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#1
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In message , Richard Clark
writes On 21 Dec 2004 14:23:10 GMT, (PDRUNEN) wrote: Hi All, I was reviewing a 75 to 50 ohm resistive matching network using two resistors, the insertion lost was 5.7 db. Hi OM, Snips However, this is not the best design for a matching network, they are usually three resistors in either a PI or T configuration. Several manufacturers of precision matching pads might disagree! Two resistors is enough, although you have to remember to add a rather odd number (unless the measuring equipment can add it for you). If you add a third resistor, you can make the correction a straight 6dB. That's probably the only virtue. Ian. -- |
#2
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On Tue, 21 Dec 2004 20:27:54 +0000, Ian Jackson
wrote: However, this is not the best design for a matching network, they are usually three resistors in either a PI or T configuration. Several manufacturers of precision matching pads might disagree! Hi Ian, I seriously doubt it, but you are free to offer examples. 73's Richard Clark, KB7QHC |
#3
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In message , Richard Clark
writes On Tue, 21 Dec 2004 20:27:54 +0000, Ian Jackson wrote: However, this is not the best design for a matching network, they are usually three resistors in either a PI or T configuration. Several manufacturers of precision matching pads might disagree! Hi Ian, I seriously doubt it, but you are free to offer examples. 73's Richard Clark, KB7QHC http://www.maxim-ic.com/appnotes.cfm...mber/972/ln/en http://www.maxim-ic.com/appnotes.cfm...te_number/3250 http://www.maxim-ic.com/appnotes.cfm...mber/972/ln/en http://www.testmart.com/estore/produ...Fsearch%2Fspec. cfm~~MICCOM~~AGILEN~~11852B~~%20~~%20|1.html http://www.g4fgq.regp.btinternet.co.uk/padmatch.pas http://www.g4fgq.regp.btinternet.co.uk/padmatch.pas http://used-line.com/b2544p1pr0-Used-pads.htm http://www.minicircuits.com/dg03-159.pdf#search='minimum%20loss%20pad' + many, many more! Ian. -- |
#4
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On Tue, 21 Dec 2004 22:51:30 +0000, Ian Jackson
wrote: In message , Richard Clark writes On Tue, 21 Dec 2004 20:27:54 +0000, Ian Jackson wrote: However, this is not the best design for a matching network, they are usually three resistors in either a PI or T configuration. Several manufacturers of precision matching pads might disagree! Hi Ian, I seriously doubt it, but you are free to offer examples. 73's Richard Clark, KB7QHC + many, many more! Ian. Hi Ian, Perhaps you can share from those many, many more, those which disagree? 73's Richard Clark, KB7QHC |
#5
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In message , Richard Clark
writes On Tue, 21 Dec 2004 22:51:30 +0000, Ian Jackson wrote: In message , Richard Clark writes On Tue, 21 Dec 2004 20:27:54 +0000, Ian Jackson wrote: However, this is not the best design for a matching network, they are usually three resistors in either a PI or T configuration. Several manufacturers of precision matching pads might disagree! Hi Ian, I seriously doubt it, but you are free to offer examples. 73's Richard Clark, KB7QHC + many, many more! Ian. Hi Ian, Perhaps you can share from those many, many more, those which disagree? 73's Richard Clark, KB7QHC The point I was trying to make was, if the L-pad was 'not the best design for a matching network', why are there so many about? It gives the minimum loss for a match in both directions (with the 43and 86 ohm resistors). What works better? Ian. -- |
#6
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On Wed, 22 Dec 2004 00:19:12 +0000, Ian Jackson
wrote: The point I was trying to make was, if the L-pad was 'not the best design for a matching network', why are there so many about? It gives the minimum loss for a match in both directions (with the 43and 86 ohm resistors). What works better? Ian. Hi Ian, The topic is Why Match? and the context is with bench gear, specifically a Spectrum Analyzer. It is pleasing that no sardonic quips as to this device's suitability for antenna matching has sallied forth. Attenuators serve a limited purpose - Isolation. They serve this well when they don't introduce uncontrolled error. They also serve as range extenders as do directional couplers, often with attenuators paired with them. In the case of using them with couplers, they insure port isolation by insuring port loading. They buffer any deviance from an expected 50 Ohm load that may be presented by monitoring gear attached through them to that port. This is by and large the context of the mini circuits links you offered. The extent of this "insurance" can be observed by computing how much load is presented to the affected instrument when the attenuator is left open, or shorted. T or PI configurations show a higher tolerance. An L Pad is a special case (less general form) of either T or PI, being that one of the three elements is replaced with either a short or an open. 73's Richard Clark, KB7QHC |
#7
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On Wed, 22 Dec 2004 00:19:12 +0000, Ian Jackson
wrote: What works better? Hi Ian, In following up the links that you provided, there is a superior reference found at the same site: http://www.minicircuits.com/appnote/an70001.pdf which in turn leads to a treasure trove on the topic that supports my favorite discussion on Mismatch Uncertainty. By following the links, they offer you articles and software to compute the accumulation of errors (and loss) found in mismatched sources looking at mismatched loads. A notable quote: "A fixed attenuator can help to lower the VSWR of cascaded (connected) components by providing isolation between the impedances, effectively masking the impedance mismatches." For both mismatched source and load, one handy shortcut offered is that the system suffers a SWR that is not the aggregation of the two, but the multiple of the two. This is not particularly significant for a source SWR of 2 seeing a load SWR of 2 (same result of 4 for either addition or multiplication), but above this value and loss begins to climb dramatically. 73's Richard Clark, KB7QHC |
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