By way of background, I've never used a wireless system.

I record orchestras, concert bands, etc in a church. I usually run XLR cables from my mics to a balcony about 80 - 100 feet from the stage and have my SD 702 upstairs. I run another pair of XLR cables out of the 702 and distribute to three cameras in the balcony for sync.

150 feet of cable doesn't sound like much, but it has to run a pretty circuitous route to get upstairs - across aisles (using protectors to keep folks from tripping on the cables,) along walls, up a staircase, etc using lots of gaffer tape. It's a time consuming project to get it all in place as a ladder is needed at a couple of points. In technical terms, it's a time consuming PITA!!!!!

I'm losing my "trained" cable laying team for the next concert so have been wondering if I could replace the long XLR cables with a wireless link of some kind. I'll be bringing the 702 downstairs and setting it up near the mics and would like to take the signal out of the 702 and send sync signal to the balcony. Since it's only for sync using PluralEyes, I think Mono would be OK and quality doesn't have to be the greatest.

Any thoughts/recommendations would be welcomed. I'd like to keep the cost under $500 or so if possible..

if you use pluraleyes to sync in post then you don't need to run from the recorder to the cameras. just use the tracks from the cameras (on a shotgun or even the internal mics) to let pluraleyes compare and sync and then delete the tracks of the cameras (that will be needed only to sync)

$500 is not reasonable for even a system with one transmitter and one receiver. And it will be expensive to assemble a system with one transmitter and three receivers because that is not the "normal" use-case.

Instead of using a cheap wireless system, maybe we don't understand why you even need to run signals into the cameras? Many of us do this same kind of thing with nothing more than the built-in mics on the cameras as a sync source. I typically don't recommend using the on-camera mic for anything. But using it as a sync source is one of the few legitimate uses, IMHO.

I agree with Richard. $500 is about the entry point for reasonably reliable single channel wireless systems for voice. If you plan for good music it gets higher. The camcorder audio should be sufficient for sync with most NLEs. System like the AT 10 discussed in recent threads are under $500 and might work, but the jury is still out on them, and, especially fed from a mixer/recorder.

Many wireless systems sell receivers only so you could have one xmitter feeding several receivers, although that is not the most common configuration.

If the camcorders are not in audio AGC mode it can often help when using the waveform for sound sync.

I concur with Richard, your better off using camera mics for sync than a cheap (unreliable) wireless system.( Though the picture, 'may' need to be bumped a frame or two due to the inherent time delay.. (.Approx.1ms per foot <> 1 frame=30 feet )
BTW, AFAIK.. with the new. low cost wireless systems from AT, Rode and Sennheiser, it's not possible to have multiple receivers with just one transmitter, which can be done with conventional VHS and UHF systems.

A couple of questions:

What is the actual distance you'll need to transmit?

Is it any problem running an additional small audio mixer and cables from the front of the balcony to the cameras to assure line-of-sight from the transmitter to the receiver?

Since it's mainly for sync, I would use a wireless set that I've written about here before. The Wi Digital WI-ALP55 (I actually have the model 35). It has an advertised range of 100 feet line of sight and I've tested mine through multiple walls out to about 75 feet before breakup.

B&H and other online vendors are currently selling this set for $199 and it comes with the additional USB transmitter "free" (and other extras depending on the vendor).

I've used this set several times in highly crowded 2.4Ghz areas with no problems, and if you just need it for a good strong sync track it would be great. The stereo audio quality is very good! It's useful for so many short-range, stereo transmitting and monitoring tasks.

To reduce your cost I would just use one set, then an inexpensive audio mixer and balanced cables to distribute in the balcony to all three cameras.

I've converted two old light stands by substituting a long wood dowel for the top section of aluminum to elevate the transmitter and receiver for better line-of-sight without having metal right at the devices.

The set I have has a latency of 3/4 of one frame, hardly anything to worry about. And the signal will be much stronger and cleaner than using the on-camera mics to get your software to sync up.

I've run them 4 hours with no problem, but you can also power them by USB if you need really long runtime.

