Hi Jeff, I will answer your questions bellow in UPPERCASE to make it easier to distinguish from the original text.
Thanks for responding, hope you can help me a bit more. Alex --- In [email protected], "Jeff DePolo WN3A" <[EMAIL PROTECTED]> wrote: > Not knowing what the Telewave and Sinclair part numbers translate into in > terms of the actual hardware in use, you'll need to provide some details. > First of all, what kind of filtering is done on the tx combiner COMBINER HAS 10-INCH CAVIETIES AND A ISOLATOR WITH TWO SMALL DUMMY LOADS ON EACH INPUT. THE COMBINER OUTPUT GOES DIRECTLY TO THE TX ANTENNA WITH A 7/8" HARDLINE. and rx > multicoupler? MULTICOUPLER HAS A 4-CAVITY PRESELECTOR AT THE INPUT, FACTORY TUNED TO 165.525. FROM THE PRESELECTOR IT GOES INTO A PREAMP ("ANGLE LINEAR" BRAND), AND FROM THERE INTO A 12-PORT POWER DIVIDER. ONLY 6 PORTS ARE BEING USED, SO THE REMAINING PORTS HAVE 50-OHM TERMINATORS ON THEM. Is the tx combiner hybrid-ferrite or cavity-ferrite? IT IS OF THE CAVITY-FERRITE TYPE. IF YOU WISH YOU CAN LOOK IT UP AT TESSCO.COM. What is > the measured isolation between antennas (if known)? HAVE NOT DONE THIS, BUT IF YOU COULD PROVIDE A TEST PROCEDURE THAT WOULD GIVE YOU MEANINGFULL RESULTS, I HAVE A IFR COM120 SERVICE MONITOR HERE WITH ME. > > Since all of the tx's are spaced at 200 kHz and all of the rx's are also > spaced at 200 kHz, if there is any nonlinearity in the receive portion of > the system (due to preamp overload, front end overload, etc.), there is a > good chance that the desired signal is mixing with the transmitters, > yielding new products that fall onto the other receive channels. Not > knowing any other details, that would be my best-guess as to what's > happening. I RAISED AND THEN LOWERED THE RX FREQ'S BY 25KHZ (IE. 160.125 TO 160.150 OR 160.100), AND IT SEEMED TO HELP A BIT, BUT UNDER CERTAIN TX COMBINATIONS THERE STILL REMAIN SOME INTERFERENCE PROBLEMS. STRANGE THING IS THAT THE CHANNEL THAT SEEMS TO SUFFER THE MOST INTERFERENCE IS ALWAYS THE ONE RELATED TO THE CONTROL CHAN NEL. WE HAVE TRIED WITH CH1, CH2, AND CH3 AS CONTROL CHANNEL, AND EVERYTIME THE RX ON THE CONTROL CHANNEL BEING USED IS AFFECTED. ANOTHER STRANGE THING IS THAT THE INTERFERENCE (UNWANTED SIGNAL) APPEARS ONLY WHEN A CALL IS ALREADY PLACED ON THE SYSTEM AND NOT BY KEYING THE REPEATER WITH A MIKE. FOR EXAMPLE IF I HAVE CONTROL CH ON CH1, AND PLACE A CALL, THE SYSTEM MOST OF THE TIME WILL PLACE IT ON CH5 OR CH6 AND WILL KEY UP THE REPEATER FOR THE CALL, BUT SO FAR NO INTERFERENCE WILL SHOW UP ON CH1. THIS WILL ONLY HAPPEN I THE PTT OF A PORTABLE THAT INITIADED THE CALL IS KEYED. AT THIS POINT IT WOULD LOOK AS IF THE RF OF THE PORTABLE IS UPSETTING THE SYSTEM, BUT WE TRIED THIS FROM ABOUT 300FT AWAY (IN LOW POWER) AND STILL THE SAME HAPPENS, SO IT CAN'T BE DIRECT RF RADIATION FROM THE PORTABLE. IF I THEN CHANGE THE CONTROL CHANNEL TO CH2 OR CH3, THE SAME THING HAPPENS AGAIN, AND ALWAYS THE RX OF THE CHANNELS ASIGNED AS CONTROL CHANNEL IS THE ONE AFFECTED, ALTHOUGH SOMETIMES MORE THAN ONE RX CH SHOWS INTERFERENCE. If this is, in fact, the case, then there needs to be additional > isolation between transmitters and receivers, either by increasing the > antenna-to-antenna isolation, or adding additional filtering ahead of the > preamp/power divider in the rx multicoupler to further attenuate the tx > carriers. THE THING IS THAT IF THE INTERFERING SIGNALS ARE CENTERED ON THE OPERATING FREQUENCIES, AS IT SEEMS IT IS, I WOULD THINK THAT THERE IS NO AMOUNT OF FILTERING THAT WOULD CURE THE PROBLEM. I COULD BE WRONG, SO PLEASE FEEL FREE TO CORRECT ME. > > The less-likely cause would be a passive (external) mix such as in a rusty > tower joint or guy wire hardware, but that type of mix is usually of the > variety of only the transmitter carriers mixing, i.e. the much weaker > receive signal transmitted by a user in the far field wouldn't contribute an > appreciable level to the mix. HOPE THAT DOES NOT COME TO THAT, ALTHOUGH AT THIS POINT I'M NOT SURE OF ANYTHING. THANKS AGAIN. > > --- Jeff > > -------------------------------------------- > Jeff DePolo WN3A - [EMAIL PROTECTED] > Broadcast and Communications Consultant Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
