Date: Sun, 8 Sep 1996 20:57:44 PST From: wb2vuo@juno.com (William K Hibbert) To: qrp-l@Lehigh.EDU Subject: [3828] The Extended Double-Zepp Message-ID: <19960908.205750.4799.0.wb2vuo@juno.com> (Psst...Wanna double your power, for Free?) Well, not for free, but almost so. Let's look at how one can "double" one's power. How, first of all, are we looking at your "power". One way is to look at the output of your rig. If you increased your output from 5 watts to 10 watts, there could be no argument that you had doubled your power. But, if your antenna had a gain of 2 [3dB], at the other end of your contact, it would LOOK like you had increased your power. Now, about the "FREE" part of this discussion. The simplest, and least expensive antennas are wire antennas. To double your Effective Radiated Power [ERP], you need a gain of 3dB over your former antenna. Using a dipole as the reference, this would be expressed as 3 dBd, or 3 dB over a dipole. So, what "FREE" wire antenna will give us 3dBd? One of the easiest, and cheapest is the Extended Double-Zepp, or EDZ. What it is, is two elements, fed in a collinear fashion, with each element extended from 1/4-wave long to 5/8-wave long. Many of the Antenna Books show this antenna fed via a 0.11-wavelength stub, which results in a 150-ohm feedpoint impedance. Nice, but when was the last time you saw 150-ohm feedline? So, you say, 'How do I feed my EDZ?' If you feed it directly with ladder line, either 300-ohm, or 450-ohm, the SWR on the line will be 2:1 or 3:1. With the inherent low loss of the ladder lines, this will never be noticed. The ATU you are using will tune out this mismatch, and make the transmitter happy. If you really insist on a 'flat' line for the antenna, then a 1/4-wave shorted line should be attached to the feedpoint, and your feedline should be tapped down to the correct spot on the line to match it. Using this method, you could even feed the EDZ with 50-ohm line. This would make the antenna a single-band antler, whereas the resonant feed with the ladder line will allow you to run the antler on multiple bands. The formulas used to calculate the lengths in an Extended Double Zepp are as follows: Leg length (feet): L= 600/F(MHz) Stub length (feet): l=108/F(MHz) [-------------L---------------] [---------------L-------------] ------------------------------o[ins]o------------------------------ \ / : ! ! : ! ! : ! ! [ l ] ! ! : ! ! : o o ----- Feedpoint ***NOTE: [ins] is the center insulator for the wire..... If you want your EDZ to be the single band version, and not use an ATU, then the stub length, [ l ], should be equal to 246/F(MHz), and the bottom of the stub should be connected together, with the feedline tapped up to the correct matching point. This point would need to be determined empirically, also known as "cut-and-try". Page 2 HOW BIG IS IT??? This is a good question, and might be the disqualifying factor for some. Here is a listing, in tabular form with dimensions. I am listing it for the bands from 160 meters up, but I don't have the room for the lower bands, myself. [Wish I did, though]. FREQ (MHz) L (Ft) l (Ft) Flattop Length (Ft) 1.85 MHz 324.3' 58.4' 648.6' 1.95 MHz 315.8' 56.8' 631.6' 3.60 MHz 166.7' 30.0' 333.3' 3.90 MHz 153.8' 27.7' 307.7' 7.15 MHz 83.9' 15.1' 167.8' 10.10 MHz 59.4' 10.7' 118.8' 14.20 MHz 42.3' 7.6' 84.5' 18.10 MHz 33.1' 6.0' 66.3' 21.20 MHz 28.3' 5.1' 56.6' 24.90 MHz 24.1' 4.3' 48.2' 28.40 MHz 21.1' 3.8' 42.2' 29.50 MHz 20.3' 3.7' 40.7' 50.20 MHz 12.0' 2.1' 23.9' 52.50 MHz 11.4' 2.1' 22.9' As you can see from the chart, many of the dimensions for an EDZ are the same as a dipole for other bands. This helps explain why a center-fed antenna, fed with ladder line, will work so well on multiple bands. It is a 1/2-wave on one band, 1-wave on others, and EDZ on yet others. Another principle that allows one to "get away" with the ladder line feed system is the good old "Gootches' Principle", which states that "RF Gotta go SOMEWHERE!" So, if you have the real estate, the time and the inclination, try out an EDZ in your Antenna Farm, and see what sprouts up in the bands... 72/73, Keith, WB2VUO, QRP-L #582 Trustee, KB2YTW/B 10 Mtr Beacon (28.2860 MHz) "In the Depths of the Great Bergen Swamp...FN13ac" ------------------------------ Date: Mon, 9 Sep 1996 08:07:44 -0400 (EDT) From: "L. B. Cebik" To: QRP-L List Subject: [3840] EDZs Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII A recent posting on the Extended Double Zepp under the title "Wanna Double your power for free?" brings to our attention an interesting wire antenna. However, it leaves out a few points that are important in understanding the antenna and deciding if you want to build one. First, the antenna is non-resonant, that is it does not operate at a point at or near zero reactance. Being about 1 1/4 wavelengths long, it will have high capacitive reactance at the feedpoint. Hence, the need for stub tuning for single band use or parallel feedline for either single- or multi-band use--the latter is usually much simpler. Second, because the antenna is non-resonant, the "formulas" for cutting one are not nearly so precise as with a resonant antenna. In fact, they come from an old and perhaps outdated habit of amateurs to try to reduce antennas to a series of cut-to-formula-and-forget exercises. In fact, the 600/F formula for each leg may give you higher than necessary reactance. As an