50 ohm BNC Panel Mount Feed through

Re: 50 ohm BNC Panel Mount Feed through

The signal loss by using a 75 ohm barrel will be negligible. Unless you are dealing with extremely sensitive gear, I wouldn't sweat it.

I actually read a report a while back that explained that using RG6 75 ohm cable had less loss and was much less expensive than using RG58 50 ohm cable. I wish I could find the link for that, because it was an interesting read.
 
Re: 50 ohm BNC Panel Mount Feed through

Arthur Skudra said:
Excellent reading:
http://www.audiosystemsgroup.com/Which_Coax_for_Wireless_Mics.pdf
Click to expand...

So why do the manufacturers always specify 50-ohm wiring? Is there some fundamental electrical reason why they can't make all these products for 75-ohm cabling?
I still have a large amount of the Times LMR cable left over from the last installation I did, would have been nice to use a bit of the 1000's of feet of West Penn RG-6 we installed for everything else!
(And the connectors are cheaper for the 75-ohm and install quicker too!)
 
Re: 50 ohm BNC Panel Mount Feed through

Craig Hauber said:
So why do the manufacturers always specify 50-ohm wiring? Is there some fundamental electrical reason why they can't make all these products for 75-ohm cabling?
I still have a large amount of the Times LMR cable left over from the last installation I did, would have been nice to use a bit of the 1000's of feet of West Penn RG-6 we installed for everything else!
(And the connectors are cheaper for the 75-ohm and install quicker too!)
Click to expand...

This study was done at the 700mhz frequency, which happens to be right around where wireless mics are used. For those purposes, 75 ohm cable should work fine. When you get into higher frequencies, the differences may not be the same. There might also be other issues with reflections and whatnot that cause other issues.

My experience is that RG-6 cable works just dandy fine for wireless mic antennas.
 
Re: 50 ohm BNC Panel Mount Feed through

Hello All,

Everything I have read and know tells me that I should be using 50ohm cable and connectors
Otherwise you get reflections in your signal path.
I would love to hear from Henry or some other RF gurus

db
 
Re: 50 ohm BNC Panel Mount Feed through

Dan Brown said:
Hello All,

Everything I have read and know tells me that I should be using 50ohm cable and connectors
Otherwise you get reflections in your signal path.
I would love to hear from Henry or some other RF gurus
Click to expand...

The reasons the use of 75 ohm coax is not a problem are:

1) The front end of wireless mic receivers and antenna multicouplers (antenna distribution) are not truly 50 ohms. They're somewhere between 50 and 75 ohms. No RF engineer at any of the manufacturers will tell you their device is exactly 50 ohms over the entire bandsplit.

2) Antennas are not truly 50 ohms. Remember that antennas are transducers and as such have a variable impedance based on frequency. The relatively wide band antennas used in production wireless can vary anywhere from less than 40 ohms to over 100 ohms depending on frequency and near field (less than 5-6 wavelengths) obstructions.

3) Your 50 ohm coax is likely no longer 50 ohms given the wear and tear from flexing of the dielectric and connectors.

4) If one refers to the Smith Chart, a [perfect] 50/75 ohm mismatch results in less than .75dB loss, while the real world presents far greater losses simply be having the talent move around.
 
Top Bottom