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Author Topic: Is this real?  (Read 1838 times)

Russell Ault

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Re: Is this real?
« Reply #20 on: February 05, 2019, 03:14:21 pm »

It's not like distributing wideband antenna signals is anything new.  The cable TV industry has been doing it for half a century already.

My impression too was that the VSWR-related attenuation caused by a 50 ohm to 75 ohm impedance mismatch (and back) is pretty nominal, at least in receive applications (not to mention that even good professional wideband antennas usually exhibit characteristic impedances somewhere between 50 and 75 ohms in their passband, so there's going to be some mismatch anyway).

-Russ
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Don Boomer

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Re: Is this real?
« Reply #21 on: February 05, 2019, 04:14:19 pm »

My impression too was that the VSWR-related attenuation caused by a 50 ohm to 75 ohm impedance mismatch (and back) is pretty nominal, at least in receive applications (not to mention that even good professional wideband antennas usually exhibit characteristic impedances somewhere between 50 and 75 ohms in their passband, so there's going to be some mismatch anyway).

-Russ

True enough if all you are considering is signal levels. But Iím thinking that varing impedances may cause havok with any passive front end filtering that commonly occurs before the first active stage.
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Don Boomer
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Russell Ault

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Re: Is this real?
« Reply #22 on: February 05, 2019, 04:37:01 pm »

True enough if all you are considering is signal levels. But Iím thinking that varing impedances may cause havok with any passive front end filtering that commonly occurs before the first active stage.

Right, makes sense, but wouldn't real-world antenna impedance variation cause similar problems?

-Russ
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Henry Cohen

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Re: Is this real?
« Reply #23 on: February 05, 2019, 09:28:44 pm »

True enough if all you are considering is signal levels. But Iím thinking that varing impedances may cause havok with any passive front end filtering that commonly occurs before the first active stage.

Not unless you're a SETI listening post, listening for signs of the Big Bang or otherwise need to discern tenths or even hundredths of a dB. The 75Ω/50Ω mismatch results in barely a .75dB loss, about the same as for an inline adapter, or a somewhat tight bend in a coax, all less than the mismatch between the receiver front end and a wideband antenna. With a filter, I'd be more concerned with the reflections from the filter's stopband(s).
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Henry Cohen

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Don Boomer

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Re: Is this real?
« Reply #24 on: February 06, 2019, 02:35:06 am »

Yes, I do realize that the change in a real world antenna and coax does vary with frequency. But you are simply stuck there. 

Seems to me that even a simple first order filter would shift itís corner frequency by half an octave moving from 50 ohms to 75 ohms. 
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Don Boomer
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Lyle Williams

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Re: Is this real?
« Reply #25 on: February 06, 2019, 03:09:54 pm »

If you filter at any point without a rock solid impedance it is wise to add a small attenuator to tie down the impedance.

If you have $15,000 worth of receivers in a rack should you buy this splitter?  Hell no.

But a cheap-ass splitter is less scary than a cheap-ass mic.
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Brandon Scopel

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Re: Is this real?
« Reply #26 on: February 11, 2019, 01:02:09 pm »

If you filter at any point without a rock solid impedance it is wise to add a small attenuator to tie down the impedance.

If you have $15,000 worth of receivers in a rack should you buy this splitter?  Hell no.

But a cheap-ass splitter is less scary than a cheap-ass mic.

I've seen Professional Wireless in a lot of large scale RF deployments.....

http://www.professionalwireless.com/product/rx-antenna-combiner-distros/
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