Re: [Repeater-Builder] Transmitter combiners

[Gareth Bennett]

Hi Ian, very informative. I wonder what calc program you recommend?   This is for Transmit combining at 83 MHz and at present I am utilising 3/4 wavelength coax (213)  from the cavities to the porcupine. There is only two transmitters on at present and the stub somehow likes to be shorter than 1/4 Wavelength.   I'm trying to replicate a system that was de-commissioned about one year back, and the tech that took over ripped everything out thinking that he knew better. Originally we were using 6 port porcupines but he threw these out and I have been fortuitous to even find an 8 port one. All unused ports are left open (Except for TX1, TX2 and the stub). We used to run "Star" combining like this in the old New Zealand Post Office and it worked great!. Just a pity I didn't obtain some of the site planned and calcs then :-(   Thanks for your help! _________________________________________________________________   Gareth Bennett   This e-mail is confidential, if you received this message in error, or you are not the intended recipient, please return it to the sender and destroy any copies. Thank you. ----- Original Message ----- From: Ian Ashford To: Repeater-Builder@yahoogroups.com Sent: Sunday, November 28, 2004 5:23 AM Subject: Re: [Repeater-Builder] Transmitter combiners Gareth,   For two transmitters the length of the circulator to porcupine jumper would be 5/8 wavelength in coax.   When these two are parrelled the common impedance  is  25+j25 ohm.   Looking at the Smith chart it looks like a paralleled s/c stub of -j25 would acheive a match to 50 ohm.   Putting these figures into lengths of RG213:    Circulator  to porcupine jumper 0.85m     s/c stub 0.58m   I dont know how many transmitters you are combining,the stub impedance is -j16ohm for 3 transmitters and -j12 for four.   There are lots of good transmission line calculators available on a google search.   Ian G8PWE www.gb3dx.com               ----- Original Message ----- From: Gareth Bennett To: Repeater-Builder@yahoogroups.com Sent: Saturday, November 27, 2004 4:11 AM Subject: [Repeater-Builder] Transmitter combiners Hi there Group :-)     Is there somebody in the group who has knowledge on "Star" transmitter combining? I am trying to remember the formula for the "Tuning Stub" that also is fitted to the star, or "Porcupine" as we call them over here. All the stubs here are less than 1/4 wavelength (Including VF of cable) and as normal are shorted at the end :-) ..     Everything else is as one would expect with the food chain going like this... Transmitter-Isolator-Cavity-"Porcupine" - Antenna.     I want to tune this as best as I can, but don't want to spend large amounts of time hacking off coax :-)     Any formula would be appreciated. I have tried to reverse engineer what we have in service to gain some formula, but nothing makes sense.   Can anybody remember?   Thanks in advance :-) _________________________________________________________________   Gareth Bennett   This e-mail is confidential, if you received this message in error, or you are not the intended recipient, please return it to the sender and destroy any copies. Thank you. 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 the Yahoo! Terms of Service.