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Why am I still experiencing dropouts???
by Dtaylor2013 on 2013-02-07 15:40:05

Scenario:

Fairly typical school hall. Sound tech lives at back of hall with rack of 8 xd-v75 receivers connected to an xd-ad8 distro unit, with one p180 directional aerial and one standard supplied rubber type aerial. Receivers are powered via the ad8 with the supplied cable.

4 sets were purchased a year ago for school production literally when the v75 had just been released. (The supplier told me that I was among the first people in the country to get my hands on them!) another 4 sets with the ad8 and p180's purchased about a month ago, ready for school production this week. All transmitters are xd-v75 headset type, worn by the performers in fabric pouches purchased for the job.

Rubber aerial is at about head height of the seated audience, but the p180 is above head height when standing giving easy clear line of sight to the stage which is about 20m away and raised above the audience. All cables connecting the receivers to the ad8 are line6 supplied, as is the cable to the p180.

I was a little disappointed with the first 2 nights of the performance when experiencing the occasional very small signal dropout- I had hoped the directional aerial would cure that having experienced it last year before its purchase. Tonight was the third night, and the problems experienced were much more severe. 3 of the transmitters suffered major dropouts with one so bad, that I would consider that it didn't really 'drop in' very much at all!

What has gone so horribly wrong tonight, when as far as I can see the only thing which has changed is the audience. Could it be that a multitude of mobile phones ganged up on my wireless mic signal?

Thinking about in-house interference, there are 2 wireless access points in the hall, one at the front, one at the back, running from an aruba managed wireless system. This hasn't changed since last year. I have used the channel scanning facility while setting the channels which the transmitters run on. Point of note:

Why do different receivers connected to the same adu and aerials, report different levels of interference on the same channels?

I consider myself an experienced audio technician as well as a very experienced ICT technician, but I am at a complete loss as to what i can possibly do to prevent a e-occurrence of tonight's very disappointing results for what is otherwise an excellent system.

All offers of advice very gratefully received!

Regards,

Derek.



Re: Why am I still experiencing dropouts???
by dboomer on 2013-02-07 16:08:46

Hi Derek

What mode are you running in?  Are ALL transmitters in same mode?  If they are mixed you will take yourself off the air.

How long is the cable connected to the paddle antenna?  Are you using a line 6 cable and if not what are you using?

How is the gain switch set on that antenna?

Is that paddle within 6 feet of a wall?

Why only one paddle?

Why an omni paddle?



Re: Why am I still experiencing dropouts???
by Dtaylor2013 on 2013-02-08 00:48:13

Hi,

All settings including power are as they came out of the box. Hi power, no modelling on the mic, no encryption.

The cable from the paddle is 4m line6 cable. The previous  2 nights the setting was on 12db but to try and compensate for the minor dropouts, I changed to 23db but had forgotten that at the time. Further reading last night suggests that is probably too high, as the gain is for the length of cable, not the distance to the mics? I didn't get any nest ructions with them...

I will check in a bit, but the paddle is probably about 6-7 ft from the wall, the radio mics being to the left of my sound desk and with a laptop in between.

Only one paddle because I didn't know exactly how they worked, and wanted to cover myself for the couple of times when the actors move up the hall. The omni paddle because my sound desk is always at the back of the hall facing the stage I can't foresee any scenario when I would want to pick up mic signals from behind me, so directional seemed the way to go.

Hope this helps...

Derek.



Re: Why am I still experiencing dropouts???
by RonMarton on 2013-02-08 03:05:25

G'day Derek...

For us to help, we need an ACCURATE picture of your rig, so please answer all of the points Don Boomer has raised.

Your remarks regarding an "omni" antenna are somewhat confusing.

Model P180 is directional. (180º hemispherical pickup with its labelled "box" side facing the "performance" area.)

Model P360 is omnidirectional or not directional. (360º "donut" pickup from all around.)



Re: Why am I still experiencing dropouts???
by Dtaylor2013 on 2013-02-08 03:18:28

Apologies is I am confusing... I have read it back and even I don't know what I am on about...

The paddle is definitely the directional p180 with the 'this side facing transmitter' sticker on it.

I am currently using just one of the pair I received in the package, along side one of the original rubber aerials on antenna b.

Have I missed anything else?

