Re: [Elecraft] KPA500 RF output wiring
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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] KPA500 RF output wiring
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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
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:Elecraft@mailman.qth.net 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
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? 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
