Nico Palermo, IV3NWV wrote: You are not replying my question, Bill. I've simply asked if you are able to listen to a -105 dBm with a + 7 dBm inteferer placed at a 2 kHz offset with your receiver.
You have two choices: 1) No, I can't. 2) Yes. I can. If the reply is #1 you should explain me why if the BDR of your receiver is declared to be 140 dB at 2 kHz spacing and you are not able to do handle a 111 dB signal dynamic range. If the reply is #2 I kindly ask you to provide me the proof and I will apologize with you. BTW, if in a real situation nobody would try to operate 2 kHz apart a strong CW signal, due to the clicks, what the ARRL Blocking Compression Gain test at 2 kHz is meant for? Is it for dummies? Don't you think that questioning the utility of the test while being so proud that your receiver is rated with that figure is a really poor argument? Can you briefly explain why you feel ARRL's definition of BDR below is not > correct? ...The blocking dynamic range is the difference between the level of the > noise floor from the level of undesired > signal that produces a 1 dB decrease in a weak desired signal... > I already know the ARRL definition. What "weak" means? Is it a signal at the MDS level, 20 dB stronger, or 50? Weak is not 1 foot, nor 2 inches/second. It is NaN, not a number. For DXers weak means S 8, for others it is right the MDS, for other it is the level of the least audible CW signal immersed in the noise, say 10 dB less than its power. If "weak" is meant to be S 8, be sure your receiver has a 140 BDR, as defined by the ARRL, but I kindly let you note that the difference between 10 dBm (the level of the interfering carrier that produce a 1 dB decrease in the weak signal in a receiver which has a sensitivity of -130 dBm) and -79 dBm (the weak S8 signal) is not 140 dB, but just 89 dB. Do the same test with a weak desired signal which is S 4 and let me know if you are able to measure the gain compression of your receiver or if instead you simply you are not, just because the phase noise of the LO is 20 dB higher and has already completely desensitized your equipment. In the case you are not able to do it, why do you claim that your receiver can handle a 140 dB dynamic range if it is not able to handle signal level differences which are much less? ###################################################### Nico I believe I finally understand your point. In simple terms, you're saying the K3's phase noise overrides close-spaced IMD and BDR performance. In this case, I completely agree with you, This has been a stumbling point that Rob Sherwood NC0B and Peter Hart G3SJX of RSGB have been making for many years now. Both Peter and Rob have used the term "phase noise limited" to tell us that phase noise is actually overriding close spaced measurements like IMD. What is truly important is the "Spurious-Free Dynamic Range" (G3SJX's term) which includes phase noise, BDR and IMD performance. SFDR is the worst case of all 3 factors, and phase noise will clearly override IMD or BDR results at close spacings in the K3. ARRL's relatively recent change in test procedure to use a narrowband spectrum analyzer to measure IMD is masking the actual SFDR result because it's using a narrow band filter to remove the phase noise component when making the measurement. Our brain/ear only has a ~50 Hz filter at best, so we will hear the phase noise in that 50 Hz bandwidth instead of the ~1 Hz (?) BW ARRL's spectrum analyzer uses. What good does it say we have extremely good IMD or BDR at close spacings if that performance is theoretical and does not represent what our ears hear? I agree it is misleading. I believe what you're actually saying is that Perseus has much better close-spaced phase noise than the K3, and ARRL's measurements of close-spaced IMD and BDR are imaginary numbers that do not represent what our ears will actually hear. In that case, I completely agree with you! Would you tell us how Perseus compares in the following phase noise performance? The following table is from a post by Eric WA6HHQ in September 2007. I've added the Flex 5000 based on measurements published after Eric's note: http://mailman.qth.net/pipermail/elecraft/2007-September/073931.html "Here are transmit composite phase noise numbers from the Lab for the K3. Needless to say, we are pleased with the results. :-) I've also included some numbers from the ARRL reviews for several late model rigs. Rig 1kHz 2 10 20 50 100 1M K3 -110 -119 -136 -140 -143 -144 -150 IC7800 -103 -112 -130 -138 -140 -140 -140 FT2000 -102 -105 -128 -129 -128 -128 -128 ORION 2 -121 -129 -126 -125 -118 -128 -138 OMNI 7 -102 -103 -120 -123 -127 -129 -126" F5000 -123 (same at all spacings de W4ZV) Perseus ? What I personally wish is that ARRL should do is go to a metric like SFDR which G3SJX has proposed. I believe this would be the most meaningful. It would show us the worst case of what our ears will hear from any of the spurious components at various spacings. I'm going on a little trip with my XYL for a few days now but will be interested to see your response about Perseus. Again, I agree with you that the close-spaced IMD and BDR results published by ARRL will be overridden by phase noise. 73, Bill W4ZV -- View this message in context: http://n2.nabble.com/K3---ADAT-ADT-200A-by-HB9CBU-tp1597981p1603484.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
