Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
The nice thing about the Ten Tec kit, is that it can be easily converted to an L network tuner, if you switch the point where the pick up circuit monitors current, and substitute a coax jack for the connection in one original hole. That way, it can be converted back to artificial ground service by use of a shorting plug, if I remember the scheme I used some years ago. -Stuart K5KVH ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
Jim, I will agree with you wholeheartedly, except for the RF Ground part --- In reality, RF ground has only to do with a zero impedance reference for RF at the frequency of operation. It can actually be up in the air (example - at the midpoint of a dipole, normally the dipole feedpoint), or at the other extreme it can be close to a physical groundpoint (like in the shack at a tuner groundpoint). It has been said that balanced antennas need no RF ground - I am just saying it differently - that the RF 'ground' is built into a balanced antenna - or at the feedpoint in the case of a properly fed vertical, etc. Let this not be construed to imply that a hamshack does not need a good RF ground - in fact, every hamshack DOES need an effective ground point for RF ground, AC safety ground, and lightning protection, AND they should all be connected together at the hamshack common grounding point. Additionally, the best station ground type is the single point ground - where each piece of equipment has a ground wire going to this common point (like a grounded entry panel through which all wiring to the shack enters). If a bus-bar type ground is used, it should be a very low impedance - as short as possible and physically large conductors. A really GOOD lightning protection ground at the shack will by its nature provide a good high current RF ground too, because to be effective it must shunt all frequencies to ground - but few hamshacks have the luxury of a protection system that effective. 73, Don W3FPR - Original Message - The way I like to look at is that there are at least four different 'grounds' that you have to worry about, and you need to provide for them separately. It's OK to think of them as fulfilling four different functions. But from a safety (and building code) perspective, ALL of these functional grounds MUST be bonded together. And HOW they are bonded together can make a huge difference when something goes wrong (like lightning). Jim Brown K9YC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
Hi, Bill- Unless I am mistaken, there is supposedly a schematic available for the MFJ-931 in Devoldere's Antenna and Techniques for Low-Band DXing. I have the 931 and use if with my EFW, both in the shack as well as while portable. It works well for me, plus one cannot have too many gadgets containing wiggly meters hanging around- hi. If you cannot get a copy of the schematic, let me know off list and I'll open up my unit and trace something out for you. As I recall, it is a simple variable L/C network whose output passes through a toroidal transformer that provides current info to the front panel meter. You could of course dispense with the meter and use a lil light bulb to help tune for maximum current. 73, Mychael/AA3WF K2#1025 ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
Ten-Tec has a kit version ($59) that in my experience works even better then the MFJ http://www.tentec.com/Tk1251.htm Mike, W9WIS ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
At the risk of seeming to rain upon the parade, let's keep in mind that the 931 can at most provide a low-impedance path to ground. Whatever that ground happens to be is what determines the success or failure of using the 931. In almost all cases, adding a simple ground connection to a station with rf in the shack problems is not the solution and may, in fact, make matters worse. Very few earth grounds constructed by the typical amateur are very effective, presenting hundreds of ohms of connection resistance to the soil. The preferred approach is to find out where the rf is coming from and correct that situation. All coax cables entering the shack should be provided with baluns at the antenna feedpoint and again at the shack entrance if needed. Antennas that place the shack equipment at other than zero rf potential should be avoided. Finally, the most effective way to place the equipment at zero rf potential is the driven ground. This consists of a 1/4 wave length of wire with one end connected to what is decided to be the station ground point and the other end unconnected. The wire can lay on the shack floor. It will carry induced current and radiate and thus is a source of RFI. But the open end will assume a high r-f potential thereby driving the connected end to very near zero potential. A wire for each band can be used if needed. 73, George W5YR Fairview, TX [EMAIL PROTECTED] http://www.w5yr.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
George, W5YR wrote: At the risk of seeming to rain upon the parade, let's keep in mind that the 931 can at most provide a low-impedance path to ground. Whatever that ground happens to be is what determines the success or failure of using the 931. George is correct. The way I like to look at is that there are at least four different 'grounds' that you have to worry about, and you need to provide for them separately. 1) The electrical safety ground. This is to prevent shocks in case the chassis of some equipment becomes 'hot' from the AC line. Electrical codes should be followed in shack wiring, all gear should have 3-prong plugs, and other grounds should be tied into this. 2) The lightning protection ground. This provides a low-impedance path for static discharges and lightning strikes to antennas. Requirements are quite stringent to do this correctly. 3) The RF ground. If you have an unbalanced antenna such as a long wire or vertical monopole, there needs to be a ground return for RF. This is what the radials of a vertical and the MFJ 931 are for. If your antenna is a dipole or beam with a balun, you probably don't need an RF ground. 4) The 'shack common' ground. All of your equipment should be connected with low-impedance straps to a common ground bus (which of course will be tied to the safety ground). The purpose of this is to insure that all the gear will be at the same RF ground potential and reduce the effect of the unavoidable ground loops created by interconnecting cables. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Like MFJ's 931 Artificial Ground ?
Vic, You are entirely correct - and I have long advocated thinking about the 'ground' terms separately. It should be common knowledge (but it isn't) that one 'ground' can be at a different potential than another 'ground'. I learned early in my hamming days because we often referred to 'chassis ground' which was a common wiring point and often had nothing to do with any earth ground. (That was before the time of the 3 wire wall outlets!!!) 73, Don W3FPR - Original Message - ... The way I like to look at is that there are at least four different 'grounds' that you have to worry about, and you need to provide for them separately. ...snip ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Like MFJ's 931 Artificial Ground ?
That's exactly what the Artificial Ground does, George. When you have a ground wire going to a ground stake it makes a lousy RF ground, but it'll be a much worse one if the wire to the stake is more than a couple of feet long because the wire is an appreciable fraction of a wavelength at HF. If the same connecting wire goes to a wonderful multi-wire counterpoise, the effectiveness of the counterpoise is badly compromised if the connection to the rig isn't very short and direct. Using very broad straps for conductors helps, but they are impractical for many situations. The Artificial Ground is simply a network to tune out the reactance in the connecting wire so the ground can act at maximum efficiency. It brings a distant ground to the rig electrically. As you said, you need a decent ground just the same, both for avoiding RF on the rig and for decent efficiency from a short (1/4 or less) end-fed antenna. But, sometimes, even a lousy ground like a stake in the soil is enough to eliminate the RF on the Rig problem, if the reactance of the connecting wire is tuned out. The Artificial Ground also allows tuning a simple counterpoise for maximum effectiveness on each band. That's how I use one with excellent results. It eliminates the need for a 1/4 counterpoise wave wire for each band in use. Ron AC7AC -Original Message- At the risk of seeming to rain upon the parade, let's keep in mind that the 931 can at most provide a low-impedance path to ground. Whatever that ground happens to be is what determines the success or failure of using the 931 ...the most effective way to place the equipment at zero rf potential is the driven ground. This consists of a 1/4 wave length of wire with one end connected to what is decided to be the station ground point and the other end unconnected. The wire can lay on the shack floor. It will carry induced current and radiate and thus is a source of RFI. But the open end will assume a high r-f potential thereby driving the connected end to very near zero potential. A wire for each band can be used if needed. 73, George W5YR Fairview, TX [EMAIL PROTECTED] http://www.w5yr.com ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
