The cable length can be tricky. (I use all Type-N connectors and Andrew FSJ2 Velocity of .83)
• First you have to find the velocity factor of the cable you are using. • Then you get the ¼ wave length in free space and multiply by the velocity factor. • Then you measure from the center of the TEE connectors. Try this... First get the ¼ wave length in free space for your frequency from this link: http://www.csgnetwork.com/freqwavelengthcalc.html Then multiply by the velocity factor of the cable you are using which should get you really close to what you want. http://www.picwire.com/technical/paper2.html http://www.rmvhf.org/thinktank/velocity.html For example 146.000 MHz = 20.21917808219178 inches X .695 for RG-400 = 14.0523287671232871 inches for ¼ wave. 14.052 Inches of RG-400 should be very close to a ¼ wave @ 146.000 MHz I used this method to make some ¼ wave jumpers using Andrew FSJ2-50B, when we checked the cables with an Anritsu Site-master, I was only 2 degrees off from a perfect ¼ wave on my frequency. CABLE VF RG-8 .66 LMR-400 .85 RG-8X .84 RG-11 .75 RG-58 .66 LMR-195 .83 RG-59 .82 RG-62 .84 RG-174 .66 RG-213 .66 RG-214 .66 RG-217 .66 RG-218 .66 RG-316 .79 RG-400 .695 LMR-500 .85 LMR-600 .86 1/2 HARD .81 7/8 HARD .81 LDF all ver .88 THEN... You have to measure from the center of the TEE connectors so you actual cable will be a little shorter than the example length of 14.052 inches depending on the connector(s) PL-259 or Type-N etc. If you follow this method and make the cables ¼ wave from the center of the tee’s or ports on your duplexer (depending on the model) you should find it will tune up on your frequency very well. Good Luck, Steve ~KA1RCI [email protected] From: [email protected] [mailto:[email protected]] On Behalf Of Ralph S. Turk Sent: Saturday, August 21, 2010 8:45 AM To: [email protected] Subject: [Repeater-Builder] Telewave Anybody in the group know the correct length of the coax for the Telewave TPRD 1556 duplexer. Need cavity interconnect and combiner lengths. RG 142 Original frequency 155.5 New Frequency 146.8/146.2 Ralph, W7HSG
