The above Ad will no longer appear after you Sign Up for Free!

Serious RF Wireless Issues

Discussion in 'Sound, Music, and Intercom' started by Anonymous067, May 3, 2009.

  1. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
    Last night at our second show of six, we had major RF issues.
    We run about 15 AT 7000 Series bodypack transmitters.
    (as a side note...if anybody has the frequency charting for these things...please send it to me....) They sell this in multiple bands and I cannot find a list of it anywhere...the one in the user manual doesn't specify what band it's for...??? (good on AT).

    The problem....
    We had audio cut-outs with 3 bars of RF....
    We had RF dropouts when the performers were standing center stage...
    we have to work with this gear...
    I've isolated what Antenna DA's don't work, and have eliminated 8 of our wireless due to bad DA's.


    I think the audio is dropping out with full RF due to squelch issues.
    HELP ME PLEASE!
    Today when I get there I will be setting all squelches back to full counterclockwise and starting over....please please please help me!
    I don't know what I can do to get rid of these RF issues.
     
  2. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

    Messages:
    1,435
    Likes Received:
    153
    Occupation:
    Engineer
    Location:
    Chicago, IL
    OK, the first step here is to figure out what frequencies these units are running on. Check the manual, page 7. I know you say they sold it in multiple bandsplits, but I don't see that in the manual so perhaps they didn't? Look at the back of the transmitter and/or receivers as the frequency range is often written there. If you don't see anything, let's assume they're all in the same split.

    Manual: http://www.audio-technica.com/cms/resource_library/literature/72ff7913df69c17a/7000ser_om.pdf

    Post back here the frequencies that you have the system set to (all 15 channels, and give me channel number and RF frequency).

    Now, by Antenna DA do you mean the distribution amplifier (i.e., active antenna splitter)? What exactly doesn't work about it? How were they hooked up, and how are things hooked up now? What kind of antennas are you using? How many? Where are they, and how far from the stage?

    Do you have anything on TV channels 57, 58, or 59?

    On squelch. The squelch control tells the receiver when to mute the audio output as a function of input signal strength. So basically when the input RF signal strength drops below a threshold, the audio gets muted. I would probably set it somewhere in the middle, maybe cheating it a bit toward CCW.

    Once I have this info, I can help you more!
     
  3. museav

    museav CBMod CB Mods Departed Member

    Messages:
    4,017
    Likes Received:
    562
    Occupation:
    Acoustical, audio and audiovisual consultant
    Location:
    Marietta, GA
    Hopefully you have 15 receivers as well rather than 15 transmitters but just one receiver. ;)

    I agree with Mike, I see the 100 channels but nothing about bands. They do show suggested Groups, but I believe that is a suggestion on the channels to use together and not limitations on what is available.

    You mentioned in another thread that you had VHF mics and were looking to rent some higher quality UHF mics for an event, are the A-T 7000 units discussed here what you rented? Just trying to understand the situation.
     
  4. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
    First of all. NO this thread is not related to the renting thread at all...just to clear this up. That was/is for church. This is for school.

    Second. The AT 7000 was sold in two bandsplits, although not listed in the manual. AT for whatever reason decided they didn't need to publish this information. Investigation at previous shows indicated some were 7000 series, while some were 7000x. Band "x" (or not X...i can't really remember) is in channels 45-47...or something....and the other set is in the 700 mhz band. I will post frequencies later this week, we have brush up rehearsal Wed.

    We have 24 total receivers. 4 of these I don't use, because the distribution unit has an issue with its power supply not working...(I've trouble shooted this perviously). Basically it just cuts the power at random times, and resetting it doesn't work...you just have to wait for it to come back on. I can't take this risk during the show, and don't use these. The next 4 receivers/trans are for handhelds. Two of the systems are dedicated to our "Lecture system"...aka the idiot system.

    Now. Four receivers (as I discovered last night, and confirmed this morning) cannot be used due to lack of RF signal from the transmitters) give about 1 bar of RF (and no audio, even with squelch all the way open) when standing DOWNSTAGE CENTER WITH LINE OF SIGHT. They give no rf when in a pocket (even with antenna out).

    Our system has 6 active dipole antennas, (Audio-Technica - Microphones, headphones, wireless microphone systems, noise-cancelling headphones & more : ATW-A54P : UHF Powered Dipole Antennas). I know we have six of these, however we also have 1/2 wave passives....and EMI didn't leave any schematics behind...so I don't really know which ones are hooked up or not. In the back of the rack, they have two antenna cables per cascaded AB out. Only one is connected. Whether it is the 1/2 waves or not I don't know.