If you decide not to use wireless, I would at least rig up a single small-diaphragm condenser mic at the front of the balcony and distribute this signal to all three cameras. You'd have slightly better audio quality and all three cameras would have the exact same delay.

If on-camera mics are used, 80 - 100 feet will introduce a delay of ~ 72 - 90 msec., although if all three cameras are the same distance from the stage that won't matter very much. Additionally, the sound at that distance will be fairly diffuse and heavy with reverberation, which might make it more difficult to sync the tracks "by ear."

How crowded is the FM broadcast band in Tucson? There are online search engines that will help you find the best "empty channels" between area broadcast stations. (Consider that most drive-in movie theatres use the FM broadcast band to distribute their sound track to cars over a radius of many hundred feet.)

For much less than $500 you could find an FM-band transmitter (most are stereo, although stereo reception actually makes coverage worse) and three portable FM broadcast receivers.

Of course, as with any wireless system, if you want to be really confident, you'd want to test this in advance of the actual event. Also, operation of an unlicensed low power transmitter like this is covered under Part 15 of the FCC rules, which includes audio transmitters (including the ones in XM and Sirius radios), and things like baby monitors, cordless phones, remote door locks for cars, and tons of other things. Still, if you have any qualms about legality, you'd have to do your own research.

I run a wireless link between my Boom Pole operator and camera using a Sennheiser G3 Plugon transmitter on his mixer output and a standard battery powered beltpack reciever on my camera which gives me mic level into the camera. You could do the same thing to provide a wireless link to the balcony. If you want that audio into all your cameras, you could then go wired using a distribution amp connected to your receiver. They make AC powered receivers too. I found 100' a stretch for my Senny G1 wireless units. So that line of sight distance on the G3 is an area to research.

I have, currently, something like 36 or so channels of radio microphones of all kinds, analogue or digital, and I can safely say that given the choice of using the receivers 80 feet away from the transmitter, or using a long cable, the cable wins EVERY time. Radio mics are exceptional, until they are not, and if you need reliability that can be predicted, then it's cable - the only sensible option.

In fact, theatres where we do most of our work, it is standard practice to have the receivers on stage, as close to the artistes as possible, and then a multi-core cable, or now cat5, gets the receivers back to the rear stalls mixer. Signal strength in a straight line, in a field, can be quite impressive - but in a building, never so easy. We use Sennheiser's mac application that can track and even record signal strength, and if you watch it, it stays most of the time at 'plenty' then suddenly takes a dive into dropout territory. Hopefully, your signal won't drop below the danger level and while you might get a 'thut', it won't die. Move the aerials further apart, and the average level is still usable, but the nulls will cut you out!

Every time you get to the end, on a system with distance in it, you breath a sigh of relief. One little 'phutt' with some of the people I work with, and they tell 1400 people the equipment AND the operator is Crap! (Thanks Mr Davidson) From time to time, people try using multi-element aerials with 10dB or more gain, but they have many side lobes and sometimes, despite all this gain, a member of the audience going to the loo can introduce just enough attenuation to cause a drop out.

With typical video kit, even with diversity types, there really isn't enough separation between the aerials to make the benefits of diversity work for you, and the small aerials at both ends (usually ¼ wave dipoles) often work without a ground plane, so are nowhere near resonant, and therefore inefficient.

The only rule is distance needs to be the shortest you can manage.

Brand wise, I've never noticed any real difference despite their range claims. The important thing is that aerials and feeder cable don't mean they'll be as good as a few pounds of mic cable.

As for a trained cable laying team? Is there something particularly complicated about it. Cable duties in my world fall to the lower end of my teams ability. If they can't lay a cable, then can they do their shoelaces up?

A thought - If this is a frequent or standing event, just run the cables permanently.

Thanks for the comments

I only need one channel - I already have a distribution box with the cameras so one input is enough.

There are usually 2 to 4 cameras close to (or on) the stage as well as the three in the balcony.

