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[Rick Earl]

I was doing a high profile event the other day, with a few days to set-up,  I set up a scanner (RF-Venue RF Explorer) to scan in addition to scans in WWB.  I was using the RF Explorer software as a scan and set the trace to show max values.  I kept getting a hit approximately centered on 587 MHz, it was rather narrow band, looking similar to other wireless devices broadcasting (Shure Axient D).  When I finally witnessed it , it was short burst, almost like two way radio.  My coordination was well planned around that, so I did not spend a whole lot of time hunting it down.  We operate on a college campus, and at the time, there was no other known wireless operating in the region.  All known wireless operate in coordinated frequency zones and on a check of those devices, they were still operating in assigned frequencies.    I also coordinated using the WWB database AND entering manually from Rabbit Ears info, nothing in TV should have been broadcasting in that band, and it was too narrow.  SO with all of that, any ideas of what it could be? I would like to find the source.

[Jordan Wolf]

It might be helpful to conduct a 24-hour scan using the Timeline feature to see if time of day is a factor, or if there is a pattern to the interference (RF discharge when a device is overloaded?).

Worth a shot, especially if you have “control” over the known RF environment.

[Russell Ault]

If it was short, randomly occurring, and looked like a wireless microphone transmission, could it have been a very strong intermodulation product? Is your scanner near an RF table? Are you keeping powered-on TXs separated?

-Russ

[Pete Erskine]

are you using any digital consoles.  they radiate rf.

[Rick Earl]

It might be helpful to conduct a 24-hour scan using the Timeline feature to see if time of day is a factor, or if there is a pattern to the interference (RF discharge when a device is overloaded?).

Worth a shot, especially if you have “control” over the known RF environment.

We were doing scans for 48 hours, no real pattern can be determined yet.

If it was short, randomly occurring, and looked like a wireless microphone transmission, could it have been a very strong intermodulation product? Is your scanner near an RF table? Are you keeping powered-on TXs separated?

-Russ

I calculated all the IM products, it was not one, and appeared when RF was not transmitting.  We kept RF separate in bread pans.

are you using any digital consoles.  they radiate rf.

THAT might be possible, we were using a Yamaha QL5,  It was near the RF rack, but not the antennas. The antenna were PWS Helical, console and most broadcast stations were pretty much sitting in the null of the antennas.  Cable was also PWS.  I can easily check the console, I might also run some scans today when the building and athletic facilities are dark.

I also tested our two way radios, police, fire and security.

The only other observation I have is it seems to occur when the building ramps up for occupancy.  It is a 6000 seat arena.  They schedule occupancy for the air handlers.  I checked, none of their sensors are wireless and the only telemetry is in the 900Mhz Band.  All other control is via wifi.   I always thought motors were broadband noise, I wonder if some component could be causing an issue?

[Jason Glass]

Sometimes when RF TX malfunction, they sporadically emit on random frequencies.  Although it seems unlikely here in light of your observations and good detective work.

The only other observation I have is it seems to occur when the building ramps up for occupancy.

Are you sure that no media ENG crews are coming onto the site with the rest of the crowd?  Are there food trucks parked outside, or media remote setups, or other potential mic users who would be oblivious to the implications?  TV remote trucks are notorious for "forgetting" that their 1/4W IFB TX are blasting from their rooftop antennas.

Does the university have a physics lab nearby?  This could be unintentional emissions from their equipment.

Portable consumer TVBD white space devices are rare out in the wild, but you might consider the possibility that someone in your area has one.

If you're eligible, it may be worth an effort to register your events on the TVBD database for protection.

[Henry Cohen]

It would help to have a better understanding of the carrier's spectral mask. With the spectrum analyzer, reduce the span to 500kHz and RBW to around 3kHz; low enough to capture a somewhat accurate picture of the spectral mask but fast enough to capture the transmission. Peak hold might be needed.

Once the occupied bandwidth and mask can be determined, it might aid in finding the transmitter.

