KAT100 on 30 Meters
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I am using the K2/100 KAT100 combination into a Carolina Windom 80. It works well on all bands (excluding 160). On 30 meters the KAT100 SWR seems to occasionally fluctuate wildly as indicated by the LEDs. The leftmost LED is always (stays) lit with power applied even during the fluctuations. A Bird 43 wattmeter with 250H slug is in line between the KPA100 output and the KAT100 input. At no time while the LEDs were fluctuating did the SWR on the wattmeter go off zero. I chalk this up to stray RF in the KAT100 even though it is grounded. I receive good clean RST reports on 30 meters at all power levels. When the KAT100 LEDs are erratic, it doesn't always mean SWR trouble. It may mean stray RF though. Grounding the KAT100 (and K2) and sanding the panels at block joints may or may not help. You just live with it or put up another antenna. Roy Morris W4WFB
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RF Ground (WAS: KAT100 on 30 Meters)
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Getting an effective RF ground at the higher frequencies isn't really
difficult, but it sometimes takes thinking about it a little differently. The problem is that wires going to an earth ground are usually quite long in terms of wavelength. That makes them ineffective. For example, you have a 23 foot wire running from the rig to a solid earth ground on 30 meters, you'll have no RF ground at all at the rig. Indeed, just the opposite will occur and the rig will tend to "float" at a high RF voltage while transmitting. The reason is that 23 feet of wire is about 1/4 wavelength at 30 meters. A 1/4 wavelength long wire inverts the impedance seen at each end. If the end at the earth ground is truly grounded, the other end of the wire at the rig will be at a very high impedance. In short, the copper ground wire will look like an excellent RF insulator at 30 meters. Most situations aren't that simple, but it gives a good example of how a seemingly innocent ground wire running to a good earth ground may not provide an RF ground at all. Even a 10 foot wire or less will show substantial impedance at 30 meters and hold the rig well "above" RF ground. We can put that impedance inversion that occurs at the ends of a 1/4 wave long wire to work for us to produce a simple, effective RF ground. Connect one end of the wire to the rig and insulate the other end. The insulated end is forced to be at a high RF impedance, so the rig end is, by definition, at a low RF impedance (i.e. at RF ground). It is important to insulate the far end of the 1/4 wavelength long wire, not just to avoid RF burns while transmitting, but to force it to remain at a high impedance. That technique gets the ground impedance down in the vicinity of 35 ohms, which is generally a very good RF ground (most grounds using ground stakes or a few "radials" on or buried in the ground have an impedance in the range of hundreds of ohms at RF). The value can be lowered even further though by shortening the wire and then resonating it to a 1/4 wavelength on the operating frequency. Some companies sell 'tuners' specifically for this purpose. MFJ makes one called an "Artificial Ground". They are also easy to construct. Basically, all that's needed is a loading coil. A coil and capacitor may be easier to tune because the taps on the coil become less critical. A low-power 'antenna tuner' can also be used. What we're doing is turning something that is a big problem if we're making an antenna into an advantage to make a good RF ground. When we're forced to use an electrically short antenna that we resonate to 1/4 wave long using loading coils or an antenna tuner, we have to accept relatively low efficiency because such an antenna has a very low RF impedance. The shorter we make it, the lower the feed point impedance. The lower the feed point impedance the lower the efficiency. If we use it as an RF ground, we put that low impedance to work for us. By resonating a short wire at 1/4 wavelength at the operating frequency and connecting it to the rig ground, we supply a very low RF impedance that keeps troublesome RF voltages off of the rig. The disadvantage of such a ground is that the system "Q", or sharpness of tuning, gets high. That means that for a given adjustment, it will provide an effective RF ground over a fairly narrow range of frequencies. Such systems normally must be retuned whenever you QSY around within the band more than a few kHz. That can be a pain to do and rather defeats the convenience of an automatic antenna tuner! For that reason, most operators use a 1/4 wavelength long wire, which has a low enough impedance to provide an effective RF ground for most purposes and which still has a low enough Q that it doesn't need adjustment while tuning across the band. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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On Thu, 18 May 2006 16:40:39 -0700, Ron D'Eau Claire wrote:
>you'll have no RF ground at all at the rig So what? The significance of an RF ground is highly overemphasized. Park next the to end of the runway of your local airport and watch the 747's take off. Call me collect when you see one trailing a ground wire. Last I heard, the onboard electronics and radios work just fine without one. The earth is NOT a sump into which noise is dumped, nor will a connection to earth make a radio more stable. An earth connection has no beneficial effect on the operation of a radio transmitter, nor on the elimination of RF interference. In fact, a connection made to earth by a noise source or receiver will act as an antenna, radiating or receiving interference. A "ground system" for a long wire or vertical antenna is really a COUNTERPOISE for the antenna -- it provides the other half of the circuit for the transmitter (or receiver) as a load. This is why it is VERY important to bond the shield of the coax in a mobile antenna system to the body of the car at the base of the antenna. It isn't noise (although it might reduce noise), it's the other half of the antenna! The surface of the earth also serves as a reflector for the radio waves radiated by the antenna. That ground system will work better (be more efficient, have less IR loss) if it is has low impedance at the frequency where it is used. High moisture content results in very low resitivity and better reflectivity in the soil. It is the combination of the reflection(s) with the direct wave from the antenna that determine the vertical directivity of the antenna system. These two mechanisms are the significance of RF ground. Jim Brown K9YC http://audiosystemsgroup.com _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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Jim K9YC wrote:
