An isolator is linear except with frequency just as a cap or inductor or feedline are. What's in an isolator that is non-linear. It is made of transmission lines, no active components...what is non-linear. You put in x power, you get x-loss out until x becomes to large then you get smoke (another discussion).
73, ron, n9ee/r >From: Jeff DePolo <[EMAIL PROTECTED]> >Date: 2007/10/22 Mon PM 09:11:21 CDT >To: [email protected] >Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever >noise budget > >> I am not sure why an isolator would cause intermod. Usually >> there are not active or non-linear components in them > >An isolator IS a non-linear device. > >> and >> they are often used to prevent intermod by preventing outside >> signals from coming in thru the feedline into the transmitter. > >As a nonlinear device, they will naturally generate harmonics on their own, >and likewise act as mixers (however lossy), which is why filtering after an >isolator is necessary. > >> In the past commerical sites would often require an isolator >> for this reason with strong transmitters close by. In better >> repeater equipment an isolator was built in. > >Yes. The isolator "isolates" the transmitter from the antenna by diverting >incoming (from the antenna) RF into the reject load rather than letting it >get back into the transmitter as a way of preventing IM from occuring. But >in some instances, that's more of an "added bonus" than the real reason the >isolator was built in to some stations - to protect the PA from anomalies >that would cause high VSWR that could damage the PA or lead to instability >issues. > >My concern, in the instant case, is that when the isolator is carrying >high-level RF from the transmitter will mix with other signals coming back >down from the antenna. I might try a two-tone IM text on an isolator to get >a handle on what might be expected. > > --- Jeff > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
