, how much Power you like to use for this antenna system?
     
  15. W6MQI

    W6MQI Member

    Well the business bought me this toy one last tax right off for 2016:biggrin:
    Kinda over kill for my needs but what the hell.

    20170128_185419.jpg
     
  16. NewWave

    NewWave Member

    That is what i mean the real equipment..Nice!!
     
  17. Chuck49

    Chuck49 Member

    Interesting topic. Measureing the antenna response at the connection to the amplifier or at the antenna feed point would require the analyzer to be calibrated at either the connection to the amplifier or the connection to the feed line in order to establish the measurement plane for the analyzer. If your analyzer is permanently calibrated at the analyzer connection point (port), you will not be able to measure the SWR (or Return Loss)/Phase of either the antenna feed point or the input to the feed line through the balun. To your specific question, you would need to calibrate the analyzer at the output of the balun in order to do the measurement you describe. There are quite a few antenna analyzers out there and I am not familiar with all of them, however if you can find one that allows calibration beyond the analyzer connection point, then you could make that measurement. Perhaps a better choice would be a Vector Network Analyzer. A good VNA will allow calibration at the feed line input or at the antenna feed point. The caveat is that most VNAs have a fixed input impedance of either 50 or 75 ohms (selectible on some models). For an QWL with a nominal characteristic impedance of 300, 450, or 600 ohms a conversion matrix would need to be developed to transform the measurement results into 50 or 75 ohm values to make sense of the VNA readings. I've done this sort of thing - VNA calibration and matrix conversions - in a past life, though the matrix math would require some 'review' to get back into the game. A good source of info regarding VNAs and their uses/limitations is either Keysight or Maury. Both have extensive on-line documentation that can be downloaded for free (mostly) that can outline the basics of getting this done. Hope this helps...
     
  18. NewWave

    NewWave Member

    In my profession we use the expensive Anritsu antenna / spectrum analyzers because all Phone providers accept only measurements by Anritsu with calibration up to six month by factory/importer.
    For home and amateur use I have the MiniVNA (0.1 - 200 Mhz.) who's working perfect. For measurements on antennas, Low Pass, High Pass, Band Pass, IF filters. All things we need for this, it's all in the Mini VNA.. Cable loss, phase measurements, calibration on each port. And all details you can see it ( in color) on your Laptop or Tablet or Phone screen.
    I have several times measurements as compared with the Professional Anritsu, but there was no difference in measurement ..

    Measurements of 600 ohms systems with an antenna tuner / balun are dependent on the tuner / balun because it's not for sure you will have the perfect match / system, even if your analyzer gives good results. You have to start with an real symmetrical antenna tuner first, (by using twin lead 600 Ohm line) there are many designs on the web to find. And if you can't find a good design, I will put some pictures here from my wide range symmetrical (inexpensive) used ATU for every Power level you will need it for.
     
  19. W5HRO

    W5HRO Administrator

    Would work with an antenna bridge as long as it has the tracking generator option, but it's still designed for 50-ohms. Does it have any other selectable impedance settings?

    If it's only 50-ohms then you could still see resonant points, but they will be very distorted with a non-50-ohm antenna system.
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  20. W5HRO

    W5HRO Administrator

    The problem trying to use a modern analyzer is even with an antenna the uses 600-ohm OWL (open wire line) feedline is that the impedance at the transmitter end will seldom be 600-ohms. That's not how it works. Sometimes the transmitter end will be like 1200-ohms, sometimes 600-ohms and something 300-ohms, etc. and it will never be those exact values anyway. That impedance will change as you change bands and frequencies so using a fixed balun won't do anything.

    Modern 50-ohm analyzers are not for checking balanced antenna systems of higher impedance. They simply will never work right for that. They do make some that are more versatile, but they are still very limited.

    This one below has selectable impedance settings, but the highest one is only 100-ohms. You need like an old HP LC RF bridge and just calculate everything from the measurements then manually draw the graph on paper.

    Untitled.png
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  21. NewWave

    NewWave Member

    Have tested my roof mounted Inverted V from 2 X 6 Meters (+/- 250 Inch) and have connected my Twin lead 400 Ohm line without Sym. / asym. balun or tuner on the VNA.
    So you can see the antenna is useful without tuner in the 12 Mhz. range (25 meter) = the whole wavelength divide by 4 = 6.25 meter 1/4 wavelength X 0.95.is
    exactly where the resonance is in this case... In the top you can see where he is working in the higher 500 / 600 Ohm range.

    20170129_190313.jpg mini vna5.jpg mini vna4.jpg

    On the other pictures you can see the 50 Ohm marker and without marker for higher impedance measurements.
    The unclear red line on the left in the curve are Broadcast stations received by the Inverted V.

    Now i connect my Atu on this Inverted V and have a look where i can go by a good SWR..


    Central Frequency Inverted V, by ATU..

    By Atu jpg.jpg

    Same antenna, same twin lead 400 Ohm feeder ...but connected by an home made symmetrical atu with 50 Ohms asym. out.
    Impedance is 49,77 Ohm and the SWR is total Flat !!
     
  22. W5HRO

    W5HRO Administrator

    Hewlett Packard made a couple of old LC bridges to where you could use an RF generator connected to the external oscillator input that would work. I used one years ago that way. Then there was also the General Radio 916 bridge, etc. Manual for that is attached below.

    This is all old-school stuff, but when using old old-school technology is often requires using old school equipment.
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    Attached Files:

  23. NewWave

    NewWave Member

    Yes Brian i know this principle, the oscillator on the picture i must have it somewhere on the roof floor..
    But on this way it work faster`and so you can see no calculator needed..

    lowest frequency.jpg
    2.798 Mhz. The lowest frequency i can get by this small inverted V by the ATU.
    SWR is the same and Impedance 49.95 Ohm 8)

    The highest frequency with a nice SWR and load, is somewhere in the 25 Mhz. range.
     
  24. W5HRO

    W5HRO Administrator

    It will still be distorted even using that software and setup.

    The problem is below is what a balanced line input looks like and it will never work correctly using unbalanced line equipment and setup. You essentially have a 3-wire component, one of which will always be invisible.
    Balanced_Line_Circuit.png
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  25. NewWave

    NewWave Member

    Yes Brian, that's the reason i say in a previous message use an real symmetrical tuner, because a nice SWR is no
    guarantee for the optimal impedance matching to your antenna.
    But calculations like this, for me it's a long time from now and have to reset my brain first..:confused:
    In my case i can look for reception on distance on the web receiver, he is 60 Km from here and gives me an real picture..:icon_angel: