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Author Topic: Simple 2-way radio mic antenna solution  (Read 688 times)

Chris Shaw

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Simple 2-way radio mic antenna solution
« on: September 08, 2019, 04:00:39 am »

Good morning,

I'm planning to purchase a couple of Sennheiser EW100 radio mics and need a simple solution for combining and elevating their antennae that avoids unnecessary cost. It is a portable system and we will be operating in the 863 to 865 MHz band.

They come with 1/4 wave antennae and the manual instructs to use the Sennheiser active antenna combiners which are both expensive and take up half a rack space. Hence I need another solution.

So I have some questions:

1) What is the difference between e.g. a Sennheiser A1031-U antenna and a (correct length) 1/2 wave stick antenna? (apart from the mounting thread and price tag)

2) What is the difference between e.g. a Shure UA221 passive antenna splitter and a 50 ohm BNC T-piece? (apart from some black plastic and the price tag?)

3) Would using 1/2 wave sticks with BNC T-pieces as above be unadvisable? (it would save me budget to do a better job of packaging)

4) Does anyone know of any off-the-shelf bracket for mounting a mic stand boom arm or similar pole to a rack? Ideally I will manage to store the whole lot in the 4U front of house rack.

Thanks very much
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Chris Shaw
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Jean-Pierre Coetzee

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Re: Simple 2-way radio mic antenna solution
« Reply #1 on: September 08, 2019, 05:39:02 am »

This has come up a gazillion times already but will rehash it again. RF is brand agnostic so a correct length 1/2 wave from sure will work just fine on Sennheiser etc.

The difference between the passive splitter and a T-piece is quite significant. When splitting RF signal you want to still present the antenna and the receiver with the correct impedance(which is 50 Ohms BTW) and the passive splitter has circuitry that ensures that, sure you do not need to buy the Shure passive splitter, I'm pretty sure that Sennheiser also has an option for that, RFVenue has also had an option in the past and you can also search the forums for that topic and there is a way to get the OEM part in-stead of buying from one of the big brands, they pretty much all use the same OEM part. I don't have the model number on hand but really just search the forum its in a lot of  threads.

When buying cable for longer runs don't use RG58/59(one is 75 Ohm and the other is 50) , you want to use LMR 400 or better, once again I'm just pointing you in the right direction, search the forums its been discussed to death.

So to summarise:

1.) None whatsoever, as long as the antenna is in the correct frequency range you can use it.
2.) Massive, use  a passive splitter
3.) People generally fabricate something themselves but there was a thread discussing literally this only a month or two ago, go and look for it.

Extra:

Use LMR400 cable for longer runs, pretty much anything better than RG58/59 is going to be better for you .
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Keith Broughton

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Re: Simple 2-way radio mic antenna solution
« Reply #2 on: September 08, 2019, 06:23:28 am »

JP covered it pretty well but I would like to add a couple of points.
To repeat...do not use the T adapter! Someone here might suggest a product from Mini Circuits for passive splitting that may be less expensive.
Also, do not use the 1/4 wave antennas supplied with the kit. Use 1/2 wave or "paddles" when mounting on a stand.
By the sound of it, your antennas will be close to the receivers so LMR 400 cable won't be too expensive for a short run.
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Miguel Dahl

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Re: Simple 2-way radio mic antenna solution
« Reply #3 on: September 13, 2019, 03:15:47 pm »

May I ask, what's the difference between this guy https://en-us.sennheiser.com/asp-212 and a T-adapter?

Just don't use any of them as combiners, but can do as splitters, or?
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Jean-Pierre Coetzee

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Re: Simple 2-way radio mic antenna solution
« Reply #4 on: September 13, 2019, 03:25:08 pm »

Far as I know you can use that guy as a splitter or combiner but I might be wrong. There is circuity in that box that matches the impedance of the outputs and the input. A T-Piece with cause the impedance to half at the output which will cause you to lose half your signal due to the signal being reflected back on itself.

At RF frequencies a major change in impedance acts quite a lot like a wall, you want to avoid that as much as possible.

This is probably the mini-circuits unit that I referenced before but couldn't remember the model number for. Will do what you want but will be cheaper than the sennheiser/shure/rfvenue options
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Miguel Dahl

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Re: Simple 2-way radio mic antenna solution
« Reply #5 on: September 13, 2019, 03:29:48 pm »

Far as I know you can use that guy as a splitter or combiner but I might be wrong. There is circuity in that box that matches the impedance of the outputs and the input. A T-Piece with cause the impedance to half at the output which will cause you to lose half your signal due to the signal being reflected back on itself.

At RF frequencies a major change in impedance acts quite a lot like a wall, you want to avoid that as much as possible.

This is probably the mini-circuits unit that I referenced before but couldn't remember the model number for. Will do what you want but will be cheaper than the sennheiser/shure/rfvenue options

The link you provided is bad, even after removing what's before https.

But thanks. I believe we've used them as combiners before, not sure though, just had to ask.
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Jean-Pierre Coetzee

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Re: Simple 2-way radio mic antenna solution
« Reply #6 on: September 13, 2019, 03:34:20 pm »

I corrected it almost immediately. When I clicked on it I noticed. Should be right now.
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Miguel Dahl

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Re: Simple 2-way radio mic antenna solution
« Reply #7 on: September 13, 2019, 03:41:20 pm »

I corrected it almost immediately. When I clicked on it I noticed. Should be right now.

There we go.

Maybe this should be singled out into it's own thread, a mod can make the call and take action if this does not belong in this thread.

The ASP 212 and the one you provided are transformers. I get it now, a simple T is what it it, a simple T.

After reading on of the papers in the link you provided: Let's say you use it as a combiner. Is there any chance of 180 phase issue, or close to it, when using different cable lengths/gauges?
« Last Edit: September 13, 2019, 03:45:54 pm by Miguel Dahl »
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Jean-Pierre Coetzee

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Re: Simple 2-way radio mic antenna solution
« Reply #8 on: September 13, 2019, 04:04:59 pm »

My best bet would be to try to get Henry or Pete or Jason to respond to that one, I'm really not sure since I've never really used one as a combiner.
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Jason Glass

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Re: Simple 2-way radio mic antenna solution
« Reply #9 on: September 13, 2019, 10:01:29 pm »

After reading on of the papers in the link you provided: Let's say you use it as a combiner. Is there any chance of 180 phase issue, or close to it, when using different cable lengths/gauges?

Phase shifting of TX combiner inputs has no detrimental affect on transmission quality when combining IEM carriers that operate at different frequencies.

However, it has enormous affect when combining carriers at the same frequency.  This is common in various DAS, laboratory, measurement, and circuit design applications, but is not something we should ever intentionally do when combining IEM carriers for TX.
« Last Edit: September 13, 2019, 10:03:52 pm by Jason Glass »
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Re: Simple 2-way radio mic antenna solution
« Reply #9 on: September 13, 2019, 10:01:29 pm »


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