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Re: [FT897] SWR Problem

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  • Alex Netherton
    Sometimes it can be the feedline length, but I am suspecting the coax connector. Barrel connectors will add in some reactance, but usually not enough to make a
    Message 1 of 9 , May 8 7:16 AM
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      Sometimes it can be the feedline length, but I am suspecting the coax
      connector. Barrel connectors will add in some reactance, but usually not
      enough to make a huge difference.


      On Wed, May 8, 2013 at 10:02 AM, jamespgrove <james@...>wrote:

      > **
      >
      >
      > Hi,
      >
      > This maybe a somewhat basic question but i am struggling to work out why i
      > get higher SWR readings when i extend my feed line to my radio.
      >
      > I have a Diamond Antenna mounted on a pole on the side of my house, i have
      > around 10m of RG8 Mini cable that feeds into the shack where my radio is.
      >
      > This works fine, SWR is flat as it should be.
      >
      > I want to use my radio in the other room so i join (using a joiner)
      > another feed line to the existing one, the same cable same specs, i also
      > add another using the same method, so total cable length is under 20m.
      >
      > However i get some higher level of SWR than i do if the radio is connected
      > in my shack. So the additional 10m of RG8 Mini is causing the higher SWR.
      >
      > Can anyone point me in the direction of the problem? I have some ideas but
      > nothing short of minor guess work, ie the cable length a loss?
      >
      > The SWR is not a huge problem, as its not dangerously high i was just
      > expecting it to be flat still.
      >
      > Any help appreciated,
      >
      > Thanks
      >
      > Jim M6BXG
      >
      >
      >



      --
      Alex Netherton
      http://blueridgediscovery.com


      [Non-text portions of this message have been removed]
    • Radio_Randy
      Jim, I m assuming you are talking about VHF or UHF frequencies? If so, standard PL259 (UHF) connectors do not have the same impedance as your cable (50 ohm).
      Message 2 of 9 , May 8 4:35 PM
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        Jim,

        I'm assuming you are talking about VHF or UHF frequencies? If so, standard PL259 (UHF) connectors do not have the same impedance as your cable (50 ohm). Every one you add, to extend your cable run, adds to the mismatch in your system, both raising your SWR as well as reducing the signal to your antenna.

        I can't imagine that the SWR is dramatically increasing, but it is probably enough to notice with your meter. It shouldn't be a problem, but there may be solutions available to you.

        My recommendation would be to use type "N" connectors and the appropriate "extender". This would get your overall impedance back to the 50 ohms you desire. Not having any experience with RG-8X, I don't know if they even make a type "N" connector for that cable. If not, you may be stuck with what you have, unless you switch to something like LMR-400 cable.

        Other possible problems may be defective or poorly installed connectors on your second length of cable, or even a bad "extender". Overall, the length of your cables should pose no problem as it sounds like your antenna is working properly.

        73, Radio Randy N7CKJ

        --- In FT897@yahoogroups.com, "jamespgrove" <james@...> wrote:
        >
        > Hi,
        >
        > This maybe a somewhat basic question but i am struggling to work out why i get higher SWR readings when i extend my feed line to my radio.
        >
        > I have a Diamond Antenna mounted on a pole on the side of my house, i have around 10m of RG8 Mini cable that feeds into the shack where my radio is.
        >
        > This works fine, SWR is flat as it should be.
        >
        > I want to use my radio in the other room so i join (using a joiner) another feed line to the existing one, the same cable same specs, i also add another using the same method, so total cable length is under 20m.
        >
        > However i get some higher level of SWR than i do if the radio is connected in my shack. So the additional 10m of RG8 Mini is causing the higher SWR.
        >
        > Can anyone point me in the direction of the problem? I have some ideas but nothing short of minor guess work, ie the cable length a loss?
        >
        > The SWR is not a huge problem, as its not dangerously high i was just expecting it to be flat still.
        >
        > Any help appreciated,
        >
        > Thanks
        >
        > Jim M6BXG
        >
      • D.J.J. Ring, Jr.
        The impedance of the antenna is transformed by the length of the coax, only being correct every 180° of electrical wave length, in addition, each coaxial
        Message 3 of 9 , May 8 9:38 PM
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          The impedance of the antenna is transformed by the length of the coax, only
          being correct every 180° of electrical wave length, in addition, each
          coaxial connector introduces non-regular non-constant illenear impedances
          (except if type N). If you are talking about 144 MHz you are talking about
          considetable loss with RG8 mini coax, maybe 3 dB, so the measured SWR will
          often appear better than it really is.

