No, I connected it directly to the siggen, because it declares to have 50-oms impedance.
Also practically, it makes things worse. The difference is evident also with the spectrum analyzer. Maybe it is simply defective. I would like to modify it as an adapter Twinax to BNC, but it is sealed and cannot be open. I am preparing a document to summarize all what I learned from this for me very interesting discussion. > Il giorno 13 ott 2024, alle ore 01:13, Bob Camp <kb...@n1k.org> ha scritto: > > Hi > > A properly done balun should give you a significant improvement in the > measured sensitivity. > > Ok since we’ve been around a bit on this … .what test method? > > 1) Test the radio straight out of a typical signal generator with no “stuff” > between the radio and the generator > > VS > > 2) Test things the same way, but put in the balun. > > If the balun is properly done *and* it’s hooked up right … 2 should be > noticeably better than 1. > > One note: some of these “adapters” are resistor based rather than having a > balun in them. That’s not the same thing. > > Keep in mind that this may not be the best thing to do overload wise, it only > is “best” if you are after sensitivity. > > Bob > >> On Oct 12, 2024, at 2:43 PM, Ing. Giovanni Becattini >> <giovanni.becatt...@icloud.com> wrote: >> >> Hi Jim, >> I am better and did the test you suggested me. The reduction is exactly 2 dB >> on the R-390A meter, with or without the DA-124 on the unbalanced antenna. >> >> Regarding the balun theme, who sold me the 390 gave me also a little balun: >> practically a twinax to bnc adapter with a fatter body. It is marked as >> specific for the 390, but with it things go much worse: more noise and less >> sensitivity. >> >>> Il giorno 12 ott 2024, alle ore 01:13, Jim Whartenby <old_ra...@aol.com> ha >>> scritto: >>> >>> Jacque , Gianni and Bob >>> Sorry for being a bit late in continuing the discussion. Life gets in the >>> way. >>> >>> In my zeal to solve for the attenuation of the DA-121, I should not have >>> combined the SG impedance with the DA-121. That would be fine for DC >>> circuit analysis but not for a transmission line. My apologies. >>> >>> I found this nifty calculator that will solve for the resistor values for >>> every type of resistive attenuator. See: >>> https://k7mem.com/Res_Attenuator.html >>> >>> I entered the following values: Z1 = 50 ohms, Z2 = 125 ohms and an >>> attenuation of 9 dB. It spit out the exact values for the resistors used >>> in the DA-121. The series resistor on the SG side of the shunt resistor is >>> less then a 1/4 ohm so it has little effect so it was obviously omitted in >>> the DA-121. The 5% resistor values given are again exactly those used in >>> the DA-121. The calculator also solves for 1% resistor values. >>> >>> 9 dB is the minimum attenuation that returns positive resistor values and >>> does the conversion from 50 ohms to 125 ohms. Any attenuation below 9 dB >>> returns a negative resistor value for R1, the series resistor on the SG >>> side of the shunt resistor. >>> >>> As Bob mentioned in a separate email, a balun would be the modern solution >>> if the ferrite core is capable of operating over the whole range of the >>> R-390. My balun experience is limited so I do not know which ferrite >>> material will do the job. >>> Regards, >>> Jim >>> >>> Logic: Method used to arrive at the wrong conclusion, with confidence. >>> Murphy >>> >>> >>> On Tuesday, October 8, 2024 at 10:30:33 AM CDT, Jacques Fortin >>> <jacque...