How are wireless microphone "bands" defined?

[Stevens R. Miller]

Times Microwave LMR240 or LMR400 or similar low-loss cable. I spec 240 for short runs (50 ft or less).

Man, that stuff costs, but it does have better specs that even RG-8X, which is what everybody was using for UHF years ago when I was more active. I suppose I don't really need much. What I'd like to do is be able to space the antennas apart enough to avoid the LO leakage interference we were talking about earlier. I doubt my venues would be happy with me I festooned their stages with a lot of RF hoses.

 

[TimMc]

The loss in cable is still less than the loss in air so a less expensive product is unlikely to compromise your RF levels. The receiver-mounted 1/4 wave antennas need a ground plane, so simply extending a lead and hanging them around will not really help. If you go to half-wave antennas and antenna distribution system you won't need a ground plane.

I've gone through this with a youth musical theater company that, until the first DTV repack and 700mHz spectrum auction, simply piled up their receivers on a table next to the SM. I found a tall and narrow wood bookcase in the PAC that I repurposed as a receiver holder; separating the receivers by 16" combined with getting them above head-height made a significant improvement in RF performance. After the DTV repack 1 of their units sat squarely in the middle of a local full power TV stations new DTV channel, so they purchased an addition unit that ended up creating IM with another of their fixed frequency systems. After a couple of disastrous performances the company decided to rent wireless mic systems and found sponsors to help pay for the rentals.

 

[Stevens R. Miller]

The loss in cable is still less than the loss in air so a less expensive product is unlikely to compromise your RF levels. The receiver-mounted 1/4 wave antennas need a ground plane, so simply extending a lead and hanging them around will not really help. If you go to half-wave antennas and antenna distribution system you won't need a ground plane.

I can see a distro system in our future. Making UHF 1/4-waves with ground planes is easy, though sixteen of them in one place would start to look like Brobdingnagian barbed-wire, I think. For a half-wave, do you envision a dipole? If so, how would you suggest I polarize them? (If I really get ambitious, I will make a set of log-periodics; they're harder to fabricate that 1/4-waves, but not that much.)

 

[TimMc]

I can see a distro system in our future. Making UHF 1/4-waves with ground planes is easy, though sixteen of them in one place would start to look like Brobdingnagian barbed-wire, I think. For a half-wave, do you envision a dipole? If so, how would you suggest I polarize them? (If I really get ambitious, I will make a set of log-periodics; they're harder to fabricate that 1/4-waves, but not that much.)

Yep, dipole. Take a look at Shure, Sennheiser, Lectrosonics, Audio-Technica offerings and you'll have a better mental picture of the stock solutions from them. Since you have the chops to roll your own you can do some things they can't, like tuning your antennae to relatively narrow bands. When a stock LPDA has nearly an octave of advertised bandwidth you know how much "extra" RF it's delivering to the receiver...

 

[Stevens R. Miller]

Yep, dipole. Take a look at Shure, Sennheiser, Lectrosonics, Audio-Technica offerings and you'll have a better mental picture of the stock solutions from them. Since you have the chops to roll your own you can do some things they can't, like tuning your antennae to relatively narrow bands. When a stock LPDA has nearly an octave of advertised bandwidth you know how much "extra" RF it's delivering to the receiver...

Good idea. Other than "paddles," I haven't come across many antenna offerings in this area. Got a link for me?

I suppose if I'm going to build finely tuned dipoles, I could take a few extra steps and make Yagis.

Or, I could really freak out my company and make helicals. (Imagine a 4x4 matrix of those monsters, aimed at you from the wings!)

 

[Jay Ashworth]

Just do the math. Look at the loss (dB/100 ft). If the loss for the actual length used is less than 3-4 dB,

*at the frequency you're working at*

don't worry about it.

I was gonna say LMR240 also; you don't generally need the heavier stuff for receive applications.

 

[Jay Ashworth]

They're log-periodics because the bands they need to cover are a significant fraction of an octave, yeah. If you have frequency agile receivers, you don't really want to custom-cut the antennas, in my opinion.

This is *also* why you use an amp and splitter; a *good*, competent antenna isn't something you wanna make 24 of.

 

[Stevens R. Miller]

They're log-periodics because the bands they need to cover are a significant fraction of an octave, yeah. If you have frequency agile receivers, you don't really want to custom-cut the antennas, in my opinion.

