Tom Lizak, K1TL, wrote: > I have been having a problem with a 6m internal birdie around 50.096 ... I > did the "birdie removal tool" thingee but seems to put a small "void" in that > area when I did it.
Hi Tom, The SIG RMV method can, in some cases, introduce a small dip in audio response at that specific frequency. The way the K3 owner's manual describes it is: "You may hear a slight tuning artifact as you tune in and out of the affected VFO segment." (See CONFIG:SIG RMV description.) This is an unavoidable side effect of how SIG RMV works. SIG RMV allows you to apply a small shift to both the first and second local oscillators, which can shift the birdie completely out of the passband while shifting the crystal filter passband only a small amount (and keeping the VFO accurate). But if the target signal happens to be close to the edge of the crystal filter passband, even a small shift could attenuate that point in the tuning range by a few dB. Generally, this is preferable to hearing the birdie. How successful SIG RMV is depends entirely on whether the birdie results from the first LO's fundamental, or from a harmonic. If it's due to a harmonic, which is usually the case, SIG RVM can be very effective. For example, shifting the LO 100 Hz would shift the birdie 1000 Hz in the case of a product involving the 10th harmonic of the LO. If the birdie you're removing is due to the fundamental of the LO, you may be forced to move it farther, creating a greater chance of an audible tuning artifact. Unfortunately there's no way to completely eliminate birdies in a high-dynamic-range superhet receiver. When we designed the new synth, we spent a lot of time tuning through the ham bands, slowly, at multiple bandwidths. We selected divider values (etc.) for the new synth such that ham-band birdies were "virtually" (but not entirely) eliminated. 6 meters is especially difficult because both the target band and its image band are both 4 MHz wide. Nonetheless, I think we did a pretty good job of minimizing birdies here. There are other things you can do about birdies if a small residual artifact is an issue. In CW mode you might try using CW reverse instead of CW normal. Or you can use a different crystal filter with a different offset. In SSB mode you can turn on the notch filter. But before taking any of these more drastic steps, I would also check the orientation of the coax cables associated with the synthesizer(s). Sometimes just moving a cable a bit can greatly attenuate one problematic birdie. Let me know if you have any further questions about this. 73, Wayne N6KR ______________________________________________________________ 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]