Regards,

Derek



Re: Why am I still experiencing dropouts???
by RonMarton on 2013-02-08 08:03:20

Now we're getting somewhere, Derek !

(Still no answer to Don's vital query "What mode are your running in...")

No matter, I reckon that the following four points should be a viable "here's how":

  1. I strongly advise grabbing all eight of your transmitters and switching them to operate exclusively in their "RF1" mode, as per this document http://line6.com/support/docs/DOC-2645 ...and discussed in more detail here http://line6.com/support/thread/91356?tstart=0.
  2. You MUST rig the second P180 identically to your first, as "mating" the first with an un-amplified "rubber ducky Antenna B" whip that's co-located 20m away has effectively denied your system the viable alternative signal path that's required for it to "see around" obstructions. (Continuous instantaneous switching from the "worse" antenna to the one which has the better signal is how antenna diversity works. Your original rig totally defeated this, ...so you were pretty much struggling along on just one almost viable "Antenna A".)
  3. The best diversity rig will have both correctly facing paddles spread as far apart as your 8m of cable will allow, with one P180 just over the height of the performers' heads and the other higher again, about as high as one such performer can reach with a fully outstretched arm, being roughly 2m above the performance floor. This will yield "diversity of height" as well as "diversity of width", thereby allowing the systems to "see better" around any RF obstructions.
  4. Given that the 20m to the receiving antennae is approaching the limits of the system, (taking into account the itinerant RF absorbtion and obstruction that attends any auditorium) switching in more than "textbook" gain at your antennae may well prove useful. While the "correct" antenna gains for your 4m LMR195 cables would nominally be the minimum "25ft" slider setting, I frequently add "1 click" more (the middle 50 ft setting) of antenna gain in situations like yours, a "trick" that's only made viable by "RF1's" greater immunity to other 2.4GHz traffic. (There's also nothing stopping you from experimenting with the higher gain setting being only on the more elevated antenna, with the lower of the two at its "correct" setting to accommodate performers who come closer.)

That should do it.



Re: Why am I still experiencing dropouts???
by dboomer on 2013-02-08 14:12:53

Hi Derek

I agree with Ron and also recommend switching the transmitters to operate in RF1 mode.  If you keep them in RF2 mode you MUST scan for clear channels  and find 8 of them (which should be do able if you have only one wi-fi channel running).  I still prefer RF1 in most cases.

It sounds like the antenna switch is turned up too high.  This is usually not a critical adjustment but with radio you never want too much.

At 6 feet from the wall you will be fine with your paddle placement.  It sounds like you have coupled the receivers in banks of four units which should be fine.  Do check your antenna connections and make certain they are "clicked" into place.  You would benefit from a second paddle in most cases but you might just be fine with one and one as it seems you have it.



Re: Why am I still experiencing dropouts???
by sdevino on 2013-02-10 20:11:48

Hi Derek,

The gain setting on the antenna should ideally be set according to the length of the cable used not the distance from the stage. You canuse the RF Performance page on the XD-V75 receivers to monitor the error rates in real time and determine the best perfomance setting for the antenna gain switch.

Try this:

1. set the XD-V75 receiver to RF performance

2. turn the encoder on the receiver front panel to the right.

This is the real time error page. This will let you see real time performance in terms of error rate and dropouts. If you have one tech at the receiver while another turns the antennas and adjusts the antenna gain, you will be able to see immediately the best setup combinations. You can also use this to identify problem spots on stage by walking a transmitter while someone watches the RF error rates.

Next: Get your antennas as far from the WiFi as possible and as close to the transmitters as possible. Typically for a stage performance the proper place for the paddles is on either side of the procenium arch. This is true if you are using the Line 6 XD-V75 or a $10000 Sennheiser 5000 series.

Next: make sure there are no laptops on or next to your receiver rack.

Next: if possible, turn of the WiFi during performances.



Re: Why am I still experiencing dropouts???
by Dtaylor2013 on 2013-02-11 02:08:17

Hi all,

Just an update on the performance on friday.

Faultless!

My apologies - before my further research, I was unaware of the RF1 and RF2 settings. previously all mics were running in RF2, but following your advice, I changed them all to RF1.

I also set up the additional directional serial instead of the rubber one, though because of the restricted area I was working in, I could only manage to get it zip tied to the other side of my 19" rack case. even so, it seemed to do the job.

