Norm, A collection of very informative information is available here: <www.repeater-builder.com/antenna/ant-sys-index.html#iso-cir>
As for what an isolator does, it ensures that your PA is working into a good 50 ohm load. If the antenna or feedline breaks, the power that would have been radiated is now reflected back to the PA- causing all sorts of problems. But an isolator shunts the reflected power into the attached 50 ohm load, thereby protecting the PA from a load mismatch. A circulator is the ferrite device that routes forward power to the antenna, but routes reverse (reflected) power to the dummy load. An isolator is the name given to a circulator that is packaged with one, two, or even three dummy loads. If you have a simple repeater that uses a single transistor PA that has no power control or high-SWR protection- such as a Hamtronics, RF Engineering, or Maggiore unit- an isolator on the output is necessary to keep the PA from burning up if the antenna or feedline faults. The other primary purpose of an isolator is to prevent mixing (intermodulation) in your PA of carriers from other nearby transmitters. Most commercial PAs have power available to them all the time, and only amplify when the exciter is providing an input. Being Class C, there is no amplification during idle periods. But, if other carriers can sneak into your PA through your duplexer, they can mix and be amplified to create new IM products. Keep in mind that most BpBr duplexers have a rather broad bandpass response, and can allow carriers far removed from your operating frequency to pass with ease. An isolator shunts such rogue carriers to the dummy load, thereby preventing the generation of spurious IM products. A ferrite isolator has a tendency to generate a second harmonic of the fundamental transmitted carrier, so it should be followed by a simple harmonic notch filter or a low-pass filter. As for the Kenwood TKR-750, I leave it to other and better-informed folks to respond to Item 2. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of NORM KNAPP Sent: Saturday, May 16, 2009 10:42 AM To: [email protected] Subject: Re: [possible spam] RE: [Repeater-Builder] Re: Isolator Loss Kinda OT, but not entirely.... 1) What does the isolator do and why would I need one? 2) I work for a Kenwood dealer. Kenwood has admitted to our company that the TKR-750 is rife with internal desense caused mainly by synthesizer birdies. Supposedly no two will have exactly the same birdies or desense on the same freqs. They have told us that there is a fix under warrantee but it has to go to them for the fix and you must provide freq info for custom fix. Has anyone else seen this problem or heard of this? 73 de N5NPO Norman knapp ----- Original Message ----- From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <[email protected] <mailto:Repeater-Builder%40yahoogroups.com> > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <[email protected] <mailto:Repeater-Builder%40yahoogroups.com> > Sent: Sat May 16 11:02:44 2009 Subject: [possible spam] RE: [Repeater-Builder] Re: Isolator Loss Do you have a low pass filter after the isolator? 73 Gary K4FMX > -----Original Message----- > From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> [mailto:Repeater- > [email protected] <mailto:Builder%40yahoogroups.com> <mailto:Builder%40yahoogroups.com> ] On Behalf Of offtrack > Sent: Saturday, May 16, 2009 11:19 AM > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> > Subject: [Repeater-Builder] Re: Isolator Loss > > Eric > > Thanks for the confirmation on this. Its an older one that was tuned for > me its a T-2200 that was replaced by the T-1530 I think, if I read > correctly at the telwave site. > > I notice that the TKR 750 is running fine with no intermod issues ect. > > I was not sure about adding that meter in line and only did a quick check. > Thanks for the warning on that one. > > The Diamond is so far working ok. I soldered all the parts in the antenna > and sealed up all the possible leak points with a compound call "through > the roof" This stuff stays semi flexible and is clear. Its located at my > home and has been in service for about 2 years for my Simplex Echolink > node I replaced with the repeater. Works pretty good, but that said I > would never put it on a remote site as your correct not at all heavy duty. > the radome is egg shell thin, I worry about it at the house as I am on a > hill and get hit with some good winds/icing. So the Isolator in line helps > ease my mind a bit. > > Thanks > KB7DZR > Scott > > --- In [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> , "Eric Lemmon" <wb6...@...> wrote: > > > > Scott, > > > > I must assume that you purchased a Telewave T-1530 Isolator, and its > > specified insertion loss is 0.4 dB. The readings you took indicate that > the > > isolator is working properly. However, it is not a good idea to insert > a > > meter between the isolator and the dummy load. The correct operation of > the > > isolator depends upon a stable 50 ohm impedance at the dummy load port. > > > > I think you made some good choices for the duplexer, feedline, and > isolator. > > The Diamond F22 is perhaps not the most rugged antenna for 2m repeater > use, > > but YMMV. > > > > 73, Eric Lemmon WB6FLY > > > > > > > > > > > > -----Original Message----- > > From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> > > [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of offtrack > > Sent: Friday, May 15, 2009 7:27 PM > > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> > > Subject: [Repeater-Builder] Isolator Loss > > > > > > > > Hi all, > > > > Thanks for the group it has helped me out a bunch. > > My system here is a Kenwood TRK K2 and Telewave TPRD-1556 6 can set. > > Feed line is Heliax LDF4-50A about 70 feet and the antenna is a Diamond > F22 > > that has been worked over and sealed up better. > > > > The system is new and today I added a Telewave Isolator to the PA output > > before the duplexer TX input. With my meter I got about 28 watts out of > > antenna side of the duplexer set when connected to my antenna with out > the > > isolator. With the Isolator I am getting about 26 watts out now. This > seems > > good to me but I am new to an Isolator. Putting the meter between the > > isolator and the dummy load it is showing around 1.6 watts going to the > > dummy load. > > > > Just want to see if this is ok for this? > > > > KB7DZR > > Scott > > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
