Doug, I have looked inside impedance matchers made by Telewave and by EMR, and both have nearly identical construction. There is an inductor made by a turn or two in a #14 wire that runs between the two N connectors, with a Johansen ceramic variable-piston capacitor connected at each end. It's just a pi network filter, with values appropriate to the band for which it is specified. Sorry, but I don't have values for the components.
Considering the amount of time and effort it takes to experiment with random lengths of cable, trying to find or fabricate one with exactly the "magic" length to match a transmitter to a duplexer, the Z-matcher is the only way to fly. For less than $100 and an insertion loss of 0.15 dB, you have a matched system in a minute or so. Here's a case history: My radio club has a Packet Node with both VHF and UHF ports, and a Yaesu FT-1500M 2m transceiver is used for the VHF side. It feeds a Decibel Products DB-224E 4-bay dipole antenna that has a very good match at 50 ohms and a 1.05 VSWR at 145.030 MHz. We set the power to about 10 watts, thinking that the radio would "loaf" at that setting, and the power was appropriate for the hilltop location. One day, the radio stopped transmitting, although its receiver was fine. A bench check proved that the M67781L PA module had blown, so another module (80 bucks!) was purchased and installed. While I had the repaired radio on the bench, I tested the radio through a Bird 43 meter into a dummy load. Hello! At the "low" power setting, the radio was very inefficient, the module was very hot, and the source impedance of the M67781L module was far from 50 ohms. In other words, the old module was toast because we ran it at low power! I then connected an impedance matcher and tinkered with the tuning and the drive level to find a happy medium. I was able to find a sweet spot where the ratio of power output versus DC current was greatest, and the PA module was running cool. In this particular application, cutting and experimenting with cable lengths to find a match is not very practical. 73, Eric Lemmon WB6FLY Doug wrote: > > I am intriqued by the Z matcher. I have never come across one and am > wondering if any one has a schematic. I am assuming that they may be a pi > filter or something similar. Would be nice if component values were known > also. 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/