I turned the gain right down to minimum on the aerials, and I turned the wifi off in the hall.

somewhere in amoing this, was the answer to my problems, as i didnt even experience the slightest dropout, and at the times i had time to glance at the receiver rack, the performers who were on stage had either 4 or 5 green lights on signal strength!

Thanks all again.

Regards,

Derek.



Re: Why am I still experiencing dropouts???
by RonMarton on 2013-02-11 05:18:33

There's nothing quite like the thrill of a successful "live" gig, is there, Derek ?

I'm wondering whether you operate your eight systems on a "show-by-show, move in, move out" basis or can enjoy the luxury of leaving them permanently rigged in the hall you used last Friday.

If the latter is the case, then permanently installing your P180 paddles "either side of the proscenium arch" (following Steve Devino's typically concise and accurate advice) would be well worth the effort and expense involved.

As Don Boomer implies, it's been my experience that Line 6's "RF1" scheme yields "set and forget" trouble-free operation of up to twelve receivers operating simultaneously, all the more so if the locally installed  WiFi is under your control.

Given the limited attention (after initial set-up) that the receivers then require, often the best approach involves running the shortest pair of LMR-195 antenna cables that are practical, by dint of locating your antenna distribution and receiver rack in the wings or backstage and permanently installing a run of star-quad multicore (stage box and "snake") from them to your FOH mixing position.

Remember that most curtain, "border" and "leg" fabric that's employed for stage "masking" can also be used to "mask" your antenna and receiver hardware, as it's "transparent" to RF.

That makes it considerably easier to permanently mount a PS ("Prompt Side") and OP ("Opposite Prompt") pair of P180 paddles in downstage wing "perch" positions for total "line of sight" coverage of the entire onstage area.

If, however, your application demands the occasional "in the round" or "back to front" use of a flat-floored "multi-purpose" auditorium, (as I strongly suspect it does) having your XD-AD8 and XD-V rack co-located with the FOH mixer (as you've just done) would seem to be the far more practical (not to mention cheaper) option.

In that case, it would be very wise to invest in a pair of sturdy boom stands (such as http://www.bhphotovideo.com/c/product/82331-REG/Atlas_Sound_PB21XCH_PB21XCH_Adjustable_Microphone_Boom.html atop something like this http://www.sweetwater.com/store/detail/KM20130BK/) that you'd reserve exclusively for elevating and aiming your P180 paddle antennae on a "show by show" basis.

A longer pair of LMR-195 cables may also help a lot. https://www.globalfulfillment.net/gfsnet/line6/10Expand.aspx?ProductCode=98-033-0018



Re: Why am I still experiencing dropouts???
by Dtaylor2013 on 2013-02-12 02:31:26

At this time, I dont have the luxury of leaving the kit out, as the school hall is also the dinner hall, however, my head teacher has listened to my pointing out that the central area at the rear of the hall is highly underused, and asked me to put a proposal together to contstruct a 'control room' in the space. This would save me having to move my very large and heavy sound desk, radio mic receivers, lighting desk and all other associated kit from the locked room with a narrow doorway every time I want to use it... it would also mean i could spread out a bit, rather than having 3 trolleys squashed againat a side wall 3/4 of the way down the hall.

Either side of the prosc would be ideal, but i dont like the idea of not being able to see my receivers to know they are on and ok before the show starts. I would need a massive pait of aerial cables to get there from the rear of the hall!

I think RF1 seems to be the way to go. Before reading up, I foolishly just assumed that RF2 is 1 more than RF1 and comes as standard on the newer v75's so must be better.

We have never required the mics to be used in the round in the main hall before, however the visits to the sports hall for end of term and christmas shows would necessitate them being de-rigged from any permanent installation. Our main hall capacity is about 250, whereas we can get up to 1000 in the sports hall.   I think based on the performance I saw on the last night, I am happy with the system now. if I can get the aerials further apart next time, I will be even happier.

On the subject of aerial positioning, would there be any mileage in me positioning 1 down the hall somewhere, and keeping the other next to the receivers at the back?

Regards,

Derek.



Re: Why am I still experiencing dropouts???
by RonMarton on 2013-02-12 08:29:13

Aah yes, Derek...

The dreaded "must fit in with other departments" scenario. We all know it well.

