http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf

In message <4F669A4D.3010303@lazygranch.com>, gary writes: >DC in a transformer raises the low frequency corner a bit. Obviously not >a problem in your case. I just double-checked, because that rang a bell. I did reinstate the capacitors as 2.2uF films in the final article for exactly that reason. As for gain, I have never missed any, I get a good healthy signal, even though I do live in the middle of a pop 30k city. >I should point out that every active device Lankford puts in the signal >chain [...] Why are you talking about Lankford at this point ? What I built was Fig 5 from this: http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf I realize that Chris Trask started out from Lankfords design, but I don't think it is fair to attribute the Fig 5 schematic to Lankford any more. There's a picture of my implementation here: http://phk.freebsd.dk/misc/ChrisTraskAntenna.jpg I feed it 15 volts on the twinax pair, pull that out of the toroids centertap, regulated it with a 12V 3-terminal. You can see the prototype in the top right corner. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

gary schrieb: > Just meditating out loud, if you were to go push pull with a ferrite > antenna AND you are winding it yourself, you could avoid the biasing > resistors by putting a center tap in the antenna itself, then tie that > center tap to an appropriate bias voltage. I haven't seen this done, so > their may be a gotcha with that scheme, but the science is good. Works with SA602. A russian web-site shows differential turns on a ferrite rod. <tested> > Generally you will get a lower noise circuit if the input device is an > amplifier rather than a buffer. Yep. > > Lanksford's input stage is essentially a push pull buffer, but I don't > see that cancelling 2nd harmonics like a push pull amp. But for a whip, > which is a single ended input, I don't see a way to get a differential > input. Not true for a ferrite antenna. You can transformer couple the input. Then the whip is at DC and it is possible to let DC-current to ground. <tested> - Henry -- ehydra.dyndns.info