Can you correlate the transmissions to defined electromechanical activities; elevators engaging; powering on lighting fixtures, video displays and the like; What other non-production equipment is turned on when the room is opened for a performance? 

Finally direction finding might be in order. It's methodical and time consuming, but even with some basic tools often works with intermittent carriers.

[Rick Earl]

Are you sure that no media ENG crews are coming onto the site with the rest of the crowd?  Are there food trucks parked outside, or media remote setups, or other potential mic users who would be oblivious to the implications?  TV remote trucks are notorious for "forgetting" that their 1/4W IFB TX are blasting from their rooftop antennas.

This was occurring 2 days prior to the event, and I know there were no ENG trucks.  The other sports facilities are across the road, and on day two, they were dark and the events were only streamed.  We communicated with media outlets before the event and knew when they arrived and monitored as they came on-line. They were all well behaved.

Does the university have a physics lab nearby?  This could be unintentional emissions from their equipment.

Physics lab is a mile away, and on the opposite side of the building from where the arena is.  I know all of the professors, and don't think any of them are doing anything with RF, but I will ask.  We are not a research institution like a lot of bigger state schools.

Portable consumer TVBD white space devices are rare out in the wild, but you might consider the possibility that someone in your area has one.

   
I was thinking about that, but I am not sure what form they may take, so I am not sure what to look for.  Whatever it is, it is in the area, and signal is pretty consistent in amplitude and bandwidth.

If you're eligible, it may be worth an effort to register your events on the TVBD database for protection.

 
 I am and I did.

It would help to have a better understanding of the carrier's spectral mask. With the spectrum analyzer, reduce the span to 500kHz and RBW to around 3kHz; low enough to capture a somewhat accurate picture of the spectral mask but fast enough to capture the transmission. Peak hold might be needed.

Once the occupied bandwidth and mask can be determined, it might aid in finding the transmitter.

Can you correlate the transmissions to defined electromechanical activities; elevators engaging; powering on lighting fixtures, video displays and the like; What other non-production equipment is turned on when the room is opened for a performance? 

Finally direction finding might be in order. It's methodical and time consuming, but even with some basic tools often works with intermittent carriers.

My next plan of action, when I get time, is to go set-up again and scan with a much smaller bandwidth as you suggested. 
I am pretty positive it is not the video boards, as I saw spikes both when they were on and off.    I was part of the design team from the conception to completion of this arena, so I am aware of all that we installed and what is operating.  The facility is just over a year old.  It is primarily used for sports, but we have done a few high profile events in there, this is the second where I had issues with that particular frequency.  The last time was at graduation, my crew had an issue in there, on that frequency, we worked around it and I kept it as an exclusion just in case.  I didn't think much about after that it until it popped up in my scans last week.  It just may be one of those things I have to deal with but it is a mystery I would like to solve.  Hopefully the process will make me better at this.

Thank you all for the help.

[Jason Glass]

Thank you all for the help.

Roger that.  You obviously know your gig very well!

FWIW, you may want to pay special attention to extended time monitoring of harmonic frequencies of the birdie, meaning 1/8x, 1/4x, 1/2x, 2x, 3x, 4x the fundamental, etc.  It's not out of the question that this is a waaaayyyyy out of band spur of an otherwise legit carrier or research device's primary emissions.

FWIW, a couple of years ago I monitored a consistent analog FM signal in the UHF band that turned out to be a harmonic of the local VHF NOAA weather broadcast.  It was strong enough to step on UHF mics and coms outdoors in downtown Nashville and I identified it with simple FM audio demod in software.

[Ike Zimbel]

Roger that.  You obviously know your gig very well!

FWIW, you may want to pay special attention to extended time monitoring of harmonic frequencies of the birdie, meaning 1/8x, 1/4x, 1/2x, 2x, 3x, 4x the fundamental, etc.  It's not out of the question that this is a waaaayyyyy out of band spur of an otherwise legit carrier or research device's primary emissions.