The rigs we've bought operate over a 24 MHz chunk near 550 MHz. We're not going to have to cope with anything like much of an octave. Regardless, fine-tuning antennas for this application is probably pointless in any case. I say that because, when you are outdoors on a flat plane with your antenna on a fixed tower, maybe you can use all those beautiful radio formulas to predict the match you'll get for a certain frequency with a certain length of radiator. Indoors, in a theater or auditorium, with lots of other gear nearby, and walls, and wiring, and people wandering around... the apparent length of your radiators is going to change no matter how precisely you cut them on the bench. I have a very successful quarter-wave with a drooping ground plane up in my attic. I use it at 446 MHz. The math says it ought to be about 15 cm long. But my SWR meter didn't agree, so it's less than 14 cm long. Probably capacitance from the surrounding in my attic are effectively lengthening it.

This is *also* why you use an amp and splitter; a *good*, competent antenna isn't something you wanna make 24 of.

And that's just to get a set polarized one way. The Samson receivers are of the kind that have two front-ends, so the device can pick the one that is delivering the strongest signal from each of two antennas polarized cross-wise. That's one reason a helical actually appeals to me. You can never make a vertical and helical match in polarization, but (unless the vertical is pointed at the helical) you always have something intersecting the E-field.

 

[Jay Ashworth]

Oh sure. Helicals are just kinda flimsy and easy to break, or difficult to build good housings for in a manufactory environment; take your pick how you wanna look at that.

I was never a real antenna guy; can you get 24MHz out of a receive helical?

 

[Stevens R. Miller]

I was never a real antenna guy; can you get 24MHz out of a receive helical?

I suppose the question is really, "How bad's the mismatch at the ends of a 24 MHz range?" The manufacturers make some pretty eye-popping claims about the commercial antennas they sell. They might even be true, and I've read some interesting stuff about helical antennas that had varying pitch in their windings, so who really knows?

What I do know is that those environmental factors always seem to make the laws of physics more like opinions in practice. Since mismatch doesn't reflect power of any significance in a receive-only context. you can get away with quite a bit. (On the transmit side, I've had a lot of success using a fat 50Ω resistor as an "antenna" on my VHF/UHG hand-held transceivers. For use in a theater, it works fine at 500mW. Saves a lot of wear and tear on your vocal cords when you're standing on the stage saying, "No, not that one, try thirty-three. No, try thirty-four," and so on.)

To be honest, I will probably never get to helical antennas. Most likely, I will start with a corner reflector, since that provides a ground plane for a quarter-wave vertical, some directionality, some gain, and is easy to make with cardboard and tin-foil. A more ambitious project might be a small quad. At the 550 MHz regime, one of those would only be five inches on a side, with a ten-inch boom. Again, cheap and easy to make.

Our first set of Samson rigs arrived yesterday. Off to pick them up shortly. Will post a review, as promised.

 

[Ben Stiegler]

Too late, perhaps, but ...
Samson ... in my experience, u get what u pay for and you’ll likely be paying again soon.

Questions that should be asked before buying anything

1) where exactly are you? Rural? Metro? How near are public safety locations or donut shops where they might congregate? Fire.police.ambulance uses a lot more to power than you can, and I’ve had to engineer special measures (far beyond paddle antennae) to fire-proof (sorry) several Bay Area venues

2) what’s max number of wireless mics and other devices you anticipate using? Low count ... might get away with analog. Higher, or lots of tv/public safety ... you need digital which is more noise resistant, and uses tinier slice of spectrum successfully.

Etc.

There a lot of math and modeling we usually do to prepare for a successful wireless deployment ... and then some ongoing monitoring / analytics to keep an ear on the spectrum as it’s used. My fingers won’t take writing the rest of the how2succeedinwirelesswithoutreallytrying treatise in here, but DM me if you’d like some help planning for success vs. doing experiments.

Good luck!

 

[Stevens R. Miller]

Too late, perhaps, but ...
Samson ... in my experience, u get what u pay for and you’ll likely be paying again soon.

...DM me if you’d like some help planning for success vs. doing experiments.

I've been testing our first two Samsons on my bench. So far, they are superb. Packs are not as sturdy as more expensive stuff, but they are smaller and lighter. Audio quality is more than adequate for our needs. I also like the continuously variable attenuator. One of my colleagues groused that there is no battery level indicator on the packs, but there is an indicator at the Rx, so you can see it during a show, which I like. (As for what it says, we use fresh cells for every single show. Unless one is bad, we kind of know what the indicator is going to say.)

After almost half a century working with radio electronics (and other electronics), I've come to the conclusion that the extra money you pay for a "name" brand does, in fact, get you something that the lesser brands simply cannot provide: the name. So-called "inferior" stuff often keeps up quite well if you treat it gently and apply an aggressive maintenance program.