          Check the coupler for problems, swap it out, join the coaxes with another
          double female, borrow spme coax, do the same thing.

          73

          DR
          On May 8, 2013 10:03 AM, "jamespgrove" <james@...> wrote:

          > Hi,
          >
          > This maybe a somewhat basic question but i am struggling to work out why i
          > get higher SWR readings when i extend my feed line to my radio.
          >
          > I have a Diamond Antenna mounted on a pole on the side of my house, i have
          > around 10m of RG8 Mini cable that feeds into the shack where my radio is.
          >
          > This works fine, SWR is flat as it should be.
          >
          > I want to use my radio in the other room so i join (using a joiner)
          > another feed line to the existing one, the same cable same specs, i also
          > add another using the same method, so total cable length is under 20m.
          >
          > However i get some higher level of SWR than i do if the radio is connected
          > in my shack. So the additional 10m of RG8 Mini is causing the higher SWR.
          >
          > Can anyone point me in the direction of the problem? I have some ideas but
          > nothing short of minor guess work, ie the cable length a loss?
          >
          > The SWR is not a huge problem, as its not dangerously high i was just
          > expecting it to be flat still.
          >
          > Any help appreciated,
          >
          > Thanks
          >
          > Jim M6BXG
          >
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >
          >


          [Non-text portions of this message have been removed]
        • Butch Bussen
          Yep, and if you don t think feed line length matters on swr measurements, try feeding an antenna with 1/4, 3/4 or multiples of a quarter wave. I use to make
          Message 4 of 9 , May 9 1:09 AM
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            Yep, and if you don't think feed line length matters on swr
            measurements, try feeding an antenna with 1/4, 3/4 or multiples of a
            quarter wave. I use to make quarter wave stubs for c b radios that ran
            quarter wave whips. Static electricity would wipe out fets. I put a t
            connector and a shorted quarter wave at 27 meg at the radio and all was
            well, dc ground, open at 27. '
            73
            Butch
            WA0VJR
            Node 3148
            Wallace, ks.


            On Thu, 9 May 2013, D.J.J. Ring, Jr. wrote:

            > The impedance of the antenna is transformed by the length of the coax, only
            > being correct every 180° of electrical wave length, in addition, each
            > coaxial connector introduces non-regular non-constant illenear impedances
            > (except if type N). If you are talking about 144 MHz you are talking about
            > considetable loss with RG8 mini coax, maybe 3 dB, so the measured SWR will
            > often appear better than it really is.
            >
            > Check the coupler for problems, swap it out, join the coaxes with another
            > double female, borrow spme coax, do the same thing.
            >
            > 73
            >
            > DR
            > On May 8, 2013 10:03 AM, "jamespgrove" <james@...> wrote:
            >
            >> Hi,
            >>
            >> This maybe a somewhat basic question but i am struggling to work out why i
            >> get higher SWR readings when i extend my feed line to my radio.
            >>
            >> I have a Diamond Antenna mounted on a pole on the side of my house, i have
            >> around 10m of RG8 Mini cable that feeds into the shack where my radio is.
            >>
            >> This works fine, SWR is flat as it should be.
            >>
            >> I want to use my radio in the other room so i join (using a joiner)
            >> another feed line to the existing one, the same cable same specs, i also
            >> add another using the same method, so total cable length is under 20m.
            >>
            >> However i get some higher level of SWR than i do if the radio is connected
            >> in my shack. So the additional 10m of RG8 Mini is causing the higher SWR.
            >>
            >> Can anyone point me in the direction of the problem? I have some ideas but
            >> nothing short of minor guess work, ie the cable length a loss?
            >>
            >> The SWR is not a huge problem, as its not dangerously high i was just
            >> expecting it to be flat still.
            >>
            >> Any help appreciated,
            >>
            >> Thanks
            >>
            >> Jim M6BXG
            >>
            >>
            >>
            >> ------------------------------------
            >>
            >> Yahoo! Groups Links
            >>
            >>
            >>
            >>
            >
            >
            > [Non-text portions of this message have been removed]
            >
            >
            >
            > ------------------------------------
            >
            > Yahoo! Groups Links
            >
            >
            >
            >

