++++++++++++++++++++ Date: Tue, 15 Oct 2002 07:56:26 -0500 To: elecraft at mailman.qth.net From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: [Elecraft] HF Verticals? George just said EVERYTHING I wanted to say, and MUCH better than I could have EVER said it. Toward the end of his reply, George makes reference to Walt Maxwell's "Reflections II", which, though I've not read it, I understand is as good as his first book, "Reflections" which I HAVE read, but which is no longer in print. For anyone interested, an EXCELLENT intro to both of Maxwell's works is now available at the ARRL web site. This is a PDF containing the contents of a series of QST articles by Maxwell (W2DU), entitled "Another Look at Reflections", which appeared in the early 70's. The series of articles was never quite completed at that time, but regardless, they contain some of the VERY BEST antenna theory you'll find anywhere. Even if you blow right by the math (and it's certainly there if you choose to get 'into' it), the articles are written so just about anyone will be able to gain a significantly better understanding of antenna matching and SWR (which is the crux of the series). To access this article, go to http://www.arrl.org and in the SITE SEARCH field at the top of the page, type in "ANOTHER LOOK AT REFLECTIONS" and click on GO. Once the search returns its results, "REFLECT.PDF" should be at the top of the list. RIGHT-CLICK on this link and then, when prompted to do so, select SAVE FILE AS (or whatever similar choice you are presented by your browser) and SAVE the file to your hard drive. DO NOT attempt to read the article on-line by merely clicking ON the link and paging thru it. The article's much too long to be viewed on-line. This should be a "must-read" for all hams. 73, Tom N0SS George, W5YR wrote: >John, I really don't know if you are anal retentive or not, but an antenna >can be resonant and still present a 10:1 SWR to the feedline. > >The absolute magnitude of VSWR is not an indicator of resonance. > >Resonance is solely, only and always the condition of a tuned circuit in >which the impedance at the port of interest is purely resistive or real. >The real component may NOT be the same as the Zo of a transmission line, >hence the SWR can be other than 1:1. > >Resonance has nothing to do with SWR. SWR is determined solely by the ratio >of the driving point impedance of the antenna to the Zo of the transmission >line, or vice versa. > >It is your choice to place so much emphasis on SWR but the facts are that >it is relatively unimportant to the actual radiation performance of an >antenna. An antenna fed with a line having any SWR will radiate all the >power it receives. If the line is low-loss, it can easily be the case that >more power is delivered to the antenna over a line with a 20:1 SWR than a >line with a 2:1 SWR. It is all a question of relative line loss, frequency, >line length, etc. > >But the resonance or lack thereof of the antenna has very little to do with >it. Every antenna that I use, except for my Butternut HF9V vertical, is >non-resonant in any amateur band. They all work great on 80 through 10 >meters, and most of my operating is QRP CW where efficiency counts. > >With all respect, John, a review of the Antenna Book on the topics of >antenna resonance might be worth your time. Walt Maxwell's "Reflections II" >will give you an entirely new outlook on this subject. Resonance is >convenient for matching purposes, but that is about all it buys for you. +++++++++++++++++ From: "Mike McCoy" To: Subject: Re: [Elecraft] HF Verticals? Date: Tue, 15 Oct 2002 08:49:53 -0500 If you're like me, most antenna theory seems to be presented in a rather mind numbing and overly complicated manner. Here is a good site (i.e. presented straightforward and simply) about the basics of L, C, Q, resonance, reactance, impedence, etc. : http://my.integritynet.com.au/purdic/electronic-basics.htm Mike - AD5IU +++++++++++++++++ Date: Tue, 15 Oct 2002 10:34:18 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: kc4kgu at enterzone.net Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] Re: [Icom] Opinions re: HF Verticals? John, this is largely off-topic for this list so this will be my last posting on this . . . John Fraizer - KC4KGU wrote: > > George, W5YR said: > > > The absolute magnitude of VSWR is not an indicator of resonance. > > Granted. When you're operating resonant