All: If it jumps up when you switch PreAmp gain settings, then disappears, what you are seeing is the "DC Spike" that is characteristic of the QSD type of receiver. It is there on all OS, you just didn't notice it before. If you are SSB or CW it is below your red line "zero beat" frequency by the amount of the IF. You can move it relative to your "zero beat" frequency by adjusting the IF frequency.
It is basically Local Oscillator (the DDS) bleed through the QSD, which is a form of balanced mixer. If you know about balanced mixers, they normally only null the LO to about -40 dB. To get it into the noise floor, you are watching a software subroutine actively nulling it to about -120 or -130 dB. Ask anyone who has built a balanced mixer, if they know how to null the LO to more than 100 dB down. :-) It just takes the subroutine a few seconds to respond to a gain (level) change and drive the null back to the noise floor. Likewise it will appear during a transition from transmit to receive for a second or so, then melt away. This is totally normal for a QSD receiver. --- Graham == On Mon, Jul 12, 2010 at 8:55 AM, DL1FUX <[email protected]> wrote: > Ups, > > I changed my OS from Vista32 to XP Prof. and now I do have this spur, too. > Direct after release of ptt or changing preamp settings it goes up about 20 > - 30 dB above noise level and falls down within 3 seconds. > Changing IF to 0 Hz puts it direct on the red line. SR does eliminate it > totally. > > I did not notice it unter Vista. > > 73, martin dl1fux > > Am 12.07.2010 14:56, schrieb Tim Ellison: > > That is probably the DDS "0 IF noise". >> >> >> -Tim >> ----- >> W4TME >> >> >> -----Original Message----- >> From: [email protected] [mailto: >> [email protected]] On Behalf Of David McKenzie >> Sent: Sunday, July 11, 2010 11:50 PM >> To: flexedge >> Subject: [FlexEdge] Flex-1500 spur >> >> Hi, >> >> On my Flex-1500, I have a spur at about -3500 at all times. Changing the >> preamp setting makes it stronger/weaker for a short amount of time when >> switching from 0 to +30 to 0, then settles back down. Anyone else see >> this? >> Seems most noticeable on quiet bands, at around -120. Doesn't appear to be >> anything in the shack. >> _______________________________________________ >> > _______________________________________________ Flexedge mailing list [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexedge_flex-radio.biz This is the FlexRadio Systems e-mail Reflector called FlexEdge. It is used for posting topics related to SDR software development and experimentalist who are using alpha and beta versions of the software.
