Quoting [EMAIL PROTECTED], on Wed 02 Jul 2008 06:53:18 PM PDT: > Jim, > > As an owner of four Lunar-Link tube amps driven by DEMI high-power > transverters, I have to agree with Mike. 50 watts of available drive > power from the transverter is considerably more convenient than adding a > brick amp into the system with existing HPA's or having to roll your own > KW+ HPA from scratch to allow for low drive levels.
That's certainly true for today... but, if you didn't have an investment in the equipment, and you had a blank sheet of paper, what would you do? (maybe you'd choose the same strategy? ) > > I haven't looked in a while, but when I looked just a couple of years ago, > the single-stage gain limitation was still in-place in Part 97 - at least > for mass-producted ham amplifiers for HF (more than one per year of a > single design from a single supplier). I need to go back and check if the > limitation applies to VHF/UHF amps. That went away this year... the only requirement now is basically zero gain in the CB band, which you could do with a very impressive band stop filter or with a microprocessor that counts the input frequency and shuts the amp down. > > The cost to hand-build, with all-new parts, a low- or medium-drive, > high-reliability solid state VHF/UHF amp with the same 1500W key-down > capabilities as a Lunar-Link is more than double that of the L-L with > tubes and power supply. I would suspect that commercially-produced SS > amps of similar stature would be triple the cost (look at the Dishtronix > HF SS amp). True.. but, consider the future, and make sure that we're considering apples to apples. Some of the venerable designs leverage off of what were once inexpensive surplus tubes and/or cavities, but are no more. If you were to start today, the cost tradeoff might not be so clear. BTW, I think that for KW power levels, today, tubes are where it's at, and likely to remain so for a while. Linear SSPAs have generally lower efficiencies (not that hams usually care about DC to RF power efficiency, but they leverage off developments of people that do..). However, some clever techniques like EER and such, partly enabled by SDRs, might help that situation. But that's another argument (overcoming the traditional system design model with exciter connected to PA) > > Replacing a 25W MOSFET brick in a transverter with a 50W unit is perhaps a > $80 or so effort per band (including beefing up the internal output > filters and T/R relay, plus some shielding to keep things stable). > Fortunately, DEMI has already done all of the necessary homework for it's > high-power transverter line. This seems like a no-brainer to me. > > While it would be great to be able to take the purist's approach and do it > all "the right way" from scratch, we generally must take the systems > integrator's approach when it comes to high-power VHF/UHF - use what's > available at a reasonable price/performance ratio on the high power side > and work with our vendors to simplify setting up such a system as much as > possible. When DEMI brought out the high-power transverters, it was a > sigh of relief for me to be able to eliminate those pesky intermediate > brick amps. I'm sure others have had similar experiences. I guess it sort of depends on where you want the F5K (and other SDRs) positioned... if the HPA manufacturers started including the brick in their box, that would also remove the pesky IPA, too..... Frankly, since you are more likely to be buying F5Ks with built in transverters than I am, if I were Flex, I'd listen to you and jack the output power up. But, since we ARE talking about radios that are changing the traditional system designs, it's worth talking about exactly *why* we want that, to make sure that we're not just fossilizing a historical accident of design. (sort of like the origins of the 1 kW limit in the first place) _______________________________________________ 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/
