Tropospheric scatter thread

In the interest of propagating knowledge, let's open discussion about tropospheric scatter.

I have doubts about its usability on ham bands. But I am a reasonable man and open to new data. Unfortunately, I haven't found much on the net about troposcatter and what little I have found has been of poor quality.

What I know:
Wavefronts strike airborne obstructions and disperse portions of RF into different directions.

The amount of dispersed power is weak and incoherent (pieces of wavefront splattering different directions).

Path loss calculators with ham gear predict > -200db of attenuation. This appears to be slightly better than EME path loss, so I'm warming up to the possibility.

Gub'ment used tropospheric scatter (ts) with gigantic antennas and lots of power. One might (falsely) assume (guilty party right here) that all this equipment and expense is required for a ts circuit to work. But when we look at the bandwidths used by gub'ment and hams, we should easily why gub'ment needs so much power. Hams use very very small amounts of bandwidth. SNR is more manageable.

Antenna polarity appears to play an import role in ts circuits. Every ts system I've found employs diversity: horizontal and vertical polarization.

Ever the skeptic, I'm curious to know how anyone can know they are using ts. Are there traits to listen for?

How does one find ts signals? Are antennas swept in both azimuth and elevation?

I'd surely like to hear from someone who intentionally built a station to take advantage of ts. I think we'd all be interested to know what decisions were made in the design of the station, and would equipment is considered essential for a newcomer interested in ts.

 

Most serious VHF stations take advantage of troposcatter. I used to regularly rag chew into NE, Chicago, MO etc with other large stations. High power helps but on VHF antenna gain and the terrain makes a huge difference. From my location in EN24gp everything slopes away from me for miles and it is flat terrain. Makes for a good ground gain multiplier. 160 watts to a pair of 2m5wl's(17 elements, 31 foot booms) on a fiberglass cross boom at 35 feet worked very very well. Sunday nights I often checked into the Lincoln NE 2 meter net when I was net control here in MN, we had net at the same time and when I point SW several of them would check in. 325 miles or so. Same for checking into nets in Chicago and a few others I can't remember.

 

Isn't that tropospheric ducting or bending? Is that not different that tropo-scatter?

Danny, W0JMP

 

Thank you for mentioning ground gain. I found a very interesting report on it here:
http://www.vk3um.com/Ground Gain_DUBUS 3-2011_ON4KHG.pdf

Good reading for anyone interested in max performance at vhf.

 

This was during during times of poor band conditions for ducting. Ducting is only present during certain weather conditions. Sure there is local enhancement but it stops at around 100 miles or so. Like tonight I am listening to a repeater from Minneapolis 120 miles away. Would conditions support easy contacts beyond that? Probably not with low pressure and snow moving in

 

I'm kinda doubtful that a repeater has the antenna gain or power output required to use troposcatter. The path losses are quite high. As I've said before: I think troposcatter sounds sexy to a lot of hams.

 

Tropospheric forward scatter is used by VHF-UHF-SHF amateurs every day. Remember, using CW or WS digi modes, S/N only needs to be a dB or two for actual communications (unlike most commercial/military applications where they strive for much more than that).

First good, relevant article I can recall reading about this was: http://www.arrl.org/files/file/History/History of QST Volume 1 - Technology/QS03-57-Morgan_opt.pdf

More detail: http://www.tpub.com/neets/book10/40k.htm

Report on government-sponsored testing, including results using TX power of 30W at 5 GHz: http://www.dtic.mil/dtic/tr/fulltext/u2/a237012.pdf

 

Well, again, if we look at the path loss, very few stations are setup for troposcatter. The last article describes a 29' dish antenna. Gobs and gobs of gain. The first article mentions 200 watts and 10db gain antennas for a fairly short link.

Troposcatter is possible. I just don't think its probable.

 

Here in Alaska, the White Alice troposcatter system was our link to the rest of the universe. It did require vast gobs of power and antenna gain, but it was very reliable for a couple of decades.

I suspect it might be "hamworthy" with some of our new DSP methods.

p.s. to a few comments.....Tropscatter is INDEED very different from ducting....and vastly more lossy. But it's always there....so might be a worthy tradeoff!

 

http://en.wikipedia.org/wiki/White_Alice_Communications_System