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[John Roberts {JR}]

The pan would have to be 1/2 wavelength away for it not to be considered "near field".  That's about 5"

But coupling efficiency probably starts to drops off well before the full half wavelength.

JR

Caveat: still don't know how significant this is, if at all. I often report I am not a speaker guy, I am not a RF guy either.

[Scott Holtzman]

But coupling efficiency probably starts to drops off well before the full half wavelength.

JR

Caveat: still don't know how significant this is, if at all. I often report I am not a speaker guy, I am not a RF guy either.

I am using data from another world to make this statement.  When installing antenna systems on tower structures the stand off brackets had to be 1/2 wavelength from the structure to avoid the near field obstructing and resulting pattern destruction.

You could also use the structure as a director or reflector to purposely alter the horizontal pattern.

Either of these cases the metal within the nearfield would detune the output stage of the transmitter and require a touch up of the tune.

It's this "detuning" that leads me to believe the statement that an operating wireless device, placed in a metal pan would change the match on the transmitter output sufficiently to increase the RF PA current draw.

[Henry Cohen]

The pan would have to be 1/2 wavelength away for it not to be considered "near field".  That's about 5"

Reactive near field is considered to be 1/2 wavelength, radiating near field is about 1 wavelength, and far field is 2 to 6 wavelengths depending on frequency and bandwidth.

[Henry Cohen]

Either of these cases the metal within the nearfield would detune the output stage of the transmitter and require a touch up of the tune.

It's this "detuning" that leads me to believe the statement that an operating wireless device, placed in a metal pan would change the match on the transmitter output sufficiently to increase the RF PA current draw.

Whereas the math is in agreement with your "belief", the typical antenna on a belt pack or integrated into a handheld is a pretty rough match to start. I can't imagine the pan is going to detune the final PA to a point beyond where the internal current limiting is already limiting. I've never noticed any shorter battery life that couldn't be attributed to battery manufacturing tolerances, screamers vs soft talkers/singers or temperature. But, it would make for an interesting measurement exercise.

[Dan Mortensen]

I've never noticed any shorter battery life that couldn't be attributed to battery manufacturing tolerances, screamers vs soft talkers/singers or temperature. But, it would make for an interesting measurement exercise.

I'm game to test this this weekend, but have some questions about methodology:

1) Since I'm still trying to get familiar with my new pile of JTS mics, which seem to be on par with Shure SLX or at least in the vicinity, they are set up in the shop already so I'll use those. Their battery life seems decent but as yet unpredictable, so this test will be helpful.

2) They are 4 channel/1 rack space receivers, so I'll put a camera on the battery indicator screen and a camera on the RF level indicators. It looks similar in that regard to the ULX-D layout. Cameras so I don't have to watch continuously, and so I can post a time-lapse on my Youtube channel so you all can see, too.

3) It seems like the methodology should be one mic in free air and one mic in a loaf pan. I'm curious if ferrous makes any difference from aluminum, so I can also do a mic in a paper pan wrapped in aluminum foil. Does that seem reasonable?

4) To account for varying battery consumption from different individual mics, the mics should be rotated through each condition. So three iterations of the test, if there is agreement that ferrous vs. non-ferrous should also be a test condition.

5) Batteries will be new Duracell AA's, all from the same package.

6) How should I position each mic relative to the receivers?
     -All in a plane horizontally, so the free mic isn't bleeding significantly into the pans? In other words, free mic in the same orientation as the others?
     -Does it matter how far apart the free mic is from the pans, or how far apart the pans are?

7) Anything else to consider?

I can start in about 3 hours from now, and am on West Coast time even though the posting time stamps seem to be East Coast.

[John Roberts {JR}]

If you use a 9V battery clip you can wire a VOM in series with an external battery using current mode on the VOM and measure the current consumption in real time as you move the DUT (device under test) into and around the metal pan.

This should quickly reveal if there is any "there" there, how serious it is, and perhaps easy ways to mitigate it.