My feeling is that (future "control room" notwithstanding) you're better off staying "mobile" as its a "pounds to peanuts"/"dollars to donuts" bet that the "committee" may well at some stage (excuse the pun) require the short-notice provision of "ad hoc" radio-miked re-enforcement at hitherto unimagined locations.

A "rolling" arrangement such as this (one for sound, another for lights, possibly each having a rack-mount drawer for "bits") may prove handy:

http://www.studiospares.com/cases-portable-rack-/skb-gig-rig-14u-19-r1406/invt/407820/

...and the tall boom-stand mounting of your pair of P180 paddle antennae would seem to be the most viable "rapid deployment" option.

http://www.studiospares.com/stands-mic-/k+m-mic-stand-and-boom-black/invt/408860/

If you click on my pink avatar at left, you'll see that the majority of my work is of exactly this "bump in and bump out" itinerant nature and I've only used RF2 exactly ONCE over the past year and a bit.

Based on my experience, I'd heartily recommend sticking to RF1.

As for one paddle half-way "down the hall", I frequently run my P180s exactly like that, with "Antenna A" "looking down the length" and "Antenna B" being at 90º to it "looking across the width" of large conference spaces, both being set-up to "back reject" WiFi "hubs" and/or Bluetooth "hotspots" and both having coverage of the entire floor area.

That's just one example of why I recommended you buy at least one longer LMR-195 BNC antenna cable. I'm guesing a 25 footer (7.5m) will probably be long enough for you and also facilitate a quicker rig and de-rig than a 50.

http://www.dv247.com/microphones/line-6-aec25-lmr-195-bnc-to-bnc-antenna-cables-7-5m--83638

(It also pays to have a spare cable on hand in case a BNC connector finds its way under a trolley wheel or gets jammed in a door.)

My preferred method of quickly "proving" the layout is a "chat out loud, worst-case walk test" conducted with the transmitter operating in its 3.3mW "Battery Save" mode while its RF signal is being deliberately attenuated by means of having its antenna totally "cupped" in and covered by the hand of the "test-walker".

Freedom from dropouts when tested like that seems to pretty much guarantee trouble-free operation at the higher-power (10mW) setting, even when presented with later "crowding" of various kinds.



Re: Why am I still experiencing dropouts???
by sdevino on 2013-02-12 09:42:34

As far as diversity goes there are a couple of principles at play here.

first in order to achieve diversity from an RF standpoint the antennas only need to be more than 1/2 wave length apart. Which in the case of 2.4 GHz is only a couple of inches.

But from a coverage standpoint you should place your antennas in such a way as to maximize coverage of the performance space while minimizing pickup of undesired RF. A great way to check this is to walk the stage and make sure you can always see both paddles no matter where you go.

The RF1 vs RF2 thing is more a matter of different tools for different purposes. RF2 is ideal when you need 14 channels, lowest latency or minimum interference with house WiFi. RF1 is best for redundant data coverage or interference immunity. RF2 provides significant setup resources that are not available in RF1 mode as well. So I would setup in RF2 mode using the RF Performance page, including aiming of antennas. Then I would switch to RF1 mode if that is your prefered mode.

Aiming paddles and detecting mute conditions on the RF Performance page is a powerful tool when maximum reliablility is desired.

Steve

Line 6 Wireless Product Manager



Re: Why am I still experiencing dropouts???
by RonMarton on 2013-02-12 16:27:46

Another beautifully explained, clear and concise reply, Steve!

Since I received my sole V75 (and consequently upgraded my eight V70s accordingly) I have indeed found Line 6's v.2 firmware's diagnostics to be an immensely powerful tool for my "pre-gig seek and destroy" missions against other 2.4Ghz traffic.

(Sadly, in reality they're merely "seek and switch off or "seek and avoid"...)

However, I've found that my "battery save" 3.3mW low-power "cupped antenna RF-attenuated walk and talk" drop-out test is also a quick and handy "predictor" for the sole operator.

Regarding antenna diversity, you may be interested to hear that (by way of a simple "guide", without reference to the physics of wavelength) we often tell less experienced assistants to ensure that all antennae are rigged at least (but preferably more than) "one antenna length" apart.

It's just a wonderful "bonus" that the well-crafted packaging and astonishing (to me) light weight of the miniature cable-compensating RF "head" amplifier in Line 6's paddle antennae allows really quick and easy deployment for a huge variation in "line-of-sight" coverage.        




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