STL dropouts....back today

FM does it with frequency!
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Dale H. Cook
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Re: STL dropouts....back today

Post by Dale H. Cook » Mon Mar 27, 2017 9:32 am

The path profile at the upper right shows significant penetration well into the .6 Fresnel zone by terrain between Oak Grove and Crofts. That is a major concern. You need more elevation at one end or both. Increasing the elevation at the south end would have a greater effect than the same elevation increase at the north end would have.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

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kkiddkkidd
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Re: STL dropouts....back today

Post by kkiddkkidd » Mon Mar 27, 2017 11:43 am

Dale H. Cook wrote:
Sun Mar 26, 2017 10:24 am
brandonb959 wrote:
Fri Mar 24, 2017 2:45 pm
Based on a very basic earth curviture calculator I found online ...
Does that calculator allow for correct Fresnel zone clearance at 950 MHz? Your path needs to clear each obstruction by at least .6 of the first Fresnel zone radius at the distance of that obstruction.
It does 950, 2.4g, 5.8g, 3.6, 11g and others.
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Kevin C. Kidd CSRE/AMD
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kkiddkkidd
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Re: STL dropouts....back today

Post by kkiddkkidd » Mon Mar 27, 2017 12:17 pm

brandonb959 wrote:
Mon Mar 27, 2017 1:29 am
I've attached my result using the simulator posted...
Brandon,

If someone showed me this plot, I would reply, "It will probably work but will probably not be reliable due to the significant Fresnel intrusion"... And will probably be worse at certain times of the year.

I reverse engineered your endpoints and ran in on Nautel's mapper and it doesn't look as bad assuming antenna's at 135m AGL. The 60% is full clear in Nautels mapper. Did you use the exact end points or license coords?

Later,
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Kevin C. Kidd CSRE/AMD
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brandonb959
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Re: STL dropouts....back today

Post by brandonb959 » Tue Mar 28, 2017 12:17 am

The map (I assume powered by Google) had my studio and transmitter site plotted and I just put the X points right on top of each one.

I cannot raise the Tx end, but I do have room to raise the Rx end about 100-150 ft.

k4om
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Re: STL dropouts....back today

Post by k4om » Wed Mar 29, 2017 10:09 am

Something you might check when this happens is this:
http://www.dxinfocentre.com/tropo.html
Bill Hepburn has been accurate with these maps for years
and heavy tropo bending could modify your signal path
or import interfering signals from a considerable distance away.
Worth a check, It's free.


Pete K4OM

brandonb959
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Re: STL dropouts....back today

Post by brandonb959 » Wed Mar 29, 2017 3:17 pm

Wow, I like those maps. That could also explain why we in South Mississippi are always getting slammed with New Orleans stations at certain times of year.

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kkiddkkidd
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Re: STL dropouts....back today

Post by kkiddkkidd » Wed Mar 29, 2017 4:22 pm

Here in middle TN, we get analog STLs taken over by distant stations almost every spring and fall. And have interference reports (but not total takeover) almost every severe wx event.

During the dropouts, if you have a way to monitor your freq in analog at the rx end, turn off your STL tx and you may hear a distant analog STL ripping in with a strong signal for a few minutes at a time. Or if the interference is a different digital format you may see signal strength but a sound similar to squelch noise from the digital data. A spectrum anaylizer connected to a T at the receiver is a great way to look at it.

The Cavell & Mertz GE plugin might give you a head start on who is causing the interference if that is what it is. Look for BAS systems to your north on your freq pointed south(ish).

If you can determine that it is a consistent source, a polarization change might fix the problem... Or make it worse.

Good luck.
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Kevin C. Kidd CSRE/AMD
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Shane
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Re: STL dropouts....back today

Post by Shane » Thu Mar 30, 2017 11:24 pm

brandonb959 wrote:
Wed Mar 29, 2017 3:17 pm
That could also explain why we in South Mississippi are always getting slammed with New Orleans stations at certain times of year.
That would do it. You need to get an amateur radio license. You'll learn a lot about propagation.

In Iowa, 90 miles west of Des Moines we could get channel 13 off the back of the TV antenna certain times of the year but only at night. Snowy picture but watchable. (Obviously, before 2009. Probably wouldn't work at all today.)
Mike Shane, CBRE
---Omaha---

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Re: STL dropouts....back today

Post by w9wi » Fri Mar 31, 2017 6:32 am

Digital television DX is not totally impossible. (it is a lot harder than it was in analog)

I have a Silicon Dust HD Homerun network-attached ATSC tuner, and a Perl program which continuously scans all 51 (for the time being) channels. I've captured, on a couple of occasions, the MPB TV station from Bude, Mississippi about 400 miles away. Channel 6 (virtual, I forget the physical channel) from Tallahassee has also made the trip. Both (and numerous closer stations) via tropospheric propagation.

On two occasions over the years it's also caught sporadic-E propagation. KNOP-TV (North Platte, Nebraska) and KOTA-TV. (Rapid City) Both on physical channel 2. I'm 25 miles northwest of Nashville.

Back before the CBS network was delivered by satellite, we had two microwave dishes in Madison. When the signal faded on the upper one it automatically switched to the lower one. That *almost* always delivered proper reception. *Almost*.
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Doug Smith W9WI
Pleasant View, TN EM66

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