    Every 4 receivers has its own DA and cascaded into groups of 8 receivers per set of diversity antennas.

    I'm pretty certain this RF issue has to be something with the DA itself, because the other four receivers on the same set of antennas work fine, and the transmitters work fine when tuned to different receiver channels.

    The antennas are located 60 feet from the stage, and are hung from the catwalks (about 2 feet below them, on the back set of cats).

    Thanks so much...

    PS-today's run went much better...still a few interference issues....but other than that better than Saturday night. Still wanna hear what you guys have to say! Thanks.
     
  5. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
  6. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
    And that would be a YES to the 57, 58, 59 question.... as thats the only frequencies one of the bands operates on.....

    And I also talked to our district people. They basically said...well if you need new equipment, you can either pay for it yourselves or live on without it....

    Our TD also said it isn't at all possible for us to get new wireless, or rent in the future.
     
  7. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

    Messages:
    1,435
    Likes Received:
    153
    Occupation:
    Engineer
    Location:
    Chicago, IL
    Great, thanks for the info. More questions and maybe some answers too. :)

    Gotta love A-T. Great, re: frequencies. That more than anything will help me help you. For now, do you know who set the frequencies currently in use, and if they were coordinated in any way?

    If you get some time, see if you can narrow this down further. Try swapping the power brick over from another DA and see if that fixes it. I know one of the Vega DA PSU's we have had to be replaced a long time ago.

    Are these receivers on the same DA? Is it possible that the DA is bad (if all four are acting up that would be my first guess)? Or, is it possible that the DA is the wrong frequency band? Speaking of which, do you have a model number for the DA's?

    You're gonna have to do some digging unfortunately. It would be immensely helpful to know what receivers are wired to what DA's, and what DA's are wired to what other DA's or antennas. Sounds like kinda a mess based on what you've described. Any chance you can take some photos of the front and back of the rack and send them to me/post them?

    So let me get this straight - antennas go into one DA, which feeds four mic receivers and another DA, which feeds another four? And you have three of these going on (for a total of 24 receivers?) Let me know if this is right.

    Sounds reasonable to me.

    Wait, let me double check. You have local TV stations on one or more of these frequencies, or on the lower split (45-47)? It would be great to know where you are located so I can pull FCC data on that area (you can PM me if you don't want to broadcast this info).

    Yeah, 60' should not be an issue at all.

    Thanks for the links to the frequency charts.

    Glad to hear the run went better, and no problem, we're here to help you!

    Mike
     
  8. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

    Messages:
    1,435
    Likes Received:
    153
    Occupation:
    Engineer
    Location:
    Chicago, IL
    One more thought. How many DA's work OK, and how many receivers work OK? Maybe you can move the bad DA's over to something else (like the handhelds, if you don't need them for the show) and that might help? Also, of the DA"s that are broken, what is the issue? It sounded like at least one had a Power Supply issue, and one has a RF problem. Finally, what model are the DA's?
     
  9. Chris15

    Chris15 CBMod CB Mods Premium Member

    Messages:
    4,142
    Likes Received:
    422
    Location:
    Sydney, Australia
    Re the excess antennas; are there a pair of 1/2 waves for each pair of Dipoles? As a means of working out which are connected, try this: power up all your antenna connected DAs and look for the power LEDs on the dipoles. They won't power up unless being juiced up by the DA.

    Maybe it's just me, but surely it would have been cheaper and easier to have installed a single pair of antennas in the first place and then split off that to the secondary DAs. Anyway, you've got what you've got...

    Do these DAs have internal or external PSUs?

    I'm tending to think the way Mike is that the DA that's only passing 1 bar of signal might be for the wrong band, and in this case the "antennas" that the receivers are using are actually the coaxes in the rack...

    Re Mike's idea of swap and change of DAs - we are yet to confirm bandwidth on these DAs and so swapping them may cause more grief than it solves...

    As noted earlier, a list of all 24 frequencies would be useful - from that we ought to be able to work out if coordination was done. :mrgreen:
     
  10. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
    The system was installed in 2001 with the building, and to my knowledge, the actual operating frequencies have not been changed. EMI, a local company, installed the system, and worked with the current band director (who had a very strong say in the system). I presume they did the coordination, but that was long before the recent wireless issues arroused.

