Gary, I've measured RG59 cable terminated into a 75 Ohm resistive load with a variable freq impedance meter. We found the coax stopped being 75 Ohms below about 0.5 MHz. The cable manufacture also verified this. Other engineers in our department knew of this as well.
We were designing security systems using video and the vertical and harizonal sync signals became very distored over long, 2500 ft. RG59 cables and this was the major reason. We had to design circuits that corrected this, but the cable had the problem. I am sure different RG59 cables have different low freq bandwidths. RG11 would also be different as well as cable TV cable. All coax has a lower and upper frequency range. Since we deal with radio this is not much of a factor until one gets real low or GHz levels. Coax also has the problem of a upper freq limit due to it's outer shield becomes large enough to act as wave guide. One will see upper freq specs will be lower the larger cable. 73, ron, n9ee/r >From: Gary Schafer <[EMAIL PROTECTED]> >Date: 2007/08/29 Wed PM 09:23:57 CDT >To: Repeater-Builder@yahoogroups.com >Subject: RE: RE: Re: Re: RE: [Repeater-Builder] Re: Duplexers >As far as bandwidth goes,,, where do you get this .5 MHz for rg59 cable as a >lower limit? > >Open wire lines begin to radiate as frequency is increased to the point >where the line spacing becomes an appreciable portion of a wave length due >to the time it takes for propagation of fields between wires. > >73 >Gary K4FMX > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
