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[Ken Barlow]

I am in the proccess of rebuilding my IEM rack to add 2 more IEM's. I went to the Sennheiser website to check on the cables I need to extend the antenna's from the back of the units to a front mounted panel for the antennas. I noticed that they use 50 OHM RG/58U coax cable but I have access to gobs of RG/59 75 OHM coax cable with Canare ends. Since the length will be under 1 1/2 or 2FT, will I lose any significant signal or distance using 75 OHM RG/59?

Thank you in advance,
Ken Barlow

[mike horn]

short answer no

but do yourself a favor and get at least one real antenna
and a piece of 58

fwiw
mh

[Ken Barlow]

I do have 1 a2003-UHF that I bought as a package with my IEM's and plan on getting another with another AC1 antenna combiner/booster for a total of 6 mixes. I guess my question was why 50 ohm cable when the rest of the world is wired with 75 ohm coax cable?

The reason I need to do this is because the GA1 tray needed to mount 2 AC1's (IEM300) side by side are no longer available, thus I need to scrap my AM1 which is the little 1/4 space rack mount antenna connector that mounts on the GA1 tray. I am building my own 1 space antenna mount to bring the antenna outputs to the front of the rack and want use what cable and connectors I have laying about.

What it all boils down to is for the life of me, I cannot figure out why Sennheiser uses 50 ohm cable. I am hoping that someone with a whole lot more RF experience than me can explain this. If it turn out I need the 50 RG59U, so be it.

Thanks,
Ken Barlow

[Mac Kerr]

Ken Barlow wrote on Sat, 11 August 2007 17:53

What it all boils down to is for the life of me, I cannot figure out why Sennheiser uses 50 ohm cable. I am hoping that someone with a whole lot more RF experience than me can explain this. If it turn out I need the 50 RG59U, so be it.

Antenna systems are generally 50 ohm. Video is 75 ohm. The cable needs to match the impedance of the equipment it is attached to. Every wireless mic I am aware of has 50 ohm antenna connections, I assume IEM antenna systems would also be 50 ohm. There has been some discussion on these forums about using 75 ohm RG59 on wireless mic antenna systems because it is a lower loss cable than RG58. Ideally you wouldn't use either one of them, you would use a good low loss double shielded 50 ohm cable like LMR-400 or one of the equivalents. My experience with the cheap RG58 from Radio Shack is that it is useless.

Mac

[Simon Lewis]

Jim Brown wrote a useful article on this topic for Syn Aud Con....

[Ken Barlow]

Simon Lewis wrote on Sat, 11 August 2007 18:35

Jim Brown wrote a useful article on this topic for Syn Aud Con....

I must say that is a very good article. So I believe I CAN get away with less than 6 ft of 75ohm cable divided between 2 antenna combiners. I have the belden RG/59 and I can't seem to find small quantities of 50ohm cable anyways.

Thanks a bunch for the enlightenment.

Ken

[Henry Cohen]

Simon Lewis wrote on Sat, 11 August 2007 18:35

Jim Brown wrote a useful article on this topic for Syn Aud Con....

An excellent paper.

One caveat though; although receiver front ends are somewhere between 50 and 75 ohms and vary with frequency, transmitter output stages are much closer to (though still not exactly) 50 ohms than not. Thus, if your transmitter output is connected to another device (hopefully 50 ohm) before the antenna, 50 ohm coax is strongly recommended. If the transmitter output is connected directly to the antenna, then it doesn't really matter as much.

In the end, it's far more important to use high quality coax (low loss, double shielded) of the right size based on length, with the correct connectors properly installed.

[Phil LaDue]

Ken Barlow wrote on Sun, 12 August 2007 12:23

I have the belden RG/59 and I can't seem to find small quantities of 50ohm cable anyways.

http://tinyurl.com/2ofnfn

[Ken Barlow]

Phil LaDue wrote on Sun, 12 August 2007 14:17

Ken Barlow wrote on Sun, 12 August 2007 12:23 I have the belden RG/59 and I can't seem to find small quantities of 50ohm cable anyways. http://tinyurl.com/2ofnfn

Thanks for the link. I looked for over 2 hours the other day and all I could find was 50 ft unterminated. Can't beat the price either.

Ken

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