All good info, Nate, but your comment about turning down the power may lead Joe down the wrong path.
Some mobile radios in the 50 watt class, especially those that use RF power modules, may burn up if run for long periods at low power. Yes, that is what I meant! I learned this lesson the hard way, when a Yaesu FT-2500M that I had in packet service died due to a toasted RF module. Because I had a hilltop site and a DB224 antenna, I found that the lowest setting of 5 watts was more than enough power for solid contacts. The other settings were 12, 25, and 50 watts. A new PA module set me back about $85, and I followed the instructions exactly when replacing it. But before putting the radio back into service, I ran some careful bench tests. I was surprised to notice that, while the RF output power settings were almost exactly on the money at 5, 12, 25, and 50 watts into a dummy load, the DC input power to the radio did not track the output power- not even close! In fact, the DC input power at 5 watts output was about 85% of the DC input power at 50 watts output. And that is what toasted the PA module- the DC input power that was not converted into RF output power was, instead, heating the driver and the PA stages to destruction. In the case of the FT-2500M, it ran much cooler at the 25 watt setting than at the 5 watt setting. Now, I will admit that the designer of the FT-2500M probably cut some corners to meet a price target (where have we heard THAT before?) and the PA stage could be designed to be much more efficient at low power settings, and most commercial radios are far more robust in this area. My point is that some radios may exhibit symptoms more serious than spurious operation when set to power levels below the recommended level. Excessive heat generation within the PA at low output levels is seldom mentioned as an issue to watch. This is understandable, since "conventional wisdom" suggests that the PA should get hotter only when driven harder. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Nate Duehr Sent: Monday, November 19, 2007 9:49 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] A couple of questions On Nov 19, 2007, at 3:45 PM, Joe Landers wrote: > Hey everyone > > I want to ask a couple of questions and see if I get any replies Replies, we can definitely do. Accurate replies require more than a mailing list, but there are some professionals here who'd love to quote you consulting fees. (GRIN - Not me.) > I am getting ready to change a frequency in a mastr II and I got to > buy some crystals Who is doing the best job at a resonable rate with > them nowadays . Ahh, the never-ending question of the list. This question has reached "religious" status with many here. :-) The general consensus: The bigger shops (International Crystal, Bomar, and maybe West Crystal) have all gotten good comments from some here, and others want to throw their rocks they received out the window. Different people, different opinions. Search the list archives for chrystal and plan on about an hour of reading. The other debate is whether to rock your own ICOM's or send the entire ICOM in for temperature compensation. That topic is contentious and near-continuous here on the list also. There's also some good information on the topic on the repeater- builder website, don't forget to look there. My comments: For public-safety applications... just going by your signature line... Send the ICOM's into a reputable manufacturer for full compensation. If they don't offer it, skip them. Get a full temperature comp done and have them install the rock. Plan on multiple weeks to get them back. Lives are on the line. Also note that they will still age over the first year or so, keep the test gear handy and re-tune a couple of times when necessary. It would help if you could be more descriptive about which band-split Mastr II you're moving and to generally what frequency. There are some tricks with ordering crystals for ham use (if you're not staying within their rated frequency spectrum) where ordering high-side injection versus low-side injection is a good thing. Kevin and Scott at Repeater-Builder also have put out some information in the past about why certain frequencies in the ham bands don't work as well with low-side injection as you push the MASTR II out of band. All up on the RB site. Good engineering information. > Secondly I have a radio I want to use for remote base use I need a > mike plug diagram of pinout diagram to make a jack for the controller > The radio info is as follows > > it is a maxon model 1520a mobile > plate on back has p/n 717810 > > no serial number No clue on that particular radio, but if it can't handle 100% continuous-duty key-down, and it's going into public safety work -- forget it. Or turn it down to where it will survive a week's keydown into a dummy load on the test bench. If it doesn't survive, buy something that can be keyed continuously and not blow up. You're the pro here, though -- I'm just an Amateur. Your mileage may vary. :-) -- Nate Duehr, WY0X [EMAIL PROTECTED] <mailto:nate%40natetech.com>
