David and All, I'm not jumping into the middle of the discussion on RF ground, but I'm certainly enjoying the commentary. It's very thought provoking.
However, I do want to "take issue", with all due respect, to your point #1. I've used a variety of MFJ accessories over the last 30 years or so, and I find most of them to be quite competent. I might agree that there is the occasional situation where a connection is bad, or something is rattling around inside the case, but I think that is certainly the exception rather than the rule. MFJ products are generally aimed to provide a lower cost approach to something. As such, they tend to be somewhat closer spec'd in order to reduce cost. Nevertheless, when used as designed, they usually work, and work well. Many of their items, like tuners, are relatively simple with few components. There's not much to go wrong, unless the item is abused, which I maintain is why many users end up being unhappy. When MFJ says it's a 200 watt tuner, they usually mean it! I don't think I've ever had a problem with an MFJ tuner, and I've had (have) a bunch of them! But I've never run more than 100 watts through them either. But if you bang one with power over the spec'd rating, or even close to the spec'd rating with a horrible load (you should tune at a reduced power first) for very long, something's probably going to blow! A lot of unhappiness with MFJ products is also due to the fact that they tend to be fairly basic--as in not too many "bells and whistles". I can't even count the number of time I've seen others opt for an MFJ item because it was cheaper than "brand X", and then discover that it wouldn't do some of the things brand X would do. Of course, brand X was twice as expensive too! But suddenly, the MFJ item becomes "junk" in their minds, and they give it a 1 or 2 rating on Eham. That's even though the MFJ item did what it said it would do--just not a lot more. MFJ isn't innocent when it comes to claiming "great results", but neither are other manufacturers. A good example is their antennas and how "wonderful" they are. They aren't! But they work, and they are comparatively inexpensive. So, I suggest that most of the whining about MFJ stuff is self induced. Either it's excessive expectation, abuse, or both. After all, in most cases now they give you a "no matter what" guarantee. As a QRPer, I've found many MFJ items to be extremely beneficial. I think Martin Jue, who owns MFJ, is "borderline genius" when it comes to identifying a niche and filling it. He's done more to accomodate the QRP community (and QRO folks too) than just about anybody. I remember over 30 years ago, when I lived in Memphis, seeing him selling his gadgets at the local hamfest. Since then he's been incredibly prolific (and successful) , and it's been to our benefit. The problem is some folks want a Cadillac for a Chevrolet price. As for the MFJ artificial ground accessory, I don't have one, and have never used one. But I bet it works--at least it probably does what it is designed to do. However, it's a compromise solution, and not a perfect solution. Accordingly, some folks are going to be disappointed. Dave W7AQK ----- Original Message ----- From: "David Gilbert" <xda...@cis-broadband.com> To: "Ron D'Eau Claire" <r...@cobi.biz> Cc: <Elecraft@mailman.qth.net> Sent: Thursday, April 02, 2009 5:49 PM Subject: Re: [Elecraft] Artificial RF Ground > > Sorry, but I believe your posting to be full of bad > advice. > > 1. Most bad reviews for companies that cater to hams are > due to bad > customer service. MFJ is one of the few that consistently > gets bad > marks for quality of construction and durability of use. > If you don't > believe that, you simply haven't been paying attention. > > 2. An "artificial ground" doesn't keep RF out of the > shack ... it just > tunes a low impedance path to something, which may or not > be a ground of > any sort. In any case, the chances of finding a > functioning "RF ground" > in an otherwise insulated basement room are not great. > > 3. Vertical antennas are notorious for putting RF on the > coax shield > when the coax is lying right alongside the radials. Why > would you > expect such an arrangement NOT to couple RF to the coax, > and therefore > right into the shack? Check around and you'll find all > sorts of > instances where people had such problems with a vertical > antenna and > used a current choke to fix it ... there are writeups > everywhere on it. > I agree with K9YC that a coil of coax will normally do the > job just > fine, although I'm not sure that the base of the antenna > is always the > best place to put it. If the coax is lying next to the > radials it seems > to me that there could still be a lot of coupling to the > coax on the run > to the shack. I'd be more inclined to put the choke > closer to the > house, but I'll defer judgment on that to the experts. > > Dave AB7E > > > > > Ron D'Eau Claire wrote: >> 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
