Bob - AF6D wrote: > Before adding a Mirage 320 our TKR 750 was putting out 50 watts into a 6 > cavity Wacom WP-642 at the cost of 2-3dB loss on TX (as the spec sheet said.) > The cans are tuned right on the money and the Hustler G5-144 fed with LMR-400 > is 1.1:1. This has worked for over a year just fine (except for grungy weak > signal audio.) > > Now add the Mirage B-320-G 200 watt amplifier. It seems to work just fine > outside of the repeater chain. On its low setting 3 watts will drive it to > 200 watts. On its high setting 50 watts will drive it to 200 watts. We plan > on adding two fans on the heat sinks and rack mounting it and running it with > only 25 watts drive. The power meter lights up all the way to the red. > > But as soon as we tune it all up and connect it to the duplexer the Mirage > SWR/Drive trips and the amp goes to sleep. A SWR meter between the repeater > and the amp shows 1.1:1. The amp to the duplexer shows 1.1:1. The duplexer to > the antenna shows 1.1:1. > > I've lost my mojo. Waz up?
We'll assume the Mirage amplifier is either tuned to a 50 Ohm output impedance by any internal adjustments or there are no adjustments to tune the amplifier to match the load. That being said, it is possible that the Mirage Amplifier doesn't like the reactive load presented by the duplexer. If so, you will need to do one (or more) of the following: 1.) Use an impedance matcher (sometimes referred to as Z-Matcher) capable of handling the output power of the amplifier. <http://www.repeater-builder.com/db/pdfs/db-z-matcher-tuning-info.pdf> <http://www.repeater-builder.com/antenna/duplexer-cabling-lengths.html> 2.) Use an Isolator or Circulator tuned to your transmitter frequency properly sized to absorb the reflected power. You still might have to use #1 or #3 to aide in matching so you aren't wasting the power reflected back to the transmitter or the power not being transferred to the duplexer, out the antenna port, as seen as a loss greater than the 2 to 3 dB stated by the manufacturer for this duplexer and your interconnecting cabling. 3.) Optimize the cable length from the amplifier to the transmitter port of the duplexer to maximize the return loss (create a better match). http://www.repeater-builder.com/antenna/duplexer-cabling-lengths.html Please also read the note about cabling lengths between the repeater and the duplexer in the section on page 4 of the following document: <http://www.repeater-builder.com/wacom/wp6xx-vhf-tuning-instructions-remec.pdf> Watch for word wrap... Doing #3 might require doing #4. 4.) Optimize the tuning of the first cavity of the duplexer from the factory setting. BE CAREFUL HERE... Assuming no one has ever tuned the duplexer from its factory settings, and assuming the factory knew what they were doing and tuned the duplexer correctly (tuned it for maximum return loss (best match at 50 Ohms on your frequencies) and best response, or a compromise of both - usually the case in a factory tuned Wacom product. Realize if any cavity is/was re-tuned at any point you are altering the response intended by the factory. It is possible, however, to optimize the cable length and lightly retouch the tuning the first cavity to fix the situation you have encountered. Optimizing the cable length will shift the impedance to create an acceptable match between the amplifier and the transmitter port of the duplexer and retouching the first transmitter cavity will nullify the reactance presented by the line. If you are not willing to re-tune the duplexer, then only consider the solutions in #1 or #2. I'm hopeful Jeff DePolo or Allan Crites will look this over and add correct what ever I missed. Kevin Custer