Cable laying is a royal pain in the A--! The cable has to cross several areas where the audience will be walking around so several lengths of cable protector have to be taped down and the cable has to be taped to the baseboard all along the run to keep a loop from snagging someone's foot since it runs down the side aisle of the church. It then has to go 10 feet up a wall so it can get led/gaffer taped across the top of the entrance doorway (this is where the ladder is needed) and then up the rest of the way to the balcony where it gets taped to the railing for another 20 or 30 feet. I typically don't have much time to get this done although the church will sometimes allow me to get in the night before to run the cable but this doesn't work if there's another event that evening as they don't want the cables in sight if something else is going on. I figure I do this setup maybe 5 to 7 times a year.

Did I say I was a one man band for all of this??? I've had a couple of folks help with the cable laying, but I can't depend on them being there all the time.

Syncing the cameras by eye is also a real time waster as the conductor is anal about the sync of the sound and the image - it usually takes us a few hours to get it "right". I used PluraEyes the last time and it saved hours of time fussing around and having two or three people looking intently at how close the sound was to fingers hitting keys etc.

Cameras are about 80 feet from the mics (line of sight) and 125 - 150 feet as the cable runs

If you need the audio just for sync, you don't need perfect fidelity. If the signal level occasionally drops below full quieting, and you get a little noise, you'll still be able to sync. Even if you have a dropout for a fraction of a second, you will still have plenty of audio for sync.

I still think a low power FM broadcast band (88.1 - 108.1 MHz) link would be perfectly adequate for this. Some "consumer" transmitters are really junk, but there are a few that put out a very respectable signal for under $50.00. Some are made with "Part 15 community radio stations" in mind, and even have an external antenna. In either case, try hard to get line of sight from transmitter to your receivers. If the transmitter has an external antenna, carefully adjust the length to match your frequency.

Believe me, a better transmitter will not be plagued with all the RF absorption issues that you have with a wireless mic's body pack and short antenna hanging against the talent's body.

For redundancy, split the camera's inputs. Mono radio link into one channel, and a camera-mounted mic on the other. As long as the radio link works, you've saved yourself a lot of painful cable running. Even if the radio link fails completely, you still have camera audio (albeit with delay and reverb) so you have something to sync to.

Take a look at this frequency finder:
Vacant Channel Search Results (http://www.radio-locator.com/cgi-bin/vacant?select=city&city=tucson&state=az&x=14&y=5)

Get yourself an acceptable portable radio, go to the church in question, and try the indicated frequencies. See if one or more are truly quiet. If so, the odds are in your favor. Even if one has very weak signal in the background, a good local transmitter should capture the channel. I'll be glad to give you more details if you want to pursue this.

Hi Greg

Interesting idea - never would have thought of that. It's worth a try

Do you know of any good transmitters?

Jim,

Since you need only one channel, use mono receivers, or combine the receiver L+R to get mono, because FM reception is much less susceptible to noise in mono mode.

One brand with a good reputation is Ramsey Electronics Ramsey Electronics® (http://www.ramseyelectronics.com/)

They have several different models with a variety of features, some with RF output too high to be legal in the US (those are sold "for export only"). One advantage is that they have external whip antennas, so you can adjust the antenna length to correspond to the frequency you choose. Many of their products are kits, but you will also find some sold on eBay pre-assembled. At any rate, you want to be sure that whatever you buy is frequency synthesized so it's easy to tune and won't drift.

If those look too expensive for you, or if you don't want to get involved with assembly, let me know and I can offer some other suggestions. I will be offline for the next two or three days, so don't be put off if I don't reply right away.

Azden offered a low cost VHF band 2-frequency wireless system (WLX Pro series).
It include a plug-on transmitter as well as body pack transmitters for about $150.
Extra receivers can be bought separately for about $85 each (e.g., from B&H).

I've used this series them for voice applications in the past.

For more money you could get a UHF model with something 92 frequencies, and plug-in transmitter (better for taking output from a mixer).

I got hold of an AudioTechnica System 10 and have been running tests here at the house, which is a tad over 100 feet end to end.

