Propagation Distance ?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by K2WH, Jul 21, 2019.

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  1. K2WH

    K2WH Premium Subscriber Volunteer Moderator QRZ Page

    I have a new antenna, a 6 meter turnstile that seems to be doing very well but I am not sure if some of the stations I contact are via skip, line of site or ground wave.

    I know certain characteristics about skip like if there is very short skip on 6 then look at 2 meter skip.

    So since I am able to make contact with stations within a 250 mile area, my question is, what propagation mode are these contacts being made ?

    What is the shortest possible skip distance on 6 meters ?

    I think they are NOT via skip and if not, my turnstile is doing very well indeed.

    K2WH
     
    Last edited: Jul 21, 2019
  2. WB3BEL

    WB3BEL Ham Member QRZ Page

    These contacts are probably via Tropo. This weekend the CQ VHF contest is going on, and there are some really big stations operating with huge antennas and QRO.
    If you are working these super-stations over this distance, this is normal. Their station capability is making this kind of distance possible with your smaller antenna.
    Another possibility is that airplane scatter is enhancing these signals.

    If you start seeing Eskip in the ~400 mile range on 6 meters then looking for Es on 2 meters makes sense.
    You should be aware that well equipped stations can routinely work via Tropo over this kind of distance and even greater on 6 meters. If these medium distance signals you are hearing are really crushingly strong, well over S9 usually, then they may be more likely to be via the E layer, and might support even higher frequency propagation.
     
  3. KL7AJ

    KL7AJ Ham Member QRZ Page

    If there is a sporadic E cloud directly above you, you can work NVIS on 6.....basically a skip distance of Zero. You can rule out ground wave with a turnstile, as ONLY vertically polarized signals can propagate by ground wave. (Direct wave is often erroneously referred to as "ground wave" but it's not).

    Line of site can include over the horizon modes like knife-edge diffraction, inversion-layering ("miraging") and a whole catalog of rarer phenomena like troposcatter.
     
  4. K2WH

    K2WH Premium Subscriber Volunteer Moderator QRZ Page

    Over my 50 years of 2 meter DX, I am well aware of Tropo but never on 6 meters.

    Tropo needs very specific conditions and those conditions can't possibly be present on the east coast these last 2 days in which we have temps in the 90's and 100's, currently at this QTH, 95F.

    So, I would attribute these contacts to the big guns antennas.

    The way I understand Tropo, you need a sudden drop in temperature and moisture content to get enhanced propagation neither of which are present here in HOT NJ.
     
  5. WB3BEL

    WB3BEL Ham Member QRZ Page

    You are describing Tropo ducting, which can be caused by a number of conditions. The most common one is the temperature inversion kind as you mention. But any of the VHF bands can support beyond line of sight communications via what many call Tropo. This can be a mix of scattering and refraction that are not as defined as the ducting variety.
     
    AI3V likes this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Exactly.

    Tropo path losses can be greatly decreased during a temperature inversion, and of course ducts do form pretty unpredictably but the ducts rarely support 50 MHz. Sometimes, they barely support 144 MHz. I've used tropo ducts that just begin working at 222 MHz and are way better at 5.7 GHz over the same path.

    The "pineapple express" duct that forms from the U.S. west coast to Hawaii doesn't seem to ever work at six meters, but can be good at 2 meters and supports propagation into the microwave region. The KH6 end is always at a high elevation but the W6 end is usually at a much lower elevation, and being too high above sea level means you can miss it entirely. The duct is like a waveguide with walls, a floor and a ceiling.

    250 mile contacts on 6m SSB-CW-Digital are super common and there isn't a day on the calendar I can't do that from home just using 100W and a modest beam. If I had some elevation, it would be better and farther.

    "Ground wave" barely exists on 6m, but if there is any, at amateur power levels and especially using horizontal polarization, it should give out in a very, very short distance -- maybe less than a mile. Works way better at MF and using vertical polarization.
     
  7. K3XR

    K3XR Ham Member QRZ Page

    I seemed to recall your QTH, especially for New Jersey, had some elevation. From your bio page "My QTH location is on 1200 foot mountain called Bearfort Mountain in Hewitt NJ."

    Would think this plays some role in your VHF/UHF propagation.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It does, but also depends what's around you.

    My home in Mt. Olive, NJ (1978-1984) was also at 1200' asl and thankfully "nothing else" higher was close by in any direction -- so although I was 40 miles from NYC, I could look out the LR window and see the NYC skyline. It was pretty unobstructed, and the homesite was selected exactly for that.

    Turns out that was a bad decision with respect to the snow and weather, though. Much worse than the lower places, most of the time.

    There were some VHF-UHF ducts that were over my head, even there. I could tell because stations on hilltops in New England were working stations on hilltops in West Virginia and I couldn't participate -- sigs very weak and not enhanced by the duct. So, one time I just took the station mobile with an 8 element "Hi-Par Hilltopper" portable 2m beam and drove up to High Point, at 1800' and only about 45 mins away. That was "in" the duct! Now, signals from both ends of the duct were very strong and I could work into NC, Tennessee and other places 400 miles away as long as they were also on hilltops and "in" the duct.

    It's exciting, but can sure be some work!
     
    K3XR likes this.
  9. W6RZ

    W6RZ Premium Subscriber QRZ Page

    100% incorrect.
     
  10. ND6M

    ND6M Ham Member QRZ Page

    100% correct, there is no NVIS @ 50 MHz.
     

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