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Author Topic: Shure SLX issues? Kept dropping audio during show.  (Read 2011 times)

Sam Costa

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #60 on: July 21, 2021, 04:23:16 pm »

Half-right: replace the whip with at least 25' of the best 50Ω coax you can afford (and can coil) and either a Shure PA805 or a Sennheiser A 2003-UHF (or something helical if you want to get fancy).

-Russ

The planets must be aligning or something because I was just approached by another LAB member friend of mine who lives around my area and has one of these (PA411) for sale. Excited to pick it up and get this going and done. Ordering a PA805 tomorrow, so hopefully by next week Ill have it all mounted and tested prior to the next set of events coming up. :)

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Ike Zimbel

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #61 on: July 21, 2021, 05:42:08 pm »

The planets must be aligning or something because I was just approached by another LAB member friend of mine who lives around my area and has one of these (PA411) for sale. Excited to pick it up and get this going and done. Ordering a PA805 tomorrow, so hopefully by next week Ill have it all mounted and tested prior to the next set of events coming up. :)
Keep a whip antenna handy. At the distances shown in your pics, an LPDA (paddle) antenna may be overkill. A helical would absolutely be overkill and potentially cause more problems than it solves.
An omni antenna, like a Sennheiser 1031-U or the Shure UA-860 might be a better choice if you are intent on remoting the antenna.
My advice would be to get the combiner first and try it with the 1/2 wave antenna, right on the combiner. If it works, you're good.
If it's better, but not perfect, then try a remote antenna.
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~Ike Zimbel~
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Tim McCulloch

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #62 on: July 21, 2021, 08:57:00 pm »

Keep a whip antenna handy. At the distances shown in your pics, an LPDA (paddle) antenna may be overkill. A helical would absolutely be overkill and potentially cause more problems than it solves.
An omni antenna, like a Sennheiser 1031-U or the Shure UA-860 might be a better choice if you are intent on remoting the antenna.
My advice would be to get the combiner first and try it with the 1/2 wave antenna, right on the combiner. If it works, you're good.
If it's better, but not perfect, then try a remote antenna.

I routinely see setups where a helical is < 20 ft from the talent, who will inevitably place themselves and the receiver outside the primary coverage of the antenna.  "Oops, it did it again."

Maybe we should put vinyl "flags" on antennae to visually approximate the coverage pattern?

Maybe what I'm looking for (a way to explain coverage) exists on the Yoo of Toob?
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Henry Cohen

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #63 on: July 21, 2021, 09:23:47 pm »

. . . Maybe what I'm looking for (a way to explain coverage) exists on the Yoo of Toob?

If you ask nicely, Jason will show you his LPDA heat maps  ::)
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Henry Cohen

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Tim McCulloch

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #64 on: July 21, 2021, 09:27:23 pm »

If you ask nicely, Jason will show you his LPDA heat maps  ::)

There might be a barbecue bribe involved...  8)
 
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Henry Cohen

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #65 on: July 21, 2021, 09:35:44 pm »

There might be a barbecue bribe involved...  8)

And as the referral, I expect a cut  ;D
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Jason Glass

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #66 on: July 21, 2021, 09:54:49 pm »

I routinely see setups where a helical is < 20 ft from the talent, who will inevitably place themselves and the receiver outside the primary coverage of the antenna.  "Oops, it did it again."

When an IEM TX helical antenna is located <20ft. from the talent, there is *almost* no such thing as "outside the primary coverage".  There are primers all over the web that describe the true meaning of antenna beamwidth, but sadly pro audio folks just don't seem to get the gist of it.

The beamwidth of an antenna is the angle, off axis, *2, at which the gain is -3 dB from maximum (on-axis).  A typical commercial audio biz helical has 9 dBi to 11 dBi of gain on axis.

EXAMPLE SYSTEM:

We'll be generous and calculate our system with a 20 mW TX source, 50 feet of low-loss 9913F7 TX antenna cable, a 9 dBi gain helical TX antenna, with RX located 60 degrees off-axis where the pattern gain is around 4-ish dBi (shown on the antenna spec sheet as a polar plot), a 20 foot free space distance, a 0 dBi RX antenna, and a frequency of 539 MHz (center of the UHF TV band).  We'll also include a 2:1 TX antenna VSWR and also deduct circular polarization to linear polarization loss.  The resulting RSS is 6200.31384702 V.  That's 6.2+ times the optimal 1000 V for a solid link.

Now let's get extreme and duplicate the variables, except we'll put the RX in a null of the TX antenna, where its gain at that angle is 0 dBi.  The result is 3912.13355986 V.  That's 3.9+ times the requirement.

Try it here: http://cleanwirelessaudio.com/Path_Loss_and_Received_Power_Calculator/main.html

If you ask nicely, Jason will show you his LPDA heat maps  ::)

Hehee!  Maybe!
« Last Edit: July 21, 2021, 11:12:03 pm by Jason Glass »
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Russell Ault

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #67 on: July 22, 2021, 01:14:28 am »

When an IEM TX helical antenna is located <20ft. from the talent, there is *almost* no such thing as "outside the primary coverage". {...}

I'm glad I wasn't the only one thinking this; my impression was that it's better to accept a bit of (proximate) directional attenuation if, in return, there's an opportunity to reduce the number and severity of possible multipaths (especially for a non-diversity RX like the P3R(A)).

{...} Now let's get extreme and duplicate the variables, except we'll put the RX in a null of the TX antenna, where its gain at that angle is 0 dBi. {...}

To stick my neck out just a little bit further than I already have, I thought the (ideal) gain in a directional antenna's null would be approaching -∞ dBi. No?

-Russ
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Jason Glass

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #68 on: July 22, 2021, 08:15:52 am »

To stick my neck out just a little bit further than I already have, I thought the (ideal) gain in a directional antenna's null would be approaching -∞ dBi. No?

You caught me!  The nulls can indeed go deep into negative gain, although I don't think we'd see -∞ dBi in a pro audio helical design.

My explanation fails to account for other factors that are prevalent at such close range and field strengths in the real world, where it's not truly a free space environment.  Propagation modes such as reflection and scattering from real objects will usually increase RSS in the nulls.

There's also the often ignored or unpublished second polar plot of a circularly polarized antenna; the gain pattern of its oppositely polarized emission.  Often there is lower but significant gain in opposite polarization, which can overlap nulls in the primary polarization plot.

Yeah, this rabbit hole is mind-bending.   ;)

Ike Zimbel

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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #69 on: July 22, 2021, 12:05:04 pm »

You caught me!  The nulls can indeed go deep into negative gain, although I don't think we'd see -∞ dBi in a pro audio helical design.

My explanation fails to account for other factors that are prevalent at such close range and field strengths in the real world, where it's not truly a free space environment.  Propagation modes such as reflection and scattering from real objects will usually increase RSS in the nulls.

There's also the often ignored or unpublished second polar plot of a circularly polarized antenna; the gain pattern of its oppositely polarized emission. Often there is lower but significant gain in opposite polarization, which can overlap nulls in the primary polarization plot.

Yeah, this rabbit hole is mind-bending.   ;)
Yeah, like getting full RSSI bars on a RAD pack from the BACK of the helical shown in this picture. It's the little dot at the end of the arrow.
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~Ike Zimbel~
Wireless frequency coordination specialist and educator.
Manufacturer's Representative (Canada)
Radio Active Designs
Pro Audio equipment repair and upgrades.
~416-720-0887~
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Re: Shure SLX issues? Kept dropping audio during show.
« Reply #69 on: July 22, 2021, 12:05:04 pm »


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