So what? The significance of an RF ground is highly overemphasized. Park next the to end of the runway of your local airport and watch the 747's take off. Call me collect when you see one trailing a ground wire. Last I heard, the onboard electronics and radios work just fine without one. ---------------------- Of course an RF ground or a connection to the earth is not essential. Indeed, my point was that a connection to the earth was NOT required. In the question I was responding to, the writer was trying to reduce the RF voltage on the case of his equipment because everything was not floating above ground, like in an airplane. I was suggesting ways he could reduce the RF voltages on the gear without a connection to an earth ground. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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In reply to this post by Jim Brown-10
Jim,
Well said - for years now I have been trying to convince folks that there is a strong need for considering 2 'grounds' at a station. The first is the Safety Ground which should be a low impedance path to earth - large conductors, lots of heavy guage wire buried in the earth and ground rods, and this must also be connected to the utility ground. Properly implemented it should serve a a lightning protection ground. The second is the RF Ground - and the Safety Ground may or may not suffice. Consider a good Safety Ground with an 8 foot connection from the antenna connection at the tuner - that combintion will likely produce a high impedance for RF at 10 meters, thus there will be no RF Ground at that frequency. In such conditions, the use of quarterwave counterpoises for each troublesome band is in order. 73, Don W3FPR -----Original Message----- So what? The significance of an RF ground is highly overemphasized. Park next the to end of the runway of your local airport and watch the 747's take off. Call me collect when you see one trailing a ground wire. Last I heard, the onboard electronics and radios work just fine without one. The earth is NOT a sump into which noise is dumped, nor will a connection to earth make a radio more stable. An earth connection has no beneficial effect on the operation of a radio transmitter, nor on the elimination of RF interference. In fact, a connection made to earth by a noise source or receiver will act as an antenna, radiating or receiving interference. A "ground system" for a long wire or vertical antenna is really a COUNTERPOISE for the antenna -- it provides the other half of the circuit for the transmitter (or receiver) as a load. This is why it is VERY important to bond the shield of the coax in a mobile antenna system to the body of the car at the base of the antenna. It isn't noise (although it might reduce noise), it's the other half of the antenna! The surface of the earth also serves as a reflector for the radio waves radiated by the antenna. That ground system will work better (be more efficient, have less IR loss) if it is has low impedance at the frequency where it is used. High moisture content results in very low resitivity and better reflectivity in the soil. It is the combination of the reflection(s) with the direct wave from the antenna that determine the vertical directivity of the antenna system. These two mechanisms are the significance of RF ground. Jim Brown K9YC http://audiosystemsgroup.com _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.392 / Virus Database: 268.6.1/344 - Release Date: 5/19/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.392 / Virus Database: 268.7.0/345 - Release Date: 5/22/2006 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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On Tue, 23 May 2006 10:29:50 -0400, Don Wilhelm wrote:
>Well said - for years now I have been trying to convince folks that there is >a strong need for considering 2 'grounds' at a station. Yes. It is also important to remember that a SAFE installation (from a lightning and power safety point of view) requires that ALL grounds be bonded together, prefereably outside the building. In other words, while we must consider the behavior of our ground systems at radio frequencies, we must also take into account how they behave at power frequencies, and how they will respond to lightning (think radio frequencies). There is a discussion of safe grounding in the Power and Grounding tutorial that is on my website. All pdf files, no cookies required, free download. While it is specifically written for pro audio systems, the same laws of physics apply equally to our ham stations. :) http://audiosystemsgroup.com/publish BTW -- sorry to have missed seeing you at Dayton -- I just completed a cross country move from Chicago to Santa Cruz, and am totally burned out on traveling for at least a month or two. So I stayed home. The good news that I'm now about 20 miles from Elecraft world headquarters! 73, Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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In reply to this post by Ron D'Eau Claire-2
W3FPR continued from K9YC:
>Well said - for years now I have been trying to convince folks that there is >a strong need for considering 2 'grounds' at a station. >The first is the Safety Ground which should be a low impedance path to >earth - large conductors, lots of heavy guage wire buried in the earth and >ground rods, and this must also be connected to the utility ground. >Properly implemented it should serve a a lightning protection ground. > >The second is the RF Ground - and the Safety Ground may or may not suffice. >Consider a good Safety Ground with an 8 foot connection from the antenna >connection at the tuner - that combintion will likely produce a high >impedance for RF at 10 meters, thus there will be no RF Ground at that >frequency. In such conditions, the use of quarterwave counterpoises for >each troublesome band is in order. Yes, important distinction & worth mentioning! When not physically close to ground level, that safety ground in the shack can bite you in the bum, such as in Don's example. Few here can establish shack safety or antenna safety grounds that are not going to do something untoward. And antennas usually require roof access, a roof that often has to be directly over your head (top floor flat). This makes RF in shack a big problem. Computer keying, mic switching & voice keyers don't like RF. In such an extreme environment, usually with no option to move