At 09:36 PM 1/8/04, you wrote: >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 -------- Thanks Eric. Well it is pretty much like I thought. Shouldn't be to hard to duplicate. When I get some time I will. I know what it is like to blow a brick. I have blown two in my 741a which is mounted under the passenger seat in my van. Th diplexer went open at the common connector and I had the swr meter in the common lead.
Take care Eric. It is now a warm -22C here at the present time. I just hope it keeps warming up. 73 Doug ve5da 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/
