K3 Low Pass Question
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Just wondering if many K3 owners have a low pass filter in their coax line? I'm starting to assemble my station in a rental apartment and have a couple commercial low pass units lying in the parts box. Worth the extra (small) effort to put one in the transmission line? In my case, no additional $$ cost, but it would add another pair of PL259's and a short length of cable to the configuration.
Jim / W6JHB |
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Jim,
One reason not to use an external LPF is that many (most) of them have a cutoff frequency above 30 MHz, and below 50 MHz - and the K3 covers 50 MHz. IIRC, Drake had one LPF that had a cutoff above 52 MHz (but the 6 meter band extends to 54 MHz). I am looking at a Drake TV-3300-LP right now and it has a minimum attenuation of 80 dB above 41 MHz. Most modern transceivers do not need external LPFs because they must comply with more stringent FCC spurious emission regulations than were in effect when many transmitters had a LPF hanging off the back for TVI prevention. So, you can use it if you want, it will not hurt anything at HF, but unless it is one with a cutoff frequency above 54 MHz, you will lose all or part of the 6 meter coverage. 73, Don W3FPR Jim / W6JHB wrote: > Just wondering if many K3 owners have a low pass filter in their coax line? > I'm starting to assemble my station in a rental apartment and have a couple > commercial low pass units lying in the parts box. Worth the extra (small) > effort to put one in the transmission line? In my case, no additional $$ > cost, but it would add another pair of PL259's and a short length of cable > to the configuration. > > Jim / W6JHB > ______________________________________________________________ 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 Jim / W6JHB
Jim,
An argument in favor of leaving the LPF in the line would be to keep strong VHF or UHF signals out of the receiver. Although there aren't as many TV stations in the VHF region any more, there are still plenty of FM broadcast signals that in an extreme case could create intermodulation distortion (or blocking) in your receiver. For example, here in Los Angeles all of the broadcasting is on one mountaintop, 3 miles north of me, consisting of about 25 MW ERP. I use an LPF for that reason. But if a situation like that doesn't apply to you, you could probably do without it. Al W6LX ____________________________________________________________ Just wondering if many K3 owners have a low pass filter in their coax line? Jim / W6JHB ______________________________________________________________ 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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Folks,
Thanks for a the input and ideas. I'm going to let my rig sit and not move it to disconnect/reconnect things again until there is an absolute must have option in a new release, like something has to be done for the P3. Until then, please private mail only. Let's close this thread. Thanks to all, de K2GN - Larry - http://k2gn.com K3 S/N - 3278 P3 S/N - ???? (Ordered) ______________________________________________________________ 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 alorona
<<<An argument in favor of leaving the LPF in the line would be to keep
strong VHF or UHF signals out of the receiver. Although there aren't as many TV stations in the VHF region any more, there are still plenty of FM broadcast signals that in an extreme case could create intermodulation distortion (or blocking) in your receiver.>>> Does that stuff really get into the receiver and bother it?? If so, I'm a little suprised and wonder why that would happen. Ground loops? Semiconductors before filters? For example, here in Los Angeles all of the broadcasting is on one mountaintop, 3 miles north of me, consisting of about 25 MW ERP. I use an LPF for that reason. But if a situation like that doesn't apply to you, you could probably do without it. Al W6LX ____________________________________________________________ Just wondering if many K3 owners have a low pass filter in their coax line? Jim / W6JHB ______________________________________________________________ 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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Well, after getting a handful of replies, I'm opting to NOT put the low pass filter in the line. Had totally forgotten about most of 'em having a cutoff at 30 MHz, and sooner or later I'm gonna give six meters a try. Thanks for the replies folks!
