An excellent summation, Jeff! I have found that some PA designs are unstable by nature, as if the maker took out expensive coils and capacitors one by one, until the amp either ran away or blew up, and then put that one part back in and started selling the product. I am sad to note that many aftermarket VHF and UHF power amplifier brands are "popular" only because they are cheap, not because they are well-designed and well-made.
I ran across a one-page paper of Z-Matcher Tuning Instructions from Decibel Products here: <http://243-646.telecom.climoilou.qc.ca/Filtration%20DB%20Producs/Z%20Matcher.pdf> 73, Eric Lemmon WB6FLY Jeff DePolo WN3A wrote: ... The original premise was that a Z-matcher was needed on the output of some > PA's because the PA itself was *not* properly matched when terminated in a > 50 ohm load. Wasn't that the original discussion? The goal wasn't to > minimize VSWR looking into the cavities. With that in mind, the "best > match" isn't necessarily that which produces the least reflected power. The > "best match" is the load Z that the amplifier is most happy transferring > power to, and the only way to know that is by looking at PA efficiency... > ... Now, if you have a PA that runs away when presented with a known-good load, > then you've got a problem that needs to be fixed IN THE PA. Using a > Z-matcher, or the crude equivalent of feedline pruning, to help tame an > unstable PA isn't a fix, it's a band-aid that will eventually come off... 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/