I put the included lav mic and transmitter at one end of the house in my office, started something playing on my monitors, and went to the garage about 100-110 feet away through a few walls and the fire door. At that distance I was getting a very occasional dropout but it sounded pretty damned good about 98% of the time.

Just for fun I went outside and around 15 to 20 feet further away I began to get a significant number of dropouts and at about 20 to 30 feet I lost the signal completely

All in all I'd say that based on this exacting scientific (ha!) test it seems more then adequate for a sync track up to about 110 feet through walls and doors.

Since I need it to work at 70 to 80 feet clear line of sight I think it will do the job. If I get a chance I'll run over to the church one day this coming week and run a quick test, but so far it's encouraging and for $449.95 it even fits the budget. And the included lav sounds much better than I thought it would. So far I'm pretty impressed with the product.

Thanks Jim

It's great to get a "real life" test. I'm sure it will work for me as at weddings I'm seldom more than 30' from the transmitter and it's line of site too with no walls!! The only thing I'm still struggling to find is a second transmitter only?? The System 10 apparently can handle up to 8 transmitters and at Church weddings I do need an extra one for bible readings ... the cost of a system 10 plus an extra transmitter would be significantly less than buying two wireless systems like I have now.

Your comments after the Church test will be appreciated ...I think it would also be good to test it in a crowd with people using IPads and phones and see if there is any conflicts.

Chris

Just an offbeat suggestion / question ...

Does the facility have a closed induction loop for people with hearing aids? And can you possibly make use of it?

Andrew

Hi Chris

There's one nice thing about recording 2 hour classical concerts - people are good about turning off phones and etc so I'm not too worried about interference (I know - famous last words...) And this is Tucson so most of the audience is too old to know what a cell phone is! I'm getting close to turning 75 and I feel like a kid at the concerts!

The biggest "interference" issue I have to deal with is the chorus of coughing and sneezing that seems to go on for the first 10 minutes of the concert. I spend a lot of time in Izotope "curing" colds and allergies. Now if only there was a plug-in to make the cure work on the people instead of just the audio track.

@ Andrew - There doesn't seem to be a closed loop system in place.

Hey, a 74 year old on the internet. Awesome! :-P

(ducks low-flying incoming object)

Andrew

I had a mis-spent "childhood" - started programming for pay in 1959 when we were still running computers on steam. Shoveling enough coal to make the steam was tough.

Actually the old disk drives used hydraulics to move the read-write heads around. There were several calibrated cylinders with varying amounts of fluid in each one and tracks were physically addressed by activating a set of pistons that would inject a known quantity of hydraulic fluid to move the heads across the platters.Simple.

Memory - well I worked on systems that used tubes of Mercury as memory, as well as systems that used CRT tubes as memory devices (Google "Univac I" and "Williams Tubes").

http://en.wikipedia.org/wiki/Williams_tube

Hi Jim

I'm not that far behind you (69 this year and still feel sprightly and can handle a wedding full day shoot with no issues)

Can you guys get transmitters only for the System 10?? I can only find the pair locally but I'll contact the agents here. AT must supply just a transmitter if the system can handle more than one.

Our frequency changes here are becoming ridiculous so I need to go to a band where they don't decide to re-allocate the frequencies to new TV and digital radio channels ... for now I can sneak into the guard band between bands as there are no transmissions there and 10mw from me won't cause any issues!

They changed the allocation on 1st January 2015 but most equipment suppliers were not ready to change frequencies and ended up telling clients they have to wait or buy new gear!!

Chris

Audio-Technica ATW-T1001 System 10 Digital UniPak ATW-T1001 B&H

http://www.bhphotovideo.com/c/product/907668-EG/audio_technica_atw_t1002_system_10_handheld.html

BH sells the transmitters and mic separately

I think you can pair anything with the receiver but it has to be "one at a time" ie if I understand it correctly you can switch the receiver from one transmitter to another, but at any time there can only be one transmitter in contact with one receiver.