Since we perform all over Loudoun county, doing experiments is a fact of life. If I were in a fixed permanent venue, it might be different. But techie work for amateur theater is, in my experience, a continuous process of putting out fires. Kind of what makes it fun, actually.

As for money: I've made this point before, that my little companies just can't take the advice I often get to spend more than we have. We only have what we have. But, again, some TLC and reasonable expectations make up for a lot. While back, a number of folks advised me against buying crummy Chinese lights instead of comparable (in terms of colors and radiation) name instruments. The name stuff cost about $500 each, as opposed to the crummy Chinese cheapies, that were $50 each. Well, those Chinese lights are still in service, working fine, and look like they'll last as long as we remember to be gentle. I know they are regarded as unreliable, but, if one ever fails (hasn't happened yet), I bought a spare. At $50 each, even we can afford to do that.

 

[FMEng]

After almost half a century working with radio electronics (and other electronics), I've come to the conclusion that the extra money you pay for a "name" brand does, in fact, get you something that the lesser brands simply cannot provide: the name. So-called "inferior" stuff often keeps up quite well if you treat it gently and apply an aggressive maintenance program.

I think that wireless mics are a strong exception to that. What you can't easily see or measure is the selectivity of the IF filter, the RF sensitivity, the tolerance for RF overload, the number of intermodulation products generated by each transmitter, etc.

A small number of less expensive units will generally perform just fine, but the challenges go up exponentially with the number of systems operating together. What separates cheap from quality is how they work when there are 6, 10, 20 of them running together, and it's why better manufacturers specify how many systems of a given type will behave together, and how much spectrum they need to do it. Some manufactures are afraid to tell us.

With cheaper systems, you may have difficulties that you chalk up to interference in the venue, or antenna placement, or a weak battery, or something else, that would have been completely avoided by better hardware. I'm not afraid to cut corners with low risk components, but I have too many scars from wireless mics to use anything but middle tier or better, from the top three manufacturers.

 

[RonHebbard]

I think that wireless mics are a strong exception to that. What you can't easily see or measure is the selectivity of the IF filter, the RF sensitivity, the tolerance for RF overload, the number of intermodulation products generated by each transmitter, etc.

A small number of less expensive units will generally perform just fine, but the challenges go up exponentially with the number of systems operating together. What separates cheap from quality is how they work when there are 6, 10, 20 of them running together, and it's why better manufacturers specify how many systems of a given type will behave together, and how much spectrum they need to do it. Some manufactures are afraid to tell us.

With cheaper systems, you may have difficulties that you chalk up to interference in the venue, or antenna placement, or a weak battery, or something else, that would have been completely avoided by better hardware. I'm not afraid to cut corners with low risk components, but I have too many scars from wireless mics to use anything but middle tier or better, from the top three manufacturers.

@Stevens R. Miller and @FMEng And then you add wireless guitars, wireless in-ears, wireless comms plus wireless DMX and an audience full of cell phones along with taxi's coming and going outside your lobby plus the two local police you've hired for security; tell me again about your low-tier successes. In the early days of wireless mics, The Stratford Shakespearean Festival was occasionally picking up taxi's outside our entrances on our Cetec Vega's of the era.
Toodleoo!
Ron Hebbard

 

[TimMc]

@Stevens R. Miller and @FMEng And then you add wireless guitars, wireless in-ears, wireless comms plus wireless DMX and an audience full of cell phones along with taxi's coming and going outside your lobby plus the two local police you've hired for security; tell me again about your low-tier successes. In the early days of wireless mics, The Stratford Shakespearean Festival was occasionally picking up taxi's outside our entrances on our Cetec Vega's of the era.
Toodleoo!
Ron Hebbard

But is it the Big Yellow Taxi?

 

[Stevens R. Miller]

I think that wireless mics are a strong exception to that. What you can't easily see or measure is the selectivity of the IF filter, the RF sensitivity, the tolerance for RF overload, the number of intermodulation products generated by each transmitter, etc.

IMD is a function of frequency choices. The Samsons have tables for groups of eight that look comparable to the tables you find in other brands' manuals, and math is math, no matter how much you spend.

RF overload from a few 10mW transmitters doesn't worry me much.

RF sensitivity is actually easy to measure and, so far, I'm pleased with my bench tests with the Samsons.

IF selectivity is another matter. Here I have to guess that, deep into the 21st century, electronics have become largely off-the-shelf. Over and over, in other areas, I've found virtually identical circuitry (sometimes genuinely identical circuitry) when comparing what's under the lids of competing products. Now, not everything is a circuit. Construction matters too. Things like mounting transformers at right angles to each other in stereo devices used to be a sign of the better brands; now you see it everywhere.