anything around, I have yet to try an artificial ground. This despite four feeders plus few control cables running straight into shack from series-fed roof tower as low band vertical - common-mode chokes have always done the trick. They also help keep noises from shack from getting back into the antennas. I could drop all the bonding between major boxes in the shack (rigs, amps, switching gear), but that is my solution for redundant safety ground when operating as total disconnect is also practiced inside during lightning. The bonding also helps a bit with computer keying (often only way to keep from latching key down when transmitting into the roof tower vertical). Few solar cycles of experience from two to 39 floors up here that may help those in more pedestrian situations. The artificial ground is like what I am trying to avoid in the station, so would really be a last resort & one that has yet to be needed. Saying that, I also will not use any end-fed wire or similar antenna that is certain to be problematic - for a temporary set-up where I had to use that sort of antenna then an artificial ground could be the ticket but then certain to hear that computer, telly, etc... unless near field dominates, choke that common-mode stuff & you're likely to prevail. 73, VR2BrettGraham _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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Brett,
I did not intend to say that you should disconnect your equipment from the safety gound - only that you may need to supplment it with an RF ground at the place where your equipment connects to the antenna system. In other words, both are necessary, and can work in conjunction with each other. 73, Don W3FPR -----Original Message----- W3FPR continued from K9YC: >Well said - for years now I have been trying to convince folks that there is >a strong need for considering 2 'grounds' at a station. >The first is the Safety Ground which should be a low impedance path to >earth - large conductors, lots of heavy guage wire buried in the earth and >ground rods, and this must also be connected to the utility ground. >Properly implemented it should serve a a lightning protection ground. > >The second is the RF Ground - and the Safety Ground may or may not suffice. >Consider a good Safety Ground with an 8 foot connection from the antenna >connection at the tuner - that combintion will likely produce a high >impedance for RF at 10 meters, thus there will be no RF Ground at that >frequency. In such conditions, the use of quarterwave counterpoises for >each troublesome band is in order. Yes, important distinction & worth mentioning! When not physically close to ground level, that safety ground in the shack can bite you in the bum, such as in Don's example. Few here can establish shack safety or antenna safety grounds that are not going to do something untoward. And antennas usually require roof access, a roof that often has to be directly over your head (top floor flat). This makes RF in shack a big problem. Computer keying, mic switching & voice keyers don't like RF. In such an extreme environment, usually with no option to move anything around, I have yet to try an artificial ground. This despite four feeders plus few control cables running straight into shack from series-fed roof tower as low band vertical - common-mode chokes have always done the trick. They also help keep noises from shack from getting back into the antennas. I could drop all the bonding between major boxes in the shack (rigs, amps, switching gear), but that is my solution for redundant safety ground when operating as total disconnect is also practiced inside during lightning. The bonding also helps a bit with computer keying (often only way to keep from latching key down when transmitting into the roof tower vertical). Few solar cycles of experience from two to 39 floors up here that may help those in more pedestrian situations. The artificial ground is like what I am trying to avoid in the station, so would really be a last resort & one that has yet to be needed. Saying that, I also will not use any end-fed wire or similar antenna that is certain to be problematic - for a temporary set-up where I had to use that sort of antenna then an artificial ground could be the ticket but then certain to hear that computer, telly, etc... unless near field dominates, choke that common-mode stuff & you're likely to prevail. 73, VR2BrettGraham _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.392 / Virus Database: 268.7.0/345 - Release Date: 5/22/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.392 / Virus Database: 268.7.0/345 - Release Date: 5/22/2006 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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: RF Ground (WAS: KAT100 on 30 Meters)
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W3FPR added:
>I did not intend to say that you should disconnect your equipment from the >safety gound - only that you may need to supplment it with an RF ground at >the place where your equipment connects to the antenna system. In other >words, both are necessary, and can work in conjunction with each other. No, I don't think you did. I have found RF ground to be pretty elusive, so don't bother. Safety ground beyond mains leads sometimes makes things worse, though has obvious downside. With 220 volt mains, a failure is more dangerous, though also more obvious. The overall situation must be kept in mind, but what I am saying is that grounding as everyone thinks it has to be done is not done here & therefore might be kept in mind when having to tame RF nastiness in some situations. Frequency of lightning even this far north drives the need for total disconnect, so that mains lead safety ground already there could be the place to stop & attention turned to choking if near field isn't dominate. Bonding of major bits at least keeps case of failed box tied to a safety ground that I keep an eye on (and usually helps tame the nasties). A compromise, but workable where no way to really build for no-need-to-disconnect. I don't think I'm implying giving up the safety ground (at least not when operating), either. If it gets too exciting, will have already yanked everything, as the 1N5711s become dominate. ;^) Artificial ground plus choking could still be the ticket for end-fed wires, etc. I just find ground makes things worse sometimes & I sit right under my antennas. Like black magic, RF is. "Extra" grounding might not be your friend. 73, VR2BrettGraham _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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