3560	2009-09-22 16:08:44	Ross	Ham radio brainstorm
Message	Date	From	Subject
A number of improbable ideas came to me this afternoon. I submit two of them for your scorn, praise, or otherwise: 1. USB cables and connectors are cheap. Google tells me that the characteristic impedance is 90 Ohms +- 15%. Odd-value coax is rare and expensive; might it be possible to use inexpensive USB cables for feedline harnesses, phasing lines, etc? A major plus is that the connectors are manufactured, hence no worrying about quality of connector. Of course, power will probably be limited to QRP, but at _least_ 5W will be okay, as that is the dc charging rate (1A at 5V). 2. Final amplifiers often have native impedances ~10-15 Ohms, which we transform up to 50 Ohms before we send it through transmatch and feedline to the antenna. Well, instead of transforming it up to 50 Ohms, why not use a tuned feedline and transform it directly to the antenna impedance? Can we design a circuit to measure the impedance and then (if within some range), adjust collector capacitance to match it directly? If we are designing a single-band transceiver, is it too much to cut a feedline to resonance? No worries about reflections, just pure, easy collector current into the antenna! Best Regards, Ross, NS7F
3561	2009-09-22 16:18:07	w4zcb	Re: Ham radio brainstorm
2. Final amplifiers often have native impedances ~10-15 Ohms, which we transform up to 50 Ohms before we send it through transmatch and feedline to the antenna. Well, instead of transforming it up to 50 Ohms, why not use a tuned feedline and transform it directly to the antenna impedance? Can we design a circuit to measure the impedance and then (if within some range), adjust collector capacitance to match it directly? If we are designing a single-band transceiver, is it too much to cut a feedline to resonance? No worries about reflections, just pure, easy collector current into the antenna! Best Regards, Ross, NS7F WRT number two, I'm happy that you're a 7 and not a 4. I would much prefer that those who build amplifiers, even QRP ones, would install a LPF between it and the antenna. (There's very little that's pure in amplifier collector cuurents.) Regards W4ZCB
3562	2009-09-22 17:08:00	Dave - WB6DHW	Re: Ham radio brainstorm
Ross wrote: > A number of improbable ideas came to me this afternoon. I submit two of them for your scorn, praise, or otherwise: > > > 2. > Final amplifiers often have native impedances ~10-15 Ohms, which we transform up to 50 Ohms before we send it through transmatch and feedline to the antenna. Well, instead of transforming it up to 50 Ohms, why not use a tuned feedline and transform it directly to the antenna impedance? Can we design a circuit to measure the impedance and then (if within some range), adjust collector capacitance to match it directly? If we are designing a single-band transceiver, is it too much to cut a feedline to resonance? No worries about reflections, just pure, easy collector current into the antenna! > > Best Regards, > Ross, NS7F > > > > > This is exactly what used to be done with tube amplifiers, usually with a Pi Network. You would "Dip" the tune capacitor and raise the load capacitor to the desired plate current. Or course, I think the output impedance of a tube amp is much higher. Dave - WB6DHW <http://wb6dhw.com>
3563	2009-09-22 17:52:33	Stephen Wandling	Re: Ham radio brainstorm
Dave, Further to the point made by W4ZCB regarding harmonic radiation, did that Pi network reduce harmonic radiation to the levels currently required? Stephen VE7NSD Dave - WB6DHW wrote: > This is exactly what used to be done with tube amplifiers, usually > with a Pi Network. You would "Dip" the tune capacitor and raise the > load capacitor to the desired plate current. Or course, I think the > output impedance of a tube amp is much higher. > > Dave - WB6DHW > <http://wb6dhw.com> > Ross wrote: > >> A number of improbable ideas came to me this afternoon. I submit two of them for your scorn, praise, or otherwise: >> >> >> 2. >> Final amplifiers often have native impedances ~10-15 Ohms, which we transform up to 50 Ohms before we send it through transmatch and feedline to the antenna. Well, instead of transforming it up to 50 Ohms, why not use a tuned feedline and transform it directly to the antenna impedance? Can we design a circuit to measure the impedance and then (if within some range), adjust collector capacitance to match it directly? If we are designing a single-band transceiver, is it too much to cut a feedline to resonance? No worries about reflections, just pure, easy collector current into the antenna! >> >> Best Regards, >> Ross, NS7F >> >> >> >> >> >> > > > > > ------------------------------------ > > Yahoo! Groups Links > > > > > -- "This business of hozho. The way I understand it . . ." He paused. The way he understood hozho was hard to put into words. "I'll use an example. Terrible drought, crops dead, sheep dying. Spring dried out. No water. The Hopi, or the Christian, maybe the Moslem, they pray for rain. The Navajo has the proper ceremony done to restore himself to harmony with the drought. You see what I mean? The system is designed to recognize what's beyond human power to change, and then to change the humans attitude to be content with the inevitable." --Jim Chee, in Sacred Clowns; Tony Hillerman, 1993
3564	2009-09-22 18:37:37	Dave - WB6DHW	Re: Ham radio brainstorm
Stephen Wandling wrote: > Dave, > > Further to the point made by W4ZCB regarding harmonic radiation, did > that Pi network reduce harmonic radiation to the levels currently required? > > Stephen > VE7NSD > > > Dave - WB6DHW wrote: > > >> This is exactly what used to be done with tube amplifiers, usually >> with a Pi Network. You would "Dip" the tune capacitor and raise the >> load capacitor to the desired plate current. Or course, I think the >> output impedance of a tube amp is much higher. >> >> Dave - WB6DHW >> <http://wb6dhw.com> >> > > >> Ross wrote: >> >> >>> A number of improbable ideas came to me this afternoon. I submit two of them for your scorn, praise, or otherwise: >>> >>> >>> 2. >>> Final amplifiers often have native impedances ~10-15 Ohms, which we transform up to 50 Ohms before we send it through transmatch and feedline to the antenna. Well, instead of transforming it up to 50 Ohms, why not use a tuned feedline and transform it directly to the antenna impedance? Can we design a circuit to measure the impedance and then (if within some range), adjust collector capacitance to match it directly? If we are designing a single-band transceiver, is it too much to cut a feedline to resonance? No worries about reflections, just pure, easy collector current into the antenna! >>> >>> Best Regards, >>> Ross, NS7F >>> >>> >>> >>> >>> >>> >>> >> >> >> ------------------------------------ >> >> Yahoo! Groups Links >> >> >> >> >> >> > > It is a low pass network. Don't really know if it would work the same with a bipolar transistor with the lower impedance. Dave - WB6DHW <http://wb6dhw.com>
3565	2009-09-22 20:00:42	ajparent1	Re: Ham radio brainstorm

3566	2009-09-23 16:07:47	davidpnewkirk	Re: Ham radio brainstorm