In this video Stephen Pavlik walks me through how to create a link budget to find out if my IEM system will work…or why it didn’t work.
Download the infographic and get all 3 training videos
There is no single point solution.
Every point in the RF signal chain can either attenuate or amplify the signal. If it goes too low, we get dropouts. If it goes too high, we get overloads. Through maximizing efficiency at every point, we can avoid dropouts and quickly troubleshoot interference.
Don’t be intimidated! There is no difficult math. The only challenge is researching the loss or gain of each piece of equipment in your signal chain.
This transcript has been generated automatically. Please let me know if you find any errors.
Stephen, what are we doing here?
This is actually kind of one of my more favorite topics about audio, because we are broadcasting signal and trying to get it to tiny little packs that are weaker than are our big receivers, their big antennas. And so we really need to focus on how much signal we’re pushing out of these antennas to get to those little packets that are hidden by skin and clothes.
And this one could be a little bit challenging so a link budget is really helpful here. This is a fun topic.
So cool. If this is the first video you’ve seen of Stephen and I, we have done two more previous. So you might want to go back and check those out. There’s one we just did about wireless microphones. And there’s one that we did about antenna placement. And so now we’re doing something similar. But for your in your monitors. OK. So just like the previous one, it looks like we’ve got to start here and a finish and we’ve got a target with these numbers here that, again, make me think of a bull’s eye.
We’re trying to get somewhere in the middle where we’re not getting so low that we have drop outs and are so high that we have overloads, correct? Absolutely. And we’ve got this tiny little antenna here that needs to catch that. And it’s moving around the stage. You know, wherever the performer is, it’s challenging little antenna.
We need it. OK.
So we’ve got this info graphic and it should be fairly self-explanatory. But I’m going to try and get through it by myself. And we’re I started stumbling. I’ll ask you questions. Sounds great. OK. OK, start. And here’s a flowchart. It goes like this and it looks like each step in the chain. I’m going to have either some gain or some loss which are signaled by these plus and minuses. Correct. OK. And just so you know, we’re gonna go through this just talking about how the link budget is done.
And then afterwards, we’re going to switch to this one, which actually has real numbers in it. So you’ll be able to we’ll talk about how you can put your own numbers for your RF setup into this linked budget. OK. So we’re starting here with a transmitter that’s in the rack or sitting on a table. And that has some amount of gain and that we just look up in our specs. Right. Yes.
Or sometimes we’ll say on the front screen, if you’re scrolling through, depending on what manufacturer using, you can set that as well. How much gain is coming out of that transmitter? So it should be able to tell you on the front screen about what’s coming out of it.
Now, this is going to be harder for me because I have only worked with IEMs a handful of times. It’s not a part of my day to day work, but I need to understand it better so I might have more questions about this. So this will be fun.
So from that transmitter, we have to use a cable to get to a combiner if we’re using one. So we’re using multiple. Yeah. OK. And so that would be if, you know, you have several musicians on stage and you don’t want to have, you know, 20 different transmitter antennas all up on stage, you just want to. Right. Yes. OK. We’re going to have some amount of loss with the cable. And then some amount of gain or loss, depending on what type of combiner we’re using.
That’s correct. OK. And I should again, I should be able to just look those things up on this fact sheet and it’ll tell me how that works. Yes. I’ve got another cables that’s going to be a loss. Looks like we we’re going to need a little minus symbol here, right?
I think the the other one has it in. And when we get to the next day, there it is. OK. There’s the minus symbol.
OK. And plus antenna gain. So. And the antenna is going to be always some amount of gain. Yes. For for our purposes. For the most part, we’re always going to see gain from an antenna or or zero. No gain. We’re pretty much not going to see a negative. That’s again, a very rare circumstance. There is one I can think of that doesn’t. But that’s a boutique or especially antenna that I think we don’t necessarily to cut around this one right now.
And is there ever omni directional transmit antennas? I think I’ve only ever seen directional antennas that would have some amount of forward gain, right?
