Hi All, I noticed an issue where I have distortion on my SSB tx audio when the drive level is reduced. I wonder if this is related to the PSK31 users who noticed increased IMD on their tx with drive level reduced.
Flex 5000A Firmware 1.3.0.8 Windows 7 x64 Ultimate Firewire driver 3.5.0.7171 PowerSDR 1.18.2, 1.18.5 and 1.18.6 (tested with different versions, including one version prior to the ALC overshoot improvements) RE-27 mic with W2IHY EQ & EQ Plus into balanced line in. TX bandwidth is 50 - 3050 Hz. Using 192k and 2048 for sample rate and buffers. I drive an Icom PW-1 so I key in tune mode and adjust drive to show 1 KW out into dummy load. Resultant drive is 23. In SSB I set the drive to 23. I have balanced line mixer one noth down from top. I adjust mic gain to show -2 dBm on mic meter during tx. THis gives me 1 KW as shown on external peak reading meter. Audio has distortion on voice peaks and does not have good high frequency articulation. DIstortion is described as "fuzzies". Almost the same sound as RFI. Now before people assume it is RFI..... I bring the drive to 100 and drop the mic gain down to give 1 KW peak on external meter (same power out as previous step) and audio does not have the distortion. High end articulation is definitely improved as well. Also with the drive at 100 and mic gain reduced average power out is improved over previous settings. I have tested this above scenario with three other local Flex 5000A owners and they all have distortion introduced into the tx audio when the drive is lowered. It is more pronounced when drive is 25 or lower. All four of us have different model amplifiers (PW-1, ALS-600, Emtron DX-2SP, FL7000) My question is, what exactly does lowering the drive do? DOes it change PA or exciter bias? Change settings in the DSP? My concern is overdrive of the solid state amp and protection of the amp. With the drive at 23 I could not overdrive the amp and K5FR's DDUtil program allows the overdrive control to set maximum power out per band. Now if the audio is a little too high it can cause overdrive and potentially damage the amp. Thanks, Dave wo2x _______________________________________________ FlexRadio Systems Mailing List [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
