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Author Topic: Active antennas and attenuators  (Read 1889 times)

Andrew Outlaw

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Active antennas and attenuators
« on: May 24, 2016, 09:17:33 am »

When using an active antenna, like the older shure ua870's (that can't be set to not amplify), and you want to put a 10db attenuator inline, does the attenuator need to be dc passing?

I'm assuming the answer is "it depends" because a DC-2k attenuator would attenuate the bias power by 10db as well, so it would depend upon your cable length whether the bias power that reaches the antenna is enough to power it. Is that correct?

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Pete Erskine

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Re: Active antennas and attenuators
« Reply #1 on: May 24, 2016, 09:50:51 am »

When using an active antenna, like the older shure ua870's (that can't be set to not amplify), and you want to put a 10db attenuator inline, does the attenuator need to be dc passing?

I'm assuming the answer is "it depends" because a DC-2k attenuator would attenuate the bias power by 10db as well, so it would depend upon your cable length whether the bias power that reaches the antenna is enough to power it. Is that correct?

The antenna won't work without power, same with the newer one.  I often use splitters which attenuate up to 8 db but also pass DC and it still works.

Why not just use a passive antenna?  In locations which have high noise floor, when i am running a long antenna cable, I put the amplification at the RX end to avoid overloading the amp.
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Pete Erskine
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Andrew Outlaw

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Re: Active antennas and attenuators
« Reply #2 on: May 24, 2016, 12:13:20 pm »

The antenna won't work without power, same with the newer one.  I often use splitters which attenuate up to 8 db but also pass DC and it still works.

So as long as the attenuator is not "DC Blocking" it should still work? OR does it need to be specifically DC Passing?
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Why not just use a passive antenna?

That's what's available in inventory
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Keith Broughton

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Re: Active antennas and attenuators
« Reply #3 on: May 24, 2016, 01:36:43 pm »

put the amplification at the RX end to avoid overloading the amp.
Just to clarify, Pete, you are saying you are trying to avoid overloading the input of the "booster" amp when it is at the antenna end in a high RF environment?
So, passive antenna, cable run, booster amp, receiver.
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Pete Erskine

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Re: Active antennas and attenuators
« Reply #4 on: May 24, 2016, 02:08:17 pm »

Just to clarify, Pete, you are saying you are trying to avoid overloading the input of the "booster" amp when it is at the antenna end in a high RF environment?
So, passive antenna, cable run, booster amp, receiver.

Correct.  When doing RF on 34th street at Macy*s the antennas often are 150-200' cable runs.  Shure UA874 amplified antennas, even at their lowest amplification range - +6dB, show overload from the very hi noise floor caused by the Empire State TV transmitters.  Using a A2003 passive antenna and adding +10 dB at the RX with a Shure UA830 gave the gain but the loss in the antenna cable protected the amp from early overload.
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Jens Palm Bacher

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Re: Active antennas and attenuators
« Reply #5 on: May 24, 2016, 02:45:40 pm »

When using an active antenna, like the older shure ua870's (that can't be set to not amplify), and you want to put a 10db attenuator inline, does the attenuator need to be dc passing?

I'm assuming the answer is "it depends" because a DC-2k attenuator would attenuate the bias power by 10db as well, so it would depend upon your cable length whether the bias power that reaches the antenna is enough to power it. Is that correct?
The Sennheiser AD3700 etc. will work without DC power, but with -6db loss compared to a passive paddle.
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Keith Broughton

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Re: Active antennas and attenuators
« Reply #6 on: May 24, 2016, 03:37:01 pm »

Correct.  When doing RF on 34th street at Macy*s the antennas often are 150-200' cable runs.  Shure UA874 amplified antennas, even at their lowest amplification range - +6dB, show overload from the very hi noise floor caused by the Empire State TV transmitters.  Using a A2003 passive antenna and adding +10 dB at the RX with a Shure UA830 gave the gain but the loss in the antenna cable protected the amp from early overload.
I have a similar situation in downtown Toronto.
Not that kind of cable length, usually, but will keep it in mind.
Thanks
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ProSoundWeb Community

Re: Active antennas and attenuators
« Reply #6 on: May 24, 2016, 03:37:01 pm »


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