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Author Topic: Cable? transmitter combiner out to LPDA  (Read 926 times)

Jason Glass

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Re: max dB loss for a given distance?
« Reply #10 on: January 03, 2019, 10:13:31 am »

Jason Glass has a nifty Android app for this exact calculation, but IIRC his calculator also accounts for gain stage noise figure and RF environmental noise floor.

Thanks, Henry.  It's not quite fancy enough to have useful and easy CNR functions, though!  I suppose if you measured the actual system noise and local noise then you could use the app to separately predict RSS and figure out the ratio.

Here's the web version of the app, which should run fine in any modern browser.  http://cleanwirelessaudio.com/Path_Loss_and_Received_Power_Calculator/main.html

Don Boomer

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Re: max dB loss for a given distance?
« Reply #11 on: January 07, 2019, 12:31:41 pm »


Salty water bag absorption loss                     -20dB

Hey Henry

Iím curious as to how you got this number. Are you just considering only the mic user or are you including an audience?  Line of sight?

Thanks
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Don Boomer
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Henry Cohen

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Re: max dB loss for a given distance?
« Reply #12 on: January 07, 2019, 08:09:04 pm »

Hey Henry

Iím curious as to how you got this number. Are you just considering only the mic user or are you including an audience?  Line of sight?

This is considering the ERP loss due to just the person wearing the pack. Between the body absorption and the de-tuning of the antenna as it rests against the body, 20dB is about the minimum I observe on a regular basis. 30-40dB is not uncommon at UHF frequencies for "larger" talent.
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Henry Cohen

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Don Boomer

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Re: max dB loss for a given distance?
« Reply #13 on: January 08, 2019, 12:23:34 am »

This is considering the ERP loss due to just the person wearing the pack. Between the body absorption and the de-tuning of the antenna as it rests against the body, 20dB is about the minimum I observe on a regular basis. 30-40dB is not uncommon at UHF frequencies for "larger" talent.

Thank you sir. What would you use for handheld?
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Don Boomer
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Jason Glass

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Re: Cable? transmitter combiner out to LPDA
« Reply #14 on: January 08, 2019, 01:12:39 am »

Thank you sir. What would you use for handheld?
I also eagerly wish to know your thoughts on this, Henry!  It's a million-dollar question in our line of work.

FWIW, when I was writing the app, I combed the web for weeks and researched everything I could find about absorption losses as a result of human tissue located within the near field.  The majority of what I found (that has credibility) was regarding mobile or cordless phones, a notable portion was regarding medical telemetry devices, and a small bit was very old military communications stuff.  Interestingly, I found very little about civilian commercial walkies. Anyway, most of it refuted my own observations and measurements over decades of dealing with artists who incessantly grip the microphone TX antenna.  My personal anecdotal examples were always operating between 470 and 800 MHz, and of course freq matters.  The mic manufacturers must know some serious mojo because I have never measured more than 60 dB loss from a full tight fist around a modern (age of wrapped flexible PCB helical) HH mic antenna referenced to free space in a clip on a mic stand.  And that 60 dB is actually quite rare.  Most often it's on the order of 10 to 20 dB, which just seems incredible to me, but measured and noted nonetheless.

I feel compelled to mention that my notes in the app all tend toward extremely conservative, so I went with the 50 to 90 dB recommendation for "surrounded by tissue" that is commensurate with the academic research that I found.  This hopefully assures the user no failure as a result of insufficient caution.

Please weigh in!

Sent from my mobile phone using Tapatalk
« Last Edit: January 08, 2019, 01:22:03 am by Jason Glass »
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Jason Glass

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Re: Cable? transmitter combiner out to LPDA
« Reply #15 on: January 08, 2019, 01:41:37 am »



The mic manufacturers must know some serious mojo...

Aargh.  It just now occurred to me that the counterpoise that is the mic housing most likely becomes the (far less efficient) radiator under antenna gripping conditions.  Not mojo or an ideal antenna, but rather a fortuitous "better than nothing" scenario.

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Diogo Nunes Pereira

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Re: Cable? transmitter combiner out to LPDA
« Reply #16 on: January 09, 2019, 04:35:42 pm »



FWIW, when I was writing the app, I combed the web for weeks and researched everything I could find about absorption losses as a result of human tissue located within the near field. 

This link provides some info and links to academic research regarding body absorption of PMSE equipment. Hope it's helpful:

https://www.apwpt.org/terminologies-a--i/body-loss-effect/index.html

The pic below is taken from the article in APWPT's webpage.

This site also has lots of information about frequency bands and licencing scenarios in different countries, and many other topics of interest to members of this forum. It provided me with many hours of browsing and reading when I first found it...

Thanks for taking the time and effort to build the app, Jason. Also good to know there's a web version I didn't knew about...

D

Diogo

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Tim McCulloch

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Re: Cable? transmitter combiner out to LPDA
« Reply #17 on: January 19, 2019, 06:55:10 pm »

End result - I liked LMR-400, the boss liked the LMR-240 (price).

Thanks for all the direct info and the very useful swerves.  Love this place!
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