Re: [Elecraft] Down-conversion
Bruce, I believe that your suspicion is correct. The sticking point in the design of a high performance up-conversion receiver at this time is the first LO, whose phase noise must be suitably low and whose cost is acceptable. There can be problems with VHF Roofing filters, but there are ways to overcome these. Regarding the use of very narrow roofing filters (crystal) in a down-conversion receiver, there is an underlying filter generated IMD problem which might or might not affect the IMD performance of the overall receiver - depending upon the IMD performance of those parts of the receiver ahead of and behind the filter. The problem is that for any given quality of quartz used in the crystals, the IMD performance of a crystal filter can be shown to worsen as the filter's bandwidth narrows. I suspect that the 6 kHz roofing filter used in Kenwood's TS-590S ahead of the IF crystal filters is there to give some protection to the narrower IF filters. 73, Geoff GM4ESD Bruce McLaughlin wrote on Wednesday, November 17, 2010, at 11:02 PM: I suspect it is going to become the standard for many if not most of the new radios. As soon as it became apparent that effective roofing filters can really improve the close in IMD performance, it seems as if a low first IF frequency has become almost mandatory. I note that the Orion and the new Yaesu FT 5000 both use down conversion for the first IF and, therefore, have effective narrow roofing filters. I wonder when, or if, ICOM and the others will follow suit. snip __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Down-conversion
That is why we built special test fixtures for us and INRAD to test strong signal IMD handling on all of our K3 filters. 73, Eric On 11/18/2010 4:49 AM, Geoffrey Mackenzie-Kennedy wrote: Bruce, I believe that your suspicion is correct. The sticking point in the design of a high performance up-conversion receiver at this time is the first LO, whose phase noise must be suitably low and whose cost is acceptable. There can be problems with VHF Roofing filters, but there are ways to overcome these. Regarding the use of very narrow roofing filters (crystal) in a down-conversion receiver, there is an underlying filter generated IMD problem which might or might not affect the IMD performance of the overall receiver - depending upon the IMD performance of those parts of the receiver ahead of and behind the filter. The problem is that for any given quality of quartz used in the crystals, the IMD performance of a crystal filter can be shown to worsen as the filter's bandwidth narrows. I suspect that the 6 kHz roofing filter used in Kenwood's TS-590S ahead of the IF crystal filters is there to give some protection to the narrower IF filters. 73, Geoff GM4ESD Bruce McLaughlin wrote on Wednesday, November 17, 2010, at 11:02 PM: I suspect it is going to become the standard for many if not most of the new radios. As soon as it became apparent that effective roofing filters can really improve the close in IMD performance, it seems as if a low first IF frequency has become almost mandatory. I note that the Orion and the new Yaesu FT 5000 both use down conversion for the first IF and, therefore, have effective narrow roofing filters. I wonder when, or if, ICOM and the others will follow suit. snip __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Down-conversion
Thanks Georges, Interesting thoughts. 73, Arie PA3A __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Down-conversion
I suspect it is going to become the standard for many if not most of the new radios. As soon as it became apparent that effective roofing filters can really improve the close in IMD performance, it seems as if a low first IF frequency has become almost mandatory. I note that the Orion and the new Yaesu FT 5000 both use down conversion for the first IF and, therefore, have effective narrow roofing filters. I wonder when, or if, ICOM and the others will follow suit. By the way, thank you so much for the new APF feature. I think that was something which was missing from the K-3 up until now. I have always found that filter to be helpful in trying to hear very weak CW signals, especially if the band is noisy. I have had good luck with it on my FT 1000D and I missed it on my K-3s. Fortunately it is no longer missing and already I found it to be very helpful. I guess I was lucky in that I really noticed no problems with version 2.17 but I'm glad to see the update to that which I have installed on one of my K-3s and it seems to be working very well. Bruce-W8FU -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Wayne Burdick Sent: Tuesday, November 16, 2010 6:32 PM To: Elecraft Reflector Subject: Re: [Elecraft] Down-conversion __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Down-conversion
Bruce, there is a limit on the upper signal frequency based on the I.F. chosen and how good one can make the input filter in order to have adequate image frequency rejection while avoiding excessive filter loss. AFAIK, up conversion became popular as a way to cover the VLF frequencies and avoid any tuning gaps (such as the K3 has between 8 and 9 MHz) by putting the first I.F. up above the highest tuning range. That wasn't practical in the past (esp. with vacuum tubes) because mixers and amplifiers with low noise figures needed more protection from very strong signals. But with more robust devices it became practical. Even so, the best performance occurs with down conversion as it always has. Ron AC7AC -Original Message- I suspect it is going to become the standard for many if not most of the new radios. As soon as it became apparent that effective roofing filters can really improve the close in IMD performance, it seems as if a low first IF frequency has become almost mandatory. I note that the Orion and the new Yaesu FT 5000 both use down conversion for the first IF and, therefore, have effective narrow roofing filters. I wonder when, or if, ICOM and the others will follow suit. Bruce-W8FU -Original Message- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Wayne Burdick Sent: Tuesday, November 16, 2010 6:32 PM To: Elecraft Reflector Subject: Re: [Elecraft] Down-conversion __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] Down-conversion
Of course we didn't invent it. But we appear to have helped resuscitated it :) It was the only choice, as far as we were concerned, to achieve our performance goals. Wayne N6KR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