            [Non-text portions of this message have been removed]
          • jeff 1
            The length of a feeder makes no difference whatsoever to the swr beyond the reduction introduced by the loss of the extra feeder. Changing the feeder length
            Message 5 of 9 , May 9 1:21 AM
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              The length of a feeder makes no difference whatsoever to the swr beyond the reduction introduced by the loss of the extra feeder. Changing the feeder length will change the complex impedance seen at the transmitter BUT all of those impedances will have the SAME vswr (small changes due to extra feeder loss excepted).

              Putting a stub in parallel is a completely different issue, but a s/c 1/4 wave, looking like an open circuit, will have zero effect *at the 1/4 wave frequency* (other than providing a dc bleed for the static, which mighty better have been implemented with a less frequency dependant resistor or inductor) .

              73
              Jeff G8HUL

              -----Original Message-----
              From: FT897@yahoogroups.com [mailto:FT897@yahoogroups.com] On Behalf Of Butch Bussen
              Sent: 09 May 2013 09:10
              To: FT897@yahoogroups.com
              Subject: Re: [FT897] SWR Problem

              Yep, and if you don't think feed line length matters on swr measurements, try feeding an antenna with 1/4, 3/4 or multiples of a quarter wave. I use to make quarter wave stubs for c b radios that ran quarter wave whips. Static electricity would wipe out fets. I put a t connector and a shorted quarter wave at 27 meg at the radio and all was well, dc ground, open at 27. '
              73
              Butch
              WA0VJR
              Node 3148
              Wallace, ks.


              On Thu, 9 May 2013, D.J.J. Ring, Jr. wrote:

              > The impedance of the antenna is transformed by the length of the coax,
              > only being correct every 180° of electrical wave length, in addition,
              > each coaxial connector introduces non-regular non-constant illenear
              > impedances (except if type N). If you are talking about 144 MHz you
              > are talking about considetable loss with RG8 mini coax, maybe 3 dB, so
              > the measured SWR will often appear better than it really is.
              >
              > Check the coupler for problems, swap it out, join the coaxes with
              > another double female, borrow spme coax, do the same thing.
              >
              > 73
              >
              > DR
              > On May 8, 2013 10:03 AM, "jamespgrove" <james@...> wrote:
              >
              >> Hi,
              >>
              >> This maybe a somewhat basic question but i am struggling to work out
              >> why i get higher SWR readings when i extend my feed line to my radio.
              >>
              >> I have a Diamond Antenna mounted on a pole on the side of my house, i
              >> have around 10m of RG8 Mini cable that feeds into the shack where my radio is.
              >>
              >> This works fine, SWR is flat as it should be.
              >>
              >> I want to use my radio in the other room so i join (using a joiner)
              >> another feed line to the existing one, the same cable same specs, i
              >> also add another using the same method, so total cable length is under 20m.
              >>
              >> However i get some higher level of SWR than i do if the radio is
              >> connected in my shack. So the additional 10m of RG8 Mini is causing the higher SWR.
              >>
              >> Can anyone point me in the direction of the problem? I have some
              >> ideas but nothing short of minor guess work, ie the cable length a loss?
              >>
              >> The SWR is not a huge problem, as its not dangerously high i was just
              >> expecting it to be flat still.
              >>
              >> Any help appreciated,
              >>
              >> Thanks
              >>
              >> Jim M6BXG
              >>
              >>
              >>
              >> ------------------------------------
              >>
              >> Yahoo! Groups Links
              >>
              >>
              >>
              >>
              >
              >
              > [Non-text portions of this message have been removed]
              >
              >
              >
              > ------------------------------------
              >
              > Yahoo! Groups Links
              >
              >
              >
              >