    Yes the four "bad receivers" are connected to the same DA, and I do presume the DA is bad. I have never had a problem with these in the past, and I have yet to tackle this issue due to lack of time. It only recently came up. I am very doubtful that the DA is in the wrong frequency range, but I will certainly check tomorrow.

    I cannot move the handhelds to the bad DA's for two reason. 1) The DA's have to work for meetings in the school, and are nice to have for other functions as well.
    2) The Handhelds are actually in a seperate bandsplit (if I remember right), so I could work around it, but all the packs in the same range as the handhelds are working fine, no reason to change this.

    Yes, you have the antennas figured out.

    Still waiting to get up tomorrow for frequencies and model numbers of the DA.

    Tomorrow I will post a detailed list of frequencies and the wiring, as well as model numbers.
     
  11. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
    Well. Here's the update.

    Turns out...we have FOUR active antennas, and two of them have 1/2 waves of them, for a total of SIX antennas. We have 24 receivers, and I had the distribution of antennas a little off. We have six DA's. Three per band split (probably the only reason for having two sets of antennas).

    The bottom most inputs feed the cascade of the second bottom most DA, and those in turn feed the third. The input of the third-from the bottom come from the antennas. Same thing up on top. For a total of TWO sets of antennas. As it turns out, two of the active antennas aren't actually hooked up to anything..(I pulled them up today and looked at them...the half waves are connected, and the actives are not). I don't know if the system is set up with both actives on one band split or one on each, I didn't have the time to look today.

    As far as the audio-drop outs.
    Like I said...the antennas cascade through 2 DA's before reaching the one it needs for the bottom set of receivers. I had turned off the middle DA in the chain, and was probably losing amplification. I found this out when I turned off the top one (the one with direct connection to the antennas), and the powered antennas actually..well..."turned off"...and also caused a NO RF situation on all the cascaded DA's/Receivers. Problemo solved, turn on and leave on all DA's.

    I still didn't have time to glance at RF freqs and model number of the DA's. I'll grab them tomorrow.

    Just wanted to update anybody following this thread still.
    Thanks.
     
  12. teqniqal

    teqniqal Well-Known Member

    Messages:
    204
    Likes Received:
    135
    Occupation:
    Theatre Consultant
    Location:
    Dallas / Fort Worth, Texas
    I think you hit the nail on the head when you said that it was all working before and that the problems just started recently. Have the orginal installer come out and get it fixed, and this time have them leave a set of frequencies and a wiring diagram.

    Also, you said the antennae were 60' from the stage, but you did not say how long the cable run was from the antennae to the DA's. My experience has been that you will get more loss in the cable than through the air. So if over-all signal strength is an issue, then you should consider relocating the antennae so they are flanking the booth and have RG8 50 Ohm coax cabling from the antennae to the DA's.

    One last item: orient the antennae pairs (A, B for each DA rig) so that they are 90 degrees from each other and perpendicular to the acting area (i.e. as you look at them from the stage, one is tilted left 45 degrees, the other is tilted right 45 degrees. This provides phase diversity. It is common for the antennae that contractors mount to catwalks to be perpendicular to the top of the proscenium opening and not perpendicular to the acting area. Also, mount them so that they are at least one wavelength away from any other metal that is coplanner to them (i.e metal wall studs, steel catwalk structure, metal lath in plaster, aluminum window frames, etc.) If you have two pairs of antennae feeding two DA systems, then set-up the second pair opposite the first pair so you don't have adjacent antennae parrallel to each other.

    Shure and Sennheiser both have frequency coordination software available on their web sites. Don't forget to include wireless devices from the gym, football stadium, adjacent classrooms, and local churches in the calculations as well as local TV stations.
     
  13. Chris15

    Chris15 CBMod CB Mods Premium Member

    Messages:
    4,142
    Likes Received:
    422
    Location:
    Sydney, Australia
    OK. I'm going to make a presumption here. I'm guessing that since all the systems are A-T and the antennas are A-T that the DAs are probably going to be A-T as well.

    On that basis: Power supplies are internal (in reference to something Mike mentioned previously), and they are a narrowband DA. The cascade output is 3dB down on the input so by rights is a passive split off the input.

