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Author Topic: Transmitters in bread pans  (Read 8085 times)

John Roberts {JR}

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Re: Transmitters in bread pans
« Reply #30 on: December 28, 2017, 03:59:12 pm »

A very rough back of napkin calculation (actually mostly in my head) puts the wavelength of 700MHz at about 450mm. 1/20th of 450 is 22.5mm, or just under an inch to mix notation standards. That seems to say any common metallic window screen should be an adequate RF shield. Have i lost a decimal somewhere?

Mac
according to google wavelength of 700MHz is 42.9 CM.   1/20= 2.14 cm  = 0.84"

Close enough for government work...

JR

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Henry Cohen

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Re: Transmitters in bread pans
« Reply #31 on: December 28, 2017, 04:04:18 pm »

A very rough back of napkin calculation (actually mostly in my head) puts the wavelength of 700MHz at about 450mm. 1/20th of 450 is 22.5mm, or just under an inch to mix notation standards. That seems to say any common metallic window screen should be an adequate RF shield. Have i lost a decimal somewhere?

You've not lost a decimal place; 700MHz is 428.27mm, 1/20th being 21.4mm. And yes, window screen works well up to about 1GHz. (Just ensure the screen material is in fact metal, and not nylon  :-\ )
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Henry Cohen

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Dan Mortensen

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Re: Transmitters in bread pans
« Reply #32 on: December 28, 2017, 04:33:42 pm »

Good info, thanks, guys.

One other thing about bread pans vs. tubes (as in an SKB type mic box with wrapped holes):

I get the impression that using bread pans allows you to still see the active frequencies but specifically cuts the intermod products. At least that's what I see when using them vs just setting on the table. And seeing those active frequencies allows you to observe something valuable in real time (what? The fact that something competing hasn't kicked in?) so that you can maintain the integrity of your coordination. This is why you just don't have the talent turn the transmitters off in between uses, in addition to not letting them forget to turn them on.

Is that right?

The bread pans have one whole side open to allow the RF out, a tube would only have a hole on top, opposite the antenna. If used as a holding pen for active but unused mics, it seems like the tubes would limit the ability to monitor the mics while in them. Yes?

If the mesh works just as well as bread pans, something like this or this might be the better option. These are cheaper than new bread pans, too, although it looks like only the second one will nest like bread pans for travel.

Thanks again for the great info.
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Henry Cohen

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Re: Transmitters in bread pans
« Reply #33 on: December 28, 2017, 04:52:15 pm »

Good info, thanks, guys.

One other thing about bread pans vs. tubes (as in an SKB type mic box with wrapped holes):

I get the impression that using bread pans allows you to still see the active frequencies but specifically cuts the intermod products. At least that's what I see when using them vs just setting on the table. And seeing those active frequencies allows you to observe something valuable in real time (what? The fact that something competing hasn't kicked in?) so that you can maintain the integrity of your coordination. This is why you just don't have the talent turn the transmitters off in between uses, in addition to not letting them forget to turn them on.

Is that right?

I think you're overthinking this. Bread pans were initially chosen because they were readily available and cheap. Yes, they do have the advantage of permitting one to see the transmitter's display in real time and readily tell the frequency, battery life and whether the unit is on.


Quote
The bread pans have one whole side open to allow the RF out, a tube would only have a hole on top, opposite the antenna. If used as a holding pen for active but unused mics, it seems like the tubes would limit the ability to monitor the mics while in them. Yes?

You may need another [attenuated] RX antenna by your mic staging area if your metal tube will attenuate the RF significantly.



Quote
If the mesh works just as well as bread pans, something like this or this might be the better option. These are cheaper than new bread pans, too, although it looks like only the second one will nest like bread pans for travel.

I'd avoid the multiple slot version (the first link) as that would present a common wall between any two TX and is an overall common conductor within the reactive near fields of all TX's: I suspect this would not mitigate the IM's as much as individual receptacles.  But since you're in the testing groove, try it and let us know  ;D
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Henry Cohen

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Dan Mortensen

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Re: Transmitters in bread pans
« Reply #34 on: December 28, 2017, 05:48:03 pm »

I think you're overthinking this.

Unquestionably, but there's a lot to think about and it's hard to tell wheat from chaff when there's so much wheat.


I'd avoid the multiple slot version (the first link) as that would present a common wall between any two TX and is an overall common conductor within the reactive near fields of all TX's: I suspect this would not mitigate the IM's as much as individual receptacles. 

And that's why I'm overthinking. That wouldn't have occurred to me.

But since you're in the testing groove, try it and let us know  ;D

I ordered a used (cheaper yet) version of the second one to do that. The common wall one doesn't lend itself to packing easily, so probably not.

Like I said somewhere else, the student should be willing to put in some serious time, and I am. I've made what seems like a lot of progress in understanding these new mics, both good and ill.
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John Roberts {JR}

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Re: Transmitters in bread pans
« Reply #35 on: December 28, 2017, 07:18:31 pm »

I still think this is an opportunity for microphone mfrs (should one be lurking around here.  ::)  )... If the loading from a nearby ground plane shorting the RF field increases antenna load, maybe sense for that and turn it off when I detects that it is "ground(plane)ed". Of course if the mechanism does not draw that much more current then it really doesn't matter.

JR
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Dan Mortensen

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Re: Transmitters in bread pans
« Reply #36 on: December 28, 2017, 08:27:25 pm »


I'd avoid the multiple slot version (the first link) as that would present a common wall between any two TX and is an overall common conductor within the reactive near fields of all TX's: I suspect this would not mitigate the IM's as much as individual receptacles.

In overthinking about this for a little while during packing for a show, does the quoted text mean that the individual bread pans can't touch each other, since if they did, they'd be creating a single wall due to conductivity of the metal? Or do the two sides of metal, even if touching,  do something different than the single wall of mesh or solid? I can certainly test touching vs. non-touching for intermod display...

Regardless, the slots in that common wall mesh container are too short for ULX-D-sized mics, so I definitely won't be getting one.
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Rob Spence

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Re: Transmitters in bread pans
« Reply #37 on: December 28, 2017, 10:05:43 pm »

Tubes would be fine for hand held mics (given you canít look at it, might as well turn it off). Not so much for belt packs and accessories.



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Ike Zimbel

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Re: Transmitters in bread pans
« Reply #38 on: December 29, 2017, 06:21:40 pm »

In overthinking about this for a little while during packing for a show, does the quoted text mean that the individual bread pans can't touch each other, since if they did, they'd be creating a single wall due to conductivity of the metal? Or do the two sides of metal, even if touching,  do something different than the single wall of mesh or solid? I can certainly test touching vs. non-touching for intermod display...
It's probably better that they don't touch...but they often do. I can tell you from my experience wearing a BTR pack while wrangling mics that when the pans are touching, I can hear lots of "static" in my headset when the pans get bumped. Is this a problem for other RF devices nearby? Not that I've been able to see. Sometimes when you need to get 14 mics on a table, in a line, the pans are going to touch. On another note, when I'm short pans, I put every other mic in a pan, so between the added distance between tx, and the sides of the pans, you still reap a benefit.
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Dave Garoutte

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Re: Transmitters in bread pans
« Reply #39 on: December 30, 2017, 02:28:54 pm »

A little gaff tape on the outside of the pans will insulate them.
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Re: Transmitters in bread pans
¬ę Reply #39 on: December 30, 2017, 02:28:54 pm ¬Ľ


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