antennas and the antenna is > supposed to presenting a 50Ohm load to your rig (via whatever _static_ > means, no adjustable transmatch here) VSWR will indicate that you're > operating outside of resonance. Since I operate all resonant antennas, I > think in terms of ANY VSWR when operating at the design frequenct == BAD Again, the basic question arises as to the supposed vs the actual merits of operating "resonant" antennas. But, that appears to be your preference . . . That assumes that you have taken care of the non-Zo-match condition by some form of impedance matching at the antenna. Almost invariably, an antenna driving-point impedance will NOT exactly match the line Zo, certainly to the 1.01:1 level, so something has to be adjusted somewhere to reduce the line SWR to whatever you or the transmitter considers acceptable. Some folks like to do it at the antenna, some folks fiddle with line lengths, others like myself prefer the convenience of doing it on the operating desk with a box with knobs called a tuner. Either way, the same thing gets done with the same result: the transmitter sees a 50-ohm resistive load. So, you have a certain VSWR - as low as possible for your taste - at some selected frequency (not necessarily a resonant frequency, by the way) - and any departure from that reference value you regard as a change in the antenna system and you equate that change to BAD. It clearly indicates a change of some sort. You are certainly within your rights to do that, but I and several others are merely telling you that there is no engineering basis for doing so. The change may produce miniscule effects on your radiated power but these are readily compensated. > > > With all respect, John, a review of the Antenna Book on the topics of > > antenna resonance might be worth your time. Walt Maxwell's "Reflections > > II" will give you an entirely new outlook on this subject. Resonance is > > convenient for matching purposes, but that is about all it buys for you. > > I beg to differ. It will also buy you different radiation patterns. Perhaps in some extreme cases, such as changing from one band to another, but consider this: you have your perfect antenna set up for 14.227 MHz; SWR is 1.007:1 and you are very happy. Your dipole antenna has the usual dipole pattern in three dimensions. Now you QSY to 14.007 MHz to work some DX. Your antenna is no longer resonant - assuming it was at 14.227 which is possible but not necessarily the case (the antenna system was resonant, not necessarily the actuall radiation "antenna") - so the line SWR changes. Now tell me what change there is in the pattern, assuming that you provide the same amount of power to the antenna as you did at 14.227. You can do this by merely changing the impedance matching of the line input to the transmitter and if necessary increasing the transmitter power output by an amount equal to the (usually) negligible added line loss. Why did changing frequency and having the radiating antenna non-resonant change the antenna pattern: how and by how much and how does one measure this change? > > > BTW, how are you measuring those 1.01:1 and 1.03:1 SWR values? And what > > do you figure that they provide for you that 1.5:1 would not? Just > > curious . . . <:} > > RF Applications VFD http://www.rfapps.com/vfd.htm I note that no accuracy specification is given at the URL for your unit. Rather they ask you to "compare with the Bird 43 . . ." The Bird is rated at +/- 5% of full scale. If you will work with that accuracy figure and go through the equations for computing VSWR from forward and reflected power measurements - which is what your instrument does wioth its microcomputer - you will find that there is no way that it could actually compute the difference between a 1.01 and a 1.03 SWR. The instrument may well display such readings, but they are an artificial artifact of the processing, not reflective of the accuracy of the raw power data. > > They provide me the piece of mind that I'm seeing 1.03:1 and not 1.5:1 or > 2:1 or whatever else. John, I think your statement there pretty well sums it up. You enjoy operating your station with instrumentation and antenna systems that show you what you regard as near perfection in transmission line operation - and recall that VSWR concerns itself with one thing only: how well the line matches the load - even though the facts of the matter may be significantly different. >From an engineering viewpoint, the additional loss, change in line input impedance, stress on the feedline, or any other attribute of "high SWR" occasioned by changing SWR from 1.01:1 to 1.5:1 can hardly be measured with any realistic level of accurary. Clearly the practical effects on overall performance are negligible. But, what makes you happy and lets you enjoy your station operation is what counts . . . Enjoy in good health! 