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Friday, July 30, 2021

Video: Rob Sherwood NC0B on Transceiver (and Especially Transmitter) Performance

 Rob Sherwood NC0B is one of the real authorities on receiver performance.  Many of us have relied on his ratings of commercial receivers for many years.  His recent presentation to the Madison DX Club has a lot of really interesting information. There is also, I think, some stuff that homebrewers will find distressing. 

Just some things that I noticed: 

-- Rob mentioned a move back to 9 MHz IF filters and a move away from dual-conversion rigs with a high IF.  He also mentioned the combination of a 9 MHz IF and a 5 MHz VFO as a way of easily getting on both 75 and 20 meters.  

-- Rob discussed phase noise from synthesizers, a topic we discussed at length (some would say ad nauseum!) a year or so ago. 

-- Rob really praised the "Pure Signal" system of one of the SDR manufacturers.  He showed the completely rectangular waterfall display of a Pure Signal transmitter.  I'm afraid that simple crystal rigs might never live up to this standard.  An embrace of this high standard could discourage the construction of simpler, HDR rigs.  We should not let the perfect be the enemy of the good!  

-- We often hear SSB ops complaining that some other SSB op is "splattering all over the band."  It often turns out that what is really happening is that a clean SSB signal is just overloading the receiver of an operator who does not know how to turn off his pre-amp or turn on an attenuator.  Rob shows us how to really know if the problem is in fact at the other end:  He looks at key clicks from two different CW signals on 160 meters.  Both are at roughly the same level in his receiver  But one is clicking all over the place while the other is not.  With this kind of comparative info, we can be sure that the problem is the transmitting station's fault. 

-- In discussing when to turn on the pre-amp (or the attenuator) Rob revives the old practice of just listening to the band noise. If you can hear the band noise when you switch from dummy load to receive antenna, you have enough RF gain.  Adding more will only make things worse. 

-- There was an interesting question about how to evaluate the performance of receivers when there are many signals inside the receiver's passband.  This is the case with FT-8.  Rob said this situation needs more research. 

I don't mean to be critical here -- Rob is the guy who evaluated commercial rigs.  And he is a contester.  So his presentation is, of necessity, going to have a very "appliance operator" orientation.  There seems to be an assumption that the only "rigs" that modern hams can use are commercial products. At one point Rob admits that most hams just can't repair these rigs. There is much for homebrewers to learn from experts like Rob, but presentations like this also remind us of what a tiny minority we really are, and how most hams have moved completely away from the old ham tradition of building our own rigs.  

Thanks to Rob Sherwood and the Madison DX Club.  And thanks to EI7GL for alerting us to this important presentation. 


  1. Several of 4Z1UG's recent interviews have either hinted at or clearly expressed pessimism over the future of technically-oriented, homebrew ham radio. Of an age myself (another IGY baby) in which disgruntled cynicism is endemic, I nevertheless found their pessimism exaggerated and perhaps a little-too conventional.

    Not that there's little evidence to back them up: recent retirements at QST and the magazine's thin technical coverage have not improved matters, and even QRP Quarterly recently found it necessary to spend more pages on UFOs in New Mexico than on VFOs in their readers's hamshacks. Even podcasts whose names might suggest otherwise--I'm thinking of Ham Radio Workbench--actually spend more time talking about store-bought black boxes, antennas, and cool things they've purchased (or want to purchase) than melting solder or winding coils. To be sure, HRWB, QRPQ, and even QST, make important contributions , but they do reflect the *proportional* decline of hands-on electronics.

    For me, though, that the *proportion* of homebrewing, technically-oriented hams has declined is not as important as the actual numbers of hams so oriented. If their proportion is down to, say, five-percent of the total number of hams in the world, that's still *a lot* of homebrewers worldwide, and now that we interact in a truly-global theater of enthusiasts, we've never had it so good when it comes to the numbers of people who share our enthusiasms.

    This question of actual numbers versus proportions can be seen in the most common modes of operation as well as on the hardware side. SSB long ago passed CW as the mode-of-choice, and now SSB is in decline *proportionally* as the weak-signal digital modes seem to be taking over. But when the bands are open, you can still tune through the lower portions of most bands and find *plenty* of CW ops at all levels of speed and clarity. CW is not dead, and in fact it's easier to learn than ever before. I expect a proportion will always see CW as essential to ham radio--enough in fact to keep them supplied with contacts to satisfy their retro-cravings and keep the tradition alive.

    I may be in the last quarter (third?) of my life, but the older I get the more I come to believe in living *three-dimensionally*. The "X" is my own time and place (a west-coast Boomer), the "Y" is my own time but other places and cultures, and the "Z" is other eras, times, and places. The "other eras and times" in the ham-radio context means I don't have to abandon tank circuits and crystal filters and vacuum tubes *merely* because other and perhaps objectively-superior technology is now at my disposal. I can use the new stuff and the old stuff, too. I'd even argue that to abandon all use of older technologies means there's been no *growth*, only "progress."

    We see this clearly enough in other aspects of the human endeavor. The computer may have totally replaced the typewriter, but it hasn't replaced pen, ink, and paper. The internet may be a superior repository of knowledge than printed books, but books and magazines are still widely used and are in some ways superior to online media. Microwave ovens cooking prepackaged, processed, and *manufactured* food are more efficient, but no one denies a meal made with raw whole foods and hand-prepared is better.

    I expect there will always be plenty of people living three-dimensionally as hams with whom I resonate. There's already a high SWR between me and *most* people anyway. I've grown comfortable with a more-narrow bandwidth--73, Todd K7TFC

  2. Beautifully put Todd. Thanks and 73 OM Bill


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