I can confirm; also with the Marconi 2022E I obtained the same results. In conclusion, with my R-390A got the following scores: symmetrical antenna: -107 dBm (1 µV), with the DA-121/U already taken into account; unbalanced antenna: -106 (1.12 µV) dBm; I did not include a loss factor for the DA-124 because the capacitive reactance of the 56 pF capacitor is negligible.
I was rather careful and repeated the tests many times, obtaining concordant results with +/- about 1 dBm. ------------ Hi Jim, Setting the SG to 10 mV I have 1) with no terminator oscilloscope side: 20 mV 2) with 50-ohm terminator: 10 mV 3) with DA-121 no terminator: 11.4 mV 4) 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. Yours Gianni  > Il giorno 6 ott 2024, alle ore 00:00, Jim Whartenby <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> 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> 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> 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 >> >> >> Il giorno 5 ott 2024, alle ore 05:13, Jim Whartenby via R-390 >> <r-390@mailman.qth.net> ha scritto: >> BobI don't know why you are speculating "Since you can use any signal >> generator" when MIL-R-13947B(SigC) on page 20 specifies the Measurements >> Corp Model 82 signal Generator, or it's equal. Your concern with matched >> impedances between the generator and the R-390 may appear to be valid but >> this seems to have been accounted for in the R-390 spec with higher input >> voltages to account for the mismatch losses. Collins and the Signal Corps >> specified the 125 ohm input impedance of the R-390 and they were surely >> aware that the standard impedance of high end signal generators was normally >> 50 ohms. >> >> Check out http://hparchive.com/Boonton/BRC-The-Notebook-03.pdf which is a >> 1954 Boonton Radio explanation for the use of Dummy Antennas. Everything >> you need is in the first four pages. It explains why the mismatch between >> 50 ohms and the receiver input impedance reduces the loading on the receiver >> input tuned circuits and recovers the Q of the receiver RF input tuned >> circuits. This also affects favorably the S+N/N measurement. There is a >> reason for the apparent madness. >> Jim >> >> Logic: Method used to arrive at the wrong conclusion, with confidence. >> Murphy >> >> On Friday, October 4, 2024 at 07:23:24 PM CDT, Bob Camp <kb...@n1k.org> >> wrote: >> >> Hi >> >> Based on a *lot* of interaction with DOD source inspectors over the years … >> it’s very much a “that depends” sort of thing. The guy you get this month >> may be *very* different than than the guy who comes in next month. >> >> Since you can use any signal generator, there is room for “trouble” with >> minimal specs. Typically the way this works out is a request to clarify >> things. Unfortunately that stuff does not get into the official specs. Yes, >> some of us have pointed that out as a problem …. never got addressed AFIK. >> >> Bob >> >> >> >> On Oct 4, 2024, at 5:19 PM, Jim Whartenby via R-390 <r-390@mailman.qth.net> >> wrote: >> >> Bob >> You are over thinking the testing. The generator is terminated but not in >> it's characteristic impedance. Collins and the agency letting the contract >> agreed on a test method and wrote it down in the test procedure. Anything >> that would affect the testing like VSWR has already been considered and >> accounted for. That Hams don't use the proper termination for the signal >> generator, according to the spec, which affects the perceived sensitivity is >> another issue. Spec is spec as they say. >> >> Not all Government Source Inspectors are knowable about the equipment that >> they are reviewing and putting their inspection stamp on. Not all Signal >> Corps equipment is inspected by Army GSIs. Every once in a while, Army >> equipment will have an anchor stamp on it and vice-versa. Sometimes certain >> specs are wavered if not considered critical, most often they are not. >> Again, spec is spec. >> Regards, >> Jim >> >> Logic: Method used to arrive at the wrong conclusion, with confidence. >> Murphy >> >> On Friday, October 4, 2024 at 02:43:36 PM CDT, Bob Camp <kb...