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 +++++++++++++++++ Date: Tue, 15 Oct 2002 11:25:37 -0600 To: "sjolin" , , From: Larry East Subject: Re: [Elecraft] Re: [Icom] Opinions re: HF Verticals? Cc: At 02:21 AM 10/15/02 -0500, sjolin wrote: > Changing the length of coax used >to feed an antenna will change the swr at the rig. I've seen cases where the >swr will change just by adding an extra couple feet of cable in the shack. That is incorrect -- if your "SWR Meter" is indeed measuring SWR. The complex impedance seen by the rig (or tuner) will change depending on the length of coax, but not the "true" SWR. For an insight into this, read Chapters 7, 8 and 9 in "Reflections II" by M. Walter Maxwell, W2DU. A most illuminating book that should be read by every "technically oriented" ham... 73, Larry W1HUE/7 PS - PLEASE lets DON'T start a big thread on SWR, complex impedances, etc.! ++++++++++++++++ Reply-To: "Bob Lewis (AA4PB)" From: "Bob Lewis (AA4PB)" To: Subject: Re: [Elecraft] SWR, Transmission lines and Antenna Matching Date: Tue, 15 Oct 2002 18:42:06 -0400 I think this is what happens. The SWR anywhere along the line is constant and is determined by the ratio between the characteristic line impedance and the load impedance. The impedance (not the SWR) along a mismatched transmission line varies with distance from the load, repeating every 1/2 wavelength. Most of the inexpensive VSWR meters we use are only accurate when placed in a 50 ohm line. As you move the meter to different points along the line you get different "SWR readings" because of the errors in the instrument when presented with different impedances. With a good reflected power meter you should get the same ratio of forward to reflected power (and thus SWR) anywhere along the line. All of this assumes zero transmission line loss. Any line loss acts on both the forward and the reflected power. At the transmitter the forward power is not attenuated while the reflected power is attenuated twice (up to the antenna and back) so the ratio looks better at the transmitter than it does at the antenna end of the line. So, if you have any significant amount of transmission line loss then you should insert the meter at the antenna to get the most accurate reading. ++++++++++++++++ Date: Tue, 15 Oct 2002 17:42:47 -0500 From: "George, W5YR" Organization: AT&T WorldNet Service To: "Bob Lewis (AA4PB)" Cc: elecraft at mailman.qth.net Subject: Re: [Elecraft] SWR, Transmission lines and Antenna Matching That is correct, Bob . . . this is another instance of confusing SWR readings with impedance readings. This admonition is frequently found in the CB literature . . . In a practical situation, if there is common-mode current on the coax outer braid, then the "indicated" SWR reading from the typical reflectometer type of SWR meter will in fact vary with position in the line. But, in the absence of CM current, the only effect on SWR readings from proper instrumentation would be assigned to loss in the transmission line. A contrived situation can be created in which the SWR reading *does* vary with position but it requires use of a very lossy transmission line having a complex Zo and an SWR instrument whose reference impedance does not match that of the line. This is not a combination very likely to be found in an amateur station installation. 