@videotron.ca> wrote: >>> >>> >>> Hello Gianni, >>> PLEASE READ MY COMMENTS IMBEDDED IN YOUR TEXT BELOW. >>> I USE THE UPPERCASE TEXT BECAUSE EVERY OTHER FONT ATTRIBUTE IS CLEARED UP >>> BY THE FORUM SERVER. >>> >>> 73, Jacques, VE2JFE in Montreal >>> >>> Hi Friends, forgive the savage who tries to understand how the clock works >>> :) >>> What you Bob say is exactly what I would like to understand, i.e., if the >>> incredibly high sensitivities I heard are real or fantasy. >>> Let's imagine that we are in a perfect word and neglect the frequency >>> effect. >>> All the discussion started, from my side, to determine the attenuation >>> factor of the DA-121. So I try to better focus my questions: >>> >>> 1) if I have a siggen with 50 ohm output and an rx with 50 ohm input, is it >>> correct to say that the voltage at the receiver’s input is that pointed out >>> by the generator’s knob? >>> >>> EXACT: MOST GENERATORS INDICATES THE OUTPUT VOLTAGE WHEN THE EXTERNAL LOAD >>> IS EQUAL TO THE INTERNAL OUTPUT IMPEDANCE. >>> (MAXIMUM POWER TRANSFER CASE) WHICH MEANS 50 OHMS FOR MOST OF THE AMERICAN >>> STUFF BUT 75 OHMS FOR THE OLD BRITISH ONES. >>> SOME HAVE ALSO (LIKE MY OLD TRUSTY HP 8657A) A SETTING THAT INDICATES THE >>> "UNLOADED" OUTPUT VOLTAGE AS THE EMF (ELECTROMOTIVE FORCE) VALUE. >>> TO BE CLEAR, WITH A "NORMAL" RF GENERATOR SET TO DELIVER 10mV IN A 50 OHMS >>> LOAD, THE INTERNAL "EQUIVALENT" GENERATOR IS A 20mV SOURCE IN SERIES WITH A >>> 50 OHMS RESISTOR (THE THEVENIN EQUIVALENT OF THE SOURCE, IF YOU LIKE). >>> >>> 2) in this specific case, I have a black box, constituted by the DA-121 >>> (68/100 ohm) and the R-390. It seems that from the generator’s point of >>> view it is equivalent to a rx with 50 ohm input impedance. So, if I set the >>> generator for 10 mV output, I have 10 mVrms at the 68 ohm resistor. Right? >>> >>> NOT EXACTLY: IF THE OUTPUT OF THE DA-121 IS UNLOADED, 11.525 mV WILL APPEAR >>> ACROSS THE 68 OHMS RESISTOR AND THE THEVENIN EQUIVALENT OF THE DA-121 >>> OUTPUT WILL BE A 11.525 mV SOURCE IN SERIES WITH A 128.81 OHMS RESISTOR. >>> WITH THE DA-121 OUTPUT LOADED BY A 125 OHMS RESISTOR, THE VOLTAGE ACROSS IT >>> WILL BE 5.676 mV. >>> COMPARED TO THE GENERATOR "SET" VALUE OF 10mV, THIS IS 4.919 dB lower. >>> >>> 3) if above is right, the effective voltage at the receiver’s input (125 >>> ohm) is the voltage at the 68 ohm reduced by the divider made by 100+125 >>> ohm. Right? >>> >>> RIGHT, IN ALL CASES. >>> >>> If so, the loss factor of the DA-121 is 3 dB ( Vin x .56). >>> 20 log (.56) = - 5 dB, not 3 dB.... >>> >>> This can be practically tested, and the voltage at the 125 ohm resistor I >>> am using instead of the R-390 for simplicity is exactly 0.56 Vin (this is >>> true also for DC). >>> >>> PRETTY CLOSE TO THE THEORICAL VALUE, RIGHT. >>> >>> This above is what I can suppose by myself but I understand you are >>> explaining to me that it is wrong. >>> >>> But If you are right, the DA-121 should have a 9 dB loss factor, and this >>> seems to be completely denied from the practical experience. Again, forget >>> the frequency effect until this point. >>> >>> SAY 4.9dB LOSS. >>> BUT IF THE DA-121 68 OHMS RESISTOR IS REPLACED BY A 50 OHMS ONE, THE GLOBAL >>> ATTENUATION (REAL OUTPUT AT THE 125 OHMS LOAD VS THE SG SETTING) WILL BE 6 >>> dB LOWER (0.5) AND THE DA-121 OUTPUT IMPEDANCE WILL BE 125 OHMS ALSO >>> (MAXIMUM POWER TRANSFER CASE). >>> >>> >>> Thanks for your patience :) >>> >>> Gianni >>> >>> >>> >>> >>> > Il giorno 8 ott 2024, alle ore 14:58, Bob Camp <kb...@n1k.org >>> > <mailto:kb...