              [Non-text portions of this message have been removed]



              ------------------------------------

              Yahoo! Groups Links
            • Radio_Randy
              This statement is not entirely correct. If your antenna impedance is 50 ohms and the feedline has a 50 ohm impedance, the transmitter load (and SWR) will be
              Message 6 of 9 , May 10 7:38 AM
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                This statement is not entirely correct.

                If your antenna impedance is 50 ohms and the feedline has a 50 ohm impedance, the transmitter load (and SWR) will be the same, anywhere along the line, at any distance from the antenna.

                The only time that line lengths will have any effect is when the impedance at the antenna end is substantially different than the impedance of the coax. If this weren't the case, we would ALL be using precisely cut pieces of coax for each band.

                73, Radio Randy N7CKJ

                --- In FT897@yahoogroups.com, "D.J.J. Ring, Jr." <n1ea@...> wrote:
                >
                > The impedance of the antenna is transformed by the length of the coax, only
                > being correct every 180° of electrical wave length, in addition, each
                > coaxial connector introduces non-regular non-constant illenear impedances
                > (except if type N). If you are talking about 144 MHz you are talking about
                > considetable loss with RG8 mini coax, maybe 3 dB, so the measured SWR will
                > often appear better than it really is.
                >
                > Check the coupler for problems, swap it out, join the coaxes with another
                > double female, borrow spme coax, do the same thing.
                >
                > 73
                >
              • jeff 1
                I think that you missed the point of what was being said. If the load is not matched to the system impedance then the complex impedance seen at the
                Message 7 of 9 , May 11 1:51 AM
                • 0 Attachment
                  I think that you missed the point of what was being said. If the load is
                  not matched to the system impedance then the complex impedance seen at the
                  transmitter *will* vary with feeder length, BUT the *actual impedance of the
                  load* will only be seen at *at the transmitter* when the feeder length is
                  1/2 wavelength or a multiple. That of course assumes lossless coax; where
                  there is loss the impedance seen at the tx will be modified by the loss only
                  and not the electrical length at the 180 degree points. The phase of the
                  mismatch *will* change with coax length, but it will repeat every 1/2
                  wavelength.

                  The swr seen at the Tx will not vary due to electrical length, just due any
                  additional loss in the coax.

                  73
                  Jeff G8HUL


                  -----Original Message-----
                  From: FT897@yahoogroups.com [mailto:FT897@yahoogroups.com] On Behalf Of
                  Radio_Randy
                  Sent: 10 May 2013 15:38
                  To: FT897@yahoogroups.com
                  Subject: [FT897] Re: SWR Problem

                  This statement is not entirely correct.

                  If your antenna impedance is 50 ohms and the feedline has a 50 ohm
                  impedance, the transmitter load (and SWR) will be the same, anywhere along
                  the line, at any distance from the antenna.

                  The only time that line lengths will have any effect is when the impedance
                  at the antenna end is substantially different than the impedance of the
                  coax. If this weren't the case, we would ALL be using precisely cut pieces
                  of coax for each band.

                  73, Radio Randy N7CKJ

                  --- In FT897@yahoogroups.com, "D.J.J. Ring, Jr." <n1ea@...> wrote:
                  >
                  > The impedance of the antenna is transformed by the length of the coax,
                  > only being correct every 180° of electrical wave length, in addition,
                  > each coaxial connector introduces non-regular non-constant illenear
                  > impedances (except if type N). If you are talking about 144 MHz you
                  > are talking about considetable loss with RG8 mini coax, maybe 3 dB, so
                  > the measured SWR will often appear better than it really is.
                  >
                  > Check the coupler for problems, swap it out, join the coaxes with
                  > another double female, borrow spme coax, do the same thing.
                  >
                  > 73
                  >




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