K2 - Low Pass Filter location
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At present, I am using the K2/100 to feed a KAT100 antenna tuner. A 160m-10m dipole is connected to the KAT100 as ANT 1 through a low-pass filter and a dummy load is connected as ANT 2, controlled from the K2. I am in the process of installing another antenna (40m-10m vertical) as my prime antenna and the dipole will be my secondary antenna. For ease of operation I would install one as ANT 1 and the other as ANT 2. To take advantage of the low-pass filter for both antennas I am considering installing it between the K2/100 and the KAT2. My concern is with non-linear components in the KAT100 RF path that would generate harmonics and negate the advantage of the filter. Sampling diodes, as in a SWR bridge, are always suspect. If this is to be a problem, I would have to get a second filter, one for each antenna, which is something that I really don't want to do unless I have to. Anyone have words of wisdom based on practical experience? -- 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Phil Kane wrote:
> My concern is with non-linear components in the KAT100 RF path > that would generate harmonics and negate the advantage of the > filter. Sampling diodes, as in a SWR bridge, are always suspect. > If this is to be a problem, I would have to get a second filter, > one for each antenna, which is something that I really don't want > to do unless I have to. This is an interesting question, because it brings back memories of the good old days when everyone needed an LP filter because of VHF TVI! Keep in mind that the diodes in the KAT100 are before the tuning elements, so that insofar as the L network acts as a LP filter it will reduce the harmonics generated by the diodes. But this will probably depend on the band and the impedance the KAT100 is working into. Also keep in mind that the LP filter is designed to work into a 50 ohm resistive load and will be either lossy or ineffective if the impedance seen on the antenna side of the KAT100 varies much from this. So I would put the LP filter before the KAT100 to deal with any harmonics generated in the K2, and hope that the tuner will eat anything the diodes make. Do you really have harmonic VHF TVI with the K2? -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K2 - Low Pass Filter location
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In reply to this post by Phil Kane-2
Phil,
I would place the low pass filter between the K2/100 and the KAT100 in any case. For any LPF to behave properly, it must be terminated in 50 ohms (or something close), and that is not realized with the LPF connected on the output of the KAT100. Any low pass filter worth its salt should not create any non-linearity - but again, if it is not properly terminated, the cutoff frequency may not be where you expect it to be. 73, Don W3FPR Phil Kane wrote: > At present, I am using the K2/100 to feed a KAT100 antenna > tuner. A 160m-10m dipole is connected to the KAT100 as ANT 1 > through a low-pass filter and a dummy load is connected as ANT > 2, controlled from the K2. > > I am in the process of installing another antenna (40m-10m > vertical) as my prime antenna and the dipole will be my > secondary antenna. For ease of operation I would install one > as ANT 1 and the other as ANT 2. To take advantage of the > low-pass filter for both antennas I am considering installing > it between the K2/100 and the KAT2. > > My concern is with non-linear components in the KAT100 RF path > that would generate harmonics and negate the advantage of the > filter. Sampling diodes, as in a SWR bridge, are always suspect. > If this is to be a problem, I would have to get a second filter, > one for each antenna, which is something that I really don't want > to do unless I have to. > > Anyone have words of wisdom based on practical experience? > > -- > 73 de K2ASP - Phil Kane > Elecraft K2/100 s/n 5402 > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K2 - Low Pass Filter location
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In reply to this post by Vic K2VCO
On Wed, 06 Feb 2008 13:29:04 -0800, Vic K2VCO wrote:
> Do you really have harmonic VHF TVI with the K2? Gosh, I hope not! But for the last 55 years of hamming I've lived in cities that had Channel 2, 5, and/or 6 stations, and although the vast majority of home TV sets are on cable or satellite feeds now, I'm still gun-shy. Having chased TVI for Uncle Sam for 30 years it would be very embarrassing for me to be the "culprit"! -- 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
Re: K2 - Low Pass Filter location
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In reply to this post by Don Wilhelm-4
On Wed, 06 Feb 2008 17:35:45 -0500, Don Wilhelm wrote:
> I would place the low pass filter between the K2/100 and the > KAT100 in any case. For any LPF to behave properly, it must be > terminated in 50 ohms (or something close), and that is not > realized with the LPF connected on the output of the KAT100. I have been lucky so far, because the B&W Wideband Folded Dipole (a resistor with wires) is pretty flat within 1:1.2 over all bands if I can believe the antenna bridge. The Cushcraft R8 claims to be the same, but I have no experience with it. Putting the LPF between the TX and the tuner was my gut feeling and it does makes sense. > Any low pass filter worth its salt should not create any > non-linearity - It was the KAT100 that I was concerned with for non-linearity. > but again, if it is not properly terminated, the cutoff frequency > may not be where you expect it to be. How very true. Thanks for the feedback. -- 73 de K2ASP - Phil Kane Elecraft K2/100 s/n 5402 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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