[Elecraft] K3 Birdies: firmware-based fix in progress
The K3 is a down-conversion superhet that uses high-level signal injection to achieve its excellent dynamic range. Short of adding many more pounds of shielding and elaborate cable dressing, there's no way to completely eliminate the few spurious signals that rise above the noise floor. These Fast-tuning birdies result from UHF harmonics of the signal sources that leak back into the main mixer. In some cases they combine and end up in either the I.F. or R.F./image range of the receiver. Typically, they involve 9th-order or higher harmonics of the VFO. That's what makes them fast: if you move the VFO 100 Hz, the pitch of the birdie will shift on the order of 1 to 2 kHz. While it is possible to attenuate some spurious responses by moving coax cables around, there is a firmware-based approach that we're working on. The general idea is to shift the 1st LO and BFO a small amount, simultaneously, when the VFO is tuned to specific frequencies. If the shift is small relative to the communications bandwidth in use, it will hardly be noticeable when the VFO is tuned over a mapped out spot in the tuning range. I have this new firmware nearly completed, and in early tests, it appears to work very well. Fast-tuning birdies that are mapped out pretty much disappear as the VFO is tuned over them. The upshot is that you can have your cake (outstanding dynamic range in a rig that weighs less than 10 pounds) and eat it, too (no annoying birdies). If you'd like to try a field-test version of K3 firmware that includes this new feature, please e-mail me directly. 73, Wayne N6KR --- http://www.elecraft.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Birdies: firmware-based fix in progress
That's very interesting. I found that I can accomplish much the same thing on CW by simply using a very narrow bandwidth (250 Hz in my case) ... the birdies tune so fast that they drop outside the passband with just a minor shift in VFO frequency. I don't use SSB as often, but there the notch filter has been effectively plinking the birdies. 73, Dave AB7E wayne burdick wrote: The K3 is a down-conversion superhet that uses high-level signal injection to achieve its excellent dynamic range. Short of adding many more pounds of shielding and elaborate cable dressing, there's no way to completely eliminate the few spurious signals that rise above the noise floor. These Fast-tuning birdies result from UHF harmonics of the signal sources that leak back into the main mixer. In some cases they combine and end up in either the I.F. or R.F./image range of the receiver. Typically, they involve 9th-order or higher harmonics of the VFO. That's what makes them fast: if you move the VFO 100 Hz, the pitch of the birdie will shift on the order of 1 to 2 kHz. While it is possible to attenuate some spurious responses by moving coax cables around, there is a firmware-based approach that we're working on. The general idea is to shift the 1st LO and BFO a small amount, simultaneously, when the VFO is tuned to specific frequencies. If the shift is small relative to the communications bandwidth in use, it will hardly be noticeable when the VFO is tuned over a mapped out spot in the tuning range. I have this new firmware nearly completed, and in early tests, it appears to work very well. Fast-tuning birdies that are mapped out pretty much disappear as the VFO is tuned over them. The upshot is that you can have your cake (outstanding dynamic range in a rig that weighs less than 10 pounds) and eat it, too (no annoying birdies). If you'd like to try a field-test version of K3 firmware that includes this new feature, please e-mail me directly. 73, Wayne N6KR --- http://www.elecraft.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Birdies: firmware-based fix in progress
Fantastic Wayne. Would that be a cake mix, al-la a K3 kit or just a recipe with ingredients, al-la, a K2? :-) 73 de M0XDF, K3 #174 -- Black holes are where God divided by zero. -Steven Wright, comedian (1955-) On 10 Feb 2009, at 17:09, wayne burdick wrote: The upshot is that you can have your cake (outstanding dynamic range in a rig that weighs less than 10 pounds) and eat it, too (no annoying birdies). __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Birdies: firmware-based fix in progress
Yea in SSB the auto notch makes very quick short order of them. Every once in a while I find myself trying to listen through it and filter with my noodle. Then all the sudden it dawns on me and a single button press later they are poof gone. On Tue, Feb 10, 2009 at 9:44 AM, David Gilbert xda...@cis-broadband.com wrote: That's very interesting. I found that I can accomplish much the same thing on CW by simply using a very narrow bandwidth (250 Hz in my case) ... the birdies tune so fast that they drop outside the passband with just a minor shift in VFO frequency. I don't use SSB as often, but there the notch filter has been effectively plinking the birdies. 