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Author Topic: Extending range of Sennheiser EW100 radio mic  (Read 2266 times)

Miguel Dahl

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #20 on: February 08, 2020, 12:36:37 pm »

Sorry to close to hijack this thread. Maybe I should make an own thread..

But regarding noise floor and boosters. Here's a scan of the surroundings I did the other day. As you can see there is "nothing" between the two DTV channels. With this I ask if using a booster is still a such a "bad" thing as if there was a noticeable noise floor present across the current open spectrum. You say it raises the noise floor, but there is "no floor" in this scan. The booster operates at 516-558 so it will raise the DTV, but I don't have any transmitters in those frequencies. They're all between the DTV channels.

« Last Edit: February 08, 2020, 12:57:26 pm by Miguel Dahl »
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Henry Cohen

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #21 on: February 08, 2020, 04:31:11 pm »

I might have this wrong: won't an amplifier in saturation produce harmonic distortion?

The non-harmonic distortion I was thinking of is the inherent noise you mentioned.

Certainly spurious harmonics are a classic symptom of an amplifier in saturation, but once it is in saturation, an amplifier can can emit all kinds of non-coherent spurious emissions.
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Henry Cohen

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Henry Cohen

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #22 on: February 08, 2020, 04:42:55 pm »

Sorry to close to hijack this thread. Maybe I should make an own thread..

But regarding noise floor and boosters. Here's a scan of the surroundings I did the other day. As you can see there is "nothing" between the two DTV channels. With this I ask if using a booster is still a such a "bad" thing as if there was a noticeable noise floor present across the current open spectrum. You say it raises the noise floor, but there is "no floor" in this scan. The booster operates at 516-558 so it will raise the DTV, but I don't have any transmitters in those frequencies. They're all between the DTV channels.

There are several issues in play here:

- Since there's no RF level scale in your scan image, we don't know the actual noise floor or the level of the DTV signals.

- The amplifier will raise the level of all RF energy within its passband plus a slope of several MHz below and above (think low Q BPF). so not only will the DTV signal levels be raised, but so will the underlying RF noise floor in the unused channel, which we can't see in this image. That noise floor will rise yet an additional amount due to the composite energy of the strong adjacent DTV carriers.

- The receiver selectivity may not be good enough to filter out the added noise of all the RF energy within the passband, mostly due to the DTV channels.

- The booster amp may be driven into saturation from the strong DTV carriers.

In short, you're far better off running a bigger low loss cable and putting a narrowband channel filter ahead of the receiver. If you insist on using the pre-amp, at the very least use appropriate BPF filtering before the amps.
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Henry Cohen

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Jean-Pierre Coetzee

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #23 on: February 09, 2020, 12:08:06 pm »

It was also mentioned earlier that what level the receiver is receiving doesn't matter. If you are having dropout issues adding the RF amp wouldn't improve that in any way whatsoever since your SNR is already bad, making it louder doesn't matter. Imagine a channel on your console with a ton of noise and hiss and you can barely hear the instrument through it. Increasing the gain does absolutely nothing to assist the situation.

Henry also mentioned that you may actually oversaturate the amp or even your receiver with the strong out of band signal that is noise. Anything that isn't desired signal is noise if it comes into the input stage of the receiver.
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Miguel Dahl

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #24 on: February 10, 2020, 09:48:40 am »

Thanks so much. I'm just digging further, theoretically. On the job I sat up there's no RF issues, I just got curious about when not to implement a booster
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Henry Cohen

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #25 on: February 10, 2020, 01:55:32 pm »

. . . I just got curious about when not to implement a booster

Only in very rare situations. Essentially, never.
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Henry Cohen

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Miguel Dahl

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #26 on: February 11, 2020, 10:16:42 am »

Only in very rare situations. Essentially, never.

So, never not implement a booster? :D

Just kidding.

I've used them on 40m stretches of 10dB/100m cables with a barrel extension between 2x20m cables, but I don't get the math to add up, although I was experiencing bad signal/dropouts into the receivers without, but it was good with, and my senn rep told me that I need boosters.
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Don Boomer

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #27 on: February 11, 2020, 12:01:58 pm »

So if it works, then it works. But there are best practices to follow that would make your system even more reliable. A great number of them are free or very low in cost.

Im guessing in your case you could switch the cost of a line amp for better coax which will result in at least some improvement in CNR as compared to a booster.  Depending on your local conditions either may work fine but having more stability would be my choice.

I would highly suggest you get a reasonable scanner so you can measure the differences between the two.  Moving forward I believe having a scanner is a requirement for anyone working with wireless mics. The job has just become too difficult to operate reliably without one. 
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Miguel Dahl

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #28 on: February 11, 2020, 12:34:49 pm »

So if it works, then it works. But there are best practices to follow that would make your system even more reliable. A great number of them are free or very low in cost.

Im guessing in your case you could switch the cost of a line amp for better coax which will result in at least some improvement in CNR as compared to a booster.  Depending on your local conditions either may work fine but having more stability would be my choice.

I would highly suggest you get a reasonable scanner so you can measure the differences between the two.  Moving forward I believe having a scanner is a requirement for anyone working with wireless mics. The job has just become too difficult to operate reliably without one.

The cables I'm using are equal to LMR400. 
I see a scanner would be handy, but comparing to what jobs we do, it would be merely be recognized as a "gadget". We do maybe four jobs pr year which is 20 up to 28 channels.
« Last Edit: February 11, 2020, 12:43:51 pm by Miguel Dahl »
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Ike Zimbel

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Re: Extending range of Sennheiser EW100 radio mic
« Reply #29 on: February 11, 2020, 02:19:04 pm »

So, never not implement a booster? :D

Just kidding.

I've used them on 40m stretches of 10dB/100m cables with a barrel extension between 2x20m cables, but I don't get the math to add up, although I was experiencing bad signal/dropouts into the receivers without, but it was good with, and my senn rep told me that I need boosters.
In this example, you are using the amp to overcome losses in the cable, which is what they are meant for. The math is seldom going to work out exactly, IOW, that the amount of gain in the amplifier is exactly equal to the amount of cable loss. Remember too that there are other areas of loss, like using 2 x 20m cables doubles the number of connectors in the chain, and each connector contributes a small amount of loss. It adds up.
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Re: Extending range of Sennheiser EW100 radio mic
« Reply #29 on: February 11, 2020, 02:19:04 pm »


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