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Author Topic: Problems with RF again - multiple units not working well stacked closely.  (Read 3152 times)

Debbie Dunkley

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #60 on: December 12, 2017, 02:01:09 pm »

Did anyone get a chance to consider the antenna I linked to on eBay? If they will work, I'm going to grab them.
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Tim McCulloch

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #61 on: December 12, 2017, 02:05:25 pm »

It is all very strange. The last time we played the same venues as these 2  shows in question was 6 - 8  weeks earlier with no problems using the old rack, same iem units, same mic unit - same everything in exactly the same position and configuration. The rack is the only difference.

Then I'd borrow another rack and swap out my RF stuff to see what happens.

I'm not buying that the rack, in and of itself, is responsible for intermittent problems in only 2 locations but it might be worth a substitution to see.  If changing racks fixes the problem there IS a difference in the racks that is not visible to the eye.  More likely is that in your rack change out, there was damage to coax or BNC connections...

But this is taking on a "Doc, it hurts when I do this..."  "Then don't do that" connotation.

The antennae you linked to appear to be suitable for your use.

Another consideration - the reassignment of TV stations and installation of new 600mHz cellular equipment means FCC construction permits and testing permits (and testing can be very intermittent) for both services.  That might help account for both the geographic and chronological differences.
« Last Edit: December 12, 2017, 02:09:08 pm by Tim McCulloch »
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Keith Broughton

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #62 on: December 12, 2017, 02:48:02 pm »

The rack is the only difference.
That you are aware of.
You may not have all the info to make that conclusion.
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Debbie Dunkley

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #63 on: December 12, 2017, 02:57:20 pm »

That you are aware of.
You may not have all the info to make that conclusion.

It is the only difference to the way the equipment is stored and used.
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."

Debbie Dunkley

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #64 on: December 12, 2017, 03:05:19 pm »

Then I'd borrow another rack and swap out my RF stuff to see what happens.

I'm not buying that the rack, in and of itself, is responsible for intermittent problems in only 2 locations but it might be worth a substitution to see.  If changing racks fixes the problem there IS a difference in the racks that is not visible to the eye.  More likely is that in your rack change out, there was damage to coax or BNC connections...

But this is taking on a "Doc, it hurts when I do this..."  "Then don't do that" connotation.

The antennae you linked to appear to be suitable for your use.

Another consideration - the reassignment of TV stations and installation of new 600mHz cellular equipment means FCC construction permits and testing permits (and testing can be very intermittent) for both services.  That might help account for both the geographic and chronological differences.


It is frustrating and quite the mystery to me. 
I switched out to this rack because it was a warranty claim with SKB. The latches on my old rack had become loose over time and wouldn't stay closed so I contacted SKB - I was told that design was no longer made and this design was the replacement.
It seems a bit sturdier than the old one.  It is essentially the same rack but different mold design.
I set it up the same way as the old one when I made the switch yet when everything was in the old one ( making sure to leave 1 rack space between iem and mic receiver) my mic worked fine. In the new one, not working fine.
With the iems switched off - the mic works fine...... with the closest iem transmitter off and within 20ft of it -works fine. So it is as if the rack change ( subtle difference in location of units perhaps) put any failing of RF over top enough now that the mic receiver is more prone to interference.
I got away with doing things the old way for 18 months so I came complacent.
It is ironic though that the less expensive plastic back up mic receiver I have works fine when placed either in or outside of the rack.
I'd use it instead but it is not rack mountable and I have to strap it to a shelf ( which I did do till I got the metal rack mount receiver).

I have placed aluminum foil between the top placed iem unit and the mic receiver - just tested it and it is working OK.... Won't hold my breath or really know till used in anger with all the nasty RF traffic at a  show.

I ordered the whip antennas and will get the coax and connectors too. Hopefully this will be enough and won't have cost me a fortune either.
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Rob Spence

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #65 on: December 12, 2017, 03:18:10 pm »

For your use, 25 cables may be a bit much. That said, I use them all the time. Sometimes with a whip and sometimes with paddles. In any case, shorter is better.



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Debbie Dunkley

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #66 on: December 12, 2017, 03:30:06 pm »

Yes, any 1/2 wave in the right freq range with the right connector will do. Personally, I do not like the Shure ones for ULX. Too limp, they spin on the bnc.

Given your propensity to do things as right as you can, here is what I would do...

Get a feed through bnc ( https://www.parts-express.com/neutrik-nbb75fg-bnc-feed-through-grounded-nickel--092-252 ).Mount it to one end of a short length of metal (3 x 1 for example). Get a female mic thread mount ( http://www.audiopile.net/DE-019 ) and mount it to the other end. The 1/2 wave whip can attach to the top of the bnc, the bracket can go on a convenient mic stand and a length of coax will connect it to the receiver.

Did this make any sense?


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Rob... that BNC is rated at 75 ohms.. do I need a 50 ohm? Should the coaxial be 50 or 75 ohm?
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."

Debbie Dunkley

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #67 on: December 13, 2017, 09:51:45 pm »

I want to make sure to get the right thing - should I get 50 ohm or 75 ohm BNC connectors and cable OR does it matter? The only Neutrik BNC feed through connectors I can find are 75 ohms.
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A young child says to his mother, "Mom, when I grow up I'm going to be a musician." She replies, "Well honey, you know you can't do both."

Mac Kerr

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #68 on: December 13, 2017, 10:16:53 pm »

I want to make sure to get the right thing - should I get 50 ohm or 75 ohm BNC connectors and cable OR does it matter? The only Neutrik BNC feed through connectors I can find are 75 ohms.

Don't add connections with a panel, just plug your antenna cables into whatever device you would have connected to the panel. Ideally cable should be 50Ω with 50Ω BNC connectors to properly mate with mic antenna systems, but anecdotal evidence suggests that RG59 (75Ω cable) will work at least as well as RG58 (50Ω) for longer runs due to generally lower loss.

Mac
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Geert Friedhof

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Re: Problems with RF again - multiple units not working well stacked closely.
« Reply #69 on: December 14, 2017, 08:24:50 am »

Impedance mismatches are to be avoided at (almost) any cost. Every time a impedance-mismatch occurs standing waves will occur, therefore degrading your signal. So: All cable, connectors and antenna either 50 ohm or 75 ohm.

NO COMBINATIONS OF THE TWO!

That being said, 50 ohm it should be. Also consider that a RG58 100 feet cable has a signal loss of more than 5 dB, according to Shure.

http://soundhub.audio/shure-whiteboard-understanding-rf-cables/
« Last Edit: December 14, 2017, 08:41:25 am by Geert Friedhof »
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