Absolutely, yeah. Only directional channels have boardgame omnidirectional tonight. Definitely can’t be used for him. And sometimes it definitely works better when you have a very, very tight space. You really don’t need a huge amount of directional gain because if you’re so tight, you have someone right next to the incentive. They may not have good coverage there. Also, a lot of times, guys that are blocked somewhere, let’s say from my background monitor engineers, a lot of guys with their cue pack on omnidirectional.
It’s a close to moderate world because we have a directional soundstage, basically artists. You’re a lot of times the normal signals try to fight through a giant metal console to get to your pack. You get a lot of dropouts doing that. And so you’ll see a lot of guys that on the inside as a monitor rule. And I said in smaller environments, I mean, it’s in us honesty are better than directional for IEM. Interesting. OK. OK.
So then we’re going to have some amount of lost due to polarization mismatch mis match. It’s hard to say it is.
We talked about this more in the last few days, so we don’t need to cover everything again. But my understanding now is that this is always going to be a loss because we’ll never have our antenna orientation and our transmitter orientation exactly matched.
That’s correct. And even if we have them, if we physically put them Side-By-Side correctly matched, our reflections are not going to be directly matched. So we’re always going to have some loss there. A lot of reflections.
And the other interesting thing that I learned from you in the last video is that even with our LPDA shark fin antennas, if we have a fixed installation, maybe we know that our microphone is going to a place like this. We we should turn our antenna sideways. And that’s why we often see people turning their antennas at a 45 degree angle. Because you’re sort of cutting your losses. Look, what’s a better way to say that to the best of both worlds, those worlds are horizontal or vertical.
If you don’t know if the microphone is going to be held like this and spoken like this or turned like this. Yeah. All right, so some amount of loss there that we can we can estimate by if we can somehow know the angle of that mismatch in degrees. But it sounds like also from our last conversation, a lot of times we just assume a negative GDP loss here.
Three is always a safe bet. You’re not going to have. You usually want to have less than that unless you have a lot of your banking on reflections and you’re able to predict that, which is pretty incredible.
You can assume 30 freespace loss. This is the signal now travelling to the ad’s left the Internet. There’s always gonna be some amount of loss as it tries to get to the air at this number here. The distance in meters has the biggest effect on this calculation. If we know the frequency and megahertz, that can make it more accurate. But really, this has the biggest effect on how far away the receiver is going to be. Yes, absolutely.
I mean, if you if you go from maybe 470 to 550, you might see a shift in one DB If you shift from twelve meters to 30 meters, you might see a shift in five or 10 TV. That’s huge. Yeah, and it is important to note that our freespace path loss is our bulk of our loss. So pretty much most the loss we’re going to see is in that actual wireless link. Which is why most people say they get their incentives.
Get your antennas closer to the transmitters because we be closing that gap. And we have less free space. Get lost in this. I mean, this seems like a moving target, really. I mean, do you really look at where’s my performer gonna be onstage? Because isn’t the whole point is that if they’re wireless, they can move anywhere. But I guess a lot of times people have like an area where they stay and. Right.
Or what’s your thinking room that you look for, the farthest area that they’re gonna go as far as they could be? Yes. Still likes it if it’s if it’s an artist. If there’s a catwalk or a thrust or a B stage, you know, make sure that you use that for your farthest point calculation. That fits talking head for the conference. If they’re going to walk through the room for Q&A type situations, we need to make sure the farthest seat in the back of the House is the measurement we use for that to make sure we look for the farthest that wireless device is going.
Gonna go and calculate the worst possible scenario.
Got it. And that’s the last step right now, so we should, if we had all those numbers, would now be able to calculate our Lync budget and know whether or not we’re hitting within our target.
Well, there’s one more point, which is the RX antenna gain.
What? Yeah. Yeah. There’s more.
So we mentioned briefly that microphones a little bit hard because they are omnidirectional and the type of antennas are using are pretty much zero DB. But we can assume basically about one dB from a whip antenna because it is quarter wave. And if we assume that a dipoles two point one, five 1/2 of that, it would be close to one. Now we do have a background plane. So we don’t have the negative side of a quarter of antenna, which is something that dial too deep here.
