The network is pretty much a standard pi version of a vhf antenna tuner (although other types are also popular). It can also be considered a filter by nature of its design and operation. It is often found in the commerical circles sold as each type of said device for +10dB more than it cost to make in parts.
The key to this type of device is min values, as in the/some Johansen caps can adjust to less than a pf (or close) when desired. One of the hard parts of building a VHF antenna tuner/match network is getting min C values from the caps and keeping the insertion loss down to a practical value. This type of device is often described in some of the VHF Sections fo the ARRL Materials (books) and project found on the web. The mentioned Johansen Caps can be found at flea markets and on Ebay for a few dollars each. One should also understand any original amplifier output low pass filter network is still in the circuit path (unless modified). Preformance of the/any internal amplifier low pass circuits designed for 50 ohm operation might be modified. cheers skipp > Eric Lemmon <[EMAIL PROTECTED]> 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. 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/