73, Dave AB7E wayne burdick wrote: The K3 is a down-conversion superhet that uses high-level signal injection to achieve its excellent dynamic range. Short of adding many more pounds of shielding and elaborate cable dressing, there's no way to completely eliminate the few spurious signals that rise above the noise floor. These Fast-tuning birdies result from UHF harmonics of the signal sources that leak back into the main mixer. In some cases they combine and end up in either the I.F. or R.F./image range of the receiver. Typically, they involve 9th-order or higher harmonics of the VFO. That's what makes them fast: if you move the VFO 100 Hz, the pitch of the birdie will shift on the order of 1 to 2 kHz. While it is possible to attenuate some spurious responses by moving coax cables around, there is a firmware-based approach that we're working on. The general idea is to shift the 1st LO and BFO a small amount, simultaneously, when the VFO is tuned to specific frequencies. If the shift is small relative to the communications bandwidth in use, it will hardly be noticeable when the VFO is tuned over a mapped out spot in the tuning range. I have this new firmware nearly completed, and in early tests, it appears to work very well. Fast-tuning birdies that are mapped out pretty much disappear as the VFO is tuned over them. The upshot is that you can have your cake (outstanding dynamic range in a rig that weighs less than 10 pounds) and eat it, too (no annoying birdies). If you'd like to try a field-test version of K3 firmware that includes this new feature, please e-mail me directly. 73, Wayne N6KR --- http://www.elecraft.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Birdies: firmware-based fix in progress
On Feb 10, 2009, at 2/109:09 AM, wayne burdick wrote: While it is possible to attenuate some spurious responses by moving coax cables around, there is a firmware-based approach that we're working on. The general idea is to shift the 1st LO and BFO a small amount, simultaneously, when the VFO is tuned to specific frequencies. If the shift is small relative to the communications bandwidth in use, it will hardly be noticeable when the VFO is tuned over a mapped out spot in the tuning range. When you do this, will you be exposing the real 1st LO frequency through CAT? Some of us are using the LP-PAN to receive and demodulate, while using CAT to move the transmit VFO around in the spectrum of the LP- PAN to zero beat a 2 kc baseband signal to the signal that is being demodulated. As it is, there is already a problem with the SHIFT knob moving the 1st LO frequency, but effect that can be discovered with CAT, and as long as SHIFT is not changed during transmission, it is workable. The real way out is to not use the SHIFT knob at all; we don't really need the shift knob when we implement our own DSP demodulators behind the LP-PAN. If the 1st LO were to move by itself, we would need to know where these magic frequencies are. One possibility is that if you only plan to nudge the receive VFO, we can just keep our receive VFO fixed to a non-magic frequency and always tune the receiver by offsetting into the LP-PAN's output. The best would be an option to be able to choose not to nudge the 1st LO. Speaking of the SHIFT moving the 1st LO frequency, does the SHIFT knob also move where the birdies occur? I haven't installed my second receiver yet and cannot perform the experiment. 73 Chen, W7AY __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Birdies: firmware-based fix in progress
Wayne, Won't the birdies still show up on a panadapter? They'll be mysterious blips that disappear when you click on them to tune them in? --Oliver Johns, W6ODJ On 10 Feb 2009, at 9:09 AM, wayne burdick wrote: The K3 is a down-conversion superhet that uses high-level signal injection to achieve its excellent dynamic range. Short of adding many more pounds of shielding and elaborate cable dressing, there's no way to completely eliminate the few spurious signals that rise above the noise floor. These Fast-tuning birdies result from UHF harmonics of the signal sources that leak back into the main mixer. In some cases they combine and end up in either the I.F. or R.F./image range of the receiver. Typically, they involve 9th-order or higher harmonics of the VFO. That's what makes them fast: if you move the VFO 100 Hz, the pitch of the birdie will shift on the order of 1 to 2 kHz. While it is possible to attenuate some spurious responses by moving coax cables around, there is a firmware-based approach that we're working on. The general idea is to shift the 1st LO and BFO a small amount, simultaneously, when the VFO is tuned to specific frequencies. If the shift is small relative to the communications bandwidth in use, it will hardly be noticeable when the VFO is tuned over a mapped out spot in the tuning range. I have this new firmware nearly completed, and in early tests, it appears to work very well. Fast-tuning birdies that are mapped out pretty much disappear as the VFO is tuned over them. The upshot is that you can have your cake (outstanding dynamic range in a rig that weighs less than 10 pounds) and eat it, too (no annoying birdies). If you'd like to try a field-test version of K3 firmware that includes this new feature, please e-mail me directly. 73, Wayne N6KR --- http://www.elecraft.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] K3 Birdies: firmware-based fix in progress
On Feb 10, 2009, at 3:12 PM, O. Johns wrote: Wayne, Won't the birdies still show up on a panadapter? They'll be mysterious blips that disappear when you click on them to tune them in? It's possible, because the panadapter can show a much wider bandwidth than the K3's crystal filter allows into its own I.F. But such signals would have to be above the panadapter's noise floor (at the buffered I.F. output). Most birdies are inaudible with an antenna connected anyway, and some might be finding their way into the second rather than the first mixer, so it's hard to predict which ones would make tiny blips on the panadapter. If this turns out to be an issue, I may be able to enhance the K3's FI command, which the LP-Pan uses to get the current I.F., to flag the occurrence of a mapped-out 100-Hz VFO segment. 73, Wayne N6KR --- http://www.elecraft.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
