This evening I was browsing one of my favorite QRP homebrewing sites, QRP Homebuilder by VE7BPO, when I stumbed upon something that really struck a nerve. Todd does a really great job in documenting his projects and experiments, as well as walking you through his thought process in many of the design decisions that he made. There’s a wealth of information here, and you’d be hard pressed to find someone who does a better job.
In this article, VE7BPO gives a very nicely detailed explanation of his methodology for testing the stability of the LC-tuned VFO circuit which is the subject of the post. He mentions that you can always use a stable receiver with a narrow bandwitdth to listen for VFO frequency shifts by ear (a perfectly valid method for homebrewer testing, in my experience). Well apparently, that’s not good enough for some of the Internet experts:
I have taken some flack on the World Wide Web and by email for using my ears as a VFO stability tester. Perhaps this is well deserved criticism, as it does not quantify drift. However, the last time I checked, receivers are meant for listening to signals and almost any drifting oscillator beat note will not stay centered in a narrow IF pass band of a stable receiver. If a VFO stays put in a narrow pass band, I am pretty sure it is stable enough for use in a home-built transmitter or receiver. From my experience, albeit limited, any drift you can measure you can also hear. I sure wish some of my critics would publish their work so I wouldn’t have to perform so many experiments to try to improve my hobby projects! The target audience of this web site is people who want to have some fun and perhaps do not have hundreds of dollars worth of test equipment. It is okay to use a receiver as a piece of test equipment if you want to or don’t have anything better to use. Apart from digitization, miniaturization and the demise of HAM radio in general, I posit some of the other reasons that analog hobby electronics is dying is lack of mentorship, imagination and fear of failure. Every design or method generally has good points and bad points. This web site is truly for people who like to experiment with and enjoy building simple electronics circuits. This is the “popcorn” niche I aspire to. I have found that it is very easy to criticize, but far more difficult to contribute. Hopefully I am in the latter group! [Emphasis mine]
It really fries me to see people like Todd, who put such much time and energy into documenting their hobby for other people at no financial gain, get a raft of crap from online bullies. There’s not much to add to his statement, since he pretty much nails it, but I’ve had a small taste of the same thing. Fortunatly, most of the hams I’ve interacted with online have been at least cordial; but I know how frustrating it can be to put a lot of energy into a labor of love, only to have it criticized by the know-it-all do-nothings of the world.
I emphasized one sentence in that quote to give everyone something to think about. It’s quite tempting for someone who is freely giving their time to the hobby to throw in the towel on sharing their work when they are forced to put up with too much of this nonsense. So please, show support to your favorite authors and bloggers, they need all they can get.
Noli nothis permittere te terere
Heh, I had to Google that. Don’t worry, they’re not gettin’ me down, just getting under my skin a bit. I’ve vented and I feel better already.
There’s nothing wrong with a well designed LC-tuned free running VFO. Call me a geek, but some of those air-spaced variable capacitors in VE7BPO’s article were just downright beautiful.
We live in such a DDS and PLL world that I think some folk are a little wary of free running VFO’s. To them I say; “Behold the beauty of an LC tuned circuit, the majesty of high Q coils and low temperature co-efficient capacitors!”
Anyway, to get back to earth, the way I see it with measuring or gauging anything, is that you always have to do it against some kind of a reference. Basic stuff I know, but some of the folk that were criticizing are maybe forgetting that if you are using a receiver with a narrow passband, then (assuming that it is a receiver that has already been determined to be frequency-stable), it serves as a perfectly fine reference. If you’re building a VFO for a CW or SSB transmitter or receiver, then if you can’t hear the drift of your VFO, you’re not going to notice it when you’re using it (and neither is the other guy if he’s listening to your signal. As long as you’re not extremely close to the band edge, you’ll be fine.
I worked for Richard Branson for 16 years. In his autobiography he talks about all the flak he has taken over the years and mentions that it is very hard to build things, and very easy for others to attempt to tear them down. As someone who follows the majority of the time, I’m immensely respectful of those who go first and build things.
Phew – you got me all riled up on a Monday morning Jason!