Of course I may not know WTF I'm talking about (as usual according to my lovely wife - whom I really miss since she's been in Japan for a few weeks now. Comes home tomorrow so I only have one more day to turn the dining room back into a dining room instead of an AV test lab)

I'd recommend the Rode (http://www.rode.com/wireless/filmmaker) approach with their new wireless kit. They've made use of the WiFi transmission standard and hence the WiFi frequency spectrum which can never be shifted because (politically) it would tick off roughly every one in the country.

I for one am looking forward to the next purchase being the last for a very long time.

Andrew

Found this on YouTube

Audio-Technica System 10 Unboxing and Product Overview - YouTube

Basically you need a pair (Transmitter - Receiver) set up - if you have multiple transmitters live at the same time you'll need multiple receivers. But you can pair any transmitter with any receiver so you can use different transmitter with a single receiver, just not simultaneously

Hi Jim

I read the specs differently but I could also be wrong ..they said you can pair up to 8 transmitters but say nothing about being only able to use one channel at a time .. however no big deal for me as at the price it's still cheaper than two UHF units. Something I would really like to know is how badly the signal is attenuated if the transmitter is inside clothing ... Could you maybe try your unit and see if it works OK if the transmitter is dropped into an inside jacket pocket?? Range for me isn't a huge deal as I'm seldom further away from the subject than 20' or so ... just need to know if it works if the transmitter is covered by material or even clipped behind the subject but still covered by a jacket ??? That would be really appreciated ..maybe drop it on your desk and throw a jacket over it and see if you get a signal say 30' away??? Since it seems to not be phased by walls I can't see an issue

Andrew?? The AT system also uses the 2.4GHz wifi band ... Rode is slightly more costly BUT what I don't like is the physical transmitter size ..it is bigger than AT's and I always need to hide the transmitter. I suspect both would have the same range

Chris

Hi Chris,

I suspect that they would be both just as reliable for the frequency transmission methods mentioned in the embedded video up above.

The body pack is a bit smaller than the Rode one, but the receiver is much bigger. Apart from being a bit of a Rode fanboi, I'd be inclined to go for the Rode one so that I could have a "normal" sized receiver on my camera.

But the AT definitely looks like a great system. Well done to them for hopping (forgive the nerdy pun) on the 2.4GHz bandwagon.

Andrew

Thanks Andrew

You win ..I only saw the pre-release unit with no dimensions and yes the TX is a fraction smaller! I wonder what local prices will be like? I'm a Rode fan too and a locally manufactured unit is ideal. I see that the pre-release price at B&H is now lower than the AT unit too !! The AT unit here is close to $500 locally so here's hoping Rode will release their's under that? B&H say it's coming on 10th May

Chris

I've seen an RRP of $499 at VideoGuys Australia, and $445 at VideoPro in Brisbane.

I do know that the first shipment will be in comparatively limited numbers, and that (unusually) there have been no initial pre-launch units for Rode's sales team to take around to the various retail business whom might wish to stock them for sale.

Andrew

If you put the cable in nicely, could you not just leave it? Throwing technology at the problem seems a bit risky to me. People are working on the premise that line of sight radio is solid. It's not. It's fine when signal strengths are high. In practice, walking away from the source until it cuts out is a very unreliable method of working out usable range, even outside. Walk till it stops, walk back until it starts again and call this range? T

Hi Paul

Absolutely ..with weddings I certainly can't afford a drop out when the bride is saying her vows!! I do also need to conceal the transmitter too and clothing does attenuate the signal ... as long as it is rock solid at 30' or less that's all I need at weddings ...the receiver is in free air but the transmitter is usually under the groom's jacket or inside his breast pocket !

Thanks Andrew .. Video Pro are my dealers anyway in Brisbane (I bought my Sony cams from them) but I didn't see anything under Rode on their website.

Chris

Hi Paul

No, I can't leave the cable in place - have to run it for every concert. Best I could do would be to put it in the night before IF there's no event in the church. And it has to come down right after the concert.

Re the receiver size, my receiver is about 25% as big as the one in the video - it's the camera-top unit.

I'll cover it up tonight and see how it works. I'm also not going to declare a victory quite yet - will definitely give it a try at the church.

