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Lo Z antenna socket

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  • Gerry Tweedie
    I ve just been glancing thru my 394 manual and was surprised to see that it advises that you use the HI z input for a random wire antenna.I ve been using the
    Message 1 of 8 , Dec 1, 2008
      I've just been glancing thru' my 394 manual and was surprised to see
      that it advises that you use the HI z input for a random wire
      antenna.I've been using the LO z input for a couple of years now with
      no problems,so I tried a swap.Performance dropped significantly,so I
      re-read the manual.Sure enough,if using a dipole it recommended the LO
      Z as the one to use,and the HI Z for the long wire.Attenuator switch
      is set to '0'.Seems I've been using the wrong input all this time.Can
      anyone clarify this for me?
    • Tom Holden
      That s the problem with generalisations, Gerry. Any antenna of a length that is a multiple of a quarter wavelength will be resonant at the corresponding
      Message 2 of 8 , Dec 1, 2008
        That's the problem with generalisations, Gerry. Any antenna of a length that is a multiple of a quarter wavelength will be resonant at the corresponding frequencies (capacitive and inductive reactances equal in magnitude and mutually cancelling) and have a relatively low resistive impedance. At the intermediate frequencies it will have a strongly reactive and much higher impedance. Where the antenna has a high impedance, the Lo-Z input will load it down moreso than the Hi-Z input and the radio/antenna system will seem less sensitive (lower S-reading). Where the antenna has low impedance, you'll see little difference. A dipole antenna will have an impedance around 50-70 ohms at its resonant frequencies but one cut for 40 meters will be resonant only around 7MHz and 21MHz.

        So then why use the Lo-Z at all? This gets a bit complicated:
        a) Only the Lo-Z input has the switchable attenuator
        b) Only the Lo-Z input has the VHF anti-image filter
        c) External devices such as preselectors, BCB filters, Low-pass filters, antenna tuners are most commonly designed for 50-75 Ohm loads
        d) Higher output from the antenna does not mean a more readable signal because terrestrial and galactic noise levels are higher than the receiver's own noise figure.
        e) Too much output from the antenna overloads the receiver.

        Why use the Hi-Z at all?
        a) Very short antennas have a high reactive impedance and output into 50Ohms may be so low as to warrant switching to the Hi-Z input, viz. the telescoping whip is attached to the Hi-Z input.
        b) Multiple receivers may be bridged across one antenna source using the Hi-Z input on all but one. Not generally a good idea because the tuning of one will affect levels into the others but works in a pinch.

        Some have found interesting effects by connecting the antenna to both inputs and switching to either one or both. In some instances, the dual connection provided higher signal levels than either one alone; in others worse.

        Connecting a different antenna to each input can provide some additional interesting and potentially useful effects, e.g., a change in directionality from either antenna alone may reduce noise or interference relative to the signal. This might become adjustable with some sort of phasing network in either or both the Lo-Z and Hi-Z legs.

        That's all I can think of at the moment.

        73, Tom

        ----- Original Message -----
        From: Gerry Tweedie
        To: RADIOSHACKDX394@yahoogroups.com
        Sent: Monday, December 01, 2008 4:20 PM
        Subject: [RADIOSHACKDX394] Lo Z antenna socket


        I've just been glancing thru' my 394 manual and was surprised to see
        that it advises that you use the HI z input for a random wire
        antenna.I've been using the LO z input for a couple of years now with
        no problems,so I tried a swap.Performance dropped significantly,so I
        re-read the manual.Sure enough,if using a dipole it recommended the LO
        Z as the one to use,and the HI Z for the long wire.Attenuator switch
        is set to '0'.Seems I've been using the wrong input all this time.Can
        anyone clarify this for me?





        [Non-text portions of this message have been removed]
      • Joseph and Mary Dubin
        Hi Gerry, I have a random length wire connected to each terminal. The approximate 50 foot one, used in conjunction with an amplified pre-selector, is
        Message 3 of 8 , Dec 1, 2008
          Hi Gerry,

          I have a random length wire connected to each terminal. The approximate 50 foot one, used in conjunction with an amplified pre-selector, is attached to the high-z and a stand alone shorter one (maybe 35 feet) is attached to the low-z. The shorter wire on low-z goes down instead of across (like the longer one).

          Began experimenting with both terminal connections about a half a year ago. At times the extra connection does little to enhance a transmission (signal just remains the same) but quite often it helps to clear up a little noise and provides added strength to weaker signals and DX. Most notable is it's ability to draw in more SSB, especially on 80 meters.

          73's
          Joe
        • William Barrett
          It may be well worth your driving an actual ground rod and using it to ground the radio case. Personally, I wouldn t go through it if it meant a large amount
          Message 4 of 8 , Dec 1, 2008
            It may be well worth your driving an actual ground rod
            and using it to ground the radio case. Personally, I wouldn't
            go through it if it meant a large amount of work or expense,
            but in those cases where antenna re-jiggering lessens noise,
            this is an indicator that an "RF-Quiet" ground will be helpful.

            It can never hurt, no matter what. In my case an RF-Quiet
            ground made everything work a little better, and some
            things a lot better.

            The building's own electrical ground is for safety, and not
            really engineered for RF purposes, which is why a seperate
            driven rod is usually quieter.

            RF grounding is a far more subtle subject than is generally
            realized.

