K3: narrow filter
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Hello,
I have in my K3, in both MAIN and SUB this filters: KFL3A-400 400 Hz, narrow 8-pole filter KFL3A-1.8K 1.8 kHz, 8-pole filter When I reduce width, I notice that it went down to 200 in CW. This is true? So that´s means I don´t need the KFL3A-250 250 Hz, narrow 8-pole filter to narrow less than 400Hz? 73, Jorge CX6VM/CW5W K3 #4077 ______________________________________________________________ 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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There are two levels of filtering going on.
The DSP (software) filtering is independent of the crystal roofing (hardware) filtering. You set the roofing filters to automatically kick in to match what you dial for the DSP. You have to tell the radio what filters you have installed and when you want them to kick in. It is all in the menus. I have mine set up so the 500 hz roofing filter kicks in when I reduce the DSP to 600 hz. Sounds to me like you don't have the filters coordinated. Buck k4ia k3# 101 In a message dated 7/14/2010 10:45:38 A.M. Eastern Daylight Time, [hidden email] writes: Hello, I have in my K3, in both MAIN and SUB this filters: KFL3A-400 400 Hz, narrow 8-pole filter KFL3A-1.8K 1.8 kHz, 8-pole filter When I reduce “width”, I notice that it went down to 200 in CW. This is true? So that´s means I don´t need the KFL3A-250 250 Hz, narrow 8-pole filter to narrow less than 400Hz? 73, Jorge CX6VM/CW5W K3 #4077 ______________________________________________________________ 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 Jorge Diez - CX6VM
On Wed, 14 Jul 2010 11:45:01 -0300, Jorge Diez - CX6VM wrote:
>Hello, >I have in my K3, in both MAIN and SUB this filters: >KFL3A-400 400 Hz, narrow 8-pole filter >KFL3A-1.8K 1.8 kHz, 8-pole filter >When I reduce width , I notice that it went down to 200 in CW. This is >true? Yes, and it can be set as narrow as 50 Hz! >So that´s means I don´t need the KFL3A-250 250 Hz, narrow 8-pole filter to >narrow less than 400Hz? Right. BUT -- let's clearly understand the function of these fixed filters. First, let's talk about how the K3 works. Older radios were built with fixed bandwidth IFs, and with crystal filters that could be switched in for wide and narrow bandwidths. The K3 does not work that way -- instead, it uses a DSP system to provide IF filtering, and you set the width of that IF when you tune the WIDTH knob. Those FIXED filters that you plug into a K3 are ROOFING filters -- that is, they sit in front of the DSP system to protect it from overload by very strong signals that are very close in frequency. That is their ONLY function in the context of general operation. In the context of heavy QRM (contesting or a pileup), the selectivity of the roofing filter does a lot more -- it ADDS to the selectivity of the IF. This only matters when the QRM is VERY strong, and is most useful when the IF is set to the same bandwidth as the roofing filter. For example, let's say that you've got a 40dB over S9 signal 200Hz away from your frequency, and you're trying to copy an S3 signal. The DSP IF set to 400 Hz might reject that 40dB over S9 signal by 10 dB, and a 400 Hz roofing filter might add another 6 dB of rejection. If you narrow the DSP IF to 200 Hz, you might get 25 dB of rejection from the DSP IF. That same 400 Hz filter still gives you that 6dB more rejection, but a 250 Hz roofing filter might give you 15-20 dB of additional rejection. This combining of filtering is called CASCADING. Until last fall, I also used only 400 Hz and 1.8 kHz filters. I added a 250 Hz filter to one of my K3s in time for the winter contests, and soon found that it really helped on weak signals in heavy QRM. I've since added 250 Hz filters to my other K3 (the one with the sub-RX). When you use the MENU to set up the K3 properly, you tell the K3 what filters are installed in which sockets, and the K3 automatically switches them in when you change the WIDTH. For example, my 400 Hz filter switches in when I reduce the bandwidth from 450 Hz to 400 Hz, and my 250 Hz filter switches in at 250 Hz. You can also cause the filters to switch at different WIDTH settings by lying to the K3 about their bandwidth. For example, you could cause the 400 Hz filter to switch at 500 Hz by telling the K3 that it is a 500 Hz filter. Some very good operators do that and like it. 73, Jim Brown K9YC ______________________________________________________________ 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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Thanks all for the info.