Since there's only one output jack (plus a headphone jack) I don't see any way a receiver could handle more than one stream. Now, if I could somehow figure out how to get the transmitter to pair with my PC, we might be able to do some parallel streams.

I picked up one of those little Raspberry Pi $35 linux PC's - about the size of a cigarette pack. I've been wanting to play around with programming again and I MIGHT be able to figure out how to get it to talk to the transmitter. And I think it's capable of handling several audio streams - might be a nice spare time project for the summer when it's too hot to leave the house! (We usually have our 1st 100 degree day by May 15 and June hits 110 or 112 - or more.)

Well now I know what a Raspberry Pi is... Time to break out the credit card again.

I know this suggestion is adding one more wireless link to the chain, and wouldn't gain any redundancy since it would be in series instead of parallel, but if I had to quickly send one of these single-paired digital wireless systems to a second destination I would use one of the JM 2.4 GHz audio transmitters that I've written about to send the main receiver's headphone output to the JM 2.4 GHz receiver.

From what I've heard and read, the R-Pi does not have very good audio capabilities per se. There's a lot of code out there using the Pi as a controller, data processor, whatever, but always using a USB I/O interface for the actual A/D and D/A processing. I have not confirmed this myself, but it seems to be a widely held belief, based on a lot of internet reading on my part. YMMV.

Hi Greg.

You're right as best I can determine. Which is why I also got an add-on sound card for the Raspberry. Takes it a bit out of the $35 range though.

It is an interesting concept. Use a $35 linux box (the RPi) to capture the data from the multi-gazillion-dollar USB sound box. Assuming the RPi is fast enough to do it without any glitches, it impresses me as a neat project.

Out of curiosity, what do you envision the RPi will do in regard to the wireless system(s)?

Good question - FM might be doable.

The gremlin in all this is that A to D to D to A might (has to???) introduce latency above what would be there if everything worked in the Analog Domain. Everyone tends to forget that even with all our digital magic, we still live in an analog world and transitions between analog and digital don't happen in zero time..

I just need to find time to play with the RPi! A zillion years ago I used to write micro-code to drive all kinds of I/O devices - like card punches,disk drives (24 inch diameter!!!), paper tape readers, magnetic tape drives, so if I would just get off my behind and write some code I could probably figure something out.

Hi Jim

Back to the System 10, I was wondering if you have had a chance to throw a jacket over the transmitter yet to see how if affects the range???

Results would be greatly appreciated ... as long as it works to 20' that's good enough for me without any dropouts. I always have line of sight so getting a signal in another room doesn't come into the equation.

Chris

Jim,

I've still got an old Rockwell AIM65 development kit for a 6502 ... that's as far back as I go with actual programming. Before that it was all discrete TTL (CMOS gates were too fragile back then; OTOH TTL was too fast so very susceptible to noise).

If you do want to pursue broadcast band FM, let me know and we can talk about specifics. I will be out of town and probably offline completely until next Wednesday or Thursday, so hopefully you aren't in a time crunch.

The gremlin in all this is that A to D to D to A might (has to???) introduce latency above what would be there if everything worked in the Analog Domain. Everyone tends to forget that even with all our digital magic, we still live in an analog world and transitions between analog and digital don't happen in zero time..


Agreed - but the new Audio Limited digital 1010 system (http://www.audioltd.com/) has a "through the system|" latency of just 2ms !

Thanks John

That looks really good. I don't know anyone who would raise a fuss over 2ms.

On the other hand, I don't know what they're using for a processor. but I'd bet it's faster than the cellphone chip in the Raspberry. I wonder what an acceptable latency would be? At 29.97 one frame = 33.4ms so maybe 10 to 12ms total latency would work.

Any thoughts?

@chris

Sorry - it slipped my mind (or what's left of it) a not so infrequent thing lately!

I'll try it today

By the way, I found the following write-up by Ty Ford - sounds like he likes it! He claims to have gotten usable signal at 200 - 250 feet.

