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Tropospheric ducting or scatter vertically polarized?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KJ4RZZ, May 8, 2017.

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  1. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    I'd really only used my HT on VHF to hit the local repeater up until recently, when I picked up a Kenwood 2M FM (25/65 watts) mobile. I put up a slim jim antenna at 30' which puts my radio horizon at around 8 miles. My buddy is around 28 miles away. With the low takeoff angle and high gain of the slim jim I was hoping to get some ducting or scatter or something so that we could reach each other simplex, but no luck. I can easily hit the repeaters past him, of course they are 500' tall and within my line of sight. His antenna is also only at 30' so line of sight is not possible.

    We've been trying for a long time to reach each other. We have some theories as to why we can never seem to work each other, and figured I'd ask the more experienced here for ideas:

    1) Vertical polarization... is this working against us for scatter or ducting? Should we switch to dipoles? Beams are not possible unfortunately, which is why I went to a high gain slim jim instead which is the best 2m antenna I've ever used, but still no FM DX.

    2) dead zone ... at 28 miles could I be bouncing over him? We've tried 10 meters also, but he was in the skip zone. We could both work DX but not each other.

    3) Attic antenna (I feel this is the biggest hinderance) ... his antenna is in his attic. A 1/4 ground plane vertical. He's in an HOA so it's difficult to get him to make a better antenna. I told him to get permission for a "flag pole" (slim jim antenna).

    4) Wrong time of day? I look at the VHF propagation maps, but they seem misleading since they are APRS repeaters and such. Are the signals being digipeated?

    I had a weird experience yesterday where I tried to key up a local repeater, and instead had a repeater 147 miles from me identify. Very strange but I could not do it again. I figured someone else triggered it an I was just hearing scatter.

    We only have FM VHF radios, so trying SSB isn't possible atm.

    Sorry for the rambling post.. we really need some direction.

  2. ND5Y

    ND5Y Ham Member QRZ Page

    You have that backwards. Slim Jims have high takeoff angle and low gain.
    28 miles is probably too close for tropo propagation.
  3. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    Are we referring to the same antenna?

    Last edited: May 8, 2017
  4. ND5Y

    ND5Y Ham Member QRZ Page

    Don't believe everything you read about antennas on the internet.
    K3RW likes this.
  5. KK4YWN

    KK4YWN Ham Member QRZ Page

    thats a challenging scenario. beams are the only real fix.
  6. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    okay ... but aren't we on the internet right now?
    W7ADC and WR2E like this.
  7. K8JD

    K8JD Ham Member QRZ Page

    I thought a SlimJim was just a variety of construction method for a halfwave J-pole. Still no gain since a halfwave antenna is the usual refrence for gain (0 dB). Size = gain, a longer vertical with elements in phase or a long Yagi with several parasitic elements (you say you cant have a Yagi :( )
    You need a colinear design with several half or 5/8 wave elements in a vertical antenna. These are usually made up to 20 ft tall. The other thing you need is more height, power or BOTH, to have reliable comms over 28 miles using FM..
    Good luck.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That's a bit deceiving, since a "slim jim" actually is a j-pole: A 1/2-wavelength vertical radiator with a 1/4-wavelength matching section.

    Radiation would be identical to a j-pole since electrically it is one. A large-diameter copper tubing j-pole would have more bandwidth and a tiny bit more gain but I doubt you could measure the gain change; you can measure the bandwidth change.

    More "height" for the antennas would definitely help.

    You're not "skipping over" anything on such a path.
  9. K8JD

    K8JD Ham Member QRZ Page

    Ducting effect lines up with WX fronts or where there is a temperature inversion usually over a hundred miles or so.
    Tropo or meteor scatter is a very weak signal that needs very high power, some very sensitive low noise receivers and a big gain antenna (like stacked Yagis, Not a short vertical) also over a hundred miles or more.
  10. KE4VNC

    KE4VNC Ham Member QRZ Page

    have you tried doing a plot on radio mobile? There may be a hill or something between you guys
    K0PJS likes this.

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