FWIW, a couple of years ago I monitored a consistent analog FM signal in the UHF band that turned out to be a harmonic of the local VHF NOAA weather broadcast.  It was strong enough to step on UHF mics and coms outdoors in downtown Nashville and I identified it with simple FM audio demod in software.

Which raises the question: Are you able to see this directly off-air with your analyzer, or, are you only seeing it through your antenna system?
If it's the latter, it may be an IMD product of something that's getting into your antennas with enough power to create intermod.
A few years ago, I was doing some work for the local arena, and while monitoring their antenna system I was picking up some strong signals just above 700 MHz. When I de-modded them, they were clearly intercom, and it was in fact, the game that was in progress. After determining that there was no legacy 700 MHz com in use, I traced it down to massive IMD in the house antenna system, caused by a BTR TX antenna, that over the years had been turned 90* by the very stiff LMR400 it was connected with. The 90 degree turn pointed it directly at a Shure UA874 antenna which was, at most , 2' away. Those antennas had been set to the +10dB gain position at one point (to drive 25' of cable... ) but I can't recall if I had corrected that by this point in the contract. I have images of both the antenna placement and the resultant trace on the analyzer, but I don't have time to find and post them right now.

[Rick Earl]

Which raises the question: Are you able to see this directly off-air with your analyzer, or, are you only seeing it through your antenna system?
If it's the latter, it may be an IMD product of something that's getting into your antennas with enough power to create intermod.
A few years ago, I was doing some work for the local arena, and while monitoring their antenna system I was picking up some strong signals just above 700 MHz. When I de-modded them, they were clearly intercom, and it was in fact, the game that was in progress. After determining that there was no legacy 700 MHz com in use, I traced it down to massive IMD in the house antenna system, caused by a BTR TX antenna, that over the years had been turned 90* by the very stiff LMR400 it was connected with. The 90 degree turn pointed it directly at a Shure UA874 antenna which was, at most , 2' away. Those antennas had been set to the +10dB gain position at one point (to drive 25' of cable... ) but I can't recall if I had corrected that by this point in the contract. I have images of both the antenna placement and the resultant trace on the analyzer, but I don't have time to find and post them right now.

My antenna system was direct into a 4 channel Axient receiver.   I set the second BNC set connectors as outputs for cascade and then ran my analyzer from that.  I also never switched to the other antenna.  This is the second time it was an issue, the previous was with a pair of   ULXD Quad receivers with a similar antenna set-up, same cable type, but I think CP Beam Helical antennas were used.  The offending frequency was causing drop-outs, it had not shown up on the WWB scan since it was using the ULX front end to scan.  I had the techs exclude that frequency and re-deploy with new data, I kept the frequency as an exclusion when working in that venue and never got around to trying to figure out what it was.  This time, with continuous  scan, I actually saw it appear, it is intermittent.  I know the house com was off.  (Clear-Com Free Speak).  I had a second analyzer with a LPDA set and ready to go to see if is could figure out a direction, but it did not show up again while I had time to mess with it.  All that to say, I have no idea if it is in the antenna system as I have only seen it through that set-up. Although you all have given me some good places to hunt.   I did test the cables today with tracking generator and they seem to check out OK, at least to my limited knowledge, there was no drop in level across the spectrum.  I have no idea if they are unintentional antennas as well, and how to test that.  I just picked up an Rohde & Schwarz analyzer with tracking generator, but still learning all it's functions.    Again, this is something I can work around, but I would like to find it, so if I encounter something like this again I know what I am dealing with and maybe even how to deal with it.

[Henry Cohen]

I did test the cables today with tracking generator and they seem to check out OK, at least to my limited knowledge, there was no drop in level across the spectrum.

If "there was no drop in level across the spectrum" then something is amiss with the analyzer setup. Coaxial cable always has loss, which is inversely related to frequency and cable length. If you were looking at a minimum of an octave span, you should have seen a gentle slope downward from the start to stop frequencies. The rate of the slope, and the initial loss at the start frequency, is dependent on the coax cable type, condition and connector attachment loss.

