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Wow. Paul...have you ever thought about trying caffeine free?
"Paul Burridge" wrote in message ... Bull****. In any class of operation, maximum power will be transferred when the impedances are matched. Period. |
Paul, please look over my various posts on this issue and tell me where I
failed to point out that you can get more power from a bare RF output stage by loading it differently. I'm gonna go fertilize my garden! "Paul Burridge" wrote in message ... On Sun, 4 Jan 2004 16:06:53 -0800, "Tim Wescott" wrote: For a stage (such as an intermediate, class A stage) where you _do_ want to verify the output impedance you can either find the resistance _and reactance_ that maximizes the power output, or you can build an RF impedance bridge (I use a noise bridge) and measure the stage output impedance directly. Just don't let it break into oscillation on the output of that poor impedance bridge! Bull****. In any class of operation, maximum power will be transferred when the impedances are matched. Period. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
Paul, please look over my various posts on this issue and tell me where I
failed to point out that you can get more power from a bare RF output stage by loading it differently. I'm gonna go fertilize my garden! "Paul Burridge" wrote in message ... On Sun, 4 Jan 2004 16:06:53 -0800, "Tim Wescott" wrote: For a stage (such as an intermediate, class A stage) where you _do_ want to verify the output impedance you can either find the resistance _and reactance_ that maximizes the power output, or you can build an RF impedance bridge (I use a noise bridge) and measure the stage output impedance directly. Just don't let it break into oscillation on the output of that poor impedance bridge! Bull****. In any class of operation, maximum power will be transferred when the impedances are matched. Period. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Mon, 5 Jan 2004 08:48:35 -0800, "Tim Wescott"
wrote: Paul, please look over my various posts on this issue and tell me where I failed to point out that you can get more power from a bare RF output stage by loading it differently. Sorry, Tim. I've no idea what you mean. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Mon, 5 Jan 2004 08:48:35 -0800, "Tim Wescott"
wrote: Paul, please look over my various posts on this issue and tell me where I failed to point out that you can get more power from a bare RF output stage by loading it differently. Sorry, Tim. I've no idea what you mean. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
Well, you're objecting rather strongly to an assertion that I never made.
In theory if you want to get the maximum available power out of a generator you _do_ match it's output impedance. In practice if you do this with most RF final amplifiers you will reduce your final element (whether transistor or tube) to slag -- that's why modern commercial radios have SWR protection circuitry. Please see my reply to your post starting with "Hi Leon" for a full explanation, and please actually read it before replying. Remember also that everything I say (including the attempt to match output impedances with the wall socket -- I was only 8 but that's no excuse) has been backed up by experament. "Paul Burridge" wrote in message ... On Mon, 5 Jan 2004 08:48:35 -0800, "Tim Wescott" wrote: Paul, please look over my various posts on this issue and tell me where I failed to point out that you can get more power from a bare RF output stage by loading it differently. Sorry, Tim. I've no idea what you mean. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
Well, you're objecting rather strongly to an assertion that I never made.
In theory if you want to get the maximum available power out of a generator you _do_ match it's output impedance. In practice if you do this with most RF final amplifiers you will reduce your final element (whether transistor or tube) to slag -- that's why modern commercial radios have SWR protection circuitry. Please see my reply to your post starting with "Hi Leon" for a full explanation, and please actually read it before replying. Remember also that everything I say (including the attempt to match output impedances with the wall socket -- I was only 8 but that's no excuse) has been backed up by experament. "Paul Burridge" wrote in message ... On Mon, 5 Jan 2004 08:48:35 -0800, "Tim Wescott" wrote: Paul, please look over my various posts on this issue and tell me where I failed to point out that you can get more power from a bare RF output stage by loading it differently. Sorry, Tim. I've no idea what you mean. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Mon, 5 Jan 2004 15:35:24 -0800, "Tim Wescott"
wrote: Well, you're objecting rather strongly to an assertion that I never made. In theory if you want to get the maximum available power out of a generator you _do_ match it's output impedance. In practice if you do this with most RF final amplifiers you will reduce your final element (whether transistor or tube) to slag -- that's why modern commercial radios have SWR protection circuitry. Please see my reply to your post starting with "Hi Leon" for a full explanation, and please actually read it before replying. Remember also that everything I say (including the attempt to match output impedances with the wall socket -- I was only 8 but that's no excuse) has been backed up by experament. Okay, so if I understand you correctly you're saying that whilst you should try to match impedances in Class A; it's inapplicable in Class C? It's just an operation class distinction? -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Mon, 5 Jan 2004 15:35:24 -0800, "Tim Wescott"
wrote: Well, you're objecting rather strongly to an assertion that I never made. In theory if you want to get the maximum available power out of a generator you _do_ match it's output impedance. In practice if you do this with most RF final amplifiers you will reduce your final element (whether transistor or tube) to slag -- that's why modern commercial radios have SWR protection circuitry. Please see my reply to your post starting with "Hi Leon" for a full explanation, and please actually read it before replying. Remember also that everything I say (including the attempt to match output impedances with the wall socket -- I was only 8 but that's no excuse) has been backed up by experament. Okay, so if I understand you correctly you're saying that whilst you should try to match impedances in Class A; it's inapplicable in Class C? It's just an operation class distinction? -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
Sorta. The distinction has more to do with whether you're following your
output stage with something that needs to see a specific impedance (like a filter in a receiver), and whether you're building a power stage. I couldn't think of a good generalization, so I listed some examples below. Then I realized that it really boils down to the fact that the impedance matching rule is a tool for predicing circuit behavior, not a guideline for life. RF stage in a receiver: you want to match the output impedance to the following filter or mixer for maximum power transfer and good filter/mixer performance. You usually _don't_ want to match input impedance because the best power transfer impedance is not the same as the best noise figure impedance. IF preamplifier (between a passive mixer and a crystal or mechanical filter): Match both input and output impedances, both to maximize power transfer and to get good performance from the attached stages. 1st buffer in a VFO: _don't_ match impedances with the oscillator! You want to purposely refrain from taking much power from the oscillator tank, because a heavily loaded oscillator is a poor oscillator. You probably _do_ want to match impedances on the output so the following stage won't need so much gain. 1-transistor transmitter: It's an oscillator, but a power stage too. Load it (match impedances) enough to get useful power on the antenna, but not so much that you screw up performance. Power output (usually): match impedances to the input, don't match impedance to the output (for all the reasons given earlier). This applies to any class of stage: A, B, AB, C, D and E (yes, there are class D and E stages). "Paul Burridge" wrote in message ... On Mon, 5 Jan 2004 15:35:24 -0800, "Tim Wescott" wrote: Well, you're objecting rather strongly to an assertion that I never made. In theory if you want to get the maximum available power out of a generator you _do_ match it's output impedance. In practice if you do this with most RF final amplifiers you will reduce your final element (whether transistor or tube) to slag -- that's why modern commercial radios have SWR protection circuitry. Please see my reply to your post starting with "Hi Leon" for a full explanation, and please actually read it before replying. Remember also that everything I say (including the attempt to match output impedances with the wall socket -- I was only 8 but that's no excuse) has been backed up by experament. Okay, so if I understand you correctly you're saying that whilst you should try to match impedances in Class A; it's inapplicable in Class C? It's just an operation class distinction? -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
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