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Lectrosonics issues

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I have been having some issues with Lectrosonics wireless lately and figured the hive mind might be able to shine some light on something I may be missing. I have been in contact with Lectrosonics technical support and currently have my wireless systems getting checked out by their engineers. They have been super helpful and friendly in figuring out what is going on. Now I have access to a different setup and am still experiencing issues.

 

I have been running into sporadic rf issues the last couple weeks, sometimes lots of clicks and pops, sometimes larger static interference. I have been trying to recreate the issues I have been experiencing without much luck. I have been able to repeatedly get clicks and pops when performing a short walk test along with, to a lesser extent, static sounding interference when a bag is shifted or moved.

 

For my short walk tests I am using mostly 411a, with one srb. I have mostly smqv, with a couple um400/um400a for my transmitters. I have tested with both a 633 and 688. I have tested powering with an audio root bds, np-1 psc bds, and internal 9-volts (sony L-series powering 633). I have a mixture of pre made xlr/ta3 cables and cables I have made myself. Some of the cables have ground terminated to the chassis.

 

While performing the short walk test I have been playing a 1khz tone through a cos11d into an smqv running at 100mW. The transmitter is gained up so that the level on the transmitter is just before the -10 light turns red and the limiter is engaged, which corresponds to 0 on my receiver. I have been trying multiple frequencies and alway choose a clean channel without any other signal showing on my 411a scan. I always use freqfinder when coordinating multiple wireless frequencies. I have been walking anywhere between 20 and 70 feet away from the transmitter carrying the bag containing one of the recorders and a receiver. The transmitter and receiver are mostly maintaining line of sight, with the occasional blockage (my body, fence, tree, etc). I am pretty consistently able to get a couple clicks out of any combination of rx/tx/recorder/power within a couple minutes. Some receivers are less prone than others, but all of them will eventually have a click. The click usually coincides with the diversity switching or a small blip in the uV reading. I have also tried this test using music and dialog being played through the transmitter with similar results.

 

In past posts about clicking lectrosonics it has been said that the clicking is due to low gain on the transmitters. I have noticed that having the gain higher results in less clicks, but does not completely remedy them. Below are the posts I am referring to.


 

My other recreatable issue is I will get short bursts of static on my wireless channels when the bag is moved or shifted in a certain way. This one has been hard to consistently recreate. It seems to be more likely to occur the more things I have in the bag. As I remove cables/power/receivers from the bag it becomes harder to recreate. A couple times it has been consistent enough where I was able to remove items from the bag one at a time and check if the static would still occur. I was able to get down to just a recorder and a receiver powered with internal 9 volts while still recreating the static. Removing the receiver from the bag by manually holding it up seemed to be the only way to remedy the issue. While the static is happening, it does not seem to correspond to any receiver/transmitter/recorder/cable. I have two bags I have been testing, and oddly the petrol seems to cause the issue more than the stingray. When the issue is occurring I have noticed the receiver is affected by other cables and receivers in the bag. I will get the static sound when moving other receivers antennas or cables. When I touch two pieces of metal together in the bag, such as the casing on two xlr cables, I will occasionally get the static sound. This will happen even if the xlr cables are not connected to the mixer and just sitting in the bag. I am also sometimes getting the sound when an antenna on an adjacent receiver is loosened and wiggled, even when the receiver with the antenna I am wiggling is not connected to the mixer or power supply. A couple times the static has occurred from my hand just touching the zipper on the bag. I am thinking this is the static sounding interference I was hearing in the field.

 

Included are some examples of what I am hearing. The DIV-CLICK file is a click I was hearing from about 20 feet away from the transmitter with line of sight. The tone being played was around 0 on the receiver, and just before the limiter on the transmitter.

 

Static_cables_not_terminated_touching is the sound of two hirosi to lectrosonics power cables touching inside the bag. Neither cable is terminated to a receiver or the power supply, the receiver was being ran off of two 9 volts. The tone on this one isn't quite 1khz.

 

static_bag_move is an example of the static sound I am hearing when the bag is moved. The static would happen when the bag was slightly shaken.

 

Sorry for the long post, I have been testing for a while and wanted to include as much information as I could. I really appreciate this forum and all the information it has given me.


 

Thanks!



 

DIV-CLICK.wav

Static_cables_not_terminated_touching.wav

static_bag_move.wav

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Somehow I can’t play your files on my phone. Anyway. So the receivers which you think are problematic are being checked out by Lectrosonics as we speak? 

I‘d suggest we wait for the results. 