After all these years, when I think back to the '70s, and how the most expensive stuff we had then compares with the cheaper stuff we can buy today, I actually don't mind (as much) that we don't have flying cars. (Speaking of cars, we don't have taxis, police, etc., near our shows. And we just ask the audiences to turn off their cell phones, mostly because even a silenced phone blares loud for an "Amber" alert; I am in that minority that does not believe cell phones emit in the microphone spectrum.)

And, again, cheap is not a choice we are making. We buy cheap or we don't buy.

 

[FMEng]

IMD is a function of frequency choices, but it is also a function of amplifier characteristics. The design of the transmitter's final stage and the receiver's input stages are also factors. IMD products can be made and re-radiated in either of those places.

RF overload can be caused by other signals in the environment, not just the mic transmitters. A room full of cell phones, or the TV transmitter miles away, can clobber a poorly designed receiver. The interference source doesn't necessarily have to be in the same band. Again, it all depends of the design of the receiver. Is the front end barn door wide, or properly filtered? There is a lot of junk out there.

I respect the fact that you have to buy what you can afford. I just don't want to leave the impression that cheaper is just fine in all cases and will work anywhere. That's just plain false. "You get what you pay for" is still valid.

 

[Stevens R. Miller]

IMD is a function of frequency choices, but it is also a function of amplifier characteristics. The design of the transmitter's final stage and the receiver's input stages are also factors. IMD products can be made and re-radiated in either of those places.

RF overload can be caused by other signals in the environment, not just the mic transmitters. A room full of cell phones, or the TV transmitter miles away, can clobber a poorly designed receiver. The interference source doesn't necessarily have to be in the same band. Again, it all depends of the design of the receiver. Is the front end barn door wide, or properly filtered? There is a lot of junk out there.

All true, but these are the kinds of issues I am willing to deal with, particularly when 90% of all problems I have ever had with any wireless microphones I have used have been at the mike-to-pack connector. (Another 5% have been at the element, and the last 5% are solved by judicious frequency choices and scheduling the right packs with the right actors.)

I respect the fact that you have to buy what you can afford. I just don't want to leave the impression that cheaper is just fine in all cases and will work anywhere. That's just plain false. "You get what you pay for" is still valid.

Just to beat this dead horse a moment longer, I will certainly agree that "cheaper is fine in all cases" is NOT true. "You get what you pay for" is also not true in all cases. I have paid quite a lot at various times in my life, only to find what I got was expensive junk. My experiences with theater tech over the last three years have very closely aligned with my experiences with ham radio over the last 45: A lot of good stuff costs a lot of money, and a lot of bad stuff also costs a lot of money. If you are cautious, willing to put in some research, do some extra work, set your expectations at practical levels, and scrutinize your precise needs, you can sometimes find inexpensive options that work well enough for your needs.

But, lest anyone reading all this get the wrong idea, I will reaffirm a point we agree on: Cheaper is NOT always fine.

 

[Aaron Becker]

And we just ask the audiences to turn off their cell phones

Believe what you want, people aren't turning them off. 100% guaranteed.

After all these years, when I think back to the '70s, and how the most expensive stuff we had then compares with the cheaper stuff we can buy today...

I can't speak for the 70s, but the industry standard wireless microphones for professional shows in the late 90s are still better than any cheap stuff manufactured today - purely by the fact that it was built to last. The only thing wrong with the Shure U series (or the equivalent Senny gear) was that the FCC auctioned off the spectrum. I had systems upon systems of U-series chugging along without an end in sight until the FCC sold off the 700 MHz band. The were built rock solid and were leaps and bounds ahead of anything else produced around the same time.

I truly hope your "cheap" gear works and the gamble pays off for you. I agree with @FMEng - wireless mics have always been - and will continue to be the exception to buying cheap and hoping it works, especially in this industry. If it was my gig and it was a choice of buying cheap vs not at all - I'd be saving my money and not buying at all - period.

 

[DavidJones]

Sometimes cheaper is fine, and sometimes more expensive things ARE actually nicer, but you don't actually NEED those nice things. Somethings are more expensive because you can still get 24-hour tech support on a 20-year-old product that you bought second, or third, or fourth-hand. You cannot expect that kind of support from a budget product, but if you have the knowledge and time to do your own testing, maintenance, and troubleshooting, maybe even modifications, you can certainly get an inexpensive product to work well.

My main observations in "Cheap" vs "expensive" is physical build quality, and ease of use. A lot of times the actual functionality is similar. Sometimes paying more is worth not having to look up what the random codes mean on the menus and what combinations of buttons to press, just to change basic settings, other times its worth extra hassle to save money.