73/72, George Amateur Radio W5YR - the Yellow Rose of Texas +++++++++++++++++ Date: Wed, 16 Oct 2002 00:17:36 -0400 To: Larry East From: Charles Greene Subject: Re: [Elecraft] Re: [Icom] Opinions re: HF Verticals? Cc: elecraft at mailman.qth.net Larry and All, I'm not disagreeing with you Larry, and here's a story to illustrate your point. I recently built and tested a portable vertical in my yard for use at a special event site in the field. The design of the antenna is not at issue here so I won't get into it. I carefully tuned the antenna by adjusting the length of the radials and radiator for a Z of 50 ohms and resonance by measuring R + jX at the base of the antenna for the point at which the X component crossed from + to -. BTW, this is not the point of lowest SWR, but close to it. I was using an Autec VA1 which measures SWR, R, X and a bunch of other stuff. On this meter you can't get X to read 0, but it will jump from like a -8 ohms to a +8 ohms as you tune across the resonant frequency. At this point the SWR read 1.02:1 at 14.2 MHz and R read 49 ohms. I was using 84' of LMR-400 coax (50 ohm low loss stuff) in series with about 16' of RG8X and an couple of antenna switches to the rig. In the shack, the SWR read 1.14:1 at 14.2, and R was 58 ohms using the VA1. My SWR/Power meter read an SWR of 1.0:1 in the shack. I couldn't get it budge off zero reflected power. Now that SWR and R was nothing to complain about and my K2 antenna tuner made short work of it, but I wondered why the readings were not repeated in the shack. I attributed it to the length of the coax. Then a couple days ago, I ran across an article by Frank Witt, AI1H in ARRL Antenna Compendium, #4 entitled "Broadband Matching Transmission Line Resonator." Basically what Frank was doing was to "tune" the antenna system slightly by varying the length of the transmission line, and thus broad banding it. In my case, I was detuning the antenna system slightly (where the system is the combination of the antenna and the transmission line) by using a random length of transmission line. In order to get the same results in the shack as at the antenna you need an electrical 1/2 wave transmission line or multiples there-of with the same impedance as antenna. Morale of this posting: 1. Don't believe your SWR meter, 2. Read Frank's article to see how varying the length of the coax "tunes" your antenna system, and 3. As long as your SWR is low but not exactly 1:1, don't worry about it as losses are low and the rig is happy. Sequel to the story. At the special event site the environment was different and the antenna resonance was way off. I retuned it by varying the length of the radiator only as I didn't have time to vary the lengths of the radials too, so the SWR at resonance was about 1.2:1. I didn't bother to read the Z at the station as the SWR/power meter said 1:1 and at this point in time I couldn't do anything about it. Morale to the sequel: Don't spend too much time tuning a portable antenna at home as you will probably have to redo it in the field anyway. At 11:25 AM 10/15/2002 -0600, you wrote: >At 02:21 AM 10/15/02 -0500, sjolin wrote: >> Changing the length of coax used >>to feed an antenna will change the swr at the rig. I've seen cases where the >>swr will change just by adding an extra couple feet of cable in the shack. > >That is incorrect -- if your "SWR Meter" is indeed measuring SWR. The >complex impedance seen by the rig (or tuner) will change depending on the >length of coax, but not the "true" SWR. For an insight into this, read >Chapters 7, 8 and 9 in "Reflections II" by M. Walter Maxwell, W2DU. A most >illuminating book that should be read by every "technically oriented" ham... > >73, >Larry W1HUE/7 +++++++++++++++++ Date: Wed, 16 Oct 2002 11:22:42 -0400 (EDT) From: kc4kgu at ENTERZONE.NET To: Stuart Rohre Cc: w5yr at att.net, elecraft at mailman.qth.net Subject: Re: [Elecraft] "Digital" SWR meter from web reference On Tue, 15 Oct 2002, Stuart Rohre wrote: > The Bird meter this meter is compared to, carries manufacturers specs of 5 > per cent as George pointed out. Few, if any, practical multiband SWR meters > are any better than that. > > I am immediately suspicious of any web site for an instrument that does not > have a bullet for "Specifications", but prominently advertises it can > customize the meter digital display with your Vanity Call! > > It is an attractive meter, but I would not give it any special properties > over a good analog readout meter on a Bird Wattmeter. > 73, Stuart K5KVH You haven't used one. There is only one piece of equipment that I have ever owned that I would recommend with as much enthusiasm and that is the K2. The VFD has an autoscaling "VU" type display when it sees RF. This makes tuning an amplifier or a transmatch go very quickly. I have a very nice crossed-needle VSWR bridge but, I look at the VFD because it's quicker. In addition, the VFD has an SWR alarm that lights a high-intensity red LED as well as provides a SPDT relay output. Put this in line with your PTT/key line or your amplifier