PX3 Anomoly (bug?) on AM
Locked
 
|
I posted this a week or so ago, and didn’t get any feedback from Elecraft or anyone on the list. Soo .. I’m going to “bump” it and post again. You never know …
In further poking at it, it matters not whether the IF shift is set to 8 Khz on the KX3, or whether Hi/Low Cut or PB/Shift is selected etc. It appears to be PX3 related. My guess is that either it’s (1) some artifact of the direct conversion process on the KX3, or (2) perhaps just showing AF bandwidth in some odd way. In any case … here’s the original post. Anyone have a clue? "If the bandwidth/shift or Hi/Lo cut is NORMalized, the green bandwidth band on the PX3 sits with it’s edges about 3 KHZ above and 3 KHz below the carrier frequency as you might expect. It’s symmetrical around the carrier. If I open up the HI setting to max (4.2 KHz) and set the LO to minimum, the green band is offset to the high frequency side of the carrier — with the low boundary about 2.2 KHz below the carrier, and the high boundary about 4.4 KHz above the carrier. These points may not be exact, but they were roughly measured using the VFO A marker — close enough to make the point. And just using the usual reduction in background hiss to retune the carrier, it appears most closely tuned when the VFO is set about 0.9 KHZ above the actual carrier frequency, although even then the green band is offset from either the actual or tuned carrier freq. So can anyone explain what is going on, and why the PX3 display (and maybe the KX3) behavior appears so odd in AM mode. Must be something I missed somewhere along the line.” Grant NQ5T K3 #2091, KX3 #8342 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
Grant,
It would appear that you are running up against the bandwidth limit of the KX3 audio when you widen the bandwidth with HiCut. I don't know what the limits are, but from your observations, it may be that the maximum bandwidth is in the vicinity of 6.4kHz. So if you have 4.2 kHz on one side, you will be restricted to 2.2kHz on the low side. If you back off the high side to 3.1kHz, is the AM response centered? I am just venturing a guess, the maximum audio bandwidth is not specified for the KX3. 73, W3FPR On 5/3/2016 8:46 PM, GRANT YOUNGMAN wrote: > I posted this a week or so ago, and didn’t get any feedback from Elecraft or anyone on the list. Soo .. I’m going to “bump” it and post again. You never know … > > In further poking at it, it matters not whether the IF shift is set to 8 Khz on the KX3, or whether Hi/Low Cut or PB/Shift is selected etc. It appears to be PX3 related. My guess is that either it’s (1) some artifact of the direct conversion process on the KX3, or (2) perhaps just showing AF bandwidth in some odd way. In any case … here’s the original post. Anyone have a clue? > > > > "If the bandwidth/shift or Hi/Lo cut is NORMalized, the green bandwidth band on the PX3 sits with it’s edges about 3 KHZ above and 3 KHz below the carrier frequency as you might expect. It’s symmetrical around the carrier. If I open up the HI setting to max (4.2 KHz) and set the LO to minimum, the green band is offset to the high frequency side of the carrier — with the low boundary about 2.2 KHz below the carrier, and the high boundary about 4.4 KHz above the carrier. These points may not be exact, but they were roughly measured using the VFO A marker — close enough to make the point. And just using the usual reduction in background hiss to retune the carrier, it appears most closely tuned when the VFO is set about 0.9 KHZ above the actual carrier frequency, although even then the green band is offset from either the actual or tuned carrier freq. > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
This may be. I don’t know if this is a bug, or just the way it is.
The fact is that it is an odd display for the mode. The P3 by comparison is quite “normal” for AM. It would be more logical to show the presumptive equivalent “IF” on either side of the carrier, or (if Elecraft ever implements the stub to a sync detector) just one sideband above or below the carrier. As it is, the display is hard to interpret. It does appear to depict the “audio” bandwidth. For example, if you bring up the lower edge of the green band to the carrier it’s clear the effect is just cutting the low frequency audio — e.g., you can’t retune the radio to center the bandwidth on the AM signal — it jut cuts the lows and renders the thing unintelligible. Now if there were a really good explanation for how to interpret it (and yours may be part of it), that would be fine, too. When the receive bandwidth is NORM'ed, it is symmetric about the carrier. But it ought to stay that way as the bandwidth is increased. There may be a perfectly good reason why it behaves the way it does. It just isn’t explained anywhere. It also doesn’t explain why it seems at least, that the KX3 needs to be tuned slightly off frequency to “center” the signal when the bandwidth is fully maximized. Grant NQ5T K3 #2091, KX3 #8342 > On May 3, 2016, at 9:46 PM, Don Wilhelm <[hidden email]> wrote: > > Grant, > > It would appear that you are running up against the bandwidth limit of the > KX3 audio when you widen the bandwidth with HiCut. > I don't know what the limits are, but from your observations, it may be that the maximum bandwidth is in the vicinity of 6.4kHz. > > So if you have 4.2 kHz on one side, you will be restricted to 2.2kHz on the low side. > If you back off the high side to 3.1kHz, is the AM response centered? > > I am just venturing a guess, the maximum audio bandwidth is not specified for the KX3. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |