+++++++++++++++++ Date: Wed, 25 Sep 2002 09:43:02 -0500 To: "Daniel" , elecraft at mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] K2 fixed, but now what? Daniel: Add a COUNTERPOISE to the antenna configuration... this can consist of nothing more than a 15'-30' (depending upon what bands you plan to operate) length of wire, connected to the GND terminal of the KAT2 and laid on the floor, but try to stretch it out as much as possible... bends are probably OK, but try to use up as much area as possible. If you can droop the wire out the window and let it hang DOWN, so much the better. Generally, I counterpoise will make the RF situation look much less 'hot' to the K2/KAT2. 73, Tom Hammond N0SS At 09:12 AM 9/25/02, you wrote: >HI GUYS/GALS, > >I FINALLY GOT MY K2 ALL REALIGNED LAST NIGHT AND WITH THE MOD FOR THE HI >CUR SIGNS AND REMOVING RF ON THE ISENSE LINE. > >BUT NOW THIS IS HOW I SET UP MY TEMPORARY ANTENNA THIS MORNING. LOW ANGLE >RADITION WIRE 20FT RAN THROUGH MY WINDOW WITH WINDOW TURNED UP AGAINST THE >WIRE, AND THE END OF THE WIRE INTO KAT2 WITH NO GROUND. I GET HI CUR AND >LOW P ON SOME BANDS. AND THE ELECRAFT RESETS ITSELF. > >I KNOW I CALIBRATED/ALIGNED THE KAT2 CORRECTLY AND THE BASE K2 (CW ONLY) >PUTS OUT ITS FULL POWER ON ALL BANDS. > >I THINK THAT MY PROBLEM IS NOW THE ANTENNA. WHAT ARE YOUR IDEAS?? > > >ON ANOTHER NOTE: >I WILL TRY TO BE MONITORING THE TWO AGREED UPON FREQUENCIES [21.332 & >18.132] BETWEEN 2PM AND 6PM. > >DANIEL ++++++++++++++++++ Date: Wed, 25 Sep 2002 08:50:59 -0700 (PDT) From: Lloyd Lachow Subject: Re: [Elecraft] K1 End-Fed Wire Antenna Recommendations To: Janet Beckett , elecraft at mailman.qth.net --- Janet Beckett wrote: > Just finished #1265 and wanted some recommendations > on the best way to > hook up an end-fed wire antenna directly to the BNC > connector. Any > suggestions? Janet, I get fabulous results with a ~200' wire up about 25' (actually, it has about a 15' vertical section on either end, and some twists and turns), and four counterpoises. I have a BNC-to-binding posts adapter, with the longwire in the red side (but only while I'm operating), and the counterpoises on the black. My K1 has 15-20-30-40, so my counterpoises are: two at about 16.5-17', and two at 33'. They're just run out along the basebopards on the floor. ===== 73, Lloyd, K3ESE K1 # 00379 - ARRL ARS #1301 - FISTS #8774 FPqrp #476 - QRParci #11147 QRP-L #2415 - SOC #530 HGT #6'1 - Wgt #190 +++++++++++++++ Date: Wed, 25 Sep 2002 11:23:31 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Cc: Daniel , elecraft at mailman.qth.net Subject: Re: [Elecraft] K2 fixed, but now what? I would like to add a coment or two to Tom's excellent suggestion. The term "counterpoise" has come to mean many things in amateur radio usage and I will steer clear of trying to give any sort of generally accepted technical definition for the term. The function of a true counterpoise differs from that of the wire under discussion, but it matters little what we decide to call it - the wire works the same regardless. Historically, the term "counterpoise" originally was used to describe a system of wires placed near but not on the ground to provide an r-f connection to ground by means of the capacitance between the counterpoise and the actual ground. The counterpoise was not necessarily designed to be resonant but was more intended to provide as much capacitance as could reaonably be obtained. A similar effect accounts for the success of our vehicular HF installations where the capacitance of the vehicle frame and body to ground provides our r-f connection to ground and thus allows our vertical whips to operate with a degree of efficiency. At 10 meters or so, the vehicle body may serve as a groundplane of sorts but clearly at 80 and 40 meters something else is needed for any degree of efficiency. The purpose of the wire that Tom is recommending is not primarily to provide a capacitive connection to the Earth (which it does to a degree) but rather is to place the cabinet, chassis, etc. of the K2 - specifically the GND post on the rear panel - at as near zero r-f potential as possible. Thus, the term "driven ground" is usually applied to a wire connected as described. If the wire is 1/4-wavelength long at the operating frequency, has its far end insulated and is not too close to the ground or metallic structures - either of which would serve to detune it - then in the near-field of the radiating portion of the antenna system, the wire has current induced in it. This current sets up a voltage gradient along the wire, with the "far end" having a voltage