The need for the specific length is to keep from seeing a false reading on the power measuring device. If the duplexer is tuned properly and the transceiver is tuned properly, the length of the cable makes no difference. The requirement for a specific length of cable is because some people insist on using a wrong range PA (ie not tuned to the frequency that it is being used on) and do not understand the complexities of assembling a system with mistuned components. By selecting a length of feedline, I can coverup an impedance problem between the transmitter and the duplexer. The use of the tuned line is to makeup for the inability to properly tune the RF components. In a properly tuned system the feedline length does not matter. The feedline is 50 Ohms, the transmitter is 50 Ohms and the duplexer is 50 Ohms. Everyone is happy.
73 Glenn WB4UIV At 10:33 PM 03/28/04 -0500, you wrote: >Where did you find (what is) the formula for jumpers from the duplexer > > to the transmitter and receiver? > > > > N7HQR > > >http://www.repeater-builder.com/ge/duptuning.html > > >I have been told that this formula, explained in Paragraph 4 of the above >site, also works for the electrical length from the duplexer to the TX-RX. >Others say that only the TX is SOMETIMES critical and a Z-Matcher will also >work. If anyone feels I have misunderstood this information, please let me >know. > >When inserting any in-line devices in to your repeater's feed line, be sure >any added feed line(s) used to connect the device (like a watt meter) are at >least one half wave length of your transmit frequency. You can calculate the >electrical length required by dividing your frequency in to 5904 and >multiplying the result by the velocity factor of your feed line. This will >yield the 1/2 electrical wave length in inches, tip to tip including the RF >connector. An example, 5904/442.275 = 13.35, now multiply 13.35 by the >velocity factor of the feed line, I'll use 66%, 13.35 * .66 = 8.81 inches. >You can use any multiple of the result 8.81, 17.6, 26.43, 35.24. Also try to >use a good watt meter like the Bird, the less expensive watt meters are not >a true power measuring device but a glorified voltage meter which can be >easily fooled by hi Q as found in a duplexer. > > > >JIM KA2AJH > > > >----- Original Message ----- >From: "Daron J. Wilson" <[EMAIL PROTECTED]> >To: <Repeater-Builder@yahoogroups.com> >Sent: Sunday, March 28, 2004 6:38 PM >Subject: RE: [Repeater-Builder] Duplexer Cable Legnth > > > > > > >> Where did you find (what is) the formula for jumpers from the duplexer > > to the transmitter and receiver? > > > > N7HQR > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > >Yahoo! Groups Links > > > > 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/