Ty Ford Audio and Video: Audio-Technica System 10 - Now With Battery-powered Receiver & More (http://tyfordaudiovideo.blogspot.com/2015/01/audio-technica-system-10-update-more.html)

@Greg - according to Ty's info there's 3.8ms latency in the system 10

I really need to start playing with the Raspberry instead of just looking at it sitting forlornly on the shelf over my desk!!!!!! Even the cat seems to be ignoring it lately.

By the way, found the following re acceptable latency FWIW

https://tech.ebu.ch/docs/r/r037.pdf

Hi Chris

As promised, I tried the AT System 10 tonight - covered the transmitter up with (well, not a coat - this is Tucson and I don't think I have one anymore) but with a very heavy 6' long bath towel wrapped around a few times - maybe 4 inches of cloth. Then I went 50 feet down the hall and into another room and recorded from the receiver. The lav mic they included was just casually tossed onto my desk near my monitors.

And it was right under my wireless access point and near the computer fans ( which you can hear clearly) which is supposedly a no-no.

Here's a link to a quick and dirty recording

https://www.dropbox.com/s/l1jpfaph45ckibv/Spring.mp3?dl=0

I recorded into my Sony PCM-D50. There's a bit of noise at the start which is me walking around the office after starting a file playing (1st movement of the Beethoven "Spring" Sonata that I recorded a couple of years back performed by my wife on piano and a violinist friend.)

I didn't think it was too bad - would like to figure out how to use a better mic or pick up the output from my SD702 though instead of the lav

Anyhow, have a listen and see what you think

Hi Jim

Many thanks indeed ..I certainly didn't detect any interference or drop outs and grooms at weddings will only have a light jacket where the transmitter is dropped into so nothing like a heavy bath towel multi-wrapped

I'm impressed and it doe show that the unit can handle attenuation from clothing without any issues.

You test is greatly appreciated!

Chris

Is there really much attenuation from clothing or fabric? I would expect none.

OTOH close proximity to a human body could very well attenuate an RF signal, probably more likely at UHF than at VHF.

If the transmit antenna is in the pocket of a coat, which is hung on a plastic hanger, hanging on a rope in the middle of an open field, I would expect little or no attenuation. But the same coat, on a groom, with the antenna 1/2" from the groom's body, might be a significantly worse situation. I know from experience that making a cylinder of one's hand (as if gripping a broomstick), with a VHF antenna in the middle of the cylinder, can seriously attenuate that RF signal.

Hi Greg

Broadcast studios will clip a transmitter on a talent's belt so that antenna is again only 1/2" from their body BUT the antenna is in "free air" ... the only difference inside a groom's inside jacket pocket is one external layer of fabric between the antenna and free air ..both are still in close proximity to the talent's body yet a belt mounted transmitter gives a far better signal. With weddings the groom often turns to face the altar so a rear mounted transmitter is not a good idea asthetically.

I'm certainly no audio engineer but I have noticed the I get better performance if the antennas are in free air .. then again, inside a jacket pocket they also have a bit of space around them as the transmitter is dropped in vertically and only one side of the antenna is subject to body attenuation so wouldn't be the same as cupping your hand over the antennas. You mention VHF is attenuated so would higher frequencies be worse or better ...my old Azden VHF units (I use them to send instructions to a 2nd camera person) are around 170mhz ..my UHF bands run up to 800khz and the unit Jim is testing is not only digital but also runs at 2.4GHz

Chris

Hi Chris,

I think there might be a few things at play here.

VHF antennas are longer. A VHF antenna hanging from a belt might be fairly straight so reasonably efficient. A VHF antenna coiled in a coat pocket, and bunched up against the bodypack, might be much less efficient.

UHF antennas are shorter (and frequently stiffer) so the "bunching" problem isn't as much of an issue. OTOH UHF would probably be attenuated more than VHF by proximity to a human body.

