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Thread: Using The ImmersionRC Power Meter To Measure SWR.

  1. #51
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    Quote Originally Posted by the.ronin View Post
    And I presume over time, the antenna degrades increasing that SWR ratio?


    While this is true in the commercial world where antennas are exposed to all types of environmental hazards and lightning, it is not so much in the hobby world, where degradations are the result of poor design or damage from gravitational errors.


    Wayne
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  2. #52
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    Got it. So the rate of degradation does not change (SWR stays constantly off 1:1). And this is assuming no crashes or any damage to the antenna too. Crazy stuff thanks ssassen.

  3. #53
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    Got it Wayne. Had to google gravitational errors will need a little time to get my arms around that one.

  4. #54
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    Quote Originally Posted by the.ronin View Post
    Got it Wayne. Had to google gravitational errors will need a little time to get my arms around that one.

    It's really very simple, an example of one type of gravitational error is where a pilot fails to provide enough lift to overcome the earth's suck and the plane hits the ground.




    Amateurs crash, the pros have gravitational errors. ;-)


    By the way, as for 1:1 SWR, it is quite possible with proper design, even in wideband antennas, for example a Dielectric DCR FM antenna can be field tuned to a SWR of 1:1.05, the reason they are designed to such a degree is power, take a hobby transmitter and it hammers out, what a watt, so with a slightly off SWR you have might a dozen or so milliwatts of reflected power, no big deal. Take that over to broadcasting where the forward power is 50 kW or so and the reflected power of a minor SWR mismatch becomes hundreds of watts and when you start messing around with those power levels the standing waves can become flashovers within the hardline and that kinda chit ain't cool at all.


    Wayne
    Everybody loves a bunny.

  5. #55
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    Quote Originally Posted by hdphilip View Post
    it's also a good idea to have a 50 ohm termination to put on the antenna port, your vswr would be 0 in the perfect world, it's a good idea test your setup before checking your antenna.
    Can you please explain how to test the transmitter using this terminator? Is it one like this? http://www.dpcav.com/xcart/SMA-RF-Te...ms-1-Watt.html

    Thanks,
    Steve

  6. #56
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    Quote Originally Posted by bomsaway View Post
    Can you please explain how to test the transmitter using this terminator? Is it one like this? http://www.dpcav.com/xcart/SMA-RF-Te...ms-1-Watt.html


    Thanks,
    Steve


    You would use the terminator in conjunction with a directional coupler to determine if the output impedance is the correct nominal 50-52 ohms.


    Wayne
    Everybody loves a bunny.

  7. #57
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    Quote Originally Posted by Channel 1 View Post
    You would use the terminator in conjunction with a directional coupler to determine if the output impedance is the correct nominal 50-52 ohms.


    Wayne
    Thank you for the explanation Wayne.
    Steve

  8. #58
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    I went and measures all of my antennas haha. Wayne, is there a reason why you have the attn set to 41 db as opposed to 30 db? Anyway here are my readings at 5800MHz and 41.0 dB ...



    For the most part, I saw what I expected - older, beat up antennas had higher SWRs. I'm using this app that has 1.8 as a cutoff where anything higher and it says "warning! check the antenna." How much credence should I put into this threshold? As you can see, a lot of my antennas go past that cutoff.

    I did notice that those SMA extensions cables that are often used in mini builds raises the SWR a bit. I also noticed readings can vary - note the [1st] try reading and [2nd] try readings which were done an hour or so later (ate lunch lol). I wonder if heat from the vtx informs these readings somewhat?

    Another glaring observation for me was that a lot of those antennas falling below the 1.8 threshold I thought were "great deals" in the classifieds lol ... live and learn.

    At the end of the day, what is considered "bad" SWR? I'm guessing it's fairly subjective.
    Last edited by the.ronin; 1st March 2015 at 05:43 PM.

  9. #59
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    Quote Originally Posted by the.ronin View Post
    Wayne, is there a reason why you have the attn set to 41 db as opposed to 30 db?


    Either an error or was using a 40dB attenuator.


    Wayne
    Everybody loves a bunny.

  10. #60
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    Quote Originally Posted by the.ronin View Post
    At the end of the day, what is considered "bad" SWR? I'm guessing it's fairly subjective.

    For me it's anything approaching 1.50.


    Wayne
    Everybody loves a bunny.

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