Nate, You'd have fewer thermal cycles, but a wider range of extremes between hot and cold, since continuous duty for four hours would get the joint to a higher peak temp.
Am I missing something? 73, Paul AE4KR ----- Original Message ----- From: Nate Duehr To: [email protected] Sent: Wednesday, November 07, 2007 10:08 PM Subject: Re: [Repeater-Builder] Part 97 question reference to Repeater control On Nov 7, 2007, at 6:41 PM, Ron Wright wrote: > A hang time is good. How long well it depends. Many repeater users > I know use it to govern the time between transmissions by letting > the repeater drop before they take it. They do this to allow > breakers. Some think it resets the timeout timer. If long say 10 > seconds would be slow QSO. Ron, the only thing that will slow down our users around here is timing out the repeater! (They're going to get a rude surprise if the time-out timer follows the courtesy tone instead of user-unkey someday. LOL!) I've actually had people say to me that they are "scared" to try to join in on our busiest ragchew/drive-time VHF machine because it flows so fast. It's somewhat amazing. Since its a stand-alone with no links to anything, and sitting at 11,440' MSL... it covers a lot of ground and a round-table is regularly 8-10 hams deep... it can move right along... > Most controllers allow for programming the hang time. I still keep > mine at 3 seconds. Some want no hang time. I have ours at the S-Com maximum for the 7K's, and would prefer it longer. I think. I'll explain below. > Cycling of the tx is not a problem. Might be with tube or big PAs. > If it were a problem then many rigs would die quickly especially HF > CW rigs, hi. I could be way out on a limb here, but we're just working our way through gathering data on a multi-year PA issue that keeps coming up on the VHF Mastr II PA's. I'm thinking more in terms of thermal cycling. Some of our sites are very cold overnight. When the morning crowd fires up, it'd be nice if the repeater would just stay up and come up to continuous-duty operating temperature and stay there, and it would be stable at some temperature and not changing sooner -- if the PA kinda stayed in lock- to-talk mode. One of our common failure modes of MASTR II PA's is the physical junction between the final and low-pass filter boards, and the "best" scientific theory we've seen is the modification available here on RB that makes that connection more "flexible"... but if the PA simply came up and stayed up... it would heat up and stay heated... less thermal cycling of that joint location. In theory -- if the tail were real long -- folks would just talk fast or slow and the PA would just stay on... for the few hours of morning or afternoon drive time, and then go down, meaning roughly 4 large- scale thermal cycles (full cold to full hot) per day for that joint, versus an unknown number with a short TX tail. (I know I could do something as silly as program the TX to come on and stay on during certain times of day, but that'd be -- well... goofy repeater behavior.) I'll also admit that I've never measured how fast/slow a M2 PA cools off when sitting in a very cold room, but I am looking forward to trying out the new A/D inputs on a 7330 up at that site someday. (That site isn't slated to get our first 7330 or our second... maybe later.) Telemetry or announcements of PA temperature extremes might be interesting data no one's had from up there before. (There are a number of other folks using M2 PA's up there that I'd be happy to share the temperature numbers with.) So far, we've only done one PA repair where we put that flexible- jumper modification in, and we're waiting to see the long-term results. These failures are spread out over a year or more -- sometimes two. It's not something that happens often, but "often enough" if you have to make a trip annually to every site just for the PA, and then add in another "general" tuning/tweaking trip, and then another trip or two for new projects and/or changes and/or antenna maintenance... you end up with a lot of trips. I love going to the sites, but 10-16 trips a year is a bit much some years. Other years, it's fine. (I doubt many fledgling repeater operators really realize it can be that many...) Since getting to mountain-top sites is difficult, risky and/or impossible (without a helicopter) in mid-winter, you end up doing that all in the summer... and 10 trips crammed into May through October with a couple trips outside the "repeater season" means two trips a month to sites, so you start to really think carefully about what you're putting "up there" and hoping it can go one whole season (and later, two seasons, and later three...) without intervention. I'm constantly thinking about questions like... "How do I engineer that site to go 3 years without a visit? Is it possible?" Thus the reason why we're using Mastr II Stations in the first place... if there's anything more "bullet-proof", I'd be happy to hear what it is. I haven't seen/heard any stories from anyone saying that they've got anything more stable that has run for 3-5 years without being touched, other than friends who have M2 Stations that get a lot less use than ours. But always willing to listen and evaluate ideas. By the way, only the VHF PA's give us trouble. Our UHF PA's, we've had two failures in five years, and one of those was a hard-driven 40W continous-duty unit that was pushed to max power for many hours at a time at a 10,000' MSL site. It died giving its all. The 100W that followed it, lost a transistor and burnt up the resistor in the Wilkinson divider... normal failure mode for these PA's when they blow a transistor. Another theory we've been discussing is that our air is thin enough up here, that no matter what the EIA-rating says for these things, they're probably getting too hot from having only convection cooling alone at 10,000' MSL and above, and I have some fans in a tray here getting ready for a test deployment at one of the sites that has extremely long key-down times in the summer heat. Even Crescend limits their 3 year warranty to 10,000' MSL and below. One of our sites is at 9,800' MSL, so if you look at it scientifically, we're 98% of the way to the warranty limit full- time... hmmm... operate it just 201 ' higher and it's out of warranty. (9,800 isn't an exact number, and it's actually closer to 9900' according to the GPS.) The other site is at 11,440' MSL... 1,339' above where the warranty goes "poof". :-) As far as UHF goes, the 75W UHF PA's are virtually indestructible, as best as I can tell, and the 100W UHF's are running a close second place. Nice balance of power level vs. cooling at these altitudes on the 75W PA, and turning back the 100W PA gives the same effect. We've seriously considered a slow conversion to "something else" for the PA's -- Crescend, Henry, and TPL are all "in the running" but it's difficult to cost-justify those, and they'd be a royal pain in the butt to install in the already full rack space at a couple of the sites -- since the M2 PA fits on the back of the station. Also to be BRUTALLY honest, if I hadn't gotten involved in a large club and were doing my own thing, there's no way in hell I'd ever bother with building a VHF machine in the first place -- what a giant PITA they are, compared to UHF! GRIN!!!! But since I am involved in the club and VHF is the "bread and butter" thanks to subsidized/loss- leader radios for VHF... I still go fix 'em and don't really mind... Two VHF PA failures happened in cold weather, at the two non- temperature controlled sites. The failure this summer (there seems to be always one!) happened at the temperature controlled site during the summer, but the room isn't cooled, only heated in winter... so it was the opposite extreme. If you'd have asked me two years ago what kills these things, I would have said "heat", but going strictly by the data... today I'd change that answer to "temperature extremes, either hot or cold". > I'm not sure what you are saying about control link. One must still > be in control of a repeater, just does not have to be at the control > point as with other Ham stations. I didn't talk about those other than to say that they're Auxiliary Stations and a couple of comments about the illegality of in-band links and simplex EchoLink/IRLP nodes on VHF prior to this year's rule change? I think you may have confused someone else's comments with mine? (GRIN) -- Nate Duehr, WY0X [EMAIL PROTECTED]