I would think 2.4GHz would be attenuated most of all. I have recently been playing with some digital systems marketed as WiAudioLink and made by Jangus Music. These work in the 2.4GHz band. Transmission is in digital mode and audio is very clean. There is NO external antenna; it's inside the transmitter. If I have the transmitter (about 1" x 3/4" x 3.5") in my shirt pocket (essentially 1/4" from my body) and I walk to a distance where dropouts start to occur, and then take the transmitter out of my pocket and dangle it by the mic cable at arm's length, I can get another 20 to 25 feet of range. That seems to confirm my theory that 2.4GHz absorption is worse than at lower frequencies (after all, microwave ovens work by RF absorption, and they operate at 2.4GHz!).

Of course there are many variables so no two systems will be the same, and may seem to defy theory. Hence the common disclaimer YMMV.

Maybe I can get the cat to hold it! There's an old expression in Japanese to say that you're really really busy - roughly translated it's "(We) want to borrow even the cat's hand"

I can do another test - start the recording in the other room and put the transmitter in my pocket and wrap myself in the bath towel. But as Greg said, fabric is pretty transparent at the frequencies involved. I should have mentioned that there were three walls and two doors and a second wifi access point in the path last night as well.

OK - I clipped on the lav and wandered around inside (and outside) up to around 80 feet.

The transmitter was in my pocket and I pretty well kept my hand around the antenna and otherwise tried to behave "badly".

Here's the result

https://dl-web.dropbox.com/get/public/SYstem%2010%20test/Walking%20the%20walk%20and%20talking%20the%20talk.mp3?_subject_uid=17745879&w=AACgMLD-DIDQ3WKFfJ1WZA-HBpHOAEx9MeZo8uPc93uRbg

Have to say I always get nervous wearing a body pack - it reminds me of the time I had a major presentation to about 600 folks in Sydney - got all wired up and decided to make a pit stop beforehand. Walked out on the stage to thunderous applause - of course the mic had been live the whole time.

That's the difference between Aussies and Japanese - in Japan (where I worked for six years) the audience wouldn't have made a sound. Oh well, livened up their day.

Anyhow, sounds damned good to me

There is basic RF theory working here.

Fabric is transparent to RF - so not significant in attenuating the signal for any practical purposes.

The free space actually is an important component. Transmitters have fairly low RF output, and the object is to get as much as possible on it's way to the receiver. For optimum power transfer, the transmitter has to be matched to the aerial. A quarter wave antenna is pretty efficient, but should really have a ground plane to work against. The physical size of a transmitter pack means that the ground plane required is simply not be enough for efficient power transfer, so by design, not all the power output of the transmitter makes it out of the antenna. Bringing the antenna close to an absorber - as in the human body, impedes the efficiency even more. The side away from the body will radiate, but the side near to the body will propagate poorly because most of the energy is absorbed by the body - which is mostly water, and very often sweaty - and the salt is of course a conductor. It's amazing that an antenna in a pocket in an armpit emits anything at all.

Testing in open spaces is a pointless exercise if the real working conditions have reflectors and absorbers that conspire against you. The usual problems are not caused by gradual drops in RF level at the receiver, they are sudden HUGE drops where the TX or RX is in a null. Lifting an arm, or rotating 5 degrees can suddenly restore operation, and the RF meter goes from 0 to full scale.

There's very little you can do at the transmit end, so the only real thing you can do is at the receive end. Many years ago, when we were using VHF systems, with much longer aerials, we had this problem on a shoot where we were working at longer distance than were ideal. One of the guys was also the rigger, and always wore a hard hat - we pinched it, lined the inside with aluminium foil, and drilled a hole in the top and attached the receiver antenna to that - the cameraman was 6' 3" and with this crazy hat on we got solid reception, simply by having the antenna a bit higher, working with a better ground plane, and a greater capture area, compared to the helically wound rubber duck on the receiver.

When I first qualified, I spent a lot of time up towers setting up radio links with much higher powers, but our business moved to radio microphones where the theory is exactly the same, but subject to all kinds of weird folklore - most of which is grounded in fact, but some is just silly.

Receivers have sensitivity differences, and selectivity differences - but the killer is aerial systems. Diversity systems on a battery operated small unit are never that good because the two aerials (and I include those who use the connecting cable as one of the aerials) are just too close together for the diversity system to work efficiently.