Wireless Terminators on RF Distros?

cekren

Active Member
Joined
Dec 3, 2012
Location
Midwest
After a quick search I did not see any related threads to this, but apologies if it's already been discussed! I am wondering if 50ohm BNC terminators should be used on unused outputs of RF distros? Specifically looking at Sennheiser ASA1's.
 

Jay Ashworth

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Joined
Feb 7, 2014
Location
St Pete FL USA
In our context, an RF Distro generally means a receiver antenna splitter. Off hand, I would say you don't -- you certainly don't need one to protect a transmitter, as you don't have any.

I don't *think* you win much on the receive side either; signal/loss ought to be pretty sizable.

On a transmitter antenna combiner for in-ears, the situation is slightly different. You still don't have to worry about hurting the transmitter finals, I don't think -- the power's too low. Whether you'll lose an appreciable amount of signal due to reflections from an unterminated transmitter port, I'm not sure.
 

cekren

Active Member
Joined
Dec 3, 2012
Location
Midwest
Whether you'll lose an appreciable amount of signal due to reflections from an unterminated transmitter port, I'm not sure.
Thanks for the response! Reflections from an unterminated output is what I'm mostly thinking about - as I understand it, passive splits should always be terminated, but active splits such as the ASA1 probably don't?
 

JD

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Jan 1, 2005
Location
North Wales PA
On an active powered distro, it can't hurt. Never did it on a passive splitter. One application where it would be a must: If you have a length of cable that goes to a receiver and you disconnect the receiver you should terminate the line, or remove it at the distro end as well.
 

teqniqal

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Apr 26, 2009
Location
Dallas / Fort Worth, Texas
passive splits should always be terminated, but active splits such as the ASA1 probably don't?
On an active powered distro, it can't hurt. Never did it on a passive splitter.
If you look at the (simplified) block diagram of the Sennheiser ASA1 in the owner's manual (https://en-us.sennheiser.com/global-downloads/file/7101/ASA1_Manual_06_2016_EN.pdf) it appears to show an RF amplifier followed by a passive splitter block, so for a passive splitter block to work optimally, all the inputs and outputs need to 'see' the correct impedance (Load). (The Sennheiser ASP1, however, is a completely passive splitter with only a DC injection circuit to power the remote antennas.) It generally can't hurt to terminate things to the recommended impedance, so when in doubt, do the right thing and you will probably be OK. I find it curious that Sennheiser doesn't bother to explicitly say anything one way or another - it seems like it would reduce the calls to their support department. At the very least, it will keep the local RF guru from seeing an unterminated line and having a coronary attack.
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
If you look at the (simplified) block diagram of the Sennheiser ASA1 in the owner's manual (https://en-us.sennheiser.com/global-downloads/file/7101/ASA1_Manual_06_2016_EN.pdf) it appears to show an RF amplifier followed by a passive splitter block, so for a passive splitter block to work optimally, all the inputs and outputs need to 'see' the correct impedance (Load). (The Sennheiser ASP1, however, is a completely passive splitter with only a DC injection circuit to power the remote antennas.) It generally can't hurt to terminate things to the recommended impedance, so when in doubt, do the right thing and you will probably be OK. I find it curious that Sennheiser doesn't bother to explicitly say anything one way or another - it seems like it would reduce the calls to their support department. At the very least, it will keep the local RF guru from seeing an unterminated line and having a coronary attack.
Well, lets say you have a 4-way passive splitter. You connect an RF generator to the input, and on one output you connect an RF signal meter.
You can actually watch the RF level drop as you terminate each of the other three outputs. Agreed that in the perfect world with a good RF signal, the proper thing to do is terminate. In the practical world, you are often dealing with marginal signals to begin with, so every bit of loss becomes important. You won't pick up many rings or standing waves on a splitter unless you have sections of cable connected to the outputs that have no termination at the other end.
The best solution is to use a splitter that has the same number of outputs as you need. If you are doing a 2-way split, use a two way splitter, not a 4-way splitter. Still, I wouldn't get too worried using a 4-way splitter on a 2 way split unless the other two outputs had un-terminated runs of cable attached.