New TV Frequency Problems

[KBToys82]

So, I turned on my wireless mics a few weeks ago after not using it since March to notice that 9 of them were getting a signal when nothing was on. Today, doing more research, because of the repack, my area just outside of NYC has obviously gone through the repack and has majorly impacted my wireless situation.

I had 12 AT 3000 mics spanning frequencies 541 - 566.375, and now it seems that I'm limited between 560.000 - 566.375 (although my 1 channel at 548.100 had no problems so I'm keeping it.) Now I need to get 11 mics between those frequencies. My question is what is a safe distance between 2 mic transmitters? I do not have any way to scan the frequencies that are available, but I do check against intermod using Audio Technica's tool that checks frequencies for you.

Also, I'm guessing that since at least one mic works at the bottom of a channel as of now, there may be a 1 or 2 I could squeeze at the bottom or top end of a tv channel. I don't have the money to get anything to scan frequencies that are available. I still have to check my other 8 mics to see if they are impacted, but want to get a head start on the larger set of 12.

 

[Aaron Becker]

Does AT have a tool have a way to punch your zip code in and find usable frequencies? That would be your best bet to start. Shy of that, you could try using an alternative vendors software (Shure, Senny) just to get some frequencies to work with. Obviously you'd want to use AT's tool for intermod checks, but you could grab some clean frequencies TV-band wise from the competition.

In terms of checking your transmitters / etc - place them all on the stage 3' apart from each other and war game them. Turn all the transmitters on, and turn each one off one at a time while watching the receiver. When the associated transmitter goes off, you shouldn't see any RX activity on the receiver. If you do, you have interference or, more likely, intermod.

Do the AT systems have a scanning feature? It's been a long while since I've used that gear, but if they do, similar concept as above, but scan for opening frequencies within the band or turn each transmitter on one at a time (and leave them on) while sequentially scanning for more good frequencies.

 

[KBToys82]

I did my zip code with Shure’s finder and told me what is available. Not sure about if it has a scan feature. Will check tomorrow.

 

[Aaron Becker]

The scan feature would be something on the AT receivers themselves. They may have "channel groups" - maximizing the usable channels in the open space. It's a good starting point combined with the frequency finders.

 

[TimMc]

I'd bet that your TV station wasn't the only one moving. While my market supposedly re-packed in Nov 2018, at least one local full power station will not be lighting up on their final frequency assignment until mid-March, 2020. Nothing is done and final in a fair number of markets, nor will it be for at least another year or so. Stations may be re-assigned, have output power and HAAT changes and operate under Special Temporary Authorization until their tower space, new antennae/feedlines, and new transmitters are installed and tested.

Know anyone with a similar-banded Shure receiver and Wireless Workbench?

@Aaron Becker the FCC database (which is what the manufacturer tools query) is notoriously out of date. See first paragraph.

And just when you thought it was safe... the FCC continues to promote TV White Space Devices. Micro$oft has $13b invested in using open TV channels to deliver internet to rural areas (like NoDak/SoDak).

 

[Aaron Becker]

I'd bet that your TV station wasn't the only one moving. While my market supposedly re-packed in Nov 2018, at least one local full power station will not be lighting up on their final frequency assignment until mid-March, 2020. Nothing is done and final in a fair number of markets, nor will it be for at least another year or so. Stations may be re-assigned, have output power and HAAT changes and operate under Special Temporary Authorization until their tower space, new antennae/feedlines, and new transmitters are installed and tested.

Know anyone with a similar-banded Shure receiver and Wireless Workbench?

@Aaron Becker the FCC database (which is what the manufacturer tools query) is notoriously out of date. See first paragraph.

And just when you thought it was safe... the FCC continues to promote TV White Space Devices. Micro$oft has $13b invested in using open TV channels to deliver internet to rural areas (like NoDak/SoDak).

@TimMc Thanks for the heads up on the Shure WWB. I haven't used it in years, since I have licensing available for IAS. Does IAS use the same?
Also, I'll have to update my location on here, I haven't been in NoDak in many years!

 

[TimMc]

@TimMc Thanks for the heads up on the Shure WWB. I haven't used it in years, since I have licensing available for IAS. Does IAS use the same?
Also, I'll have to update my location on here, I haven't been in NoDak in many years!

I'm pretty sure they all use the same database, but you'd have to ask the IAS folks as to which one they use.

Yeah hear about the 2 Harley riders from NoDak? Last summer they couldn't get past the first chain removal area.... /humor

 

[KBToys82]

So reading one of the replies and my original post, I should clarify one note.

My question about spacing was in regards to frequencies since AT already checks for intermod. If I put one unit at 560.000, what is the next lowest frequency I should use? The AT units go up by .025MHz, meaning if it wasn't an issue, I could put 3 packs at 560.000, 560.025 and 560.050MHz, but since I doubt transmitters and receivers are that fine tuned to differentiate between .025MHz, what distance would you feel comfortable with?

 

[KBToys82]

Latest update, so I will be having up to 24 channels of wireless (although probably never that much). 12 Audio Technica's 541-566MHz, 8 Creative Audio mics 490-510MHz & 510 - 530MHz (Bodymics brand which I recommend!) and eventually 4 Shure SLX channels on the G5 band 494-515MHz. Using the the frequency finder and typing in all of the frequencies that Shure uses and figuring out what is available to me, I have 2 sets of microphones that will be within .200MHz of each other. Would this be a sufficient space between mic packs or should I try to expand them?

