STL dropouts....back today

FM does it with frequency!
brandonb959
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STL dropouts....back today

Post by brandonb959 » Thu Mar 09, 2017 3:54 pm

I think I posted about this a couple of years back. We have two 950 Moseley Starlink systems on the same path about a 20 mile hop. We have the Crescend 10 watt amps on the studio end, and we also have the big 6' Mark Grid antennas on both ends. On paper there are no issues with the separation in frequency, I had a consulting engineer look at that. Off the top of my head I think one is 950.0 and one is 951.5 or similar.

But anyway, we've been dealing with dropouts in the morning hours at certain times of year, it seems like most often in March, April, May. Originally, one system was vertical and the other was horizontal. The horizontal was always the most sensitive to dropping out, so we had a tower crew repolarize that system vertically and re-peak both ends, (we even have the stabilizer arms!!) Previous to today we had not had any real issue with this system in about a year and a half, but today both were dropping out simultaneously around 5-7am central time. One of these receivers typically reads about -58 and the other around -59 or 60.

So my question is what in the world else can we do? Does someone make an in-line booster that could go on the receive end that would push more signal into the receiver to keep us above the threshold on these bizarre mornings? Thanks!

jammerdave
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Re: STL dropouts....back today

Post by jammerdave » Thu Mar 09, 2017 4:04 pm

A booster may not help, and may actually hurt you. You have plenty of signal. It could be that there is another signal(s) that is ducting in at times, or some sort of local area temperature inversion layer may also be a culprit. If a non-same digital signal or an analog signal ducted in, it would essentially mute your receivers. A spectrum analyzer on the receive antenna with your own transmitter shut off may reveal a culprit.
brandonb959 wrote:
Thu Mar 09, 2017 3:54 pm
I think I posted about this a couple of years back. We have two 950 Moseley Starlink systems on the same path about a 20 mile hop. We have the Crescend 10 watt amps on the studio end, and we also have the big 6' Mark Grid antennas on both ends. On paper there are no issues with the separation in frequency, I had a consulting engineer look at that. Off the top of my head I think one is 950.0 and one is 951.5 or similar.

But anyway, we've been dealing with dropouts in the morning hours at certain times of year, it seems like most often in March, April, May. Originally, one system was vertical and the other was horizontal. The horizontal was always the most sensitive to dropping out, so we had a tower crew repolarize that system vertically and re-peak both ends, (we even have the stabilizer arms!!) Previous to today we had not had any real issue with this system in about a year and a half, but today both were dropping out simultaneously around 5-7am central time. One of these receivers typically reads about -58 and the other around -59 or 60.

So my question is what in the world else can we do? Does someone make an in-line booster that could go on the receive end that would push more signal into the receiver to keep us above the threshold on these bizarre mornings? Thanks!

grich
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Re: STL dropouts....back today

Post by grich » Thu Mar 09, 2017 5:19 pm

Happens with our TV STL a few times a year, and at about the same times you list.

The only thing you could do is get a second antenna in the spot the ducting forces the signal to. The telco folks have designed space-diversity into many of their MW systems for years...a second dish is mounted a specific distance below the main dish.

http://www.burnsmcd.com/insightsnews/in ... ty-that-is

Here's a link that has some more information.

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Deep Thought
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Re: STL dropouts....back today

Post by Deep Thought » Thu Mar 09, 2017 5:48 pm

I'm pretty sure that was suggested last time we discussed it.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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jantonuk
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Re: STL dropouts....back today

Post by jantonuk » Thu Mar 09, 2017 6:37 pm

A couple of years ago I had to put a 950 pass filter on such a link to get rid of LTE.... just sayin'

brandonb959
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Re: STL dropouts....back today

Post by brandonb959 » Fri Mar 10, 2017 3:09 pm

We have one of those 950 bandpass filters from Moseley and it has historically still dropped out with it in line. I stopped by the site last night and the signal was as always excellent. I did change the Attenuator setting on the Receiver to "OFF" rather than automatic. According to the manual:

"OFF: This mode disables the attenuator completely. Use this mode if strong
bursty interfering signals are sporadically triggering the attenuator leveling control
and causing errors (this is a fairly low likelihood)."

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jakebechtold
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Re: STL dropouts....back today

Post by jakebechtold » Sun Mar 12, 2017 1:54 am

We have one STL path that is roughly 25 miles in length, and also had similar issues with a Moseley Starlink. We tried different filters, different amplifiers, different frequencies, and different gear. We finally concluded that the path was getting some weird ducting/inversion, in particular in the spring when the humidity would vary drastically through the day (a good part of this path followed a major river in the area). When one of the two FM's at this site the Starlink was feeding moved to a different site, we converted it to composite and we haven't had an issue since.

So, me thinks you have an issue with the path. You mentioned the frequency separation is good... has anyone confirmed that? As jammerdave suggests I would take a spectrum analyzer to both ends and verify there isn't something operating on a rouge frequency close to your licensed STL frequency. It might also be worth shutting off your station transmitter and see if the issue occurs with it off.

I would also draw out the path on a map and see if there are any large bodies of water, or any factories or plants that could produce wild temperature/moisture swings in the air.

If you've exhausted both of those, I would take a serious look at an STL change. Don't know if composite is an option for you or not. Otherwise I would look at T1 or Internet services. While I am a huge fan of digital everything, sometime ol' analog is the better choice for the job.
Jake Bechtold, CBT, CBNT
Assistant Engineer, Radio FM Media
Fargo, ND
KDØTGA
@jakebechtold

W2XJ
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Re: STL dropouts....back today

Post by W2XJ » Thu Mar 16, 2017 10:48 pm

Get off 950 and move to 6 or 11 gig.

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Shane
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Re: STL dropouts....back today

Post by Shane » Sat Mar 18, 2017 1:15 pm

Make more room for the rest of us. ;)
Mike Shane, CBRE
---Omaha---

brandonb959
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Re: STL dropouts....back today

Post by brandonb959 » Fri Mar 24, 2017 2:45 pm

So, more thinking on this. Perhaps we don't have enough antenna height on the receive end.

STL transmit antenna site 97.5 M =319.88 ft sea level? + approx. 170 ft of antenna height

STL receive antenna site 73.0 M =239.501 ft sea level? + approx. 250 ft of antenna height

Distance is approximately 30 miles.

Based on a very basic earth curviture calculator I found online, the hidden heighth on the receive tower would be 131 feet (assuming all things equal) and once you calculate the difference in sea level, @250 ft the receive antenna would be just 38ft above the horizon? Would this make it susceptible to fog, which is the typical culprit?

I think that i have room to move this antenna another 100ft up the tower, I just need to add on to the line. Do you all think this might be worthwhile?

rfn
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Re: STL dropouts....back today

Post by rfn » Sat Mar 25, 2017 6:12 pm

Is there any body of water between the transmit and receive points?

I've never had fog cause the kind of problem you describe but I have had temperature conditions create a sort of "lens" above a small lake that caused what you describe. Moving up might get you above it but, oddly enough, moving down just a bit might be equally as effective.

brandonb959
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Re: STL dropouts....back today

Post by brandonb959 » Sat Mar 25, 2017 7:50 pm

There are no large lakes between the two sites, there are some creeks, etc.. We shoot from our studio to 3 different transmitter sites and this is the only site that experiences issues. The other two sites receive dishes are higher than the studio, this one is lower.

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kkiddkkidd
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Re: STL dropouts....back today

Post by kkiddkkidd » Sun Mar 26, 2017 8:21 am

brandonb959 wrote:
Sat Mar 25, 2017 7:50 pm
There are no large lakes between the two sites, there are some creeks, etc.. We shoot from our studio to 3 different transmitter sites and this is the only site that experiences issues. The other two sites receive dishes are higher than the studio, this one is lower.
I think that it has been suggested before but have you done a path study on all 3 paths? Is the path clear (including the Fresnel at 950)?

https://airlink.ubnt.com/#/

Is a pretty good calculator/mapper and will show if you have Fresnel zone problems.

Later,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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Dale H. Cook
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Re: STL dropouts....back today

Post by Dale H. Cook » 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.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

brandonb959
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Re: STL dropouts....back today

Post by brandonb959 » Mon Mar 27, 2017 1:29 am

I've attached my result using the simulator posted...
Attachments
RockStlpathcurrent.jpg

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