Wireless Problem

[Chris15]

There really isn't a rule of thumb here. You need to know how strong your signal is at the input of your receivers with various levels of splitting. If you have a very strong signal, you can certainly use two or three passive splits. However, if you have a weaker signal, you should probably use an active splitter with a narrow bandwidth. The second part is very important, as you absolutely do not want undesired signals, such as adjacent TV stations, amplified as well - they'll only serve to desensitize your receivers (especially if they're lower end models with poor filtering inside).

Now I remember where I pulled those numbers from, the Shure stuff on antenna distribution and placement. They say that 5dB of loss is about the maximum acceptable level. A passive split drops 3dB, so a second passive split would be 6dB and opening the door to problems. If you then have say a 10m or more coax run between antenna and receiver, then you need also to consider the loss caused by that cable.

Amplifiers mounted to antenna can help to overcome cable losses etc. But you can have too much and sometimes less is more.

Wideband v Narrowband - It's all about the right tool for the job. It may be that you are running a substantial number of systems and hence need to have systems on more than one band, then you will need a wideband splitter. This given Log Periodic antennae or Helical or other such wideband antennae. But if you have that many systems, the better option would probably be to use a wideband as the primary split and then run all the secondary splits with narrowband. Best of both worlds then. Of course if you are needing this sort of number of systems, you really need to be using high end systems which will have decent filtering built in...

 

[BNBSound]

well im the first person, so im going to offer the simplest answer crosstalk, and not knowing the US radio frequencies i would say you might be picking up a radio station tv station and the receiver doesn't know how to interpret the new signal, the reason it works close to the receiver is the mic's signal is stronger than all over sources until you move away when other signals become stronger

There's a couple issues with interference from broadcast sources. The first is the FM capture effect, wherein an FM receiver locks on to the strongest signal and decodes that to the exclusion of all others. The other and probably more likely culprit (but from the same source) is front end overload. Strong RF from any source can overwhelm the receiver's front end. If it's strong enough it doesn't even need to be in the same frequency range. Example: TV channel 2 (neighborhood of 50 MHz) totally overwhelming a guitar wireless (way up in UHF) at a nearby club.

 

[mbenonis]

There's a couple issues with interference from broadcast sources. The first is the FM capture effect, wherein an FM receiver locks on to the strongest signal and decodes that to the exclusion of all others. The other and probably more likely culprit (but from the same source) is front end overload. Strong RF from any source can overwhelm the receiver's front end. If it's strong enough it doesn't even need to be in the same frequency range. Example: TV channel 2 (neighborhood of 50 MHz) totally overwhelming a guitar wireless (way up in UHF) at a nearby club.

Yes indeed - both of these are potential problems. One of the frequencies posted above sits on top of a TV station's video carrier, just killing the bodypack's signal.

With regard to the UHF system being overwhelmed by the channel 2 TV station, that must be a very poorly designed wireless system! One would hope that even low-end RF systems would have SOME kind of band-pass filter on its front end! Any half-decent system should not see any problems from a 50 MHz noise source.

 

[Chris15]

With regard to the UHF system being overwhelmed by the channel 2 TV station, that must be a very poorly designed wireless system! One would hope that even low-end RF systems would have SOME kind of band-pass filter on its front end! Any half-decent system should not see any problems from a 50 MHz noise source.

One would hope so, but given some of the stuff coming out of Asia these days... But honestly, a band pass filter is what a few cents?

 

[mbenonis]

One would hope so, but given some of the stuff coming out of Asia these days... But honestly, a band pass filter is what a few cents?

Yep. It really makes you wonder why they're not included...

 

[BNBSound]

With regard to the UHF system being overwhelmed by the channel 2 TV station, that must be a very poorly designed wireless system!

I wasn't remembering the situation with total accuracy. The club is actually located within 1/4 mile of an FM broadcast station around 107 MHz. The RF in the room is so strong that some of the outboard gear is rendered totally useless, and wireless anything is right out. The outboard thing may be because of the patch cables being close to a resonant wavelength. Full wavelength at that freq would be a little over 4.5 feet, Hosa 3 meter patches would be about 2 wavelengths, while 2 meter versions would be less resonant.

 

[Chris15]

Reminds me of something I read. There was a regular gig in what constitutes the alps down here where a keyboard was picking up FM. Turn it 90 degrees and it all went away. I think something was muttered about needing balanced lines and shielding in instruments...

 

[Hughesie]

Yep. It really makes you wonder why they're not included...

well when things are done "on the cheap" things get left out,

seriously would you buy this system
ebay link

highlights
< OVERALL TRANSMITTER>.
Frequency responce 100Hz-10000Hz
RF Power output 20mW(max)
Antenna Type Built-in type
mic Type Dynamic mic
Current consumption Less than 25 mA
Battery Life 8 Hr

Each microphone is marked with red and green stripes which represent two separate frequencies