But we can assume assume close to one dB for antenna gain on the R X antenna or the the eye impact. Or if you want to be super safe, you can put zero again and assume worst case scenario. It go. OK. So we’ve done all our steps to kind of talk through it, should we look at the example now?
Sure. Today, yes, it just got a whole lot more complicated than this, wasn’t it? Those weren’t enough steps and just the talk first recap for a second about the motivation here. Why do I want to look at this before I show? Why should I spend you know, why should I spend my valuable time going through all of the steps in my RF signal chain?
Well, I mean, I think actually, let’s equate this to audio. We don’t. Let’s say that you are a monitor engineer. You don’t just guess that that Mike’s not going to feedback and say, hey, think it’s gonna be fine? And then walk out, then boom feedback. And then you’re stressed and struggling the whole night or same thing for front of house. You don’t just set your pin up and soon. Yeah, it’s gonna be great.
And then, you know, you have some sort of crazy phase error or a 30 millisecond delay on your, you know, whatever your left side because you’re trying some fancy thing to actually test it. We need to basically be aware of what we what our limits are, what our limitations are.
And also this visualization basically kind of gets us more thinking about every single step in our F system, because one thing that’s hard about troubleshooting RF is that it can be a lot of things and it could be any one of those things each time. So if you have a drop, it could be this tiny cable in the right or it could be this factor here. And it could just be a factor that decrease your signal by two or three. DB took it out.
But going through this and understanding what step every single step in the chain can kind of help you troubleshooting or wrap your mind around the entire wrap your mind around the entire RF system as a whole to kind of have some ideas of where to go when things start going south. If they do or if you do your homework right, they don’t work great. OK, cool. So if if a problem is that I’m making assumptions about my game staging of my aura system, then the solution is the link budget to write it all down.
Sure. Yeah. We, we can have some solid confirmation of yes. This is the plausible situation which is going to work well, or we can know that this isn’t gonna work for us. So we need to change something and we eliminate the guessing.
So tell me about the system we’ve got here. We’re starting with a Sennheiser G3 set at 30 milliwatts. Is that what’s happening? Yeah. And so for this one, because we’re talking about items, Sennheiser G three is probably the most common that’s out there for mid-level type stuff. So I think most of us, if we have you, I m we’d probably use something similar to a G three. So I thought that was a good example for this.
And other maximum output is 30 milliwatts. And so we will be using that, for example. And for this one, I just decide to change it up from LASO six megahertz, which is illegal because six or eight is our cutoff at this point. And then we’re gonna have six feet of RX8X Cable, which is actually excessive. But again, I want to throw a curveball in there. That’s saying six feet in your rack. And maybe you have a really tall rack.
Six feet from your combiner, from a transmitter to your combiner. And then for this one, we’re actually not using a an active combiner like, you know, I’m just using to pass it once or see some loss in there. That’s very interesting. OK. Yeah. So, again, it’s important to know the specs of the gear using it for using active combiner. You’re going to have is called a unity game. And we’re going to have zero dB because it compensates for loss that it creates.
But in this case, with your passive using something similar to this guy, we have really be of loss. So we need to add that into our calculations. So each system is so different. And when you make sure we know what each step is and added in there, from there we can have a long shot. We’re going on 50 feet. But we’re using 99 13 F7. What that is, it’s that’s the big low loss cable.
So we’re gonna save ourselves a little bit of lost there because we’re using a low lost cable as opposed to we use RG8X 50 feet run. Now we’re gonna go into a helical antenna was gonna have a higher gain for us to run to compensate for some of that loss for three dB, which that’s nothing to think about. If you’re designing a system, if you know you’re gonna have a lot of loss. We can make it for gain.
And things like antennas or less loss and cable so we can kind of start balancing work, designing systems. OK. So what we’re going to see negative 3 dB because we are fixed. So no matter how we orient the receiver pack, we know we are locked in 3 dB. And then from there, we’re gonna say that our ah artist, a performer or speaker, is 40 feet away. These two antennas are 40 feet away and freespace. And so we’re going to calculate that path loss by knowing our distance.
