Ha, ha! There are "MFJ Bashers" just like there are those who must complain about just about every company. As my Grandmother used to say of such people, "He'd complain if they hung him with a new rope."
To your point, yes the MFJ "Artificial Ground" works FB. One the MFJ tuners I have around is the MFJ-934 which has the AG built in and I've used it quite successfully with a variety of antennas. If you have Moxon's "HF Antennas for All Locations" he discusses such grounding schemes in detail, but it seems to be something ignored in many texts. What you are doing is arranging a 1/4 wave wire connected to your rig. At 1/4 wave, it presents a rather low impedance to the rig, which keeps it at a low RF voltage. The AG is nothing more than a simple single-wire "tuner" to establish that condition with almost any wire across the HF spectrum. The tuner circuit is a tapped coil in series with a variable capacitor that can be adjusted to compensate for a wide range of reactance values present at the end of your "ground" wire attached to the tuner. Since you are working for the lowest impedance at that point, it includes an RF ammeter in series with the circuit. You adjust the coil and cap for maximum reading on the ammeter. At any given power, maximum current equals lowest impedance equals lowest voltage. As Moxon points out, you can do the same thing with any length of wire that is < 1/4 wave and a simple loading coil at the rig, just as you might do with a short antenna. (The variable capacitor in the AG covers situations where the "ground" wire is longer than 1/4 wavelength). A small flashlight bulb in series with the wire will indicated the proper amount of inductance. Adjust the power for some indication and set the coil for maximum brilliance. You can remove the bulb when you find the right setting so it won't burn out at higher powers. It's not a panacea. There are some situations where it doesn't cure the problem. As others took pains to point out in the other recent thread, there is no "perfect" (zero ohm) ground. As frequency increases, dealing with reactance becomes more of an issue and, at RF, we have significant conductor resistance as skin effect enters into the equation. But that doesn't mean the effort is useless or ineffective. You raise an interesting issue though, saying you're using a vertical with radials on the ground. Those antennas aren't typically RF feedback prone antennas. What are the "feedback" symptoms. Does the feeder show a low SWR at the Antenna? Is the shield of the coax properly connected to the radials with a good, low resistance connection? Ron AC7AC -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of NG3V Sent: Thursday, April 02, 2009 2:43 PM To: Elecraft@mailman.qth.net Subject: [Elecraft] Artificial RF Ground Good Evening Group, All this talk of RF grounds has re-kindled my desire to run more than 10 watts without RF feedback in the shack (yeah, I know 10 watts is enough, I just like the ability to have more). Anyway, my shack is in an enclosed room in the basement with no direct access to the outside world. My antenna is a ground-mounted vertical about 15 feet from the house with buried radials. The feedline is laying on the ground. Poor arrangement, but best I can do for the time being. I asked DX Engineering if they thought their Feedline Current Choke might help and Bob, N8QE, replied with a very nice message suggesting that I look at the MFJ-931 artificial RF Ground. Have any of you had experience with this thing? The eham reviews were mostly what we've come to expect about MFJ stuff. Buy it, open it, fix it, use it. I'm interested in the 'use it' part. TIA es 72, Tom, ng3v ______________________________________________________________ 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
