KPA500 RF output wiring
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Hello Group,
The connection between the RF deck to the RF SO239 output is a pair of twisted wires instead of a coaxial jumper. Is there any reason for such a design? >From reading of the manual, there is no mention of spurious emission and 3rd order distortion (two tone test). Where can I find these information? Thanks for your help in advance. TNX & 73, Johnny VR2XMC ______________________________________________________________ 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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Johnny,
Twisted pair is just as effective as coax, and easier to work with. I am not certain that was the reason for that design, but there is no problem with it. 73, Don W3FPR On 9/8/2011 1:53 AM, Johnny Siu wrote: > Hello Group, > > The connection between the RF deck to the RF SO239 output is a pair of twisted wires instead of a coaxial jumper. Is there any reason for such a design? > > > From reading of the manual, there is no mention of spurious emission and 3rd order distortion (two tone test). Where can I find these information? > > Thanks for your help in advance. > > TNX& 73, > > > Johnny VR2XMC > ______________________________________________________________ > 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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Hello Don,
Thanks for your reply. I am just curious because the output socket using twisted wire but the input socket using coaxial jumper. I am still looking for the information about spurious emission and 3rd order distortion of KPA500. TNX & 73, Johnny VR2XMC 從︰ Don Wilhelm <[hidden email]> 收件人︰ Johnny Siu <[hidden email]> 副本(CC)︰ Elecraft <[hidden email]> 傳送日期︰ 2011年09月8日 (週四) 8:52 PM 主題︰ Re: [Elecraft] KPA500 RF output wiring Johnny, Twisted pair is just as effective as coax, and easier to work with. I am not certain that was the reason for that design, but there is no problem with it. 73, Don W3FPR On 9/8/2011 1:53 AM, Johnny Siu wrote: > Hello Group, > The connection between the RF deck to the RF SO239 output is a pair of twisted wires instead of a coaxial jumper. Is there any reason for such a design? > > From reading of the manual, there is no mention of spurious emission and 3rd order distortion (two tone test). Where can I find these information? > Thanks for your help in advance. > > TNX& 73, > > > Johnny VR2XMC ______________________________________________________________ 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 Johnny Siu
On 9/7/2011 10:53 PM, Johnny Siu wrote:
> The connection between the RF deck to the RF SO239 output is a pair of twisted wires instead of a coaxial jumper. Is there any reason for such a design? Sure. Twisted pair is a VERY effective transmission line, and that is what is needed. In fact, it is a MUCH older form of transmission line than coax, which was developed in the 1930s. Twisted pair was first used in telephone transmission, and is still widely used for pro audio, and for computer data (CAT5, for example). This particular use is entirely appropriate for several reasons. First, it is physically smaller than coax that would be suitably rated. Second, it occupies less space. Third, it costs less. 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 Johnny Siu
> On 9/7/2011 10:53 PM, Johnny Siu wrote:
>> The connection between the RF deck to the RF SO239 output is a pair >> of twisted wires instead of a coaxial jumper. Is there any reason >> for such a design? Twisted pair is a highly effective transmission line, and easier to work with than coax in tight quarters. That TP in the KPA500 is short. A suitable size piece of coax would be pretty stiff. I don't have any quantitative data [ask Jim, K9YC, I'm sure he does], but I've also found balanced twisted pair to often be less susceptible to RFI than shielded cable. In the early 70's, I was working on a process control system hosted on a Data General Nova mini-computer. The boards were about 40cm square. For unexplainable reasons, the CPU stopped when the FORTRAN compiler encountered a DO statement [don't ask me how it knew that :-)]. DG finally brought in the guru, wearing what appeared to be the same clothes for a week, and he finally said, "cut these two traces in two places and replace them with a piece of tightly twisted pair." Problem solved. Obviously, he wasn't being paid the big bucks because of his wardrobe, but twisted pair did the trick. 73, Fred K6DGW - Northern California Contest Club - CU in the 2011 Cal QSO Party 1-2 Oct 2011 - www.cqp.org ______________________________________________________________ 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 for all the replies from Don, Jim and Fred and some others
73, Johnny VR2XMC 從︰ Fred Jensen <[hidden email]> 收件人︰ Elecraft Reflector <[hidden email]> 傳送日期︰ 2011年09月8日 (週四) 9:57 PM 主題︰ Re: [Elecraft] KPA500 RF output wiring > On 9/7/2011 10:53 PM, Johnny Siu wrote: >> The connection between the RF deck to the RF SO239 output is a pair >> of twisted wires instead of a coaxial jumper. Is there any reason >> for such a design? Twisted pair is a highly effective transmission line, and easier to work with than coax in tight quarters. That TP in the KPA500 is short. A suitable size piece of coax would be pretty stiff. I don't have any quantitative data [ask Jim, K9YC, I'm sure he does], but I've also found balanced twisted pair to often be less susceptible to RFI than shielded cable. In the early 70's, I was working on a process control system hosted on a Data General Nova mini-computer. The boards were about 40cm square. For unexplainable reasons, the CPU stopped when the FORTRAN compiler encountered a DO statement [don't ask me how it knew that :-)]. DG finally brought in the guru, wearing what appeared to be the same clothes for a week, and he finally said, "cut these two traces in two places and replace them with a piece of tightly twisted pair." Problem solved. Obviously, he wasn't being paid the big bucks because of his wardrobe, but twisted pair did the trick. 73, Fred K6DGW - Northern California Contest Club - CU in the 2011 Cal QSO Party 1-2 Oct 2011 - www.cqp.org ______________________________________________________________ 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 Brown-10
> Sure. Twisted pair is a VERY effective transmission line, and that is
> what is needed ... Hey Jim, what kind of twisted pair could I use to feed my [mostly 50 ohm] HF antennas? Coax is expensive in ZL so I'm willing to try alternatives. I'm even thinking of homebrew balanced line with baluns at the bottom (a coax-fed remote antenna switch in my case). 73 Gary ZL2iFB ______________________________________________________________ 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 9/10/2011 11:05 PM, Gary Hinson wrote:
>> Sure. Twisted pair is a VERY effective transmission line, and that is >> what is needed ... > Hey Jim, what kind of twisted pair could I use to feed my [mostly 50 ohm] HF > antennas? Coax is expensive in ZL so I'm willing to try alternatives. I'm > even thinking of homebrew balanced line with baluns at the bottom (a > coax-fed remote antenna switch in my case). Coax is expensive in the US too :) The key to loss is conductor size and impedance. The parallel wire cable sold for use with loudspeakers would make decent parallel wire antenna line. Twisting has the advantage of greatly reducing crosstalk and radiation/pickup to/from the line. RG8 uses #14-#10 for the center conductor, most copper braid shields are equivalent to #10 at DC and a much larger conductor on the higher HF bands (thanks to skin effect). #12 parallel wires or twisted pair would probably be equivalent in loss to very good RG8, and in the 50-70 ohm range for impedance. At HF, dielectric loss doesn't matter, but the dielectric will affect Vf. You will need common mode chokes at both ends -- remember, most real world ham antennas are unbalanced by their surroundings. It's a mistake to call cable like this a balanced line. It's a parallel wire line or twisted pair line. 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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