maximum and the end connected to the radio a near zero voltage level, due to its 1/4-wavelength dimension. Thus, the "driven ground" serves to collect r-f from the "antenna" for the purpose of *driving* the radio "ground" to near zero r-f potential. Because of the current in the wire, it is actually a radiating part of the overall antenna system and should be treated as such. Even with our 5 watt power levels, substantial voltages can be developed at the open end. Radiation from the driven ground wire is normally not a great problem in most field setups - it probably helps! - but in home stations, some care should be taken in how the wire is placed to minimize r-f pickup in nearby devices. >From a theoretical viewpoint, the actual impedance to "ground" - whatever and wherever that mystical reference point may be - from the KAT2 ground post is probably much much lower with the driven ground than one could obtain by using a ground rod with a wire between it and the K2. An exception might be if one uses a series-tuned resonant circuit in such a lead to minimize the overall impedance. Before rushing out to pound several 8-10 ft ground rods into Mother Earth, be aware that most ground rods are fine for 60-Hz and possibly for lightning abatement, but are essentially worthless for r-f "grounding" purposes. Even if they did manage to maintain a low-impedance connection to "ground", connecting the station equipment to the rods involves conductors with finite and frequently large impedances. Hence the use of the "ground line tuners" such as those sold by MFJ. Incidently, if you want to build one, the circuit diagram of the MFJ-931 is in ON4UN's "Low-Band DXing" on page 11-22. In over 57 years of amateur radio I have never used a "station ground" other than the safety ground for 60 Hz provided by the power line system. R-f ground requirements for antennas are best resolved at the antenna, not in the shack. 73/72, George Fairview, TX 30 mi NE of Dallas in Collin county EM13qe Amateur Radio W5YR - the Yellow Rose of Texas In the 57th year and it just keeps getting better! Tom Hammond NØSS wrote: > > Daniel: > > Add a COUNTERPOISE to the antenna configuration... this can consist of > nothing more than a 15'-30' (depending upon what bands you plan to operate) > length of wire, connected to the GND terminal of the KAT2 and laid on the > floor, but try to stretch it out as much as possible... bends are probably > OK, but try to use up as much area as possible. -- snip -- +++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: Subject: RE: [Elecraft] K2 fixed, but now what? Date: Wed, 25 Sep 2002 10:17:24 -0700 Excellent comments George. I'm sure that you remember when a "dipole" meant that it was a HALF WAVE radiator. Whether or not it was fed at the center, at one end or somewhere in between did not matter. Accordingly, an antenna was not a half wave long is NOT a dipole, even if it's fed in the center or sold with "Dipole" written all over the packaging. Well, that's still true in Engineering circles, but out here in "hamdom" the meanings get changed radically. It's with some trepidation that I start allowing "ham" definitions into my vocabulary because it makes life so darn confusing when talking with engineers. You make an excellent point about "counterpoises", It's one that I've gotten careless with. Following up on your statement, it might be useful for ops just discovering them that one of the best ways to "adjust" such a "floating ground wire" for the best length is to adjust it for maximum current flowing into it at the rig end. The idea is to have the lowest possible r-f impedance at the rig end. Lowest impedance = largest r-f current for any given power level and minimum r-f voltage at the rig end. That's the idea. Keep the rig cabinet at r-f "ground" or as close to it as possible. You can adjust the length of the...er....ahhh.."counterpoise" wire for maximum current or use a simple little "matching" network. MFJ makes a so-called "artificial" ground which employs a simple L/C network to adjust a "counterpoise" wire for maximum current. I have one such "artificial ground" built into an MFJ 934 ATU that works very well. Another approach is to use a slightly short wire and a small coil to bring it up to "resonance". The MFJ comes with a rudimentary but effective r-f current meter for adjusting it for peak current. With a homebrew circuit, maximum current is easily measured with a 50-cent r-f ammeter - what most of use recognize as a flashlight bulb. At QRP levels such a device works very well to indicate r-f current when placed in series with the wire. Remove it from the circuit when you have 'tuned' for maximum brightness. Buy two, at least. It's amazing how easy it is to burn them out . 