Hello Juan, Thanks for your e-mail. I will reply in full after I return home this evening, off-list if my answer is long.
The symptoms, and the cures suggested, strongly suggest that it is a well known type of IMD problem caused by the IF hardware - which includes the roofing filter. I understand the AGC recovery problem that you mention, but do you know if the in-passband IMD products of the FT1000MP were actually measured? To measure IMD products with both test signals inside a CW bandwidth passband usually requires crystal controlled generators for reasons of low phase noise, especially if the receiver's in-passband odd-order dynamic range is large. Increasing bandwidth to allow much wider spacings of the test signals usually paints a false picture, because the signal handling capability of narrow bandwidth crystal filters is usually worse than that of the wider filters. 73, Geoff GM4ESD On Sunday, February 07, 2010 at 12:57 PM, Juan EA5RS <[email protected]> wrote: Are you guys sure this is a frequency domain problem? Has anyone measured those IMD products under the mentioned conditions and concluded from the results that they are the culprit for the mushy (somewhat vague description) audio that makes impossible to copy the different callsigns? Some W6s measured in a lab test setup a similar effect on the FT1000MP years ago and found that the problem was the AGC recovering too fast (in between symbols) making all signals sound as loud as others. The solution was to increase the time constant. The loudest signal would then set the radio gain level. Then characters in-between from weaker signals sounded weaker making them distinct (or maybe buried). I cant think why you would ever need a recovery time constant any shorter than say 150 ms, while shorter time constants are normally used -reading Clifton I think the FAST setting in the K3 is 73 ms-. At 60 WPM, a dit is 20ms long if I am not mistaken, and an intersymbols spacing (7 time units) to full gain recovery seems the shortest time that would be necessary for the receiver to recover full gain. 73 de Juan EA5RS ______________________________________________________________ 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
