This is another one of those subjects that seems to have advanced on rumor and inuendo. Actually measuring in-band IMD is not as simple as it looks. Basically (whether included on a single chassis or not) the apparatus must be able to generate a pair of signals which are combined in a way that precludes IMD in the test signal to start with. Then the frequencies must be set so that A, B, 2A-B, and 2B-A are all inside the passband, (inside the roofing filter for the K3 with dsp bandwidth set to match) .
Hams without a laboratory grade hamshack are not reliably equipped to run this, hence the lack of specific reports that such and such ran a test on K3 serial number, obtaining xxxx results using such and such equipment, such and such a hookup and such and such procedure. Note that measuring the outside the bandpass kinds of IMD is now popularly left to a relatively few reputable labs who have a good deal at stake maintaining their independent reputations and procedures, such as Sherwood or ARRL. There are reasons for handing off this task: the difficulty of the task, to get measurements free of private agendas and to eliminate vigilante mob mentality deprecation of commercial products without hard accurate facts to back up accusations. And unfortunately, there are those who will author text on the internet just to cause consternation and get a response (trolls) even if what they are writing technically is libel. I for one would like to see some hard lab-grade facts on the existence or non-existence of this "problem". 73, Guy. On Thu, Jan 14, 2010 at 4:55 AM, Geoffrey Mackenzie-Kennedy <[email protected]> wrote: > Randy, > > It sounds as though this "fellow" is talking about the *In Passband* IMD > performance of a receiver, usually expressed in terms of 3rd Order Dynamic > Range when BOTH test signals are inside the receiver's passband. This > information can provide, for example, a useful indication of how a receiver > will cope in a "No Split" pile-up situation with non-stop callers inside the > passband. > > The ARRL does not publish this information in their regular reviews, but > have in their expanded test results for some receivers - the K2 being one > example. > > 73, > Geoff > GM4ESD > > > Randy Downs wrote on Wednesday, January 13, 2010 at 9:25 PM: > > > >> I'm a bit confused about an email I received. A fellow said "The >> TS870S is probably still in your shack because of its INBAND IMD >> performance. The ARRL does not do the inband IMD test anymore. Many of >> the complaints about the K3's receiver is related to its poor inband >> IMD performance. However there is various opinions on this." >> What is he referring too? I'm not aware of this issue.Randy >> K8RDD > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