 

[mbenonis]

The Shure Wireless Frequency Finder is kept up to date these days by a team at Shure. I'd recommend using it as a one-stop tool to know what TV channels are free in your area--then you can plug this data into WWB, IAS, etc. Of course, if you have some Shure QLX-D, ULX-D, or Axient Digital laying around, you can also do a local spectrum scan with WWB.

 

[Aaron Becker]

So reading one of the replies and my original post, I should clarify one note.

My question about spacing was in regards to frequencies since AT already checks for intermod. If I put one unit at 560.000, what is the next lowest frequency I should use? The AT units go up by .025MHz, meaning if it wasn't an issue, I could put 3 packs at 560.000, 560.025 and 560.050MHz, but since I doubt transmitters and receivers are that fine tuned to differentiate between .025MHz, what distance would you feel comfortable with?

it’s not a matter of comfort - it’s a matter of intermodulation which depends on a number of variables - which is why you need software or a chart of frequencies that work together as published by the manufacture.

 

[FMEng]

Aaron has it right. It's not a simple matter of spacing. Intermod products are a complex mathematical relationship. This is why many manufacturers publish or pre-program channel groups, with seemingly random frequencies, to avoid intermod problems. The frequencies in a channel group are not random at all.

The simple way to deal with this is find a quiet-ish TV channel, and use the frequency assignments from the group for that channel. Some models of receivers may not be able to reliably fit 12 systems in one, 6 MHz TV channel. I suspect 12 might be pushing it with AT 3000 series.

Some manufacturers specify how many units will work in a 6 MHz channel. AT says 40 per band, which is useless information or stupid marketing in the current RF environment.

 

[ACTSTech]

I posted a similar problem a while back, but they weren’t my mics. After calling the five major tv stations in the area (which was actually three because ABC, CBS and FOX are all the same ownership group), they all sort of grumbled about the FCC and tried to explain that there’s some modulation. I told them I understood that and thanked them, but all of them told me the same thing: you just have to deal with it.

The stations all have gone through rough repacks, and with an Air Force base that plays with EVERY signal (radio, tv, satellite) around, they can’t even trust their equipment sometimes. The PBS tech I talked to was frustrated that they were granted Digital 29, and have begun the transition, but there’s an analog 29 in the area that won’t give up their transmitter yet. He said because it’s a low powered religious channel, it doesn’t have to play by the same rules, and even though they’ve been granted digital 30, they aren’t ready to move, so PBS has to deal with the interference. And, surprise surprise, the mics that my contact was having trouble with lie right in that battle range. We’re going to try some things in a few weeks, relocate the rack (just in a travel case so no problem) and scan until we can’t scan any more for free frequencies, but all the tv guys seem to think it’s a crap shoot.

 

[Aaron Becker]

I suspect 12 might be pushing it with AT 3000 series.

It's been a long while since I've worked with AT so I'm not familiar with which "Version" of the 3000 series it is (IIRC, AT likes to re-brand the same "series" year after year), but it really will depend on which TV channels are in use. 12 channels inside a ~25 MHz range is doable, but you'd need a large majority of the range to do it. Throw one or two TV channels in there and some neighboring interference plus a spare channel, yeah, it may be a stretch.

 

[Aaron Becker]

He said because it’s a low powered religious channel, it doesn’t have to play by the same rules

We are all low-powered users and I don't think it's possible to get a license for overlapping frequencies in the same geographic area. But either way, it sounds like unusable space for you. Either way, you'll have to vacate the space.

 

[KBToys82]

These series covers Channels 26 - 29, and currently 26 - 28 are in use. I found about 4 frequencies within 26 - 28 that were fine. So that just left finding 8 channels within Channel 29. Already checked for intermod with Audio Technica's tool.

Cheapest tool I've seen on Sweetwater to check the spectrum and integrate it with WWB is $500 which right now is out of the budget, considering I still have 10 other channels outside of the AT's that are playing nice with the TV frequencies.

Tomorrow have to check all the transmitters interactions while they are turned on.

 

[Aaron Becker]

You won’t need a spectrum analyzer to tell you those TV channels are in use. If they’re in use - you’re almost certainly out of luck for those channels entirely now that the broadcasts are digital and take the entire 6 MHz.

That leaves you with 6 MHz to get 12 channels into. Unfortunately, this is going to be difficult. Check your documentation on the AT units for compatible frequencies in TV channel 29.

What version of the ATs are you using? feel free to leave that and someone else here may be able to take a second look for you (Including myself).

 

[FMEng]

It is possible to put something like 18 mics into 6 MHz, but it takes digital modulation, such as Shure QLXD or ULXD.

 

[KBToys82]

I'm using the 3rd generation ATW - 3110b or really just the 3000.

 

[NickVon]

I'm in NJ in the Metro NYC area as well, and there has defiantly been a distinct change even since October. I run a 10 Sennheisers in the most in the A, and a couple in the A1, B ( Duplex Gap) and have had to retune them for the last couple of shows each time. The AT you have are less agile if i recall, those the Gen 3 stuff might tune in .025mhz increments, most that i've worked with in schools systems have Gen 2 stuff which tunes in .125mhz incrememnts and getting them to work in the tighter spectrum has been a loosing battle.

Best bet is to fiddle around with WWB (wireless workbench 6; from Shure) and see if it can work out 12 frequencies for your area.

Let us know your specific zip and some of us may be able to assist more specifically to your use case.

If you don't have proper antenna distro and placement, now (well a year ago ) would be the time to optimize everything else about the RF environment you do have control over.

Those $2k per channel ULX-D's from sure are looking better and better.