And by knowing the megahertz, the frequency that we’re working in, we can calculate out the formula down here. And we can get our number of freespace plus. And actually, we actually use this formula quite a bit. If you’re running with minus twenty seven point five, five is that’s the correction because this is normally a bleep gigahertz and kilometers. So that is the that’s a constant ship down to what we’re used to working in, which is megahertz.
And then from there, it’s pretty easy to convert to meters. OK. And we should posit quick, because last time you taught me how to. Milliwatts to DBI, which we use in this whole formula here in this link budget. And so why don’t I do that now? So 30 milliwatts, I’ll go over to my calculator. I’ll put in 30 lugg 10 times 10, and then I’ll give me fourteen point seven seven, which is what you have here.
There it is. Yeah. That’s that number NDB. Perfect. Yeah.
I learned a thing. I remember this tomorrow. Maybe we should actually add this to the info graphic here. Said it’s not super clear that how we got from here to here. Yeah, I be great. OK, great. We’ll add that.
OK. So we we stopped at freespace, path loss. Yes. So from there, we we had our actual R.F. link, which is the path lost from antenna two antenna, and then so once we get to the other antenna, which is the little quarter way with guy here on our impact, we have a little bit of gain there because a quarter of a whip does have a small amount of gain. That gain somewhat depends on the the actual ground around it.
But we can say best case scenario, let’s say one. If you want to shoot for worst case scenario, we can say zero. But just for fun, these are put in one TV on this one to see what we come up with.
OK. OK. So then we just add all those numbers together, whether or not it’s a gain or at a loss at each stage in our chain here. And you came up with negative three 30 DBE, which puts us safely above negative 40. Our green number here and you’ve been telling me that that that number will most likely be lower when we get down to the field. So it’s good to shoot for a higher number. Absolutely. We’ll have we’ll have loss.
But things that are hard to predict, like body loss and there’ll be some fading multi path loss. So it’s good to shoot high and understand to have maybe 20, 30 dB of loss the field. So that puts us there’s no way we could save maybe 30 is getting a little too high. But that’s part of it because the rewards narrows that down a little bit. We’re in a great spot for the receiver. And also, if we we factor in that 3 dB of mismatch, lost that election.
But in there, we’re at negative thirty three. If we want to be super particular. But yeah, that’s still puts us in a very good, very good area. So I would say that if we had this system and our artists or our whoever it is using the IBM is 40 feet away there. You have great signal they’re not going to have any problems.
Awesome. Stephen, thank you so much for putting this together. This is a lot more clear for me now that I’ve gotten to talk with you about it, even though I looked at it ahead of time. So if it’s OK with you, I would love to invite people to post their own. I am link budgets here below this video. And then I’ll just ask you if they want if you can give them feedback on. Yeah, great. So this looks like a lot of work, but I think, you know, if anyone wanting to work on this just takes it step by step, make out your list.
What I need to know next. Look it up in the specification sheet or, you know, take the estimation. What’s the farthest distance that receiver away could be away on stage and plug the numbers in. Then all you have to do is add them up. Beyond that, the math isn’t very complicated.
No, no, just just keeping keeping account of everything in that chain is the main is the hardest thing is knowing every single piece in that chain and what kind of loss or gain is going to attribute. Awesome. Well, Stephen, thank you again for putting this together and for those of you out there watching this video. I’d love to hear how you do this. You know, if you think that we’re doing it wrong and you do it a different way, that’s better.
That’s fine. We’d love to hear about it. So comment on the video and we’ll keep the conversation going.
Niklas Harju says
Hello Nathan and Stephen! These videos were really great, thank you! One thing though that I don’t understand, since I never took advanced math in school 🙂 How do you actually calculate the free space path loss? I just can’t get the numbers to add up in the calculator.
Stephen pavlik says
I’m glad you liked the videos! And no worries, it’s all about the order of operations. You have to preform the log function first, then the multiplication and then the addition and subtraction. For the IEM example with a distance of 12.2 meters and a frequency of 600MHz it goes like this.
The infographic shows the answer as 49.73 that could have been how I was rounding or a typo (I honestly don’t remember )