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Author Topic: How accurate are your RF scans?  (Read 4528 times)

Kevin Maxwell

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How accurate are your RF scans?
« on: January 07, 2016, 07:18:49 pm »

How accurate are your RF scans?

I did something last month to test my test gear. I had a matinee and an evening show where we were using only 6 wireless mics and I had a lot of time between the 2 shows. So I turned on the wireless and separated them with about 6 feet between them. And I ran some scans and compared the results. I scanned using Shure Wireless Workbench (WWB) version 5 and 6 and using the Shure UHFR receivers as the scanners. And I also used my WinRadio G305e to scan using WWB5. And I used the WinRadio software with the WR G305e. With each method the frequencies were off (by as much as 250k) except for the Spectrum scan in the WinRadio software. I was surprised to say the least. After seeing the results of the scans I donít think I can trust the methods I have been using and I am working on a new procedure to get reliable scans. And I think I have it licked or at least almost. It involves using the WinRadio software with a plugin called Hit Counter, I have written a macro for Excel that then changes the text file it outputs to the format I need and I can then save that as a CSV file to import into Shure WWB6.

BTW my standard procedure for frequency coordination is with all of the transmitters off I scan the environment (with WWB using the Shure receivers networked to my computer) looking for what the antenna system is picking up. Then I do the database lookup to see what is within about 30-40miles of my location (zip code) and might cause interference or intermods. If I am not able to get enough channels looking out to 40 miles I will narrow it down to 30 miles out. This method has worked very well for me and I havenít had any issues with interference. But there have been a few times where I am using non-Shure wireless that are outside the range of the Shure receivers being used as the scanners. Or at a church that is using the Sennheiser EW series of wireless, so I have wanted to use the WinRadio to scan the environment in those cases. This brought about the curiosity as to how accurate my test system is.

Have you tested your system with known transmitters?


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Pete Erskine

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Re: How accurate are your RF scans?
« Reply #1 on: January 07, 2016, 08:40:59 pm »

How accurate are your RF scans?

I scanned using Shure Wireless Workbench...And I also used my WinRadio G305e to scan using WWB5. And I used the WinRadio software with the WR G305e. With each method the frequencies were off (by as much as 250k)...
For me there are two parts to spectrum analyzer use in coordinating.  First of all I am not doing calibrated measurements, I am doing relative measurements.

     1. Initial wide band scans to verify what DTV stations are active at and inside my venue.  This is because the FCC database is notoriously incorrect...in every venue I have been in, there is a DTV on an unregistered channel or there is the absence of one which is listed.  To be safe I always assume the dark channel may come alive and I avoid it.  AND, since I can see the unknown channel, now I can avoid it too. 

My channel scans typically are 60MHz at about 250KHZ resolution so I won't really see any single carriers.  I just want to see the DTV channels in use.  Accuracy is not so important ... if your SA cant tell channel by channel what is there you have a bigger problem.

     2. After I select my intermod free freqs I zoom in to 1MHZ full screen on each freq and look for the other unknown single freqs.  Here again accuracy is not so important...if I see any carrier closer than 300KHZ to my selected freq, I move.
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Cameron Stuckey

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Re: How accurate are your RF scans?
« Reply #2 on: January 07, 2016, 11:29:21 pm »

If I suspect that my device isn't reading correctly and I want to quickly self-calibrate and see the drift I'll either tune to the local NOAA Weather Station or a strong DTV channel.

NOAA operates FM weather stations all over the US on one of these 7 frequencies. They're reliable to my knowledge and shouldn't deviate by more than 5kHz at the most.
162.400 MHz
162.425 MHz
162.450 MHz
162.475 MHz
162.500 MHz
162.525 MHz
162.550 MHz

Second, the pilot for each DTV channel as set by the ATSC standard is 310kHz above the lower edge of the TV channel. For example, TV14 starts at 470MHz and the pilot can be found at 470.310MHz, TV52 starts at 698 and it's pilot can be found at 698.310MHz. I'm not sure what the tolerance is in the ASC spec but I've always trusted those pilot tones to be 1kHz or less deviated.
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Kevin Maxwell

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Re: How accurate are your RF scans?
« Reply #3 on: January 07, 2016, 11:43:49 pm »

For me there are two parts to spectrum analyzer use in coordinating.  First of all I am not doing calibrated measurements, I am doing relative measurements.

