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Sorry everyone, but I just retested with no cable and the results I obtain are
precisely the same. The coax cable was only 26" long anyway. So forget about that transmission line stuff. It's irrelevant here. What I want to know is why the VSWR indications are the way they are. If anyone's interested, I can email a small spreadsheet that deals with this simple circuit (V0-R-jX-r-jx) and allows you to set a) R,X and r, and vary x b) R,X and x, and vary r. I plot side by side on the two corresponding graphs - modulus of total load voltage - modulus of load resistor voltage - modulus of load reactance voltage - power dissipated in load resistor - VSWR between source and load - "conjugate VSWR" between source and load. One more time with feeling - What I want to know is why the VSWR indications are the way they are. Best, Andrew "Cecil Moore" wrote in message ... Dave wrote: nope, all done. reg is here and cecil can't be far behind. i've had my fun, time to do other more productive things than watch them re-hash conjugal matches for the next month or two. I guess I need to say this again. My take on discussions of conjugate matching in ham antenna systems is that it is a waste of time. If reflected energy is not allowed to reach the source, e.g. typical ham Z0-matched systems, the source impedance is irrelevant and doesn't affect anything in the system except for efficiency. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
probably because the meter is not measuring what you think it is. remember,
vswr meters are meant to be showing what the vswr is in a transmission line of a given characteristic impedance. they are not impedance meters, nor are they proper power meters even though they are often calibrated in watts... they are only accurate in the specific characteristic impedance system they were 'calibrated' for... and then only roughly in most cases. if you want to make proper measurements give up on the vswr meter and measure the voltage or current with an oscilloscope or properly calibrated rf voltmeter. "Lord Snooty" wrote in message nk.net... Sorry everyone, but I just retested with no cable and the results I obtain are precisely the same. The coax cable was only 26" long anyway. So forget about that transmission line stuff. It's irrelevant here. What I want to know is why the VSWR indications are the way they are. If anyone's interested, I can email a small spreadsheet that deals with this simple circuit (V0-R-jX-r-jx) and allows you to set a) R,X and r, and vary x b) R,X and x, and vary r. I plot side by side on the two corresponding graphs - modulus of total load voltage - modulus of load resistor voltage - modulus of load reactance voltage - power dissipated in load resistor - VSWR between source and load - "conjugate VSWR" between source and load. One more time with feeling - What I want to know is why the VSWR indications are the way they are. Best, Andrew "Cecil Moore" wrote in message ... Dave wrote: nope, all done. reg is here and cecil can't be far behind. i've had my fun, time to do other more productive things than watch them re-hash conjugal matches for the next month or two. I guess I need to say this again. My take on discussions of conjugate matching in ham antenna systems is that it is a waste of time. If reflected energy is not allowed to reach the source, e.g. typical ham Z0-matched systems, the source impedance is irrelevant and doesn't affect anything in the system except for efficiency. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 23 May 2004 20:42:59 GMT, "Lord Snooty" wrote:
The amp is single-ended out of an MRF136, so I presume it's Class A. The amp's designation is H-10 (I bought it surplus). It's rated at around 15W, 0.1 - 30 MHz. The circuit diagram shows no hint of current limiting circuitry. If one is serious about proper design of a matching network - a network, I might add, which attaches *directly* (near as dammit) to the Tx output - then one is all at sea without a proper knowledge of source impedance. See my comments in the other thread about this. Hi Andrew. Specification sheets respond to these issues quite well. The MRF136 is a 400MHz device, normally offering 15W max with about 16dB gain at 28Vdc (although rated higher) in a class A configuration (showing about 60% efficiency). As would be expected, it covers a lot of turf. In the HF, the output Z runs easily near 50 Ohms in push-pull circuit configurations; otherwise it is simpler to describe it in the teens to tens of Ohms across any number of variables you do not disclose (like frequency, the actual configuration, additional interface components). 1 - 10 MHz does not bode well towards the best implementation of an UHF device. Load pulling is vastly simpler than S-parameters (also specified in the data sheets for this device, down to 1MHz), why you want to marry the two is a mystery. 73's Richard Clark, KB7QHC |
Richard Clark wrote:
Load pulling is vastly simpler than S-parameters (also specified in the data sheets for this device, down to 1MHz), why you want to marry the two is a mystery. A laboratory bench setup is simpler than a calculator and a couple of sheets of paper? Egads Richard, s-parameter analysis was invented in order to make things "vastly simpler" - and it does! -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 23 May 2004 21:19:23 GMT, Richard Clark
wrote: [snip |in a class A configuration (showing |about 60% efficiency). Huh? |
Cecil wrote, Richard Clark wrote: Load pulling is vastly simpler than S-parameters (also specified in the data sheets for this device, down to 1MHz), why you want to marry the two is a mystery. A laboratory bench setup is simpler than a calculator and a couple of sheets of paper? Egads Richard, s-parameter analysis was invented in order to make things "vastly simpler" - and it does! -- 73, Cecil http://www.qsl.net/w5dxp S-parameters are supposed to work best on small-signal analysis, where everything is fairly linear. In this case, the MRF 136 is a power fet and Motorola says you can use s-parameters as a first approximation. In the data sheet, they provide a list of common source scattering parameters from 2.0 Mhz up to 800 Mhz. I suppose that's useful to someone familiar with s-parameter techniques. 73, KA6RUH |
Wes wrote,
On Sun, 23 May 2004 21:19:23 GMT, Richard Clark wrote: [snip |in a class A configuration (showing |about 60% efficiency). Huh? The data sheet doesn't say it gets 60% efficiency in a class A configuration. It just says, under one bullet, that "Efficiency = 60%." Further down the column it says, "Ideally Suited For Class A Operation." 73, Tom Donaly, KA6RUH |
Tdonaly wrote:
S-parameters are supposed to work best on small-signal analysis, where everything is fairly linear. Therefore, should work well on transmission-line analysis, where everything is linear. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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