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Jesse Flaitz

RF issues with RF multi + SNA600

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I've been having some frustrating RF issues recently.  I picked up a couple SNA600s to use in a bag set up.  Running Nomad 10 and SRb/SRc RX in the bag going through an RF multi to the SNAs.  The performance has been underwhelming to say the least (I should note that my Lectro LP 620 shark fins work great in this set up).

 

Here's a link to the PSC RF multi for those that don't know it: https://www.bhphotovideo.com/c/product/842473-REG/psc_fpsc0006c_psc_rf_multi.html?ap=y&gclid=CjwKCAjwwdTbBRAIEiwAYQf_E_1S_jEFWqlm_9-uDjgKZKk2ZRhf1R3kX6pTybfXDSRRuOgT9ZHcNBoCqLoQAvD_BwE&smp=y

 

I have the SNAs set to ~540Mhz length running block 19/21 TX.  SMQV/SMv TX set to 100mw.  Receivers, Nomad and RF multi all running off the same BDS. 

 

This week I was in a high RF environment (16 wireless on talent, camera hops and 4-5 house wireless) and I figured the RF multi/dipole set up would help me out a lot.  It didn't help at all and became a liability very quick so I switched back to whips and everything was fine.  I was getting full RF strength drop outs regularly.  The RX would read full reception, but audio would glitch and drop out in a bad way. I was getting almost full black out on scans that would clear up instantly if I switched back to whips.

 

I have a second BDS system so I powered the RF-Multi from a separate source to try and isolate a grounding issue (but again, the shark fins don't have this problem), but it didn't make a difference in the scans at least.

 

My assumption is user error, but there isn't much to error about in that RF signal chain.  Any help would be appreciated.  I attached several scans with info about them (these pics are in my apartment, not from the job this week).  The scans aren't nearly as bad as on the job (Flatiron district in Manhattan), but show clear amplification of RF noise in the environment.

 

I'm again getting a weird 200 Error trying to upload pictures here.  No idea why, here is an imgur album with notes showing the different RF read outs: https://imgur.com/a/r83CfFQ

 

Thanks for any ideas.

 

Jesse

 

 

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Did you try the Lectro fins on site that day? Perhaps a shield issue on one or both of the antenna cables connected to the RF Multi? 

 

Were the issues present on both the SRB and SRC units? My SRC units are more prone to interference (regardless of board version) as compared to SRB tuned to same  frequency. 

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I'm a bit puzzled here. The problem could be that the SNA's are close to the bag and picking up low level RF from the mixers, recorders etc. They all have low levels of garbage, some worse than others. That doesn't explain why the whips work well since they would be close also. The RF multi (whatever that is) could be the culprit but that works well with the sharkfins. The sharkfins would be farther from the bag but that doesn't explain why the whips work. The whips and the SNA600 have the same effective gain within a dB or so.

 

One possibility is the  RF multi (?) goes into oscillation when presented with the narrower band load of the SNA600's but not with the broader sharkfin load. Or the SNA600 is picking up RF from the output of the RF multi (?) because it is in close proximity and you have a feedback loop. Rf output to the SNA600 to the RF input of the RF multi. The sharkfins are farther away so they don't pickup the RF output and the whips are immune because they don't use the RF multi. Does the RF multi (?) have excess gain from its input to its output?

 

Or you could just be using generic incense rather the the Lectro approved Tibetan Blue brand.

Best Regards,

Larry Fisher

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20 minutes ago, Frido Beck said:

Have you terminated the unused SMA outputs on the antenna distribution with SMA terminator plugs?

 

 

I have not done this, I don't have sna terminators, but I wouldn't have thought of that as thing.  I'll look into it.

4 hours ago, DanStewart said:

Did you try the Lectro fins on site that day? Perhaps a shield issue on one or both of the antenna cables connected to the RF Multi? 

 

Were the issues present on both the SRB and SRC units? My SRC units are more prone to interference (regardless of board version) as compared to SRB tuned to same  frequency. 

 

I did not have the shark fins on site to test.  I tested them with the same cables at my apartment and got noticeably less RF spray on the scans (you can see in the pics, I took one with shark fins attached).

 

The issue is present on both units, but noticeably more so on the SRc (I have also noticed the performance difference, SRb does seem superior but that's just my experience). 

