Tropospheric scatter thread

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KK4YWN, Nov 8, 2014.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: abrind-2
ad: Left-3
ad: Subscribe
ad: L-MFJ
ad: Left-2
  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think it's not only probable, but explains most of the very solid and repeatable contacts many VHF-UHF-SHF'ers make over 200-300-400 mile paths using amateur power levels and good antennas.

    I can work over to Phoenix (400 mi) or up to the Bay Area (350 miles) "any old time" on 70cm, just running 200W and four Yagis (with the other guy doing about the same)...repeatedly, every day. That's w-a-a-a-a-y over the horizon, and it's not a duct because when we're lucky enough to catch a duct, signals go from S1 to S9+ very quickly and stay that way until the duct fizzles out. Almost every experienced VHF-UHF guy I know can do the same kind of thing.

    Now, many can also work meteor scatter every single day, and those path losses are worse. It doesn't take huge power or huge antennas, it takes knowing how to do it, and with lower power can be achieved using a weak signal digital mode that keeps trying until the contacts are completed (like FSK441). Prior to that, I worked m.s. literally every evening (or very early morning) on 6m by running 1500W to four 5-L beams, or on 2m running 1500W to four 21-L beams using SSB (and talking fast!) and so did everybody else who wanted to do this and was similarly equipped -- which is an awful lot of stations! The m.s. contacts were usually in the 500-900 mile range, sometimes a bit more.
     
  2. KK4YWN

    KK4YWN Ham Member QRZ Page

    I'm ok with what you are saying. It makes total sense. High gain antennas and lots of power = potential from troposcatter.

    My point of contention is with the frequency at which hams claim to use troposcatter. Especially when talking about repeaters.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If by "repeaters" they mean conventional FM repeaters which are typically 100W output to an omni vertical and use nonlinear detection such that you can't even tell if somebody's there until the signal is about 12 dB quieting in about a 12 kHz bandwidth...I agree that doesn't sound very likely at all.

    My experience with tropo scatter is it works on 2m, but often works "better" as you go up the spectrum to several GHz -- using the same path, at the same time, with similar "e.r.p." levels on the bands. And it doesn't take high power for a narrow bandwidth mode and very good receivers, 10W to a 36" dish on 5.7 GHz works. That what most of our local "rover" stations use, and make 200 mile contacts all the time with that over some mountainous paths.
     
  4. K0RGR

    K0RGR Premium Subscriber QRZ Page

    Here's a video of a buddy of mine who's a local VHF DXer. He does have a moonbounce array, but in this demo, he's using a single yagi. The first part of the video shows him receiving an 8 watt beacon near Chicago. Get your map out, and look at the distance between Chicago and Rochester MN. Then remember that this beacon is 8 watts at a distance of over 200 miles of flat prairie. It's readable here on a single yagi most of the time, except when a weather front comes through. http://www.youtube.com/watch?v=POyXfy-qxAw The rest of the video is him making an aurora contact using his big antenna...

    A coverage radius of about 300 miles is pretty typical. There is also often an 'overwater' path from here to eastern Michigan, Ontario, and New York. I guess Wisconsin is swampy enough that it works like water. That often resembles ducting more than scatter, with much stronger signals as you go higher in frequency.

    We also get tropo ducting here, usually when the ground is very cold and a warm front moves in to create an inversion layer, with colder air trapped under the incoming warm air. Those ducts can be amazing, and are usually heard on FM repeaters first. I've worked Kansas City (350 mi.) from here several times through their 146.82 repeater, and I sometimes check into the Rockford, IL net on 147.255. Those are ducts, not scatter.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Well, you know if it walks like a duct and looks like a duct...

    Seriously, though, I invented some adhesive tape to keep these going when they try to fall apart. Yeah, it became famous and is now known as "duct tape," but now everyone knows where it started.:eek:
     
  6. KG5RZ

    KG5RZ Ham Member QRZ Page

    AN/TRC-80B Tropospheric Scatter Radio Terminal Set

    [​IMG]

    4.4 to 5 ghz at 1000 watts into an 8 foot inflatable parabolic. Longest usable tropo shot I was a part of was a little over 300 miles. Average was about 100 miles.
     
  7. KK4YWN

    KK4YWN Ham Member QRZ Page

    thats probably a wide-band setup.

    who doesn't want an inflatable parabolic though?
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Sure, the military does stuff on a big scale. Some hams do also, but most of us can't.

    And they probably go for 99% or 100% readability on a link, and it's likely not CW. Hams don't have such restrictions.

    I can deal with 20% readability, and using 100 Hz bandwidth filters, and CW.:eek:

    Maybe that's why they call it "amateur" radio, and I'm fine with that.
     
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    I might mention that while White Alice was severely criticized because of its cost overruns (actually underestimates), it was extremely successful and appreciated by all parties involved. There WAS no competing system of any kind at the type. It was probably largely responsible for Alaska eventually becoming sorta semi civilized.
     
  10. W1VT

    W1VT Ham Member QRZ Page

    I run 3 watts and an 18 inch DSS dish on 10GHz--assuming a similar station on the other end--the allowable path loss is around 250 dB.

    This is more than enough to exceed the troposcatter range of a 150W 2M SSB station using a 4 element Yagi.

    In practice, from a popular beach parking lot in Southern Connecticut (perhaps 20 ft ASL), I can work many mountaintops within a 200 mile range.

    Why go there? I can drive there in less than an hour and set up in another 15 minutes. There isn't any convenient mountaintop that allows such a short drive and setup time from my home. There is also a great seafood place open year round just 5 minutes away :D

    The downside is that most of my contacts are weak troposcatter contacts. I have the skills to deal with this, but a less experienced operators may find this frustrating--for them, spending another two hours to get to the top of a good mountaintop may make more sense as that they can gain experience with frequency offset and antenna pointing issues using really strong signals.

    Zack W1VT
     
    Last edited: Nov 11, 2014
Thread Status:
Not open for further replies.

Share This Page