Tropospheric Ducting still happening?

[jeffbyk]

I was wondering if we are still seeing abnormally high reception levels due to tropospheric ducting.  I am curious because I just tried an RS UHF only Yagi and am having great results with it.

My E86 receiver was out of commission for awhile when everyone started posting messages of spectacular reception, so I am not sure if these conditions still exist at some level.

I am now able to get all of the networks from Chicago stations with signal levels above 90 (many are at 100) and even with the Yagi pointed to Chicago, I can get Channel 4 digital at 70-100 and CBS58 Digital at about 58 (I can always throw a switch and revert back to my RS Double-Bow tie and get CBS 58 above 90).

Am I done experimenting, or should I expect serious degradation over the winter months?

Jeff

[Gregg Lengling]

I guess a little explanation of Tropospheric ducting is in order.  I am a wireless communications engineer and we have to plan for disruptions in service caused by this.  Yeah most people such as TV watchers and ham radio operators love the stuff because it allows them to receive signals that are normally beyond their reach.

Tropospheric Ducting is a very apt description of what actually occurs.  Being near Lake Michigan makes it all the more interesting because it is more frequent when you have a cold body of water to play with.  What happens is during certain weather formations you get a warm layer of air trapped between 2 cold layers.  IE:  The upper regions are very cold and you have Lake Michigan at 40 some degrees (during the height of summer, the higher water temps only occur near the shore line).  In between you have a warmer layer of air.  What this becomes is like a Wave Guide (wave guide is used at microwave frequencies, it is basically a hollow retangular tube that the microwaves are conducted to or from the antenna feed horn), this creates a great medium for Radio Frequency Waves (it's call radio but could be any format, tv, radio whatever) to bounce back and forth with little or no loss of signal power.  This is how the distant signals make it from places like Chicago up to Port Washington or even farther.  (The longest distance I've done 2 way communications on VHF/UHF frequencies use ducting is over 1500 miles so it moves well and that was signals with less than 10 watts of RF power).

This is very common late in summer when fronts come through.  With the lake added in it occurs anytime the air tempature is a good variant higher than the ground temp.

Well that's the laymen's dialogue so that I'm not talking over anyones head.

Hope that helps.  So to answer you question, ducting is most prevalent in our area in late July, all August, and early September.....BUT....it can happen anytime the conditions occur.  The more pronouced the difference in temperature the higher the MUF (maximum usable frequency) is.  So mild ducting will affect the VHF stations before the UHF.  It's really hot when you start receiving stations in the 50's and 60's like we did about 3 weeks ago.

Enjoy HDTV...and spread the word.....


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Gregg R. Lengling
RCA P61310 61" 16x9
glengling@ameritech.net

[ReesR]

wonderful explanation Gregg!

And yes, because it's warmer today we have the necessary conditions and hence your seeing better coverage areas.

Enjoy it.  And yes, spread the word.



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Rees Roberts
Racine, WI
reesr@wi.net

HDTV Receiver:  Sony KD-34XBR2
Bi-directional Yagi Antenna at 30 feet

[jeffbyk]

Thanks Gregg and Rees for the explanation.  I guess a more specific question would be is whether or not people are experiencing today and yesterday abnormal levels of reception.  I now understand the theory, but now I am seeking hard data.

Anyone else noticing a difference today and yesterday?

By the way, Rees, thanks for the guidance with the preamp!  It made a world of difference in my case.

Jeff

[Tom Snyder]

Getting 90's on the local channels tonight, and nada on the Chicago stations I can usually pick up when conditions are right...