K3: use of 1.8 filter - clarification
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K3: use of 1.8 filter - clarification
 
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IMHO, there are few folks in the contest world that are better
technically than Bill (W4ZV), so I would suggest that everyone take his comments very seriously. Bill...I do have a question or two, with respect to your statement below. 1. Just how often do you find that you run into a situation such as you describe below? I don't mean simply, "during every a contest," I mean more like how often during a contest? For how many Q's? 2. If the really close and really strong signal is pumping your AGC, why not just turn off the AGC and ride the RF? This is not a rhetorical question, because I know you do this. So I'd like to learn why you would, in some situations, prefer to not do that. I would love to learn a new trick! 3. And just out of curiosity (on SSB), how long would you tolerate being so close to someone who would pump your AGC? Of course, for me (QRP), the answer is zero seconds. :-) W4ZV said: I agree IMD reduction is not a big issue on SSB but blocking dynamic range (BDR) is the primary reason I sometimes need a narrower filter. If you have an S9+25 SSB signal CQing next to you (sometimes the case in crowded contests), a narrower filter will prevent it from de-sensing your receiver. If part of the interfering signal falls inside your 2.7k filter, signals on your frequency will be gain modulated by his signal (commonly called AGC pumping). In this case a narrower filter will prevent the problem. Of course when this happens, we still have to contend with his transmitted "splatter" (typical SSB TXs run -35 dB IMD which would result in ~S7 splatter from an S9+25 signal), but at least you can still copy signals at S7 or above (and lower when he's not transmitting). 73, Bill ______________________________________________________________ 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 |
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Can't speak for Bill, but for myself, all night long on 75 and 40 meters.
There are people that show up with amps and antennas that you almost never hear outside of a contest. NQ4I near Atlanta has a 12 element LPDA for 80/75 meters fixed northeast. 4 or 5 elements active on any given frequency. What do you suppose that's like downwind? 73, Guy. On Sat, Jan 14, 2012 at 9:06 PM, DOUGLAS ZWIEBEL <[hidden email]> wrote: > IMHO, there are few folks in the contest world that are better > technically than Bill (W4ZV), so I would suggest that everyone take > his comments very seriously. > > Bill...I do have a question or two, with respect to your statement below. > > 1. Just how often do you find that you run into a situation such as > you describe below? I don't mean simply, "during every a contest," I > mean more like how often during a contest? For how many Q's? > > 2. If the really close and really strong signal is pumping your AGC, > why not just turn off the AGC and ride the RF? This is not a > rhetorical question, because I know you do this. So I'd like to learn > why you would, in some situations, prefer to not do that. I would > love to learn a new trick! > > 3. And just out of curiosity (on SSB), how long would you tolerate > being so close to someone who would pump your AGC? Of course, for me > (QRP), the answer is zero seconds. :-) > > W4ZV said: > I agree IMD reduction is not a big issue on SSB but blocking dynamic > range (BDR) is the primary reason I sometimes need a narrower filter. > If you have an S9+25 SSB signal CQing next to you (sometimes the case > in crowded contests), a narrower filter will prevent it from > de-sensing your receiver. If part of the interfering signal falls > inside your 2.7k filter, signals on your frequency will be gain > modulated by his signal (commonly called AGC pumping). In this case > a narrower filter will prevent the problem. Of course when this > happens, we still have to contend with his transmitted "splatter" > (typical SSB TXs run -35 dB IMD which would result in ~S7 splatter > from an S9+25 signal), but at least you can still copy signals at S7 > or above (and lower when he's not transmitting). > > 73, Bill > ______________________________________________________________ > 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 > 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 |
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In reply to this post by DOUGLAS ZWIEBEL
Hi Doug,
##### You asked: Bill...I do have a question or two, with respect to your statement below. 1. Just how often do you find that you run into a situation such as you describe below? I don't mean simply, "during every a contest," I mean more like how often during a contest? For how many Q's? ##### Fortunately not very often. I operate 10m almost exclusively in SSB contests. If a hippo comes near my watering hole, I first make my presence known (ask him to QSY, etc). But rather than pointlessly (pun intended) slugging it out, I'll move (lots of room on 10m). Of course moving is not an option on many bands (e.g. 20m) in SSB contests, otherwise you'll not make many QSOs at all. 2. If the really close and really strong signal is pumping your AGC, why not just turn off the AGC and ride the RF? This is not a rhetorical question, because I know you do this. So I'd like to learn why you would, in some situations, prefer to not do that. I would love to learn a new trick! ##### Remember that you CANNOT turn the hardware AGC off because it's always on to protect the ADC in the DSP stage. HAGC will still cause pumping even if the DSP AGC is turned off. Of course you can use an attenuator but that also has consequences for copying weaker signals on your frequency. 3. And just out of curiosity (on SSB), how long would you tolerate being so close to someone who would pump your AGC? Of course, for me (QRP), the answer is zero seconds. :-) ##### It depends. If I think someone is intentionally trying to steal my run frequency, I may stay longer than if I think it's accidental. In the recent CQ WW, I had one station try this twice but they left after ~5 minutes each time. The top operators NEVER do this but I keep a mental list of some folks who routinely try it and sometimes return the favor. ;-) It often helps to point one antenna in my 3-stack toward someone who "accidentally" lands on my run frequency, so they can hear me better. :-) Fortunately this does not happen often on 10m (unlike more crowded bands). 73, Bill W4ZV said: I agree IMD reduction is not a big issue on SSB but blocking dynamic range (BDR) is the primary reason I sometimes need a narrower filter. If you have an S9+25 SSB signal CQing next to you (sometimes the case in crowded contests), a narrower filter will prevent it from de-sensing your receiver. If part of the interfering signal falls inside your 2.7k filter, signals on your frequency will be gain modulated by his signal (commonly called AGC pumping). In this case a narrower filter will prevent the problem. Of course when this happens, we still have to contend with his transmitted "splatter" (typical SSB TXs run -35 dB IMD which would result in ~S7 splatter from an S9+25 signal), but at least you can still copy signals at S7 or above (and lower when he's not transmitting). 73, Bill |
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