Great detective work, Eric. That looks like the explanation! Rather than landing exactly on an FTW for 50.000 MHz, we're going to instead hit 50 MHz +/- 1.53 KHz.
Bob has mentioned there's an issue (with 200 MHz clock feedthru?) if the 9854's FTW is set for exactly 50.000 MHz. But my panadapter display looks great when the FTW is set for 50 MHz (i.e. FTW = 0x400000000000 ) - much better than it does with spur-reduction turned ON. (You can check this out on your own radio, too. Just turn spur-reduction Off and then tune to 50 MHz plus IF offset - you'll see a picket-fence of spurs that come closer and closer together as you approach the target frequency and then completely disappear *at* that freq.). I know Bob is currently very busy overseas - so we should probably explore this further upon his return. Best regards, - Jeff, WA6AHL -----Original Message----- From: Eric Wachsmann - FlexRadio [mailto:[EMAIL PROTECTED] Sent: Friday, December 09, 2005 8:15 AM To: 'Jeff Anderson'; flexradio@flex-radio.biz Subject: RE: [Flexradio] Interesting behavior when connected to a dummy load Jeff, I believe the answer lies in the spur reduction algorithm. This line is the key: ======================================================================== = long sr_tuning_word = (tuning_word & ~(0x80007fffffff)) | 0x000080000000; // clear first bit, low 31 bits; set bit 31 ======================================================================== = Setting bit 31 for the spur reduced tuning word (sr_tuning_word) may be what is keeping it from being a perfect 50MHz on the hardware. Eric Wachsmann FlexRadio Systems