 

3 hours ago, Philip Perkins said:

Same cables used for both sets of antennas?  How did the SNAs do if you moved them away from your rig a bit?

 

Yes same cables for both antennas. I did not test with the SNAs away from the bag, but if that's a solution it sort of defeats the purpose of using the SNA in a bag set up.  I've seen a few other mixers with SNA dipole rigs in the bag, I'm not sure how they do it different.

11 minutes ago, LarryF said:

I'm a bit puzzled here. The problem could be that the SNA's are close to the bag and picking up low level RF from the mixers, recorders etc. They all have low levels of garbage, some worse than others. That doesn't explain why the whips work well since they would be close also. The RF multi (whatever that is) could be the culprit but that works well with the sharkfins. The sharkfins would be farther from the bag but that doesn't explain why the whips work. The whips and the SNA600 have the same effective gain within a dB or so.

 

 

Thank you for the reply Larry.  In the tests I just did in my apartment I tested reception with the shark fins basically in the bag like the dipoles were, just sitting in a side pouch.

 

The RF multi I'm referring to is this PSC RF Multi: https://www.bhphotovideo.com/c/product/842473-REG/psc_fpsc0006c_psc_rf_multi.html?ap=y&gclid=CjwKCAjwwdTbBRAIEiwAYQf_E_1S_jEFWqlm_9-uDjgKZKk2ZRhf1R3kX6pTybfXDSRRuOgT9ZHcNBoCqLoQAvD_BwE&smp=y

 

11 minutes ago, LarryF said:

One possibility is the  RF multi (?) goes into oscillation when presented with the narrower band load of the SNA600's but not with the broader sharkfin load. Or the SNA600 is picking up RF from the output of the RF multi (?) because it is in close proximity and you have a feedback loop. Rf output to the SNA600 to the RF input of the RF multi. The sharkfins are farther away so they don't pickup the RF output and the whips are immune because they don't use the RF multi. Does the RF multi (?) have excess gain from its input to its output?

 

This is an interesting explanation, but I'm sure many other people have used dipoles with the RF Multi.  I know several mixers who use it in a bag in conjunction with the mixplexer which is, I assume, more or less doing the same thing as the RF multi (where the narrow band oscillation might be a problem).

 

11 minutes ago, LarryF said:

Or you could just be using generic incense rather the the Lectro approved Tibetan Blue brand.

 

 

Not me, I only smoke the good stuff ;)

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Another thought, does the RF multi (not knowing the brand) have a preamp in it by chance.  Looking at your photo the noise floor on the entire spectrum is raised.  Now I do not know what the sensitivity of the Lectro SR receivers happens to be, but it appears you are overloading the front end of the receiver.  Which would explain going back to the 1/4 wave with no active device in the signal chain made everything happy again.  

Unless you have a very selective preamp you might be creating more problems as you are amplifying quite a bit of RF spectrum.

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2 minutes ago, drpro said:

Another thought, does the RF multi (not knowing the brand) have a preamp in it by chance.  Looking at your photo the noise floor on the entire spectrum is raised.  Now I do not know what the sensitivity of the Lectro SR receivers happens to be, but it appears you are overloading the front end of the receiver.  Which would explain going back to the 1/4 wave with no active device in the signal chain made everything happy again.  

Unless you have a very selective preamp you might be creating more problems as you are amplifying quite a bit of RF spectrum.

 

The PSC RF Multi has power to active antennas, but that's off for my passive LP620s and the dipoles.

 

This is a good question I'd like some clarification on.  This RF issue is basically just a signal to noise issue is it not? 

 

In a high RF environment, if I'm amplifying my reception broad band in order to target a specific frequency on which I'm transmitting, does that also just raise the RF noise around the signal as well?  Essentially overloading the receiver with RF so it can't isolate a target frequency.  But that can't be the whole story because part of the reason to use the larger antennas and a wireless distro is to navigate heavy RF environments (or just for range in regular RF environments).

3 minutes ago, DanStewart said:

Was Antenna Power and Main Power engaged on the RF Multi?

 

No, main power only, I don't use the antenna power on my LP620s or the dipoles.