Jim your email is very clear for me, I not understand too much how works roofing filers and DSP, buy you clarify me something. I have the same filters you have, and seems will be good to add the 250Hz filter, since I am in contests and I notice QRM of stations near my frequency. I not have too much 59+ station here, not too much hams here..., but seems will be good to have also the 250Hz filter. So now I have another question, I think I have room for only one more filter, so how will affect DIVERSITY if I have 250Hz, 400Hz, 1.8kHz in MAIN and 400Hz, 1.8kHz in SUB? I cannot do DIVERSITY with a 250Hz narrow filters (because I will not have it in both receivers), buy the K3 will work OK using the 400Hz I have in MAIN and SUB? Thanks, Jorge CX6VM/CW5W K3 #4077 -----Mensaje original----- De: [hidden email] [mailto:[hidden email]] En nombre de Jim Brown Enviado el: Miércoles, 14 de Julio de 2010 12:52 p.m. Para: Elecraft Reflector Asunto: Re: [Elecraft] K3: narrow filter On Wed, 14 Jul 2010 11:45:01 -0300, Jorge Diez - CX6VM wrote: >Hello, >I have in my K3, in both MAIN and SUB this filters: >KFL3A-400 400 Hz, narrow 8-pole filter >KFL3A-1.8K 1.8 kHz, 8-pole filter >When I reduce width , I notice that it went down to 200 in CW. This is >true? Yes, and it can be set as narrow as 50 Hz! >So that4s means I don4t need the KFL3A-250 250 Hz, narrow 8-pole >filter to narrow less than 400Hz? Right. BUT -- let's clearly understand the function of these fixed filters. First, let's talk about how the K3 works. Older radios were built with fixed bandwidth IFs, and with crystal filters that could be switched in for wide and narrow bandwidths. The K3 does not work that way -- instead, it uses a DSP system to provide IF filtering, and you set the width of that IF when you tune the WIDTH knob. Those FIXED filters that you plug into a K3 are ROOFING filters -- that is, they sit in front of the DSP system to protect it from overload by very strong signals that are very close in frequency. That is their ONLY function in the context of general operation. In the context of heavy QRM (contesting or a pileup), the selectivity of the roofing filter does a lot more -- it ADDS to the selectivity of the IF. This only matters when the QRM is VERY strong, and is most useful when the IF is set to the same bandwidth as the roofing filter. For example, let's say that you've got a 40dB over S9 signal 200Hz away from your frequency, and you're trying to copy an S3 signal. The DSP IF set to 400 Hz might reject that 40dB over S9 signal by 10 dB, and a 400 Hz roofing filter might add another 6 dB of rejection. If you narrow the DSP IF to 200 Hz, you might get 25 dB of rejection from the DSP IF. That same 400 Hz filter still gives you that 6dB more rejection, but a 250 Hz roofing filter might give you 15-20 dB of additional rejection. This combining of filtering is called CASCADING. Until last fall, I also used only 400 Hz and 1.8 kHz filters. I added a 250 Hz filter to one of my K3s in time for the winter contests, and soon found that it really helped on weak signals in heavy QRM. I've since added 250 Hz filters to my other K3 (the one with the sub-RX). When you use the MENU to set up the K3 properly, you tell the K3 what filters are installed in which sockets, and the K3 automatically switches them in when you change the WIDTH. For example, my 400 Hz filter switches in when I reduce the bandwidth from 450 Hz to 400 Hz, and my 250 Hz filter switches in at 250 Hz. You can also cause the filters to switch at different WIDTH settings by lying to the K3 about their bandwidth. For example, you could cause the 400 Hz filter to switch at 500 Hz by telling the K3 that it is a 500 Hz filter. Some very good operators do that and like it. 73, Jim Brown K9YC ______________________________________________________________ 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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On Wed, 14 Jul 2010 14:12:45 -0300, Jorge Diez - CX6VM wrote:
>So now I have another question, I think I have room for only one more >filter, so how will affect DIVERSITY if I have 250Hz, 400Hz, 1.8kHz in MAIN >and 400Hz, 1.8kHz in SUB? >I cannot do DIVERSITY with a 250Hz narrow filters (because I will not have >it in both receivers), buy the K3 will work OK using the 400Hz I have in >MAIN and SUB? It is BEST to have the same filters in both RX for diversity, but diversity will still work with different filters, maybe not as well. The reasons relate to amplitude and phase response in the IFs of the two receivers. The only reason I can think of for not putting it in both receivers is money. But you're going to want two, so order two now and save the cost of the second shipping. :) 73, Jim K9YC ______________________________________________________________ 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 Jorge Diez - CX6VM
Yes diversity will work OK since both filters have offset = 0. For very narrow BWs, I can even use a 200 5-pole in Main and a 500 8-pole in Sub with no problems (warbling sounds). 73, Bill |
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