Meanwhile take your transmitters to a friend who has receivers which match your tx and play around a bit with the other setup. Do the problems occur there as well? 

Have you got any other receivers? 

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Suggestion would be to purchase a set of cables, both power and interconnect that are made by a reputable vendor, use your PSC BDS and NP-1.  Remove all of your other cables.  From your notes I believe you may have grounding issues.  Start simple, confirm operation, then add another component using the know cables.

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I am currently testing with someone else's receivers/transmitters and getting the same issues. I've been mixing my cables/power/mixer with this other setup so there may be a constant variable somewhere. I will try recreating the static starting with all new cables and slowly add items. Thanks for the suggestion drpro.

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Are you sitting next to a fan??  If there is one set up next to you... you MAY be getting slammed with garbage thrown out by a small cooling fan... one for yourself or around you.. I know that sounds funny, but believe me.. I had one haunt me for a few days until I discovered it was my VTR friends little personal cooling fan... After checking out everything, out of desperation, I looked over and said...turn off that fan.... and away went my problems... just like that.

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Have done these tests in a bunch of different spots. Sometimes I have a ceiling fan going but not always.

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Is it expected to hear static when unpatching an antenna on an adjacent receiver? I am hearing intermittent rf interference when unpatching an adjacent antenna even when the adjacent receiver is not plugged into power or xlr. I also hear static whenever a piece of metal touches the bnc connector on an antenna currently receiving signal, but I am pretty sure that is expected. This is consistent across multiple receivers/cables/mixers/transmitters/powering options.

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Years ago I had issues like this, and they were related to how I was powering the RX, as well as other gear on the rig, especially how the power was distro'ed and the cabling to do that.  If you can power yours with internal batteries maybe try doing that while they are hooked up to the rest of your rig.  Do your audio interconnect cables have pin 1 (or the ground) connected to the shell of the connectors ?  Do have any continuity between your power box and pin 1 of the RX? 

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I think that Phillip Perkins is onto something , I’ve had similar issues in the past , all traced back to ground loop problems. Separating power to devices has made those issues go away. 

 

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Thanks for the responses everyone.  

 

On 6/8/2018 at 7:27 PM, Philip Perkins said:

  Do your audio interconnect cables have pin 1 (or the ground) connected to the shell of the connectors ?  Do have any continuity between your power box and pin 1 of the RX? 

 

Some of my audio patch cables have ground to shell, and some do not. I have been using this as one of the variables in my testing, but it does not seem to make a difference.

 

On 6/8/2018 at 7:27 PM, Philip Perkins said:

Do have any continuity between your power box and pin 1 of the RX?  

 

There is continuity from the ground on the power cables going into the 411a to the ground on the audio pin 1 and to the outer shell of the bnc connection at each antenna. There is not continuity between the ground going into the lectrosonics power jack and the chassis on the power supply. This is consistent across both the audio root and psc power star distro.

 

I believe I have always started my testing with everything setup, including power supply. Once I am able to somewhat create the static issue (it is very sporadic and sometimes is not heard) I start taking things out to try and eliminate all the variables. I am usually shaking the bag/moving the bag around to recreate this issue. The first variable I have been removing is the power supply and switching to internal batteries, but the interference usually remains. The one variable I can think of that changing caused the issue to stop was removing all the extra cables out of the bags other pockets. I usually keep some time code cables in a front or side pocket of a bag in case I need to rejam or whatever, and whenever I remove these extra cables I am no longer able to recreate the issue. This doesn't make any sense to my knowledge though, as they are not plugged into anything and just sitting in the bag. If the static/interference is around, I can usually touch together two of the timecode connectors and cause interference sounds, such as the example I posted in the original post (Static_cables_not_terminated_touching.wav). This will even sometimes occur after I remove the cables from the bag and hold them a foot or two above the bag. I was able to do some testing with someone else's similar rig, and eventually got the same static sound when these time code cables were stored in the front pocket of their bag.

 

On a potentially unrelated note, on someone else's setup I tested moving an antenna around the bnc connector on an unpowered, unpatched receiver adjacent to a receiver receiving signal from a transmitter. I still received the same sounding static/interference. This seems to happen on every lectrosonics 411a/smqv I test, but did not occur on a zaxcom setup. Not sure this is related at all to the issues I am experiencing, but the sound is very similar to what I am hearing when my bag has static from being moved.


I am starting to think this may just be a cable management issue. I usually try to keep things tidy, but maybe I need to be more diligent about keeping separation between my cables and prevent conductive material from sitting in my bag.

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Could the inputs of the recorder be causing your static trouble? Or does it happen on both 6-series?  I’ve had this trouble too. 