    On that basis: Power status of middle DA should have no effect on passthrough to next DA. DA connected to active antennas will always need to be on, because otherwise there is no 12V "phantom" applied to the coax to run the preamp and you get zilch RF. Note that A-T have the 54 model for that 500 MHz band and the 64 model for the 600MHz band, they will not interchange.

    With all due respect to teqniqal, the maths simply does not support a greater loss in coax than in free space. I did the sums not a week ago when someone made that same claim in one of the other threads.

    It's looking like we have a suspect DA at least if not 2. As time permits, try bypassing the one that was giving trouble - plug the coaxes straight between DA4 and DA6 if 5 if the dodgy one. I think that is the cause of these problems. Component failure after 8 years would not be unexpected, particularly if it's all racked up with sub optimum ventilation.

    I fail to see the advantage of angling the antennas off on 45 degree angles. The diversity effect works because one antenna will hopeful have a signal path when the other doesn't. You need them to have the same coverage area for this principle to work. Note in this particular case that is a moot point anyway as the anennas are dipoles and thus (in general terms at least) an omnidirectional antenna. You can point one left and one right and you'll still have a vertical dipole.

    Comments on antenna placement vs coplanar architectural metal are salient to note, but may actually be used in you favour in some cases - planning required.
     
  14. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

    Messages:
    1,435
    Likes Received:
    153
    Occupation:
    Engineer
    Location:
    Chicago, IL
    Yes and no. Yes, dipoles do have a (relatively) omnidirectional pattern, but they are polarized antennas. Thus, if you place one dipole orthogonal and broadside to another dipole a certain distance away in a test chamber or in free space, you will notice a change in transmission (s21 as measured on a network analyzer) between the two antennas compared to them being parallel and spaced apart. I believe the figure is 20 dB, but I could be wrong.

    HOWEVER - this is true in a test chamber or free space. In real life, what the antenna sees is (hopefully) the original signal, followed by an infinite number of echos caused by reflections in the space. What we want is for these echoes to add up in phase and/or be very weak with reference to the original signal (say, 30 or more dB down). What really ends up happening is that these echoes tend to cancel out the effects of polarization in a situation with heavy reflections.

    All of this said, I honestly don't see a great advantage or disadvantage to mounting the antennas in an orthogonal manner, so I say if it makes you feel better go for it.

    Yeah, it could go either way. Theoretically speaking if you could get it 1/4 wavelength away you could create a directional pattern...
     
  15. Anonymous067

    Anonymous067 BANNED USER

    Messages:
    833
    Likes Received:
    28
    I'm not authorized to move the antennas, so I don't really care about that part...sorry. Still good information however.

    Umm...I think the status of the second DA does matter, it passes a signal, and it amplifies it no?

    And yeah..my bad on turning the top DA off..that would obviously kill the active antennas.

    We have four antennas actually hooked up, two active and two dipole 1/2 wave. So I might check tomorrow if it's set up active 1 and active 2 to AB of one band split, or if it's one active and one dipole per band split.

    All our gear is narrowband, so we can't really "change" or move stuff around.
     
  16. teqniqal

    teqniqal Well-Known Member

    Messages:
    204
    Likes Received:
    135
    Occupation:
    Theatre Consultant
    Location:
    Dallas / Fort Worth, Texas
    Well, as they say, it depends... What cable were you modelling, at what frequency band, and how long was the cable vs the free-space line-of-sight distance? I ask this because I have found projects where the cables were small (rg58) and several hundred feet long (in the real world, electrical contractors go twice around the building when they connect junction boxes with conduit - 100' from antenna to receiver results in 200 plus feet of cable). In a large venue, with the booth at mid-house, the free-space from the performer to the receiver may be 50-75', and the cables from antennas flanking the proscenium are almost 300' long by the time they get from the stage to the equipment room, then to the booth. They may also have a splice or two in them, knocking-off a few more dB. Run the numbers for 300' of rg58 at 700 MHz -vs- 50' of free-space plus 10 feet of RG8, let us know.

    Go with me on this for a minute (let's just assume it is an outdoor event with no metal trusses for right now) . . . assume you have a performer on stage with a handheld mic facing stage right . . . his mic is at about 45 degrees to the stage. The house left antenna is also tilted that way, so it gets a good signal. The house right antenna is 90 degrees from that and gets a crappy signal. In this situation, spacial diversity has little to do with it, and phase diversity has everything to do with it. When the performer turns around and faces stage left, then the opposite is true and the other antenna gets the good signal. Everything in-between is just both antennas trying to get a signal and the receiver's diversity switching logic trying to figure-out which antenna has a 'better' signal. Phase diversity on antennae may not always help, but in our world we need all the help we can get. It costs nothing to do it. Why not? FWIW, this works with dipole, log-periodic (unidirectional paddles), and helical antennae (you use a right-hand and a left-hand spiral pair).

