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Author Topic: RF problems in new HS stadium install  (Read 7825 times)

David Buckley

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Re: RF problems in new HS stadium install
« Reply #20 on: September 12, 2016, 05:27:05 pm »

STL (studio-transmitter links) like the Marti are licensed operations with strict power limits, frequency assignment, and transmitter location. They should be used with tuned, highly directional antennas (usually Yagi type) pointing directly at the receiver site. If the operator is using an omni antenna and blasting full power to reach the receiver, this must be corrected or your problems will continue.

What you say is true for a STL, but this isn't a STL link, its an OB link.  OB links are usually licenced over an area, because the remote box could be anywhere.   Ours is licensed to transmit anywhere in our state, which is a far larger area than a Marti could ever cover!



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Denn Cimo

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Re: RF problems in new HS stadium install
« Reply #21 on: September 12, 2016, 06:41:29 pm »

STL (studio-transmitter links) like the Marti are licensed operations with strict power limits, frequency assignment, and transmitter location. They should be used with tuned, highly directional antennas (usually Yagi type) pointing directly at the receiver site. If the operator is using an omni antenna and blasting full power to reach the receiver, this must be corrected or your problems will continue.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Thanks so much for the input.. They are definitely using a yagi and are likely pointing in the direction of the receiver site.   I just found the public record of their FCC license for that frequency (161.640.) The station class is:Mobile (probably similar to what David said their license was for)   They are licensed for 30Watts of output power.
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Scott Holtzman

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Re: RF problems in new HS stadium install
« Reply #22 on: September 12, 2016, 06:57:58 pm »

Thanks so much for the input.. They are definitely using a yagi and are likely pointing in the direction of the receiver site.   I just found the public record of their FCC license for that frequency (161.640.) The station class is:Mobile (probably similar to what David said their license was for)   They are licensed for 30Watts of output power.

30W of output power? I would think that would be ERP.

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Scott AKA "Skyking" Holtzman

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Jason Glass

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Re: RF problems in new HS stadium install
« Reply #23 on: September 12, 2016, 07:14:22 pm »

30W of output power? I would think that would be ERP.
I'm with Scott on this. If their licensed power is specified in ERP, it means that the amp should be outputting just under 2W (33 dBm) to a 14dBd Yagi for compliance.

See https://apps.fcc.gov/kdb/GetAttachment.html?id=fzlsGm%2Fe68Ymx58IAmzNbw%3D%3D&desc=412172%20D01%20Determining%20ERP%20and%20EIRP%20v01r01&tracking_number=47469

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Denn Cimo

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Re: RF problems in new HS stadium install
« Reply #24 on: September 13, 2016, 08:41:58 am »

30W of output power? I would think that would be ERP.

License shows 30.000 output power. The maximum ERP column on the license is blank (no entry). This license was originally granted in 1964. My guess is that back then a maximum ERP field was not required by the FCC. From what I understand, unless the license is modified, the information on the license is not required to be updated.
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Denn Cimo

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Re: RF problems in new HS stadium install
« Reply #25 on: September 19, 2016, 10:25:11 am »

Please let us know what you eventually find is the cause and solution.
Wanted to provide an update to everyone who took the time to respond to my post. I did get some data with my RF explorer. I am attaching a couple of screenshots that I feel are the most relevant. Two Scans from 100MHz to 700MHz.  Both are after the game on Friday night and from the perspective of our wide band paddle antenna.  The first is after everyone else except for the AM station had turned their equipment off. The AM crew was interviewing a coach and were the only ones left in the press box. I waited until they turned their Marti off and took another reading. So the difference between the two traces is definitely the influence of the 160.640 transmitter. I am not sure what acceptable tolerances for transmitter spurs are. This looks pretty bad to me, but I'm just a newbie. Was hoping that some of you could take a look at these traces and give me an opinion. I also have some traces with higher freq resolutions in various bands if that would help.


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Jason Glass

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Re: RF problems in new HS stadium install
« Reply #26 on: September 19, 2016, 11:13:45 am »

Wanted to provide an update to everyone who took the time to respond to my post. I did get some data with my RF explorer. I am attaching a couple of screenshots that I feel are the most relevant. Two Scans from 100MHz to 700MHz.  Both are after the game on Friday night and from the perspective of our wide band paddle antenna.  The first is after everyone else except for the AM station had turned their equipment off. The AM crew was interviewing a coach and were the only ones left in the press box. I waited until they turned their Marti off and took another reading. So the difference between the two traces is definitely the influence of the 160.640 transmitter. I am not sure what acceptable tolerances for transmitter spurs are. This looks pretty bad to me, but I'm just a newbie. Was hoping that some of you could take a look at these traces and give me an opinion. I also have some traces with higher freq resolutions in various bands if that would help.
Nice detective work!

It's very difficult to say, from those measurements, whether the spurs shown are actually being transmitted by the Marti or are rather occurring inside the measuring instrument. Unfortunately, the overload compression warning with the Marti operating is an indication that the latter is likely, and reveals the trouble with using inexpensive instruments for this kind of measurement; they just don't have enough dynamic range to remain linear when measuring strong signals among weaker ones.

On the bright side, this may be an indication of what's also happening inside your mic receiver's front end.

I recommend that you try inserting a high pass filter on your antenna coax and repeat the experiment. It very well may solve your problem.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

Kevin Maxwell

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Re: RF problems in new HS stadium install
« Reply #27 on: September 19, 2016, 01:39:42 pm »

Nice detective work!

It's very difficult to say, from those measurements, whether the spurs shown are actually being transmitted by the Marti or are rather occurring inside the measuring instrument. Unfortunately, the overload compression warning with the Marti operating is an indication that the latter is likely, and reveals the trouble with using inexpensive instruments for this kind of measurement; they just don't have enough dynamic range to remain linear when measuring strong signals among weaker ones.

On the bright side, this may be an indication of what's also happening inside your mic receiver's front end.

I recommend that you try inserting a high pass filter on your antenna coax and repeat the experiment. It very well may solve your problem.

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

I have never had to do that YET, I have been lucky. Where does one find an RF high pass filter to do what needs to be done and exactly what would the device be (Range?) that would block the problem frequencies? It sounds like something I should have in my bag of tricks.

Sent from my computer after composing it in MS Word. But still, please excuse my inevitable spelling and grammatical errors.  :D
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Scott Helmke

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Re: RF problems in new HS stadium install
« Reply #28 on: September 19, 2016, 01:46:58 pm »

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Jason Glass

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Re: RF problems in new HS stadium install
« Reply #29 on: September 19, 2016, 02:08:55 pm »

Filters!

http://www.minicircuits.com/products/Filters.shtml
Yessir. 500 MHz is a good general purpose HPF for UHF systems.

http://www.minicircuits.com/MCLStore/ModelInfoDisplay?14743077420300.8613180731067597

Sent from my mobile phone. Please excuse the inevitable spelling and grammatical errors.

ProSoundWeb Community

Re: RF problems in new HS stadium install
« Reply #29 on: September 19, 2016, 02:08:55 pm »


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