John, One thing to keep in mind about a particular PA's tendency to "go spurious" is that it will probably be well-behaved when tested on the bench while feeding a dummy load. A good dummy load is purely resistive, while a duplexer input is highly reactive- just what a flaky PA needs as a trigger to become unstable. Any additional triggers, such as loose connections, aging coax, or an antenna with loose elements, can quickly become a nightmare. It may be helpful to monitor your repeater's emissions on a spectrum analyzer when the noise occurs. Use a short whip on the analyzer to pick up the signal- don't connect into the feedline at all, since doing so will upset the conditions you want to monitor. It's possible that the radio itself may have a problem, and I don't think that has been ruled out yet.
73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of W3ML Sent: Monday, October 05, 2009 7:25 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Radio for repeater use Response to Tom's comments Thanks Mark, I will go read that article. Thought I read them all, since January, trying to learn all I can. That is when I decided to get into this repeater business. It has been a great learning experience for sure. 73 John, W3ML --- In Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> , "Mark" <n9...@...> wrote: > > John, > > I'll chime in here and agree with Chuck's suggestion to try a little more > "fire in the wire"... > > It sounds as if your PA is less spurious now than before, but you need to > dial it up more to eliminate all the spurious products. Solid state PAs, > especially mobiles, are noted for this when run at considerably less than > rated output. If I remember the beginning of the thread, this was a > Mastr-II mobile... > > Seems as if I remember a rule of thumb that a solid state PA won't be stable > beginning around 60-70% of its rated output. If you're at 55W now, another > 10-15W won't make much difference in the received signal strength, but will > help a LOT to stabilize the PA. > > This article: http://www.repeater-builder.com/ge/mastrIIgeneral.html <http://www.repeater-builder.com/ge/mastrIIgeneral.html> says > not to run Mastr-II PAs at less than 40%. In your case, you're at about 50% > now and still a little spurious, so... crank her up a tad more (to maybe > 70W) and see if that clears it all up. ;-) The article also has other > suggestions on how to deal with desense. > > 73, > Mark - N9WYS > > -----Original Message----- > From: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> On Behalf Of W3ML > > I probably will turn it up more to see what happens. When I had it at 5 > watts out we had no problems at all. > > Over the 10 watts is when the noise was really bad. Now at 55 it works and > then it doesn't and then it works again. > > So, yes I still have something wrong and maybe one of these days I will get > another grant and convince the club to buy another GE Mastr II and and a new > antenna and coax. Maybe that will fix it. > > People we got radio from are not answering. > > John > > > --- In Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> , "Chuck Kelsey" <wb2edv@> wrote: > > > > I'd suggest turning the power up more. You have it set at about 50% and > the > > transmitter may be intermittently spurious at that level. > > > > Watch the wattmeter when things act up and see if anything changes when > you > > notice the desense happening. You can also pull the TX ICOM when the > problem > > is happening and see if the receive clears up on the local speaker. > > > > There are so many things that could be at fault - loose connector, bad > > antenna, problem with transmitter, problem with receiver, intermod issue, > > etc. > > > > Ask the people you got the radio from if they had the same problem with > it. > > > > Chuck > > WB2EDV >