     1. Initial wide band scans to verify what DTV stations are active at and inside my venue.  This is because the FCC database is notoriously incorrect...in every venue I have been in, there is a DTV on an unregistered channel or there is the absence of one which is listed.  To be safe I always assume the dark channel may come alive and I avoid it.  AND, since I can see the unknown channel, now I can avoid it too. 

My channel scans typically are 60MHz at about 250KHZ resolution so I won't really see any single carriers.  I just want to see the DTV channels in use.  Accuracy is not so important ... if your SA cant tell channel by channel what is there you have a bigger problem.

     2. After I select my intermod free freqs I zoom in to 1MHZ full screen on each freq and look for the other unknown single freqs.  Here again accuracy is not so important...if I see any carrier closer than 300KHZ to my selected freq, I move.

If I am reading your reply correctly are you saying I am being too picky? With the WR-G305e I am doing 25k step scans and the accuracy is very good. I was planning on using that in addition to the lookups and then use the Shure WWB6 to make sure everything works together. I was using WWB5 for a long time but have switched to WWB6. I am still working with Shure regarding a network communication problem I have experienced a few times when monitoring the wireless receivers during a show. These are UHF-R UR4D systems. And I have talked to them about the inaccurate results I found I was getting when using these receivers as the scanner in WWB. I am planning on running more tests in as controlled an environment as I can and see if my results are consistent or was in some sort of weird anomaly.   

You are doing things way more complicated than I am doing now. And I really appreciate you input. I donít think you are located too far away from me. The most complicated thing involving RF that I have had to do lately involved just over 30 wireless mics for a musical. Sometimes I have to deal with wireless comms also. But I have had really good results with what I have done the way I did it, I am just now questioning some of my results due to the inaccuracies I have noticed in my tests.

My first exposure to wireless mics was many years ago where if you could say cut letís do that again, you might consider wireless mics. And there were some systems in use that would have stepped on anything else within a long distance away. But there were very few being used together. As I got involved with using more and more wireless mics I have gotten into the whole frequency coordination end of it. I want it to work right. I think one thing that made me get more involved was a show where we rented a system including wireless and I was told that they were frequency coordinated but it turned out they were done at their shop around 60 miles away and they didnít in any way consider where the show was. The first rehearsal was a wireless disaster. I donít remember the name of the first program I used for this, it was British and all it did was make sure that the wireless I was using didnít interfere with each other.

I think the basic nature of RF that the strongest thing at the receiver wins is what has made it almost look like I knew what I was doing. I remember one time (many years ago) where as long as the actors were on stage the wireless worked fine but one receiver as soon as it lost that strong signal when the actor left the stage the receiver was picking up interference that was very intense. It sounded like pink maybe even white noise. Now I always had the actors channel down when they werenít on stage but the signal (this was using an analog console) was so intense it bleed thru the adjacent channel on the board and could be heard thru the sound system. We retuned that one and the problem when away.     

Thank you for your input.
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Pete Erskine

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Re: How accurate are your RF scans?
« Reply #4 on: January 08, 2016, 11:53:27 am »

If I am reading your reply correctly are you saying I am being too picky? With the WR-G305e I am doing 25k step scans and the accuracy is very good.
Yes, I think you are spending too much time on the Spectrum scans and looking with too much detail.  Your SA does seem to be quite inaccurate in any case.  Usually on my TTI, R&S, and Explorer if I enter a freq to look at a carrier it's pretty much right on. 
Quote
I am just now questioning some of my results due to the inaccuracies I have noticed in my tests.
As far as resolution on your scans it does add a lot of extra time to do the scan and the exact details of the spectrum can really only be seen by zooming in on the freq so it is less than 1Meg window.  On my TTI and R&S that makes each graticule line 100k and I can see quite clearly any other freqs near mine.  Each 60MHz scan is averaged 8 times within 2 seconds.  This video shows one complete scan of 60MHZ: 
Quote
I was told that they were frequency coordinated but it turned out they were done at their shop around 60 miles away and they didnít in any way consider where the show was.
You know what they say about assume.....I always run any pre coordinated freqs through my own process.  Last year I went to a show which was part of an Olympic style sporting event and the over all coordinator presented me with MY list of assigned freqs.  Right away I saw that there was almost no intermod calcs done on the list of over 80 frequencies.