@n1k.org>> ha scritto: >>> > >>> > Hi >>> > >>> > Another wrinkle in this: >>> > >>> > If your generator is set to 1 uV, that should mean you get 1 uv across a >>> > 50 ohm load on the generator. The impedance at that point is 25 ohms (50 >>> > ohms for the load in parallel with 50 ohms from the generator). >>> > >>> > If your receiver happens to be a high impedance input (as many are ….) >>> > you get 2 uV at the input to the radio and the impedance is 50 ohms. >>> > >>> > Maybe take out some random load resistor and you just doubled the >>> > sensitivity. >>> > >>> > Why would you do this? (though maybe not at HF …) >>> > >>> > When you go from 25 ohms to 50 ohms, the thermal noise from the >>> > resistor(s) goes up by 3 db. Your signal went up by 6 db. You are now 3 >>> > db further above the thermal noise floor. >>> > >>> > Not a big deal on the typical HF setup. It is a big deal as you go up in >>> > frequency. Yes this makes some other things you do up there “fun” …. Even >>> > at HF, folks racing to get that 0.001 uV sensitivity number (or some >>> > equally absurd number) probably are doing this as well. >>> > >>> > So: counting on this or that radio to supply a matched input …. maybe not >>> > a good idea without testing out the specific radio at the operating >>> > frequency. >>> > >>> > Bob >>> > >>> > >>> > >>> >> On Oct 8, 2024, at 3:31 AM, Ing. Giovanni Becattini via R-390 >>> >> <r-390@mailman.qth.net <mailto:r-390@mailman.qth.net>> wrote: >>> >> >>> >> Hi Jim, >>> >> >>> >> I am not sure I can follow you. As I told, I am not using the R-390A but >>> >> just a 125 ohms resistor as a terminator. >>> >> >>> >> So: >>> >> 68 // 225 = 52.21 (seen from the generator) >>> >> >>> >> The voltage on the rx is then the siggen’s output voltage divided by >>> >> 100+125, i.e. Vin x 0.556. In dB, 3 dB, that is what I wanted to know. >>> >> >>> >> I tested that also in DC, with the same results. Luckily for this time >>> >> practice and theory are completely in accord. >>> >> >>> >> Things could be different increasing the frequency, obviously, and using >>> >> the real R-390A, but in my case, @ 7.5 MHz, they are rather similar. >>> >> >>> >> Am I wrong? >>> >> >>> >>> Il giorno 7 ott 2024, alle ore 22:28, Jacques Fortin >>> >>> <jacque...@videotron.ca <mailto:jacque...@videotron.ca>> ha scritto: >>> >>> >>> >>> Jim, I do not know if I can follow you correctly in your explanations >>> >>> below. >>> >>> How does this DA-121 adaptor is made ?? >>> >>> >>> >>> 73, Jacques, VE2JFE in Montreal >>> >>> >>> >>> -----Message d'origine----- >>> >>> De : r-390-boun...@mailman.qth.net >>> >>> <mailto:r-390-boun...@mailman.qth.net> <r-390-boun...@mailman.qth.net >>> >>> <mailto:r-390-boun...@mailman.qth.net>> >>> >>> De la part de Jim Whartenby via R-390 Envoyé : 7 octobre 2024 12:42 >>> >>> Cc : r-390@mailman.qth.net <mailto:r-390@mailman.qth.net> Objet : Re: >>> >>> [R-390] Official specs >>> >>> >>> >>> Well, mailman not only strips photos but also any changes in typeface >>> >>> so the larger type and bold letters are stripped as well. >>> >>> Logic: Method used to arrive at the wrong conclusion, with >>> >>> confidence. Murphy >>> >>> >>> >>> On Monday, October 7, 2024 at 10:53:50 AM CDT, Jim Whartenby via R-390 >>> >>> <r-390@mailman.qth.net <mailto:r-390@mailman.qth.net>> wrote: >>> >>> >>> >>> GianniComments in BOLD >>> >>> >>> >>> On Monday, October 7, 2024 at 02:43:53 AM CDT, Ing. Giovanni Becattini >>> >>> <giovanni.becatt...@icloud.com <mailto:giovanni.becatt...