I'm building stubs for a DXpedition, and also for my own shack. I always study the wisdom of others before undertaking a project, and came across this gem on K1TTT's website. He's quoting W8JI. The q
Hi Jim: I always wanted to test the 1/4 wave "insertion" theory, but never got around to it. I would love to hear what the difference is - if you can experiment. 73, Tim K3LR I'm building stubs for a
What Tom says is right on the mark, as long as the last component in your amplifier is a capacitor to ground, which is probably the case 90+% of the time. In Jim's case, the last component is a serie
Hi Jim, Tom has it exactly right. Think of it this way: Let's say that your quarter wave stub provides a 10 ohm impedance at the harmonic frequency. It the impedance of the amp is say 25 ohms at the
I think this may be why I designed my amp with a Pi L output circuit, although I'm not a big contest station and have never really measured the harmonic output. Gene ./ W2LU _________________________
Yes, as always, Tom's logic make perfect sense to me as well, for exactly the reasons you noted. I did the math mentally, you put it in an email. :) BUT -- at Rick correctly notes, the last component
Hi Tim, OK. As noted, my Titan 425s (original) are not a good output stage to test this, but I've got a Hercules II that does use a traditional pisection (C-L-C) as the output filter. When I have tim
Jim, You should be able to get an idea of the output impedance of the amp at the second harmonic frequency by checking with an impedance meter at the output, like with an MFJ. You may need to place a
Yes, I thought about doing that, but didn't get as far as simulating the tube. You can't just shut down the amp though -- you've got to leave it up with the antenna relay pulled in. All in all, a lot
You don't want to have the amp on when you connect a measuring instrument to the output. Just the static conduction (noise) developed in the tubes will probably zap the front end of your meter. Use
1/4 wavelength at the second harmonic is only 1/8 wavelength at the operating frequency. If you make the connection 1/4 wavelength away at the operating frequency, the described transformation does n
Which is why W2VJN's stub cookbook shows some interesting behavior with 1/8 wave connecting lines <G>. Without getting the book off the shelf, I believe he was using 1/8 wave between the amplifier a
Using TLW a while back, I was modeling a 1/8-wave line and it looks like no matter what the termination Z at the end of 1/8-wave line, the Z seen at the transmitter is always the line Zo. Depending
--Original Message-- I'll go for the lumped design (certainly easier and more predictable), and the recommendation for Elliptic/Cauer (especially if you need some notches, and don't care about ultima
--Original Message-- Which is why a computer to model it is nice<grin>... Or a set of decent design equations. I'll bet there's a nomogram or set of templates for a Smith Chart that does this kind of
A rule of thumb is that an inductive stub has the Q of a coil of the same diameter. Thus RG-8 coax is not even as good as a coil on a 1/2 inch diameter form. The Q of capacitors made from coax is not
Interestingly, there's an IEEE paper on designing filters using transmission line segments and stubs (and coupled lines, too). I can look for the reference. But, in general, yes, you want to put the
Tim, I haven't done any measurements, but I did do a literature search of QST product reviews to learn what output circuitry is used by power amps that you and I are likely to be using. What I learne
Jim, SB-220 is similar to Kenwood 922 - both use pi network. -Rex Rex Lint, Consultant 26 Brek Drive Merrimack, NH 03054 PH: 603-860-7651 Tim, I haven't done any measurements, but I did do a
Thanks 73, Jim _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/list