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Author Topic: Transmitters in bread pans  (Read 6509 times)

Keith Broughton

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Re: Transmitters in bread pans
« Reply #20 on: December 19, 2017, 07:13:26 am »

As for pan liners, a piece of the rubber matting used as household drawer liners works great.
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Scott Helmke

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Re: Transmitters in bread pans
« Reply #21 on: December 19, 2017, 10:02:05 am »

I don't usually use any gain on the rx antenna for only 50 feet of quality cable. You are raising the rf noise floor which can get you closer to rf overload faster.

+1.  Antenna or in-line amplifiers are only there if you need to compensate for running long cable.
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Keith Broughton

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Re: Transmitters in bread pans
« Reply #22 on: December 19, 2017, 12:04:19 pm »

+1.  Antenna or in-line amplifiers are only there if you need to compensate for running long cable.
Using antenna gain for "better mic reception" is another common mistake.
In fact, the new Shure antennas have a -3 db setting  along with the usual +gain settings.
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boburtz

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Re: Transmitters in bread pans
« Reply #23 on: December 23, 2017, 02:12:58 pm »

I bought a wooden flatware organizer from one of the department stores and covered it in foil tape. It works as well as the breadpans and can be kept in the wireless drawer for transport and brought out onto a table for the show. It only holds four handheld mics, though.
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Ike Zimbel

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Re: Transmitters in bread pans
« Reply #24 on: December 27, 2017, 03:13:08 pm »

I bought a wooden flatware organizer from one of the department stores and covered it in foil tape. It works as well as the breadpans and can be kept in the wireless drawer for transport and brought out onto a table for the show. It only holds four handheld mics, though.
This points to another solution I have seen: If you already have foam fitted trays in a work trunk (or other road case...) to carry your mics in, you can just fit some heavy foil (I've seen black wrap used a lot) in the antenna end of the cutout. The downside of this is if your transmitters fit snugly in the foam, it can slow the ins-and-outs of the mics. On some shows, they move pretty fast...
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Dan Mortensen

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Re: Transmitters in bread pans
« Reply #25 on: December 27, 2017, 07:48:26 pm »

This points to another solution I have seen: If you already have foam fitted trays in a work trunk (or other road case...) to carry your mics in, you can just fit some heavy foil (I've seen black wrap used a lot) in the antenna end of the cutout. The downside of this is if your transmitters fit snugly in the foam, it can slow the ins-and-outs of the mics. On some shows, they move pretty fast...

It's interesting you brought this up, as I've been trying to figure out a variation on this.

There was a vendor on the NAB side of the last NY AES Convention selling cut foam inserts with or without cases.  mycasebuilder.com

The sweet thing about it was that you can have literally any cutout or combination of cutouts in the foam, an unlimited number. You use the app on their site to create new or use predefined shapes that meet your need (FYI Safari on laptop or old iPad are crap for the app, Chrome on a laptop works great) and their computer cutters make them. There was a now-expired convention discount which made it a sweeter deal. And if you are not sure of your exactitude, you can get do-over insurance for something like $10.

I more or less replicated an SKB micbox layout in a deeper case, with deeper holes for ULX-D size handhelds, and was wondering about having them slice squares around each hole, then wrap that square with aluminum foil, putting the transmitter end down into the hole, with a layer of foil on the interior bottom of the entire case. The foil would be protected by foam on each side, and you could do a checkerboard foil/no foil for the interior holes to take up a little less space.

Their foams are either expanded polyethylene in white (special order) or gray, or the normal case soft foam that works great but deteriorates over time. There is also a premium foam that is about 20% more than those, which looked and felt nice but wasn't needed for this project.

Prices seemed to be not a whole lot more than buying a big chunk of foam and spending hours trying to figure out how to make nice even holes/shapes in it.

The cases came just after Thanksgiving, and look really good and work well so far, although I didn't do the foil thing since the loaf pan discussion happened subsequent to order placement. Also, I didn't realize foil would work as well as solid metal. Did get the do-over insurance, though...

Questions:

It seems like just putting foil in the holes would wear the foil quickly. Did you notice that?

Does the foil/metal need to be contiguous (like a loaf pan) to be effective, or are isolated bits as described above just as good? I was going to try it to see before calling about re-ordering the foam.

Regarding deterioration of the foil, it seems like a mesh would be just as effective as solid up to a point, since the wavelengths are quite a bit longer than the bread pans/foil, so some holes don't matter?
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John Sulek

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Re: Transmitters in bread pans
« Reply #26 on: December 27, 2017, 11:16:46 pm »

Does the foil/metal need to be contiguous (like a loaf pan) to be effective, or are isolated bits as described above just as good? I was going to try it to see before calling about re-ordering the foam.

Regarding deterioration of the foil, it seems like a mesh would be just as effective as solid up to a point, since the wavelengths are quite a bit longer than the bread pans/foil, so some holes don't matter?

This is from Tim Vear of Shure in their "Operation and Selection of Wireless Microphones". Lots of good non brand specific info.

Interestingly, a reflecting metal object can be porous,
that is, it can have holes or spaces in it. As long as the
holes are much smaller than the wavelength, the metal
surface will behave as if it were solid. This means that
screens, grids, bars, or other metal arrays can reflect radio
waves whose wavelength is greater than the space
between the array elements and less than the overall array
size. If the space between elements is larger than the
wavelength, the radio waves will pass through the array.
For example, the metal grid on the glass door of a microwave
oven reflects microwaves back into the oven but
allows light waves to pass through so that the inside is visible.
This is because microwaves have a wavelength of at
least one centimeter while visible light has a wavelength of
only one-millionth of a meter.
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Henry Cohen

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Re: Transmitters in bread pans
« Reply #27 on: December 28, 2017, 11:34:22 am »

This is from Tim Vear of Shure in their "Operation and Selection of Wireless Microphones". Lots of good non brand specific info.

Interestingly, a reflecting metal object can be porous,
that is, it can have holes or spaces in it. As long as the
holes are much smaller than the wavelength, the metal
surface will behave as if it were solid. This means that
screens, grids, bars, or other metal arrays can reflect radio
waves whose wavelength is greater than the space
between the array elements and less than the overall array
size. If the space between elements is larger than the
wavelength, the radio waves will pass through the array.
For example, the metal grid on the glass door of a microwave
oven reflects microwaves back into the oven but
allows light waves to pass through so that the inside is visible.
This is because microwaves have a wavelength of at
least one centimeter while visible light has a wavelength of
only one-millionth of a meter.

As long as the holes or openings in the screen or mesh material are 1/20th of a wavelength or smaller, the material will be 99.9% effective as a shield or reflector for that frequency and lower.
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Henry Cohen

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John Sulek

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Re: Transmitters in bread pans
« Reply #28 on: December 28, 2017, 11:41:36 am »

As long as the holes or openings in the screen or mesh material are 1/20th of a wavelength or smaller, the material will be 99.9% effective as a shield or reflector for that frequency and lower.

Thanks Henry!
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Mac Kerr

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Re: Transmitters in bread pans
« Reply #29 on: December 28, 2017, 03:36:37 pm »

As long as the holes or openings in the screen or mesh material are 1/20th of a wavelength or smaller, the material will be 99.9% effective as a shield or reflector for that frequency and lower.

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
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Re: Transmitters in bread pans
« Reply #29 on: December 28, 2017, 03:36:37 pm »


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