I was told that no changes could be made.  In order to not rock the boat too much I did a recalc on the TX freqs (BTR TX, IEM and IFB TX) for my ideal list for them and recalced a few of the other non TX (Wireless mics) freqs which were clearly on DTV or near other interference - there were about 6 I changed in the RX freqs.  Again I was told they couldn't be changed.

Eventually I was able to bully my way to get the changes before quitting the job because I felt it was going to fail.
Quote
I think the basic nature of RF that the strongest thing at the receiver wins...
This is so true.  I always try to put RX antennas on each side of the stage to maximize the RX level above the noise floor.  When you are using analog wireless interference messes up the audio with squeaks and birdies or if its not right on just bad reception.  With digital it is cleaner, the stronger signal comes through cleanly even if the interfering carrier is the same freq but your transmitting distance is less.

Years ago I joined a major musical tour, in the round, with the entire stage floor made of LED screens which raised the overall UHF noise floor 15 dB.  The IEM G2 packs didn't work well at all.  Before I got there the Tour Audio dept had bitten the bullet and suspended 5 TX antennas over the stage 15' above the performer over 300' antenna lines.  With an agonizingly long war game, every show, were able to make them work.

War Gaming all your freqs is paramount to make everything work.  Turn on all TX and one by one turn each off and look at RX levels on receivers and the spectrum under your carrier.  If you have interference, change the carrier and start your war game all over again.  Be sure to separate all TX by 3-6' or have them in tins to minimize the near-field intermod.  This is where I spend the most time during coordination.
« Last Edit: January 08, 2016, 12:38:59 pm by Pete Erskine »
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John Daniluk (JD)

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Re: How accurate are your RF scans?
« Reply #5 on: January 08, 2016, 12:39:38 pm »

Over the years I have had the privilege of working with some expensive RF analyzers.  What you see on the screen is very limited by the bandwidth, sweep speed, and other issues of the test device.   

Try this;

draw a vertical line on paper,  this will represent a rf signal.  Take a pencil and move it vertically across the paper,  This represents your scanner and the pencil is the bandwidth of the scanner.  The leading edge of the pencil will show the line (rf signal) and the line will be 2x the width of the pencil if you plot it out.  This is why what you see with various scanners may be confusing.   

The bandwidth and speed of the scan, will determine what you see. 

I hope I did not confuse you too much.....

jd

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Brad Harris

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Re: How accurate are your RF scans?
« Reply #6 on: January 17, 2016, 04:55:55 pm »

...  I scanned using Shure Wireless Workbench (WWB) version 5 and 6 and using the Shure UHFR receivers as the scanners. And I also used my WinRadio G305e to scan using WWB5. And I used the WinRadio software with the WR G305e. With each method the frequencies were off (by as much as 250k) except for the Spectrum scan in the WinRadio software....




Hi Kevin,


This is a known issue with WWB5 with any compatible hardware (UR, WinRadio, etc). I haven't bothered much with WWB6 aside from initial setup of units for med-large scale systems.


Which is one of the main reasons I shy'd away from WWB5 for coordination after it first came out (as well as networking issues for control with the various UR firmware updates ... and sadly WWB6 now).


There are a lot of great information out there on the internet (one of which being Pete's excellent resources on his BestAudio.com website). Another I like is W2AEW on YouTube. There are a lot of relevant information regarding to our uses of Spectrum in his video posts.


Here is a great one explaining how scanners with WRT RBW VBW https://www.youtube.com/watch?v=Ffhs9Ny03lM (which JD was referring to).


BRad
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Kevin Maxwell

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Re: How accurate are your RF scans?
« Reply #7 on: January 17, 2016, 11:11:23 pm »

Snip>>>>>
Which is one of the main reasons I shy'd away from WWB5 for coordination after it first came out (as well as networking issues for control with the various UR firmware updates ... and sadly WWB6 now).
<<<<<<<<snip


Can you please explain a little bit more about this part of your reply or maybe post a link about this problem? Especially about WWB6.
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Re: How accurate are your RF scans?
¬ę Reply #7 on: January 17, 2016, 11:11:23 pm ¬Ľ


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