Ron, A simple but effective method of tuning a single junction isolator (3 tuning ports) can be done by using a few basic steps.
First tune the input and output trimmers (usually found on the lower part of the isolator opposite the attached dummy load) for maximum power through the devise. To do this, connect a high power 2 meter mobile (set to the frequency you want to tune up the isolator on) to the input port. Connect your watt meter and dummy load to the output port. Key the radio and tune for max output. Next reverse your power source (2 meter mobile rig) and transmit into the output port of the isolator with your watt meter and dummy load connected to the input port. Tune the third trimmer cap (nearest to the isolators dummy load) for MINIMUM a reading on your watt meter. You're really going to have to get up close and personal with your watt meter because at this point because there wont be a lot of power there to deflect the meter. If your meter has a SWR / Calabration setting, you may need to run the SWR calibration knob all the way to the max just to get meter deflection. Tune for a MINIMUM meter reading. You are wanting as much power as possible going into the dummy load in this step. IMPORTANT: Ohm out your dummy load to be sure it is 50 ohms before you start the tuning procedure. Loads can overheated and change in value. Also, because a isolator is a ferro-resonate device, be sure to do all your tuning (and mounting) on a NON-magnetic surface. Lastly, when it comes time to install the isolator, place your watt meter in line on the input port of the isolator. While keying the transmitter, tweak the input trimmer for a MINIMUM SWR reading on your meter. At this point, you should be good to go. Now, was that as precise as using a tracking generator, spectrum analyzer and return loss bridge? Perhaps not, but it will be darn close. However, if you had a dual junction isolator that needed tuning, that's a whole different story! :) Give me a call if you get stuck and I'll be glad to walk you through the procedure. 73, Steve Allred / K6SCA RF System Engineer 209-948-9611 --- On Wed, 11/12/08, Eric Lemmon <[EMAIL PROTECTED]> wrote: From: Eric Lemmon <[EMAIL PROTECTED]> Subject: RE: [Repeater-Builder] isolator To: [email protected] Date: Wednesday, November 12, 2008, 8:20 PM Ron, Contact EMR and request a copy of the bulletin, "Field Tuning of Isolators." Be aware that typical circulators and isolators can be field-tuned perhaps +/- 2% from the frequency for which they were made. If you want to use it at a new frequency that is more than 3 or 4 MHz away, it probably will need to be remanufactured at about 1/3 to 1/2 the cost of a new unit. You should use a vector network analyzer, or at least a spectrum analyzer with tracking generator and a return-loss bridge, to properly tune a circulator or isolator. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@ yahoogroups. com [mailto:Repeater-Builder@ yahoogroups. com] On Behalf Of Ron Wright Sent: Wednesday, November 12, 2008 8:01 PM To: Repeater-Builder@ yahoogroups. com Subject: [Repeater-Builder] isolator Hi all, I have aquired a EMR Isolator, model 7450/4 for 150-170 Mhz and tuned to 155 MHz. It has 3 tuning adjustments so need to retune it. Can anyone give info as to how to tune it or where I can get info. EMR has good info on what it does and how it works, but found nothing at their site on tuning. Tune for low SWR, max power out, min smoke, etc??? 73, ron, n9ee/r
