On Jul 2, 2008, at 1:33 PM, Jim Lux wrote: > Quoting Brian Lloyd <[EMAIL PROTECTED]>, on Wed 02 Jul 2008 > 12:40:10 PM PDT: > >> >> On Jul 1, 2008, at 11:23 PM, David Hilton-Jones wrote: >> >>> I suggest that there are two important issues to consider: >>> >>> 1) Power output. I have a strong preference for 50-60 watts - that >>> allows driving of a 13db triode to 1kw. Intermediate amplifiers are >>> undesirable. >> >> You also want lower outputs needed by mixer stages for microwave >> converters. > > > Well.. that's sort of a system design/configuration thing. You're > going to need gain to get from the 0 dBmish levels out of the QSE up > to your +60dBm and that gain's going to be in steps. So the > question is do you put it inside in the F5K or inside the amp or as > a separate box.
Well, I was thinking that the transverter is going to have its own driver and PA stage to reach that +47dBm output level. It would be useful to tap off 10-20dBm from the predriver to drive a mixer in a microwave TX/RX converter. So you aren't adding extra hardware. Frankly, if they are going to go to the effort of putting in a +43dBm PA, they probably aren't adding any extra stages to have a +47dBm output PA. There is probably enough gain in the driver and PA devices (or PA module) to reach either +43dBm or +47dBm. So the only question is whether or not to provide access to the lower-level signal that normally would provide power to the driver. > I'd advocate, generally, for a design that puts out +10dBm or so, > because that lets you pad it a bit and drive a mixer's IF port > (assuming the LO comes from somewhere else). Maybe a bit more, > depending on if you want to do a passive divider scheme to drive > multiple converters.. Maybe +20dBm? Precisely what I was thinking. > After that it's just figuring out what the optimum (for each user) > arrangement of gain blocks is. The +13dB gain in a box for the high > power amp is kind of a holdover from earlier days when a) HF amps > are limited in gain by the FCC and b) they'd be just a single stage. > > I would think that a modern UHF amp building block wouldn't use a > +47dBm (50W) drive... even a watt seems like a lot. In the > microwave area, a HPA gain of 40 or 50 dB (e.g. 0dBm in for 100W > out) isn't unusual for a TWTA. Well, PA modules that expect +20dBm to +30dBm at their inputs are not uncommon. Heck, if I were designing a transverter that is what I would use as the PA. There are a lot of class AB/C PA modules for two-way VHF/UHF transceivers. That greatly reduces time-to-market and probably reduces the effort needed to get FCC type-acceptance. And it is easy to pad down even a +23dBm signal to whatever you need to drive a DBM. > Yes, there's a substantial installed base of low gain HPAs out > there, but I would think that one would want to design the building > blocks for a more modern system architecture. Most commercial amps > (not ham) seem to have a fair amount of gain (e.g. the Harris HF > amps take 0dBm to +10dBm in for 1kW out, ditto the Amplifier > Research amps we use at work). Could be. Perhaps it would be useful to look at what is generally available to the consumer. What reasonably-priced 2M and 70cm amplifiers are out there? What are their drive requirements? Most of these amps are single-stage triodes or tetrodes unless they are solid- state. (Ah, the venerable 4CX1000.) Anyway, I think we are on the same page here. Perhaps it makes sense to go back to first principles, i.e. what will it get used for. I think the answer is: 1. to operate as a barefoot transceiver for terrestrial and satellite work (+45dBm to +50dBm); 2. to drive a legal-limit amp for terrestrial work (+43dBm to +50dBm); 3. to drive microwave transmitting converters (+10dBm to +30dBm). That probably gets the bulk of the customers and can be accomplished by stealing the power before the PA module. -- 73 de Brian, WB6RQN Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com _______________________________________________ FlexRadio Systems Mailing List [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kb.flex-radio.com/ Homepage: http://www.flex-radio.com/