@icloud.com>> >>> >>> wrote: >>> >>> >>> >>> Hi Jim and thanks for your patience, but I still don’t understand. >>> >>> The generator sees 50 // (100+125), 50 // 225 = 52.22 ohm No, this >>> >>> should be 40.9 ohms not 52.22 ohms! R in parallel = 1/ (1/50 + 1/ >>> >>> 225) so 1/ (1/50 + 1/225) = 40.9 ohms or if you prefer >>> >>> >>> >>> >>> >>> product over sum = (50 X 225) / (50 + 225) = 11,250 / 275 = 40.9 >>> >>> ohms >>> >>> >>> >>> >>> >>> The result of two resistors combined in parallel will always be a lower >>> >>> value then the lowest of the two combined resistors. >>> >>> Going a step further, 40.9 ohms in parallel with the Signal Generator >>> >>> impedance of 50 ohms results in an impedance of 22.5 ohms so the SG now >>> >>> sees about half of the expected impedance. You can think of the SG as >>> >>> being a current source feeding a 50 ohm resistor. If the current >>> >>> source now sees half the expected impedance, the voltage output of the >>> >>> SG will now be half of the set voltage. >>> >>> >>> >>> Now applying the voltage divider rule to the series 100 ohm and shunt >>> >>> 125 ohm resistors, the voltage across the 125 ohm resistor will be the >>> >>> SG voltage X (125 / 225) = SG voltage X 0.55 We already know that the >>> >>> signal generator output is half of what the SG attenuator says so 0.5 X >>> >>> 0.55 = 0.27 so the output of the DA-121 is now approximately one fourth >>> >>> of the SG dial setting. >>> >>> I checked with the VOM using a 125 ohm terminator instead of the R-390A >>> >>> and read 52.4 ohm. You must have a wiring error! The DA-121 should >>> >>> read approximately 40.9 ohms at the SG terminals when the DA-121 output >>> >>> is terminated with 125 ohms. This is what was calculated above. If >>> >>> you now put a 50 ohm resistor across the DA-121 input, the resistance >>> >>> of the input to the DA-121 should measure approximately 25 ohms. >>> >>> To be sure that I was not tricked by the cables, I made the same test >>> >>> at 100 kHz with 10 mV and that below is what I read, again using the >>> >>> 125 ohm terminator on the oscilloscope side. >>> >>> Probably I am doing something wrong, but what? >>> >>> Your experimental data should closely agree with the math, it does >>> >>> not. There is at least a simple wiring error or the BNC to TWINAX >>> >>> adapter is not wired properly. As I mentioned in the email below, >>> >>> one of the TWINAX pins should be directly connect to the BNC center >>> >>> conductor, the other TWINAX pin should be directly connect to the >>> >>> shell of the BNC connector. There should not be any measurable >>> >>> resistance, ideally a short circuit for both ohmmeter readings. Can >>> >>> you verify this? Thanks again Gianni Regards, Jim >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> Il giorno 6 ott 2024, alle ore 17:05, Jim Whartenby <old_ra...@aol.com >>> >>> <mailto:old_ra...@aol.com>> ha scritto: >>> >>> Gianni >>> >>> >>> >>> >>> >>> There is something wrong with your measurements. They do not agree >>> >>> with the mathematical analysis. >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> Reducing the resistances of the DA-121 with the input resistance of the >>> >>> R-390 to a single resistance results in the total resistance seen by >>> >>> the SG of 25 ohms. So the generator output should fall from 10 mV to 5 >>> >>> mV which you confirm although there is an error of some 14% ((5.7 mV - >>> >>> 5 mV) / 5 mV). But as you say, the resistors are not perfect. >>> >>> >>> >>> >>> >>> What is apparently the problem is that your adapter from BNC to TWINAX >>> >>> does not measure correctly. One TWINAX pin should connect to the BNC >>> >>> center pin and the other TWINAX pin should connect to ground. If this >>> >>> does not happen, the second voltage divider, the 100 ohm in series with >>> >>> the 125 ohm is not connected to ground. This error would give you the >>> >>> voltage that you