73, Jim / W6JHB |
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It begs the question what we should do with the 1000s of LP filters out
there. Some are built very well, like my Drake, but I also have a couple made of "bent tin." There was a QST article on them a few years ago showing different construction styles and quite intriguing how costs could be reduced. I was idly wondering if I should convert them to something useful, perhaps to a band pass filter. There's room to fit small toroid inductors instead of the solenoid types. Then again, with the Elecraft line up I probably wouldn't benefit much, but it would be an interesting project. David G3UNA > > Well, after getting a handful of replies, I'm opting to NOT put the low > pass > filter in the line. Had totally forgotten about most of 'em having a > cutoff > at 30 MHz, and sooner or later I'm gonna give six meters a try. Thanks for > the replies folks! > > 73, Jim / W6JHB ______________________________________________________________ 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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> It begs the question what we should do with the 1000s of LP filters out
> there. Some are built very well, like my Drake, but I also have a couple > made of "bent tin." There was a QST article on them a few years ago > showing > different construction styles and quite intriguing how costs could be > reduced. They are somewhat useful as low pass filters for some or many high power HF RF amplifiers, and with many older tube type or hybrid radios with pi-network outputs. They are also useful for systems having active T/R switches like this one: http://www.w8ji.com/johnson_tr_switch.htm I looked back through some amplifier tests, and the worse case harmonic or spurious on the solid state ALS1300 above 30 MHz was a level less than -60.4 dBc with a carrier level of 1200 watts. That was one pip just out of analyzer noise that could have been a mixer product in the analyzer! HF rigs like the K3 look just as clean or cleaner. Some harmonics in tube type amps are not nearly that well suppressed, and my data on older gear from the 1970's and earlier indicates they could result in a substantial improvement in VHF harmonic suppression from some 30-watt output transmitters. Those old 30-100 watt output transmitters exceed the absolute harmonic power levels produce by newer 1500 watt amps. :-) I'd say save them in case you get an old boatanchor, because converting them to something else like an HF bandpass would only yield the sheet metal and connectors as recyclable. Then of course nearly all low-band VHF TV transmitters are gone over here. There are none within range of me, even those that someone said were on. :-) 73 Tom ______________________________________________________________ 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 |
Re: K3 Low Pass Question
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In reply to this post by David Cutter
David,
A Low Pass filter cutting off above 6m is useful here, because our not so local FM BC station operates just above 100 MHz. I suggest that if you do convert a LPF, do not use small toroidal inductors (unless "air wound") if the filter is to be used between a receiver and an antenna feeder. Small cores can create IMD problems ftom BC stations etc, which is one reason why the solenoid type of inductor is used. 73, Geoff GM4ESD David Cutter wrote on Friday, June 18, 2010 9:27 AM: > I was idly wondering if I should convert them to something useful, perhaps > to a band pass filter. There's room to fit small toroid inductors instead > of the solenoid types. Then again, with the Elecraft line up I probably > wouldn't benefit much, but it would be an interesting project. ______________________________________________________________ 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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This post was updated on .
In reply to this post by W8JI
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Brgds,
Dave, N3HE Cincinnati OH |
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In reply to this post by Geoffrey Mackenzie-Kennedy
Hi Geoff
I didn't know that about small cores, but, if I were to take on this idea, I would use the biggest I could get in there, which is around 45mm. There's a local radio station on medium wave which has given me grief in the past, (pre K3 mind you) and I could change it into a high pass filter just for that. Come to think of it, I wonder if I could make such a filter for use with the MFJ259; that might be a better idea. David G3UNA > David, > > A Low Pass filter cutting off above 6m is useful here, because our not so > local FM BC station operates just above 100 MHz. > > I suggest that if you do convert a LPF, do not use small toroidal > inductors (unless "air wound") if the filter is to be used between a > receiver and an antenna feeder. Small cores can create IMD problems ftom > BC stations etc, which is one reason why the solenoid type of inductor is > used. > > 73, > > Geoff > GM4ESD > > > David Cutter wrote on Friday, June 18, 2010 9:27 AM: > >> I was idly wondering if I should convert them to something useful, >> perhaps >> to a band pass filter. There's room to fit small toroid inductors >> instead >> of the solenoid types. Then again, with the Elecraft line up I probably >> wouldn't benefit much, but it would be an interesting project. > > > ______________________________________________________________ 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 W8JI