            73,
            KW1B


            ----- Original Message -----
            From: "Joseph and Mary Dubin" <mjgardenia@...>
            To: <RADIOSHACKDX394@yahoogroups.com>
            Sent: Monday, December 01, 2008 9:58 PM
            Subject: Re: [RADIOSHACKDX394] Lo Z antenna socket


            > Hi Gerry,
            >
            > I have a random length wire connected to each terminal. The approximate
            50 foot one, used in conjunction with an amplified pre-selector, is
            attached to the high-z and a stand alone shorter one (maybe 35 feet) is
            attached to the low-z. The shorter wire on low-z goes down instead of
            across (like the longer one).
            >
            > Began experimenting with both terminal connections about a half a year
            ago. At times the extra connection does little to enhance a transmission
            (signal just remains the same) but quite often it helps to clear up a little
            noise and provides added strength to weaker signals and DX. Most notable is
            it's ability to draw in more SSB, especially on 80 meters.
            >
            > 73's
            > Joe
            >
            >
            >
            > ------------------------------------
            >
            > Trim all but the core of this message when replying to keep replies from
            mushrooming in size.
            > For archives of prior messages, files, links, photos, user survey, members
            info, etc., visit our group on the WWW.Yahoo! Groups Links
            >
            >
            >
            >
            >
            >
          • Joseph and Mary Dubin
            Hi Bill, I was actually told that the second wire actually like a ground which explains why the noise level drops on some stations. Can t drive it into the
            Message 5 of 8 , Dec 1, 2008
              Hi Bill,

              I was actually told that the second wire actually like a ground which explains why the noise level drops on some stations. Can't drive it into the earth since we live in an apartment building but I do have thick coaxil wire attached to the electrical socket from the 394's ground terminal anyway.

              73's
              Joe
            • William Barrett
              You know the old one, cited in so many old-timey bits of advice on shortwave: a cold water pipe. Hot is only slightly less preferred---they usually go to the
              Message 6 of 8 , Dec 2, 2008
                You know the old one, cited in so many old-timey bits
                of advice on shortwave: a cold water pipe. Hot is only
                slightly less preferred---they usually go to the same places.

                Of course, in houses with all plastic pipe, no joy. The
                idea is the cold water pipes find an Earth ground a little
                sooner than the hot water pipes--but of course, only
                copper counts at all. ;-)

                73,
                KW1B

                ----- Original Message -----
                From: "Joseph and Mary Dubin" <mjgardenia@...>
                To: <RADIOSHACKDX394@yahoogroups.com>
                Sent: Monday, December 01, 2008 10:32 PM
                Subject: Re: [RADIOSHACKDX394] Lo Z antenna socket


                > Hi Bill,
                >
                > I was actually told that the second wire actually like a ground which
                explains why the noise level drops on some stations. Can't drive it into
                the earth since we live in an apartment building but I do have thick coaxil
                wire attached to the electrical socket from the 394's ground terminal
                anyway.
                >
                > 73's
                > Joe
                >
                >
                >
                > ------------------------------------
                >
                > Trim all but the core of this message when replying to keep replies from
                mushrooming in size.
                > For archives of prior messages, files, links, photos, user survey, members
                info, etc., visit our group on the WWW.Yahoo! Groups Links
                >
                >
                >
                >
                >
                >
              • Gerry Tweedie
                ... Ok guys,I ve read all this and although some of it is over my head,I ve gleaned that a good earth is probably the most important.I ll need to find a way of
                Message 7 of 8 , Dec 3, 2008
                  --- In RADIOSHACKDX394@yahoogroups.com, "William Barrett" <bill@...> wrote

                  Ok guys,I've read all this and although some of it is over my
                  head,I've gleaned that a good earth is probably the most
                  important.I'll need to find a way of doing this properly tho' as it
                  will involve a bit of work.
                  I should have added in my OP that there is an ATU in circuit as
                  well,but I still didn't find any difference when I bypassed this.I
                  think I'll leave well alone for now but as I said,I'm pulling stations
                  in quite well.We'll see what difference a good earth will make tho'
                  knowing my luck,it'll probably be nowt!Thanx for the input.
                • William Barrett
                  If you need a low-profile solution, even if you re on the second floor or higher, run a light wire---yes, heavy is better, but we re talkin low-profile---out
                  Message 8 of 8 , Dec 3, 2008
                    If you need a low-profile solution, even if you're on
                    the second floor or higher, run a light wire---yes,
                    heavy is better, but we're talkin' low-profile---out a
                    window and straight down the side of the building
                    to a short rod driven right there. Angle the rod away
                    from the building as is possible. Again, "long" is good;
                    as long as one can manage, even if it's only a foot or two,
                    will be an improvement,

                    73,
                    KW1B


                    ----- Original Message -----
                    From: "Gerry Tweedie" <gerrytweedie@...>
                    To: <RADIOSHACKDX394@yahoogroups.com>
                    Sent: Wednesday, December 03, 2008 8:29 AM
                    Subject: [RADIOSHACKDX394] Re: Lo Z antenna socket


                    > --- In RADIOSHACKDX394@yahoogroups.com, "William Barrett" <bill@...> wrote
                    >
                    > Ok guys,I've read all this and although some of it is over my
                    > head,I've gleaned that a good earth is probably the most
                    > important.I'll need to find a way of doing this properly tho' as it
                    > will involve a bit of work.
                    > I should have added in my OP that there is an ATU in circuit as
                    > well,but I still didn't find any difference when I bypassed this.I
                    > think I'll leave well alone for now but as I said,I'm pulling stations
                    > in quite well.We'll see what difference a good earth will make tho'
                    > knowing my luck,it'll probably be nowt!Thanx for the input.
                    >
                    >
                    >
                    > ------------------------------------
                    >
                    > Trim all but the core of this message when replying to keep replies from
                    mushrooming in size.
                    > For archives of prior messages, files, links, photos, user survey, members
                    info, etc., visit our group on the WWW.Yahoo! Groups Links
                    >
                    >
                    >
                    >
                    >
                    >
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