Hi Johhny, I'll probably get flamed for saying this, or someone more knowledgeable that I will point out how ignorant I am, but here is my layperson's understanding of this issue: Assuming a MDS of -128 dbm, and an S9 signal equivalent to -73 dbm, IMD will begin to be a problem when two out of passband signals combine as follows: IMDDR Signal causing IMD = Noise Floor 55 db S960 db S9 plus 5 db65 db S9 plus 10 db70 db S9 plus 15 db75 db S9 plus 20 db80 db S9 plus 25 db85 db S9 plus 30 db90 db S9 plus 35 db95 db S9 plus 40 db100 db S9 plus 45 db105 db S9 plus 50 db You can see that if your rig has an IMDDR of 90 db, it would take a signal S9 + 35 db before you would likely notice any adverse affects from IMD caused by two out of passband signals (at the required spacing). So, a person who has a rig with an IMDDR of say 95 db would only notice an improvement in the IMDDR when they are exposed to two out of band signals causing an IMD product when those signals are more than S9 plus 40 db. The question you need to ask yourself is, how often are you faced with that situation? The constant pursuit for improved IMD performance, it seems to me, is a worthy goal, but whether it benefits a particlar amature operator depends on whether he or she is faced with two out of passband signals that combine with the spacing required to cause an IMD product in his or her rig, AND the number of times those signals are sufficiently strong to exceed the IMDDR of their rig. For some contestants, this is a BIG factor, but for other folks it rarely matters. It all depends on your operating environment....
I'm am sure this is not 100 correct, as I am not an engineer, but you should get the general idea 73, Bob/AA6VB ______________________________________________________________ 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 Message delivered to [email protected]