Specific coaxial cable losses at frequency vs length is an industry standard specification provided by all reputable cable manufacturers. Generic cable type losses (e.g. RG58, RG8X RG213, RG8) can be found with basic web search (here's one).

[Rick Earl]

If "there was no drop in level across the spectrum" then something is amiss with the analyzer setup. Coaxial cable always has loss, which is inversely related to frequency and cable length. If you were looking at a minimum of an octave span, you should have seen a gentle slope downward from the start to stop frequencies. The rate of the slope, and the initial loss at the start frequency, is dependent on the coax cable type, condition and connector attachment loss.

Specific coaxial cable losses at frequency vs length is an industry standard specification provided by all reputable cable manufacturers. Generic cable type losses (e.g. RG58, RG8X RG213, RG8) can be found with basic web search (here's one).

I would guess there is something amiss with my set-up, as the analyzer is but a week old and I am still learning, I was also only looking at a 25' cable from 500-600MHz as that is where my frequencies fell out.  There may have been a gentle slope, but I would guess I didn't have the resolution set up well enough to see it.

I also forgot to mention in the entire set-up I was using  PWS UHF 470-618 In-Line Filter on each antenna at the receiver.

I am reading how to use the demodulation function and hope to set up later this week and see if I can do some more investigating.

[Henry Cohen]

I would guess there is something amiss with my set-up, as the analyzer is but a week old and I am still learning, I was also only looking at a 25' cable from 500-600MHz as that is where my frequencies fell out.  There may have been a gentle slope, but I would guess I didn't have the resolution set up well enough to see it.

Since your were looking at only about 18% bandwidth, and your scale was probably set to 10dB/Div, you would not have seen any perceptible slope, and you would have minimally seen the fundamental insertion loss of the coax itself, a couble of dB, presuming you calibrated the unit prior to measuring.

I also forgot to mention in the entire set-up I was using  PWS UHF 470-618 In-Line Filter on each antenna at the receiver.

In today's congested, high RF noise floor environment, broadband filters aren't quite useless; they can attenuate strong LMR and LTE on top side and LMR on the bottom, but do nothing for  the adjacent channel high power DTV station. In the case of UHF TV band wireless equipment, 6MHz high Q channel filters are the best option.

I am reading how to use the demodulation function and hope to set up later this week and see if I can do some more investigating.

The R&S can only demodulate AM and FM, if you have that option enabled.

[Loren Miller]

This thread is like reading a geeky Nancy Drew novel...loving it!!!!

Loren

[Rick Earl]

In today's congested, high RF noise floor environment, broadband filters aren't quite useless; they can attenuate strong LMR and LTE on top side and LMR on the bottom, but do nothing for  the adjacent channel high power DTV station. In the case of UHF TV band wireless equipment, 6MHz high Q channel filters are the best option.

I used those for a few reasons.  I knew there were going to be a large number of law enforcement, university security and private security as well as a rescue squad/first aid room about 20' away from on of my antennas, there are also 64 high powered Access Point deployed in the arena, I know they are way out of band, but I figured the filter probably wouldn't hurt.   Although aware of them, I am not experienced enough to start figuring out how to design a system around narrow band filters or how to specify them that fits within our budget.   I would speculate that they are items available for rent, but again, I need to learn a lot more.

The R&S can only demodulate AM and FM, if you have that option enabled.

I do have it enabled, I enjoyed some light reading of the manual and was able to tune in to a local FM broadcast.  Since I don't know what the mystery signal is, I figure I might as well try to listen to it.  I also read up on screen captures and hopefully have enough understanding of the settings  to narrow in my search and see if I can capture the spectral mask.  Luckily the areana is dark the next few days and I had an event postponed, so I may have time to try this week.

[ProSoundWeb Community]