keying line and you have auto-shutdown in the event that something catastrophic happens to your antenna system or transmission line while you're operating. The SWR that indicates an alarm is user selectable. In addition, the VFD is excellent for working in low light conditions. My bird doesn't have a backlight and I don't even think they have a model that does. Kinda useless if you can't see it. Anyway, like I said, I like it, I recommend it. It is a very nice piece of equipment and it has saved my equipment once already when I had a catastrophic antenna system failure caused by a tree falling during mid QSO. Since my shack is in the basement, I would have had no idea and with no "in your face" light and "rig stops keying, amp key circuit disabled down" action on on the bird, I would not have known about the antenna problem until it was too late. 73 de John - KC4KGU K2/100 #2490 Elecraft WAS #8 ++++++++++++++++ Date: Wed, 16 Oct 2002 08:42:59 -0700 From: Vic Rosenthal Organization: Transparent Software To: elecraft at mailman.qth.net Subject: Re: [Elecraft] "Digital" SWR meter from web reference Regarding the VFD digital SWR/power meter, I have one it and it does have some very nice features. I use the SWR alarm relay to protect my solid-state amp and I like the readability of the display. But (there's always a 'but'): the unit has a 3KW full-scale. I suspect that in order to get such a wide range the designer sacrificed accuracy at the very bottom end; mine is pretty inaccurate below about 15 watts. So if you are interested in QRP you probably should also have one of those nice OHR units or a Bird with several slugs. Vic K2VCO ++++++++++++++++ From: "Stuart Rohre" To: Cc: , Subject: Re: [Elecraft] other SWR Power meter for QRP Date: Wed, 16 Oct 2002 15:30:26 -0500 The VFD has lots of features for the fixed station running high power, but the Bird requires NO AC nor Batteries. For QRP at the most popular levels of 5 watts, and 10 w pep ssb, there is an excellent value kit power meter. A very good, and calibration easy meter for QRP use is the Ten Tec T kit SWR Power Meter. Mine was $49.95, and an easy build from an excellent manual. They may have gone up a bit, but still are an excellent buy. To convert from 20 watt scale to 2 watt scale, I just turned a calibration pot, to make a known power of 2 watts read that. The scales can be 20w or 200 w as built, unless you recalibrate. It does need one 9 volt battery, but has low drain. It also has pickups for both HF and for VHF/UHF. Although not sold as a 440 MHz unit, I found it works fine for finding a good swr null with 440 equipment. 72, Stuart K5KVH ++++++++++++++ From: "Ed Lambert" To: Date: Thu, 17 Oct 2002 09:16:18 -0400 Subject: [Elecraft] Lines, Waves and Antennas I was first licensed in 1961 while in high school. Paradoxically, amateur radio was responsible for me going into electrical engineering and was also responsible for me having the greatest difficulty completing, successfully, a course I took called "Lines, Waves, and Antennas". The reason for my difficulty was that much of what I "knew" about the subject from my amateur experience and from amateur radio publications did not "square" with the engineering literature, with the mathematics, or with the laboratory. My "mastery" of the subject was very hard won. Periodically I review engineering subjects taken in college and outside my field of practice. This fall I have been reviewing electromagnetics just about the time the "SWR" thread started to appear on this reflector. As part of that review, I picked up "Reflections - Transmission Lines and Antennas" by Maxwell, W2DU. Some amateur publications in the field of lines and antennas have contained things that are just plain wrong. This one, however, is not in that category; it is quite good in all the areas it covers and, unlike many engineering texts, has a strong experimental basis. I strongly second the recommendations of W5YR, W1HUE/7 and others who have recommended this book; it "squares" the amateur experience with engineering theory. Chapter 21 is, indeed, a "must read" chapter. I started the post with the date I was licensed. The same discussion occurring on this thread was going on then in a different format. I suspect it has been going on since the beginning of amateur radio and that our thread will neither change nor divert its inevitable infinite course. Ed Lambert KD3Y K2 1999 ++++++++++++++