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15 hours ago, Jesse Flaitz said:

[snip] but I'm sure many other people have used dipoles with the RF Multi.  I know several mixers who use it in a bag in conjunction with the mixplexer which is, I assume, more or less doing the same thing as the RF multi (where the narrow band oscillation might be a problem). [snip]

Your RF Multi could be acting differently than other RF Multis. Just because one RF device works doesn't mean the next one will. Keep in mind, I'm down to grasping at straws.

 

I would try remoting the SNA's just for diagnostics. A few feet or so should be enough and if that "fixes" the problem, that is big information. I also would try turning all the other devices in your bag off and see if the SNA, RF Multi, and receivers is now normal. With weird problems like this, methodical divide and conquer is the best process.

Best Regards,

Larry Fisher

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17 hours ago, ProSound said:

Call PSC and talk to Ron he is VERY helpful and might offer some suggestions 

 

Yes, Ron spent about 20 minutes on the phone with me.  He was immensely helpful.  Didn't resolve the issue exactly, but he educated me quite a bit on RF signal flow, gain staging etc.  I think the problem I had comes down to my mismanagement of equipment.  I had assumed going into an RF heavy environment I'd want the most powerful transmitters and receivers to get above the noise, but that's not how it works because physics and stuff.  More power can be a solution in high RF environments, but so can less power on a clear frequency.

 

RF issues are by far the most conceptually difficult aspect of sound mixing for me, but I think this episode helped shed a bit of light on it.  Thanks for all the help.

2 hours ago, r.paterson said:

The psc multi adds 6-8 db gain which can add to issues in bag setup i found..

 

I'm going to do another A/B/C test another day when I have time.  I want see what happens when I get both the RF multi and dipoles out of the bag a bit.  On my cart set up, both are out of the bag by default, but I've never done a test against reception.

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On 8/17/2018 at 9:40 AM, Jesse Flaitz said:

 I had assumed going into an RF heavy environment I'd want the most powerful transmitters and receivers to get above the noise, but that's not how it works because physics and stuff.  More power can be a solution in high RF environments, but so can less power on a clear frequency.

 

Less is sometimes more with RF and Ron is a wealth of knowledge always looking to help.

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On 8/17/2018 at 9:40 PM, Jesse Flaitz said:

 

Yes, Ron spent about 20 minutes on the phone with me.  He was immensely helpful.  Didn't resolve the issue exactly, but he educated me quite a bit on RF signal flow, gain staging etc.  I think the problem I had comes down to my mismanagement of equipment.  I had assumed going into an RF heavy environment I'd want the most powerful transmitters and receivers to get above the noise, but that's not how it works because physics and stuff.  More power can be a solution in high RF environments, but so can less power on a clear frequency.

 

RF issues are by far the most conceptually difficult aspect of sound mixing for me, but I think this episode helped shed a bit of light on it.  Thanks for all the help.

 

I'm going to do another A/B/C test another day when I have time.  I want see what happens when I get both the RF multi and dipoles out of the bag a bit.  On my cart set up, both are out of the bag by default, but I've never done a test against reception.

But i would also vote for Larry suspect , he suggesting this is wired situation even in any RF environment i guess 

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 I have a similar set up and it has helped my reception.  Nomad 10, PSC Rf multi, two SNA600, four LR receivers with battery replacers powered by common battery.  I don't have the unused SNA connectors terminated.  The unit lives in the bottom of my bag.

 

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I experienced similar issues using that same exact setup (SNA600a's/PSC Multi/SRc's&Srb). I brought it up recently on one of the sound facebook groups and it was interesting to see many other mixers say they also witnessed the same issues (taking hits) and many of them had abandoned that rig all together for bag use. I too have since abandoned it. The dipoles do offer more gain (you can see it in the scans - compared to whips) and I believe that gain is overloading the receivers front end? It can't help to be running a hop transmitter less than 12" away either (and most of us are in a bag rig). That said... the dipoles do out perform the whips by almost double the distance (according to my field test) however the unfortunate trade-off is that they don't do well at close range (approx less than 50'). Perhaps Lectrosonics might design a SNA600B (B for "bag", optimized with an attenuator and/or PSC could offer some adjustable band pass filtering/attenuation) until then I'm sticking with whips in my bag. 

PS I considered trying 1 Dipole & 1 Whip, for 'best of both worlds' but as the OP pointed out: the RF signal isn't dropping when these hits/dropouts happen - so I believe diversity-wise, the RX would still choose the channel with the most gain. Too afraid to find out though ;)

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