I have 9V battery clips laying around but no wireless gear, so that doesn't do you any good.

JR 

[TJ (Tom) Cornish]

If you use a 9V battery clip you can wire a VOM in series with an external battery using current mode on the VOM and measure the current consumption in real time as you move the DUT (device under test) into and around the metal pan.

This should quickly reveal if there is any "there" there, how serious it is, and perhaps easy ways to mitigate it.

I have 9V battery clips laying around but no wireless gear, so that doesn't do you any good.

JR

considering that his mics (and virtually all mics these days) use AAs, even if your clips and his mics were in the same vicinity it wouldn’t help much.

The best way to tap the circuit is two pieces of tin foil with an insulator between sandwiched between a battery and a contact.

[John Roberts {JR}]

considering that his mics (and virtually all mics these days) use AAs, even if your clips and his mics were in the same vicinity it wouldn’t help much.

The best way to tap the circuit is two pieces of tin foil with an insulator between sandwiched between a battery and a contact.

It's clear I am not in those trenches these days....

JR

[Dan Mortensen]

It's clear I am not in those trenches these days....

JR

I do have some mics that use 9V, but want to learn more about these rather than those.

We are 8:50 into the experiment and the batteries are all at 3 bars out of 5. I did notice a couple hours ago that the ferrous set were at 3 bars while the other two were at 4 bars, but the tell will be at the end and not in the middle.

It occurs to me that I'm really not super interested in spending a LOT of time trying to (as scientifically as I can) disprove James Stoffo and RF Venue's experiential statements that battery life is less with the loaf pans.

I AM interested in learning more about these mics, though, and this little experiment provides some data points in that quest. Plus, Henry's comment about battery life under use (rather than idling like these are) is much more interesting than the (unlikely) disproval of experience, so after this phase concludes I'm going to rotate the mics once to get different conditions for each and have a speaker play into them to see how activity reduces battery life. Since I want to know the latter anyway, and have a bunch of batteries, might as well look at the loaf pan thing, too.

Also, it will be interesting if there is a sustained difference between ferrous and aluminum foil in terms of battery life. When I was messing around yesterday with tuning mics in loaf pans as well as mics in aluminum foil/paper pans, both seemed to work equally well in terms of reducing intermods.

And, JR, I like your idea of measuring in real time as being very much easier than this but that also doesn't answer some of the points above, so that's why it's worth spending this time and effort.

Tom, that's a clever way to do it with AA's. Glad you thought of it 'cause I sure didn't...

[John Roberts {JR}]

I do have some mics that use 9V, but want to learn more about these rather than those.

We are 8:50 into the experiment and the batteries are all at 3 bars out of 5. I did notice a couple hours ago that the ferrous set were at 3 bars while the other two were at 4 bars, but the tell will be at the end and not in the middle.

It occurs to me that I'm really not super interested in spending a LOT of time trying to (as scientifically as I can) disprove James Stoffo and RF Venue's experiential statements that battery life is less with the loaf pans.

I AM interested in learning more about these mics, though, and this little experiment provides some data points in that quest. Plus, Henry's comment about battery life under use (rather than idling like these are) is much more interesting than the (unlikely) disproval of experience, so after this phase concludes I'm going to rotate the mics once to get different conditions for each and have a speaker play into them to see how activity reduces battery life. Since I want to know the latter anyway, and have a bunch of batteries, might as well look at the loaf pan thing, too.

Also, it will be interesting if there is a sustained difference between ferrous and aluminum foil in terms of battery life. When I was messing around yesterday with tuning mics in loaf pans as well as mics in aluminum foil/paper pans, both seemed to work equally well in terms of reducing intermods.

And, JR, I like your idea of measuring in real time as being very much easier than this but that also doesn't answer some of the points above, so that's why it's worth spending this time and effort.

Tom, that's a clever way to do it with AA's. Glad you thought of it 'cause I sure didn't...

It's good to eliminate as many variables as possible when performing experiments.

JR

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