Quoting Mike Valentine <[EMAIL PROTECTED]>, on Wed 02 Jul 2008 05:43:27 PM PDT:
>> Subject: Re: [Flexradio] 144 and 432 - Low vs High Power Design > >> [SNIP} > >> 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. > >> 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). > >> Jim, W6RMK > > Dearest Jim, > > I don't know how to put this gently, but you might like to actually try > to put out a KW signal on VHF/UHF before summarily dismissing what > people have been saying about the subject of drive level. > <snip of good discussion of the practical problems in getting high power> > > The commercial comparison doesn't apply well here because few hams have > commercial budgets with which to work. The state-of-the-art (and > expense) in amateur EME amplifiers are 2 x 3CX800 designs by K1FO > (Lunar-Link). They need way more than 0 dBm to drive them. > > Sorry for the rant, but every other post of yours is quite lucid and > informative. I take exception with this one. > I think you're sort of misinterpreting my comment... My idea was that rather than designing the next generation of transceiver (i.e. the F5K mark II or whatever) to accommodate the last generation of PA strategy, why not take a step back and say, what would be the best overall solution, 5-10 years from now. Sure, the folks that have existing PAs (or currently available ham PAs) need more drive, but maybe their model should be to have a third box; a booster amp (well integrated with automated controls) in the system, rather than putting the booster into the transceiver. I think that newer PA designs are going to go to more automation (auto tune, auto bias, etc.) anyway, so why not assume that the new PA should take a relatively low level input (e.g. a watt, max), and include multiple gain stages. The same applies to HF, as well, especially since the FCC did away with the "must be driven by no less than 50 Watt" rule. There's a sort of chicken and egg problem here, particularly for hams.. (oh my, that's sort of funny, especially if the ham has smoked some parts in the past).. On the one hand, you want your new box to make best use of your existing hardware (in which you've made a substantial investement), but on the other hand, maintaining plug-compatibility at all levels impedes implementing totally different architectures. So, throwing it out for discussion, what's the sort of building blocks you need.. the commercial world, which is cost sensitive, but not in the way that hams are, has gravitated to gain blocks with sub 1 Watt levels on the input. This is mostly because it's relatively easy to get there with a single MMIC device, at least up to 30-40 GHz, and your filters and such don't have to handle a lot of power, and you don't have to work hard to avoid high power breakdown, and it's high enough that the SNR (against kTB noise) is decent on your interconnects, not to mention, it's safe to disconnect and connect things at that power level (while energized) without risking injury. If one were building, say, a phased array, you'd like to do your phasing at the +10dBm levels to +20dBm levels, rather than at the 50-100W level. If you're driving a translator/transverter, you want those tens of mW levels too. I don't know the real answer here... the discussion is interesting.. Jim, W6RMK _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz 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/
