DIY antenna splitter - a good idea?

[samchurchill]

Hi,

I'm getting a little concerned that our Sennheiser wireless mic receiver units are being battered around a bit with all of the events we take them to so was thinking of mounting 4 of them in a flight case.

I looked at the Sennheiser ASP2-NT1 to use as the splitter for the antennas but was rather shocked when I saw the price of £350 here in the UK (about $600US). This is a passive splitter and certainly looks that way from the wiring diagram in the manual.

Therefore, is there any good reason why I shouldn't just use a few BNC splitters for the antenna and the original power supplies securely strapped to the inside of the flight case to make it cost about 10% of the price?

Thanks,

Sam

[tedanderson]

I'd say it's worth trying if you don't mind making the investment to use as a learning experience. I often follow the philosophy that if something is unexplainably expensive, then there is a good a good reason why. But I've also learned that some of the cheap low-buck substitutes often work just as good (if not better) than the recommended item.

[technerd]

I would not use anything different than what is recommended by the manufacturer. You can loose signal strength if you go the cheap way. The splitters also have power to run YOGI antennas and boosters so that you can be far off from the stage. The rule of thumb I use is, don't go the cheap route to get God's message to his people. One drop out can loose a person's train of thought and turn them away from being touched by a needed message.

[Gracetech]

The true secret sauce to passive splitters for antennas is the fact that they are frequency specific. They use bandwidth filtering circuitry to keep noise from other RF from interfering. Other than that they are just your average everyday splitters. Keep in mind that passive splitters will reduce your wireless power performance but usually you need to reduce the power anyway to keep the reflections down to a minimum. The usual rule of thumb is to split no more than 3 times although some say split no more than twice. Each time you split you take a 3dB hit so if you split three times it's -6dB which would be fine as long as you have an active antenna or directional antenna.

On a side note. I like the way i'm seeing newer wireless systems developed with antenna pass through connections to basically daisy chain together for a integrate antenna combining system. Cool stuff to be sure.

crt

[Arlin]

Originally Posted by Gracetech

On a side note. I like the way i'm seeing newer wireless systems developed with antenna pass through connections to basically daisy chain together for a integrate antenna combining system. Cool stuff to be sure.

Which ones? Can you give examples?

[Arlin]

I did this and it works very well for me.
Used an 8-way CATV splitter and CATV RF amplifier with very good results.
Here are some pictures I took from a portable system I did:
http://www.churchmedia.net/MXC/showgallery.php?cat=663

I no longer use that system... but I did the same in our sanctuary with the same stuff.
I only use antenna distro on ONE side of the receiver. So each receiver has one factory antenna and the other is connected to the splitter.
The amplifier I used is a Tru-Spec TA-25.
I do notice more intermod interference, but it usually is only a problem when the mic is not transmitting (a receiver might pick up stray signals from another mic, but when its matching transmitter is on, it is not a problem).

[Gracetech]

Originally Posted by Arlin

Which ones? Can you give examples?

The only one i can remember off the top of my head is Lectrosonics Venue system but i'm pretty sure i've seen others...i just have to remember where.

crt

Edit: I just remembered one of my favorite wireless manufactures also did this with it's new rack mount system Audio Limited RK2040.

[Brad Weber]

Chad nailed it, you can use standard RF components and this is often done but they are wideband and will pass everything while the wireless mic manufacturers' antenna distribution products typically integrate some bandwidth filtering. I would also avoid using amplification unless there is bandwidth filtering before it and in most wireless mic applications a 25dB, fixed gain, wideband RF amp such as that linked can cause more problems than it solves.

[samchurchill]

Those modular systems look really good but I guess it's the sort of thing you need to get when you've just been given a nice big budget rather than when you're building up equipment over the years.

I tried it with a passive BNC splitter today to get one set of antennas into 2 receiver units and it worked fine. I think what I'm actually going to do is mount the receivers in the ABS rack box and just have all 3 sets of antennas on the back across a 1U strip. We'll start with 3 receivers in there and, if I have to go to 4 then I might pair a couple of them onto the same antennas. Not ideal I know but there are much more important things to be spending £350 on at the moment!

Thanks for all the tips and tricks.

Sam