On 2010-06-18 12:18, Tom W8JI wrote:
> Then of course nearly all low-band VHF TV transmitters are gone over here. > There are none within range of me, even those that someone said were on. :-) > > 73 Tom > Gone here too. But we have the FM BC band around 100 MHz so they could be useful. I remember back in the 70´ties having problem with the 7:th harmonic from 14 MHz, used T-4XB/C transmitters and a 4-1000A amp, those where the days! / Jim SM2EKM ______________________________________________________________ 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 |
Re: K3 Low Pass Question
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In reply to this post by David Cutter
Hi David,
If of any interest to you I can send you "off List" some results of my most recent two tone "IMD" tests on bandpass filters for use in a receiver's front end, which would give you some idea of the effect of a core and its size. These show each filter's 3rd order Output Intercept vs. core size vs. some core mixes. Bands covered are 160m to 6m inclusive. Please let me know "off List" if you are interested. 73, Geoff GM4ESD From: "David Cutter wrote on Friday, June 18, 2010 2:47 PM: > Hi Geoff > > I didn't know that about small cores, but, if I were to take on this idea, > I > would use the biggest I could get in there, which is around 45mm. > > There's a local radio station on medium wave which has given me grief in > the > past, (pre K3 mind you) and I could change it into a high pass filter just > for that. > > Come to think of it, I wonder if I could make such a filter for use with > the > MFJ259; that might be a better idea. > > David > G3UNA ______________________________________________________________ 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 David Windisch
On Fri, 18 Jun 2010 05:04:28 -0700 (PDT), David Windisch wrote:
>I lived <1500' from an am/fm/tv broadcast hotspot in Cincinnati and enough rf >came in the pipe to activate the reverse-power cutback/shutdown on a TS440. >A Johnson MatchCarton or a generic lopass would take care of the situation. Yes, depending on their circuitry, some antenna tuners may help reject out of band signals and harmonics. >Had rfi from 1360-am and 700-am with '1000D's. An ICE ambc-rejection filter >took care of that one. Good advice. The ICE filters are not the world's greatest, but the AM BC filter is fairly good. I needed one when I lived in Chicago, and the two that I own measure fairly well. If you buy one, DO check it for proper tuning -- I've seen significant QC problems with several filters I've bought directly from ICE. 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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In reply to this post by David Cutter
This topic greatly interests me, because I have never found saturation or
non-linearity in typical cores an issue. This might be an opportunity to explore something new that I have never seen. ----- Original Message ----- From: "David Cutter" <[hidden email]> To: "Geoffrey Mackenzie-Kennedy" <[hidden email]> Cc: "Elecraft Discussion List" <[hidden email]> Sent: Friday, June 18, 2010 9:47 AM Subject: Re: [Elecraft] K3 Low Pass Question > Hi Geoff > > I didn't know that about small cores, but, if I were to take on this idea, > I > would use the biggest I could get in there, which is around 45mm. > > There's a local radio station on medium wave which has given me grief in > the > past, (pre K3 mind you) and I could change it into a high pass filter just > for that. > > Come to think of it, I wonder if I could make such a filter for use with > the > MFJ259; that might be a better idea. > > David > G3UNA > > > >> David, >> >> A Low Pass filter cutting off above 6m is useful here, because our not so >> local FM BC station operates just above 100 MHz. >> >> I suggest that if you do convert a LPF, do not use small toroidal >> inductors (unless "air wound") if the filter is to be used between a >> receiver and an antenna feeder. Small cores can create IMD problems ftom >> BC stations etc, which is one reason why the solenoid type of inductor is >> used. >> >> 73, >> >> Geoff >> GM4ESD >> >> >> David Cutter wrote on Friday, June 18, 2010 9:27 AM: >> >>> I was idly wondering if I should convert them to something useful, >>> perhaps >>> to a band pass filter. There's room to fit small toroid inductors >>> instead >>> of the solenoid types. Then again, with the Elecraft line up I probably >>> wouldn't benefit much, but it would be an interesting project. >> >> >> > > ______________________________________________________________ > 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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