measure. >>> >>> >>> >>> >>> >>> There is agreement between us that when the 68 ohm resistor is >>> >>> connected to the SG that the output will fall from 10 mV to about 5 mV. >>> >>> Putting the two remaining resistors into the circuit results in a >>> >>> series 100 ohm resistor and a parallel 125 ohm resistor. Applying >>> >>> voltage divider analysis to this we have (5 mV X 125 ohms) / 225 ohms) >>> >>> which equals 2.28 mV. 2.28 mV divided by 10 mV gives a ratio of 0.23 >>> >>> which is in agreement with the DA-121 reducing the SG output from 10 mV >>> >>> to 2.5 mV or 4:1. >>> >>> >>> >>> >>> >>> The above analysis agrees completely with figure 3, the analysis of a >>> >>> T-pad, which was done in the 1950s. It changes the SG impedance of 50 >>> >>> ohms to the receiver impedance of 72 ohms with a voltage loss of 4:1 >>> >>> which I again enclose in this email. >>> >>> >>> >>> >>> >>> Regards, >>> >>> >>> >>> Jim >>> >>> Logic: Method used to arrive at the wrong conclusion, with >>> >>> confidence. Murphy >>> >>> >>> >>> On Sunday, October 6, 2024 at 01:46:02 AM CDT, Ing. Giovanni Becattini >>> >>> <giovanni.becatt...@icloud.com <mailto:giovanni.becatt...@icloud.com>> >>> >>> wrote: >>> >>> >>> >>> Hi Jim,Setting rge SG to 10 mV I have1) with no terminator >>> >>> oscilloscope side: 20 mV2) with 50-ohm terminator: 10 mV3) with >>> >>> DA-121 no terminator: 11.4 mV4) with DA-121 and 125 ohm terminator >>> >>> (which simulates the receiver): 5.7 mV >>> >>> >>> >>> exactly as I would expect. Now I am going to pickup another generator >>> >>> to see if it behaves like the 8640. In the afternoon I tell you the >>> >>> result of the test. >>> >>> YoursGianni >>> >>> >>> >>> Il giorno 6 ott 2024, alle ore 00:00, Jim Whartenby <old_ra...@aol.com >>> >>> <mailto:old_ra...@aol.com>> ha scritto: >>> >>> >>> >>> Giovanni >>> >>> >>> >>> If you measure twice the voltage with no load on the SG then the actual >>> >>> voltage when the SG is properly loaded with a 50 ohm termination, what >>> >>> does the meter read when you put a 25 ohm resistor on the SG output? >>> >>> It should now read a third of the unterminated SG voltage. >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> Enclosed is page 51 of the Measurements catalog. Figure 3 shows a T >>> >>> pad to match 50 ohms to 72. The resistor values are chosen to reduce >>> >>> the SG output voltage by half at the input to the T pad and to 1/4 at >>> >>> the output of the T pad when the T pad is terminated with a 72 ohm >>> >>> resistor. >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> The same is done with the DA-121 but the impedance transformation is >>> >>> now from 50 to 125 ohms. Can you measure the voltages at the output of >>> >>> the SG with an oscilloscope? It should be 2X of the SG meter reading >>> >>> with no load on the SG, 1X with a 50 ohm load and 1/4X of the SG meter >>> >>> at the output of the DA-121 when the DA-121 is terminated with a 125 >>> >>> ohm non inductive resistor in place of the R-390A. If you do not >>> >>> terminate the DA-121 with a 125 ohm load then what you report as 0.56 >>> >>> of the SG meter reading would be correct. >>> >>> >>> >>> Regards, >>> >>> >>> >>> Jim >>> >>> >>> >>> >>> >>> Logic: Method used to arrive at the wrong conclusion, with >>> >>> confidence. Murphy >>> >>> >>> >>> On Saturday, October 5, 2024 at 03:14:58 PM CDT, Ing. Giovanni >>> >>> Becattini <giovanni.becatt...@icloud.com >>> >>> <mailto:giovanni.becatt...