73, Ron AC7AC K2 # 1289 ++++++++++++++++ From: "Stuart Rohre" To: , Date: Wed, 25 Sep 2002 20:02:29 -0500 Subject: [Elecraft] Re: The tuning of a counterpoise and RF current meter protection Very good summary of how to adjust a counterpoise, And mention might be made of the Ten Tec T kit Artificial "ground" tuner, which like the MFJ is only a series resonant circuit with current indicating meter, but I paid only $49 for the kit and one evening assembly. Might be $59 now, but worth it. The series tuned circuit of course has minimum impedance and therefore maximum current when tuned to resonance with the random wire on the rig ground. A way to preserve high quality thermocouple ammeters for RF circuits is to shunt them with a carbon resistor until you are sure the circuit you are trying to measure does not have current higher than the thermocouple meter rating. 73, Stuart K5KVH ++++++++++++++++ From: "Wallace, Andy" To: elecraft at mailman.qth.net Date: Thu, 5 Dec 2002 08:37:19 -0500 Subject: [Elecraft] multiband counterpoise with K1 > -----Original Message----- > From: Thom LaCosta [mailto:baltimoremd at baltimoremd.com] > FWIW, for years I was frustrated with bad locations, RF all over the > place, etc.....until I made up "The Bundle", a series of 1/4 > wavelength wires for each band I use. Taped them all together and > stretched it out around the secnd floor of my house. The antenna is an end > fed wire about 89 feet long, and all of 15 feet high. Thom, thank you for this idea! I just tried it. My ant is just a 35' or so random sloping down to a clothesline pole. The rig is a fair distance away from the window so I use a length of RG8X to get there. I've got a barrier strip attached to the wall and the coax attaches here, with the antenna wire attaching to the corresponding terminal. So I have the coax shield terminal for a counterpoise - in trying a random length of that, it didn't help much. I made a bundle as you described for my 4-band K1 (40/30/20/15) and drooped it down the stairwell. Seems to work. The KAT1 is happy about it. I'm in MA -- had a ragchew with a guy in NM on 20, and worked LX0LT in Luxembourg on 40 as well. Bands may seem a little quieter -- perhaps this helps on receive also. I'll hang it (unfortunately inside) more properly tonight and keep experimenting. I'll be happy if it reduces TVI, too. I don't see any references for such a counterpoise in a quick search. If anyone has pointers, please post them. I am curious how the four different lengths affect each other, electrically. Should the lengths change? I guess it would be similar to a fan multiband dipole, except with the elements against each other. I used insulated wire, of course!!!! Before someone suggests -- unfortunately I have no prospects of a better antenna outside... :-/ Someday! -Andy ++++++++++++++++ From: "George, W5YR" To: "Wallace, Andy" , Subject: Re: [Elecraft] multiband counterpoise with K1 Date: Thu, 5 Dec 2002 10:22:57 -0600 Andy, I have posted on this topic at least a dozen times over the past two years. This "bundle of wires" is not a true counterpoise in any sense of the word. It is, rather, a "driven ground" in which the wires being in the near-field of the antenna develop a current and associated voltage. By being 1/4 wavelength long and open at the "far end" the end attached to the station equipment is driven by the induced r-f to a near zero r-f potential, effectively "grounding" the equipment. Generally, this produces better results that any attempt to physically connect to an Earth ground. "Ground"is not all that it is supposed to be for r-f purposes - I suspect that more problems are created by efforts to "connect the station to a good r-f ground" than by omission of any such connection and concentration on the antenna system configuration. Keep in mind that the wires need be only approximately resonant but length is to some degree important. The open ends can achieve quite high voltages so they must be insulated. The wires will radiate and can be a source of RFI. Being bound up in a bundle will detune them all to some extent, but as long as they "work" that is what counts. Good luck with your new discovery of a very old application of the "driven ground." <:} 73/72, George Amateur Radio W5YR - the Yellow Rose of Texas In the 57th year and it just keeps getting better! Fairview, TX 30 mi NE of Dallas in Collin county EM13qe K2 #489 Icom IC-765 #2349 Icom IC-756 PRO #2121 +++++++++++++++++