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Author Topic: Terrific tips for good antenna placement  (Read 6683 times)

Karl Winkler

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Re: Terrific tips for good antenna placement
« Reply #20 on: August 24, 2016, 11:02:12 am »

Think of your antennas like lighting fixtures.  You have to put them in the right place.  On the floor behind the roadcase mountain wouldn't be great for a light, and wouldn't be great for an antenna either.

Lyle, that's a great way to describe it!

One additional thought, though, is that light from typical stage fixtures is usually quite directional, while antennas are less so. Also, antennas can interact with each other, thus the large spacing evident in Jason's diagram.
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Scott Holtzman

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Re: Terrific tips for good antenna placement
« Reply #21 on: August 24, 2016, 01:16:23 pm »

Not BDC's: they are RF over fiber media converters. RF in - light out / light in - RF out.

We play loosely with that term.  The cable outside plant engineers call the media converters block converters.  I guess because these guys have been around the block they accidentally add the "down" part referring to the satellite RX's.

We are taking the same, it takes a swath of RF and converts it to a broad spectrum lambda for transmission over fiber.  At the other end it gets converted back to RF.

I am sure you know that fiber behaves just like any other waveguide.  If you get an impedance mismatch you get reflections and intermodulation products. 



The amplifier with a measure of filtering making up solely for coaxial losses is pretty much the idea behind the better designed active LPDA's from Sennheiser, Shure and Wisycom. But with proper coax, and RF system gain structure, preamps are unnecessary. As for the 7/8" feedline: Forgetting for the moment even the cheapest variant is about $2.50/ft and connectors are $40ish each, that coax is not design for more than one deployment - the shield will kink, distort or break after just a two or three wraps. And never mind the physical space a couple hundred foot coil would take up. I've used 7/8" flexible on a couple of shows but was essentially bought by the production and discarded afterwards or permanently installed for use each year by the returning event.

I was speaking back to land mobile analogies for the preamps.

For the VHF and UHF frequencies the loss of 7/8 LDF was acceptable.  When we got pushed up into 800Mhz trunk systems you needed 1 1/4 or 1 5/8 for or air dialectric.  If you used a tower mounted preamp you could reuse the 7/8 for the RX line.  That was my reference.

6' is about the bend radius of 7/8 - Any tighter and you distort the aspect ratio of the center conductor, dialectric and shield which is a key component of impedance.
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Jerome Malsack

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Re: Terrific tips for good antenna placement
« Reply #22 on: September 02, 2016, 08:59:06 am »

With those uhf antennae, and the move to the VHF bands will there be some of those updates on the antenna for the VHF like the UHF.  Going back to using TV Yagi  ?
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Keith Broughton

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Re: Terrific tips for good antenna placement
« Reply #23 on: September 02, 2016, 09:11:56 am »

With those uhf antennae, and the move to the VHF bands will there be some of those updates on the antenna for the VHF like the UHF.  Going back to using TV Yagi  ?
Yagi antennas are not specific to VHF band use.
They can be tuned to a variety of ranges but they are quite narrow band so are great for a specific, tight range like a TV channel.
We could be using Yagis now but they are not as useful for broad band tuning applications as in most RF mic systems.
The lower the frequency, the larger the antenna so Yagis for VHF would be rather large.
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Karl Winkler

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Re: Terrific tips for good antenna placement
« Reply #24 on: September 02, 2016, 09:47:11 am »

With those uhf antennae, and the move to the VHF bands will there be some of those updates on the antenna for the VHF like the UHF.  Going back to using TV Yagi  ?

I do think we will start seeing some interesting VHF antennas on the market soon.

The problem with TV antennas is that they are typically designed for horizontal polarization, while wireless mic antennas are designed for vertical polarization. Not that they wouldn't work in a typical installation, but perhaps not optimally.
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Scott Helmke

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Re: Terrific tips for good antenna placement
« Reply #25 on: September 02, 2016, 10:09:24 am »

With those uhf antennae, and the move to the VHF bands will there be some of those updates on the antenna for the VHF like the UHF.  Going back to using TV Yagi  ?

The classic big rooftop TV antenna is usually a log periodic, just like those black paddles everybody uses for UHF mics.
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Keith Broughton

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Re: Terrific tips for good antenna placement
« Reply #26 on: September 02, 2016, 10:11:34 am »

I do think we will start seeing some interesting VHF antennas on the market soon.

The problem with TV antennas is that they are typically designed for horizontal polarization, while wireless mic antennas are designed for vertical polarization. Not that they wouldn't work in a typical installation, but perhaps not optimally.
Turn it 90 deg? Should work. :)
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Jerome Malsack

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Re: Terrific tips for good antenna placement
« Reply #27 on: September 02, 2016, 07:32:52 pm »

I tested a 12 dbi  antenna with horizontal so after the storm leaves DC area I will try the vertical.  I strapped it to a speaker stand.
Body pack was able to get extra 30 ft with horizontal.  If we move back to VHF the antenna on the speaker stand would put the long axis down 20 to 24 inchs below the ceiling height.
So the venue needs to have a high ceiling.  Some churches would work well to do the wedding, But the large antenna becomes eye sore. 

oh and yes  I was on the 75 ohm RG 6 cable  so some mismatch and loss there as well.  cable was under 20 ft. 

any one wanting to work with this testing and measuring  pm.   I am south of DC.
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Joel T. Glaser

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Re: Terrific tips for good antenna placement
« Reply #28 on: September 10, 2016, 11:24:55 am »

Great info. Thank you all for sharing your vast knowledge!

Joel
Glaser Audio Productions
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Re: Terrific tips for good antenna placement
« Reply #28 on: September 10, 2016, 11:24:55 am »


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