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2 hours ago, Derek H said:

Could the inputs of the recorder be causing your static trouble? Or does it happen on both 6-series?  I’ve had this trouble too. 

 

The issue happens on both 6 series and a zoom f8.

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@jerryray The receivers are all turned all the way up (+5) with my mixer set for line level.

 

@John Blankenship I have tried setting my cell phone to airplane mode and with the tone coming from a laptop instead of a phone.

Most of my issues seem to be cleared up by having better discipline with my cable management. I used to let extra power/audio/tc cables lay in my bag when they weren't in use and removing these has prevented any more of the static issues. I am still hearing the occasional diversity click in the field. I have been playing with my tx gain and my receiver distance from potential rfi sources to lessen these audible clicks.

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5 minutes ago, afewmoreyears said:

For what it's worth..0db is fine...  you don't need to be at +5...  I'm always dubious of "all the way up"

The receiver is alway running at a +5 setting internally anyway. At 0 dB, you are putting 5 dB of attenuation after the receiver output stage. That's fine of course, but if you need the slightest reason  for +5 sometime, there is absolutely no reason not to run it there.

Best Regards,

Larry Fisher

 

5 hours ago, pankid said:

[snip] I am still hearing the occasional diversity click in the field. I have been playing with my tx gain and my receiver distance from potential rfi sources to lessen these audible clicks.[snip]

Try setting the transmitter gain according to the manual, if you aren't already. That is, turn up the transmitter gain until the talent is hitting the limiting indicator on the receiver occasionally. The limiting indicator on all the Lectro receivers lie a little in that they indicate the onset of limiting about 4 dB or so before it occurs. And, it isn't clipping or distortion, it is soft limiting. Hopefully, doing this will show you the direction to head, in order to reduce the tics.

Best Regards,

Larry Fisher 

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The receiver is alway running at a +5 setting internally anyway. At 0 dB, you are putting 5 dB of attenuation after the receiver output stage.

 

Larry,  Good to know...  I guess if you NEED the extra gain at least it wont hurt..With all my 411s I have never needed anything above the 0...   Are you saying we should all default to +5..?  in a why not scenario??   We COULD all back down our trim a bit...

  Again, I simply for no good reason never liked everything running full tilt.. I guess this is an exception to that...

 

I still know guys running the 411s at -20...  Then turning things back up to make up for the attenuation...  I never thought that was a good idea..

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Another way to look at it would be if you need 5dB of attenuation then it’s ok to run it at 0. 

 

The other big signal flow question is if it’s better to set your Sound Devices to mic level and then use something like -20 or -30 on the Lectro receiver since the line level setting on most Sound Devices machines just adds a 50 dB pad in front of the mic pre. So technically if you’re trying to minimize pre-amp gain you’d use the mic input and something less than 50 dB of attenuation on your receiver. 

 

Of course, then you’re running a weaker signal through your cabling which could be prone to inducted troubles and interference. 

 

In in an ideal world I think SD would add an option for a “-10 consumer line” setting which would match better for most wireless systems that aren’t a true line level. 

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5 hours ago, afewmoreyears said:

Larry,  Good to know...  I guess if you NEED the extra gain at least it wont hurt..With all my 411s I have never needed anything above the 0...   Are you saying we should all default to +5..?  in a why not scenario??   We COULD all back down our trim a bit...

  Again, I simply for no good reason never liked everything running full tilt.. I guess this is an exception to that...

 

I still know guys running the 411s at -20...  Then turning things back up to make up for the attenuation...  I never thought that was a good idea..

The best reason for running full tilt, is that ground loops, less than perfect power supply issues, and any induced noises in the cable between the Lectro receiver and the mixer are greatly suppressed. As you said, "why not". The receiver is running full tilt anyway (and perfectly happy doing it).

 

The only reason I ever heard for running at mic level out, that made any sense, was that the operator could switch from wireless to a hard wired mic cable at the input of the mixer without radical gain changes. Or that the device being fed by the receiver only had mic level inputs.

 

Finally, let's play with some numbers: 

If you have the world's best mic preamp with a noise floor of -132 dBm and you run the Lectro or other receiver at -50 dBm out max, the best signal to noise ratio you can have is an 82 dB SNR. Pretty good but not the best. Considering that some folks dial in too much headroom (YMMV) for another 20 dB of lost signal and also that the gain staging in the mixer is rarely perfect, your best SNR is now less than 62 dB. Who needs a fancy recorder when a refurbished Nagra will work as well.

Best Regards,

Larry Fisher

 

 

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