    As for tilting the antennae so the strongest reception lobe is pointed towards the performer . . . it's just like a light or a speaker -- point it at the people! Diffuse off-axis signals don't work well for light, sound, or RF, unless that is the aesthetic you are shooting for.
     
  17. museav

    museav CBMod CB Mods Departed Member

    Messages:
    4,017
    Likes Received:
    562
    Occupation:
    Acoustical, audio and audiovisual consultant
    Location:
    Marietta, GA
    What you are saying is valid, but seems a bit biased. For one thing, most large houses I've worked on have the wireless receivers on or near the stage. And all the facilities I've worked on have the antennas direct to the receiver location, not through some intermediary equipment room. So the antenna run length would indeed typically be longer than the direct free air path, but not usually four to six times as long.

    Also, RG-58 for a 300' run to wireless mic antennas seems a bit unusual while the comparison of RG-58 for that and then RG-8 for a 10' run seems a little too much like trying to obtain a desired result than it is trying to present a fair comparison. I believe that most wireless mic manufacturers recommend RG-8 for cabling to remote antennas, I don't offhand know any that recommend RG-58, and for a 300' run many people would probably use RG-11 or LMR-400.

    Another factor not considered by looking only at path losses is multipath, an antenna 50'-75' from a transmitter is subject to significantly more multipath interference than one 20'-25' away from the transmitter. Direct loss is not the only factor.

    I don't doubt that you may have experienced what you described as a worst case composite scenario or even on one particular project, but that seems more representative of examples of poor design and installation than it is a valid general comparison. I would think a more valid general comparison using might be more like 75' of free air plus 10' of RG-8 versus maybe 150' of RG-8 or at that run length, more likely RG-11.
     
  18. waynehoskins

    waynehoskins Active Member

    Messages:
    782
    Likes Received:
    49
    Location:
    Arlington, TX
    RG-8 is crap above 50 MHz. RG-213 is good up to 150 MHz. LMR-400 is crap above 450 MHz. That's based loosely on the cable's 3dB-per-100-feet frequency and general practice in the amateur world. With our wireless systems operating at, typical worst case, 700 MHz, and being low-power, I'd really be looking at LMR-600 or hardline for a long (longer than 100 or 150 feet) run.

    RG-58 is crap at 30 MHz. :)
     
  19. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

    Messages:
    1,435
    Likes Received:
    153
    Occupation:
    Engineer
    Location:
    Chicago, IL
    For long runs (greater than 100 feet), I'd generally agree--but in those cases you should probably be checking cable specifications carefully. Then again, you can make up the cable losses with an LNA (low noise amplifier) at the antenna, and an antenna with some gain.

    Also, you failed to mention RG-6, which provides decent performance at UHF (-6dB/100ft or so) at a VERY reasonable price point. Mismatch losses are fairly low too (assuming both your antenna and your receiver were matched to 50 Ohms to begin with, which is often a stretch...)
     
  20. waynehoskins

    waynehoskins Active Member

    Messages:
    782
    Likes Received:
    49
    Location:
    Arlington, TX
    True. RG-6 is a decent compromise, and you're right, that small an impedance mismatch is nothing to a receiver, which (at least used to) have high-impedance inputs anyhow. I was just going through some of the 52-ohm coaxes I'm familiar with. The 75-ohm coaxes are also good candidates, and RG-6 is much more readily available than 9913 or LMR stuff.

    I do wonder what impedance the log-periodics in common use are: 52 or 75 ohms? But a simple dipole is 72 ohms in free space, give or take, and so ideally it should be matched to a 75-ohm transmission line. A vertical is theoretically half that, 36 ohms in a perfect world, so it's a closer match to 52-ohm cable. Again, not that the difference is worth bothering over. :)

    Match the feedline to the antenna terminal impedance, and then match the transmitter (or receiver, as applicable) into the load.

    (And I know that's nothing new to you; I put it out there as general advice)

    I wonder what ladderline is like at UHF? :)
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice