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Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K1KTF, Mar 20, 2018.

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  1. K1KTF

    K1KTF Ham Member QRZ Page

    Hi Friends:

    Over the last month my SWR has been flickering when tuning regardless of the band resulting in default issues when I transmit.

    My G5RV has been hanging up there for at least 5+ years without any maintenance or review. When I took the G5RV down I noticed the insulation was worn away and some of the wire was frayed. The ladder line and coax appear to be in good condition with no exposed or worn wires. I also have been using a 4:1 Balun during the life of the G5RV with no issues.

    (So dumb question) Could the exposed wire be part of the SWR issue since it's weathered many of a storm here in New England?

    Thanks again for all your insight. 73~Steve (K1KTF)

    Attached Files:

  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Could be, it depends on the extent of the insulation damage and things like whether water is now collecting between the open insulation and the antenna wires. It's not necessary to use insulated wires in a G5RV or any similar antenna including a dipole but if you do use insulated wire then that insulation impacts antenna tuning for a given length of wire. And if the antenna is absorbing water between the wire and the cracked insulation jacket then the dielectric of that insulation is changing with weather conditions and that could definitely impact antenna tuning on dry vs wet days or even as temperature changes.

    If you otherwise like the antenna, I'd probably pull it down and replace the main antenna element wires. You could use purpose made insulated antenna wire or you could replace it with something like 14 gauge THHN or even bare wire. You might have to trim the antenna a bit if you change wire type dramatically. For instance, bare wire will typically be a few percent longer than insulated wire for the same overall tuning.

    If you're seeing dramatic and instantaneous SWR changes while transmitting then I doubt it's as simple as cracked insulation and subtle dielectric changes. I'd suspect an oxidized connection or arcing somewhere if you see sudden jumps in SWR while transmitting, but if the SWR seems to move with weather conditions then yeah, cracked insulation could be the culprit.

    Have you tried testing the antenna, one subsystem at a time? For instance try putting a dummy load out at the end of the coax where it meets the 4:1 balun. Is the SWR stable with a dummy load at the end of the coax or does it still jump around? That could indicate water ingress in the coax, one or more oxidized connectors or some other cable problem.

    Can you find a 200 ohm resistor, ideally non-inductive in the 20 watt or higher range? If so, disconnect the antenna and place it across the terminals where the balanced feed line normally connects to the balun. Then test the coax run, the 4:1 balun through to a 200 ohm load at low power. Does that give you stable SWR while transmitting at a power below the resistor's power rating? If so that part of the system checks out(at least at low power), if not perhaps you have an internal issue with the balun like water ingress or nesting bugs or other things that can cause balun troubles.

    IOW, divide an conquer when trouble shooting problems like this. Sometimes you can find intermittent connections with simple ohm meter testing but some are harder to track down, especially arcing that may only occur at full transmit power. Still if possible it can help to test out portions of the system, one at a time to eliminate possible suspects like bad coax, a bad balun or bad coax connections.

    Good luck,
  3. NH7RO

    NH7RO Ham Member QRZ Page

    If it turns out to be dead (and is not just playing possum) you could give it a decent burial as a devoted ground radial or two. Wire is wire---and if you have any vertical antenna already installed it will appreciate the additional radials (regardless of any prior life oriented horizontally).

    Rather than G5RV Rest In Peace; G5RV Rest In Pieces:)
  4. AI3V

    AI3V Ham Member QRZ Page

    No, not missing insulation or frayed wires per say, but you have either

    Water where it should not be

    A intermittent connection, either going open, or two wires touching that should not.

    Usually, but not allways, at a connector or connection.

    NH7RO likes this.

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