@icloud.com>> wrote: >>> >>> >>> >>> Thanks for replying, I am very intrigued by this theme. >>> >>> See below please and tell me your opinion. >>> >>> >>> >>> >>> >>> Il giorno 5 ott 2024, alle ore 20:33, Jim Whartenby via R-390 >>> >>> <r-390@mailman.qth.net <mailto:r-390@mailman.qth.net>> ha scritto: >>> >>> Giovanni >>> >>> >>> >>> I need some clarifications. >>> >>> >>> >>> 1) You said: "It attenuates the signal voltage of 0.56 V, i.e. 5 dB."So >>> >>> the Signal Generator (SG) meter indicates that the output voltage is >>> >>> 0.56 volts or are you are measuring 0.56 volts at the output of the >>> >>> DA-121/U when the SG meter reads 1 volt? If so, how are you measuring >>> >>> this voltage? Is it peak or peak to peak or RMS? The assumption here >>> >>> is that it is RMS. >>> >>> I wrote wrongly; I meant that the DA-121 is a voltage divider that, >>> >>> considered 125 ohm the input impedance of the receiver, multiplies the >>> >>> siggen voltage x 0.56. >>> >>> >>> >>> 2) The DA-121/U contains two resistors, a 68 ohm resistor in >>> >>> parallel with the signal generator output and a series 100 ohm >>> >>> resistor to the center pin of the BNC output connector. You are >>> >>> then adapting the BNC output connector of the DA-121/U to TWINAX and >>> >>> then connecting it to the balanced RF input connector on the back of >>> >>> the R-390A, correct? Yes >>> >>> >>> >>> 3) What are the two resistor values in the DA-121 when you measure with >>> >>> your DMM? How close are they to what is expected? I am guessing that >>> >>> these two resistors are carbon composition and are a bit off in value. >>> >>> It is interesting to note that carbon composition resistors will change >>> >>> value when soldered into a circuit. No, it is not the original, I built >>> >>> it with new components. >>> >>> >>> >>> 4) When you measure the BNC to TWINAX adapter, one of the TWINAX pins >>> >>> goes to the center pin of the BNC connector and the other TWINAX pin >>> >>> goes to ground? Yes Both read close to zero ohms? each other yes, but >>> >>> they are open to ground. >>> >>> >>> >>> 5) How old are the coax cables used in your measurements? In other >>> >>> words, how lossy are they? Coax ages so the cable losses will increase >>> >>> and it will have an affect on your measurements. The coax is 50 ohms? >>> >>> Yes, they are normal BNC/BNC, 1 meter long, with 50 ohm cable, bought >>> >>> new ready to be used. >>> >>> >>> >>> The way I see it, 50 ohms in parallel with 68 ohms = 29 ohms. 29 ohms >>> >>> in series with 100 ohms = 129 ohms which is approximately your >>> >>> impedance transformation needed from 50 to 125 ohms. Because of the 68 >>> >>> ohms is in parallel with the SG output, the voltage at this point >>> >>> should be half of what the SG meter indicates. I am not sure it is so. >>> >>> The siggen indicated voltage is in Vrms and it is true when you have a >>> >>> 50 ohm load. If you don’t have the 50 ohm load, the voltage is double. >>> >>> I am sure of this, I tested more times with different generators and >>> >>> oscilloscopes. >>> >>> >>> >>> >>> >>> The second voltage divider of 100 and 125 ohms is again reducing the SG >>> >>> output voltage by another half so the actual voltage applied to the >>> >>> receiver is 0.5 X 0.5 or 0.25 times the SG meter reading. In other >>> >>> words, actual voltage applied to the R-390A receiver is 1/4 of what the >>> >>> SG meter indicates or 12 dB down. No, I am sure of 0.56. In the doubt, >>> >>> I built a 125 ohm terminator and checked with the oscilloscope. >>> >>> Starting with 10 mVrms I read 5.7 mVrms because the resistors are not >>> >>> perfect. And thus reduces the voltage by 5 dB. Do you agree? >>> >>> >>> >>> So what this means to the original discussion is that the 6.5 microvolt >>> >>> limit in the R-390A specification is actually 1.6 microvolts that is >>> >>> applied to the R-390A balance RF input for a 10 dB S+N/N reading when >>> >>> all of the losses in the test setup are accounted for. So the spec has >>> >>> simplified the measurement and eliminated all of the above math. >>> >>> Again, spec is spec and those who wrote it knew what they were doing. >>> >>> >>> >>> This back of the envelope analysis does not agree with what you have >>> >>> measured. I am interested in what you find when you have a chance to >>> >>> take a closer look. >>> >>> >>> >>> Jim >>> >>> >>> >>> Logic: Method used to arrive at the wrong conclusion, with >>> >>> confidence. Murphy >>> >>> >>> >>> On Saturday, October 5, 2024 at 01:48:09 AM CDT, Ing. Giovanni >>> >>> Becattini <giovanni.becatt...@icloud.com >>> >>> <mailto:giovanni.becatt...@icloud.com>> wrote: >>> >>> >>> >>> Hi Jim and thanks for your reply. I read the very interesting document >>> >>> you pointed out. I did not understand everything, but for my practical >>> >>> interest it confirms that the impedance matching is mandatory. >>> >>> I am using an HP8640B as a signal generator. Let’s suppose it is >>> >>> ideally calibrated. I use also the DA-121/U impedance adapter which >>> >>> shows 50 ohm to the siggen and 125 to the receiver. It is the fourth >>> >>> type of pad of figure 4 of the article. >>> >>> My practical question is how to take in account the DA-121? >>> >>> It attenuates the signal voltage of 0.56 V, i.e. 5 dB. So, >>> >>> - in volts: the voltage value for the 10 dB S/N I read on the >>> >>> generator’s scale should be multiplied by 0.56. >>> >>> - in dBm: the dBm value for the 10 dB S/N I read on the generator’s >>> >>> scale should be reduced by 5 dBm. >>> >>> >>> >>> Is this correct? >>> >>> Thanks >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> ______________________________________________________________ >>> >>> R-390 mailing list >>> >>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>> >>> Help: http://mailman.qth.net/mmfaq.htm >>> >>> Post: mailto:R-390@mailman.qth.net >>> >>> >>> >>> This list hosted by: http://www.qsl.net <http://www.qsl.net/> Please >>> >>> help support this >>> >>> email list: http://www.qsl.net/donate.html >>> >>> ______________________________________________________________ >>> >>> R-390 mailing list >>> >>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>> >>> Help: http://mailman.qth.net/mmfaq.htm >>> >>> Post: mailto:R-390@mailman.qth.net >>> >>> >>> >>> This list hosted by: http://www.qsl.net <http://www.qsl.net/> Please >>> >>> help support this >>> >>> email list: http://www.qsl.net/donate.html >>> >>> >>> >>> ______________________________________________________________ >>> >>> R-390 mailing list >>> >>> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>> >>> Help: http://mailman.qth.net/mmfaq.htm >>> >>> Post: mailto:R-390@mailman.qth.net >>> >>> >>> >>> This list hosted by: http://www.qsl.net <http://www.qsl.net/> Please >>> >>> help support this >>> >>> email list: http://www.qsl.net/donate.html >>> >> >>> >> ______________________________________________________________ >>> >> R-390 mailing list >>> >> Home: http://mailman.qth.net/mailman/listinfo/r-390 >>> >> Help: http://mailman.qth.net/mmfaq.htm >>> >> Post: mailto:R-390@mailman.qth.net >>> >> >>> >> This list hosted by: http://www.qsl.net <http://www.qsl.net/> Please >>> >> help support this >>> >> email list: http://www.qsl.net/donate.html >>> > >>> >>> >> > ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:R-390@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