@n1k.org> >> wrote: >> >> Hi >> >> Ok …. but ….. >> >> If it is simply a resistor, then the generator is unterminated. It’s >> designed and calibrated to run into a 50 ohm load. If all that’s there is a >> series resistor the generator is not properly set up (and thus not >> calibrated ….). Yes some generators deal with this better than others. >> >> My guess is that there’s more to the load circuit than just that resistor. >> Without a schematic …. who knows …. >> >> Bob >> >> >> >> On Oct 4, 2024, at 12:53 PM, Jim Whartenby via R-390 <r-390@mailman.qth.net> >> wrote: >> >> Bob >> But we do know what the interface is between the signal generator and >> antenna input. On document page 20, the balanced RF input is in series with >> a 125 ohm non-inductive resistor and the unbalanced RF input is in series >> with a 50 pF capacitor. Both interfaces do not include the generator's >> output impedance. >> >> As for the sensitivity not being what the R-390/URR or the R-390A/URR is >> capable of, well there are perhaps 100's of tests that the receiver must >> successfully pass before it is accepted. Tightening any of the specs to >> exactly what the receiver may be capable of passing will guarantee that no >> one receiver will ever pass all of the acceptance tests. Then there is the >> added problem of your test equipment's error tolerance and being traceable >> back to the NIST standards. Is your 10 microvolts from the signal generator >> really 10 microvolts? >> >> Unless otherwise stated, the specification calls out a value that the >> receiver must do better than. A sensitivity of just under 6.5 microvolts >> for a 10 dB S+N/N with an audio power output of 10 milliwatts seems >> reasonable over the range of 2 to 32 MHz for either balanced or unbalanced >> RF inputs. This is perhaps typical for just about all HF receivers built >> for the military, at least for what I am aware of, but I am sure that there >> will be the rare exception. >> >> Regards, >> Jim >> Logic: Method used to arrive at the wrong conclusion, with confidence. >> Murphy >> >> On Friday, October 4, 2024 at 09:39:26 AM CDT, Bob Camp <kb...@n1k.org> >> wrote: >> >> Hi >> >> The gotcah here is that we really don’t know what the interface between the >> signal generator and radio looked like for these official tests. Despite the >> document going into a lot of detail, they did not include a schematic or a >> part number. (or at least not one that I could find). There are a *lot* of >> ways they might have been doing things ….. >> >> Bob >> >> >> On Oct 4, 2024, at 10:19 AM, Ing. Giovanni Becattini via R-390 >> <r-390@mailman.qth.net> wrote: >> >> But when we perform the classical sensitivity test with a modulated signal, >> do we get the AM or CW value? >> >> Following the instructions I got a value of -104 dBm, i.e. 1.41 uV. Because >> I used the DA-121, the real value should be even better, far from 5 uV. And >> surely my R-390A is not as good as it could be . >> >> Is my reasoning correct? >> >> >> Il giorno 4 ott 2024, alle ore 16:13, Barry <n4...@knology.net> ha scritto: >> >> I don’t think of 1uV as “bad” but most of these radios will beat that. >> >> Thanks, >> Barry >> >> >> On Oct 4, 2024, at 8:55 AM, Ing. Giovanni Becattini via R-390 >> <r-390@mailman.qth.net> wrote: >> >> Wow, thanks! >> >> By the way, do you know why the sensitivity values were so bad? Are we the >> ones who are taking measures that are too lenient or are they the ones who >> were too conservative? >> >> Thanks again >> >> Gianni >> >> >> Il giorno 4 ott 2024, alle ore 15:37, Larry Haney <larry41...@gmail.com> ha >> scritto: >> >> Hi Gianni and Barry, Tom Marcotte and Al Tirevold (SK) obtained and cleaned >> up the specs for the 390A and put it on our website. Here's the link: >> mil-r-13947b– (r-390a.net) <https://www.r-390a.net/mil-r-13947b.pdf>. >> Unfortunately, the entry in References page indicates it is for the R390(), >> but it is also the the 390A. I will be changing that shortly. >> >> Regards, Larry >> >> >> On Fri, Oct 4, 2024 at 4:49 AM Ing. Giovanni Becattini via R-390 >> <r-390@mailman.qth.net <mailto:r-390@mailman.qth.net>> wrote: >> Have ever been released official specs for the 390A? >> >> The manuals report few data and neither too correct, for what I can >> understand (e.g., sensitivity) >> >> 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 <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 >> >> >> >> >> ______________________________________________________________ >> 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 >> >> >> ______________________________________________________________ >> 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 >> ______________________________________________________________ >> 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 >> >> >> >> ______________________________________________________________ >> 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 >> >> >> >> ______________________________________________________________ >> 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 >> >> >> ______________________________________________________________ >> 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 > > > <DA-121 calculation.pdf> ______________________________________________________________ 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
