Ron, Thank you for the references. I found the information very interesting to say the least. Parts here would be an issue, but the construction and methods to check and adjust the tuner were most valuable. Now just to have some drawer space! As Don had mentioned in an earlier post, getting the balanced feed line to the shack can be quite a challenge, especially for those of us who have rebar enforce concrete with no simple method to feed through the wall. I think even the double coax systems to be a difficulty especially when having to drill into the side of the house and miss all the surrounding materials, esp. the rebar. This may not be my last shack so I have filed the project and will see what I can find for parts now before this stuff gets extinct. That copper tubing is really becoming scarce and I am not even sure how much copper really is in the tubing and what impact it has on the coils if not of the same purity.
I did locate some surplus Comet vacuum capacitors in the $800+ range??!!! 73, Bill K9YEQ -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Ron D'Eau Claire I have often had a voltage loop at the rig end of my open wire feed line and have never experienced a problem with stray RF, even though a neon bulb lying near the ATU blinked as I sent CW. HOWEVER - I do use a homebrew link-coupled ATU with open wire line. It lacks the dual-differential tuning capacitors that Johnson used to adjust virtual coil taps for the feed line in the Matchbox, but mine has a much wider matching range using actual taps on the coil. (The Johnson Matchbox is only rated to match balanced lines with impedances up to 1200 ohms). Link coupling has a number of advantages including a high order of suppression of stray signals since there is no direct electrical connection between the antenna and the rig. Everything coming in (or going out) has to pass magnetically across the link coupling and through the tuned circuit. That's especially handy if you live near a broadcast station. And of course, you can use the same tuner with unbalanced lines (e.g. coax). Just connect the shield to the center of the coil and tap the center conductor out to either side. WZ5Q has a great example of a beautifully link coupled tuner at: http://www.wz5q.net/index/shack_data/tuna.htm It's bigger and neater than mine but the circuit is the same right down to the RF current sensors. Ron AC7AC -----Original Message----- If you do encounter a high impedance feedpoint on any band, that will place a high RF voltage point at the shack end - add or subtract some feedline to bring the feedpoint impedance down. If you do not understand how the feedpoint impedance changes with the length, take a look at the Antenna article on my website www.w3fpr.com 73, Don W3FPR 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