exercise, I modeled an EDZ for 20 meters at 35' up (that is a half wavelength up). I used the formula and then lengthened the legs twice and here is what I got for feedpoint impedances. Leg Gain R+/-jX Beamwidth 42.86' 11.29 229 - 1094 38 degrees 44' 11.30 173 - 902 36 45 11.20 141 - 756 34 Note that both the R and the X go down as we lengthen the antenna away from the very high R and X of a 1 wavelength antenna. Exact figures will vary with the antenna height in fractions of a wavelength above ground. Notice that we pass the point of absolute max gain to get the lower resistive and reactive components, but 0.1 dB difference will never be detectable in any operating situation. Third, the price of gain in a bi-directional antenna is beam width, and this is a serious consideration for anyone contemplating this antenna. The beam width (signals down by 3 dB relative to the point of highest signal strength) for a dipole on 20 at 35' is about 88 degrees, and the pattern is a big peanut. Your orientation need only be approximate to hit a broad swath of stations, like all of Europe, etc. The beamwidth of an EDZ is in the 30s, as the chart about shows. That's a lot narrower than most long Yagis. You will have to decide within fairly narrow limits just where you want your antenna to point--and hope that both sides are doing some useful work. (This might be for some Europe off one side and VK-ZL off the other; for others, it might be over the poles; for still others, the off side pointing "nowhere" may be the ticket to reduced QRM for the on side.) If you live in Texas and broadside a dipole up to the US, you will work from coast to coast, although AZ and FL may be off the sides. If you do the same with an EDZ, you will Work All Minnesota in a week and wonder where the east and west coasts have gone. The quartering side lobes of the EDZ are a good 10 dB below the main lobe, which puts them about 7 dB below the quartering angles from a half-wavelength dipole. So learn all you can about an antenna and do not jump at one just because it promises gain. Gain is cheap. Getting an antenna to put its gain and other properties just where you want them to go gets expensive--whether in money or time or energy. You can find a discussion of the basic properties of the EDZ in Communications Quarterly about 3 issues back--you can even learn how to make an EDZ parasitical beam. Had fun putting that one together for the article. Best of all, the EDZ beam produces patterns that look like faces with interesting ears--antenna modeling is full of surprises, and not all of them are technical. -73- LB, W4RNL ------------------------------ Date: Mon, 9 Sep 1996 08:36:53 -0400 From: Scott Cranston To: qrp-l@Lehigh.EDU Subject: [3842] re: EDZs Message-ID: <9609091236.AA29184@falpha.zk3.dec.com> Attached is some sample output and source code from a brute force C program for calculating EDZ deminsions. Enjoy, Scott cranston@zk3.dec.com KB1NW Enter Design Frequency in Mhz: 7.040 Design Frequency: 7.04 Mhz Electrical Wavelength: 139ft, 9.3in Length of Each Leg: 89ft, 5.5in Total Element Length: 178ft, 10.9in Single Element Matching Section: 19ft, 2.2in Phased Array Matching Section: 4ft, 0.7in Phased Array Matching Stub: 1ft, 5.7in Phased Array Element Spacing: 17ft, 5.7in Phasing Line Length: 8ft, 8.8in /* *********************************************************************** * Program to calculate the dimensions for an Extended Double Zepp * * Antenna. This is based on the formulas given in the August 1988 * * issue of QST, page 51. * * * * Created 12-AUG-88 kb1nw * *************************************************************************/ #include ft_to_in(length) /* convert a floating point measurement in feet */ float length; /* to feet and inches */ { int num; num = (int)length; length = (length - (float)num) * 12.0; printf("\t%dft, %2.1fin\n", num, length); } main() /* calculate EDZ deminsions */ { float wave_length; /* electrical length of the wire in feet */ float leg_length; /* length of each leg of the antenna */ float tot_length; /* total length of antenna */ float match_single; /* matching section length for a single EDZ */ float match_phased; /* matching section length for a phased EDZ */ float stub; /* length of matching stub for phased EDZ */ float freq; /* design frequency */ float space; /* spacing between phased elements */ float phase_line; /* phasing line length */ printf("\nEnter Design Frequency in Mhz: "); /* get design frequency */ scanf("%f",&freq); /* input from user */ wave_length = 984/freq; /* electrical wavelength */ leg_length = wave_length * 0.64; /* run through the EDZ formulas */ tot_length = leg_length * 2.0; match_single = (52.0/360.0) * 0.95 * wave_length; match_phased = (11.0/360.0) * 0.95 * wave_length; stub = (4.0/360.0) * 0.95 * wave_length; space = wave_length/8.0; phase_line = space/2.0; /* print out the results in feet and inches */ printf("\n\nDesign Frequency:\t\t\t%6.2f Mhz\n\n", freq); printf("Electrical Wavelength:\t\t"); ft_to_in(wave_length); printf("Length of Each Leg:\t\t"); ft_to_in(leg_length); printf("Total Element Length:\t\t"); ft_to_in(tot_length); printf("Single Element Matching Section:"); ft_to_in(match_single); printf("Phased Array Matching Section:\t"); ft_to_in(match_phased); printf("Phased Array Matching Stub:\t"); ft_to_in(stub); printf("Phased Array Element Spacing:\t"); ft_to_in(space); printf("Phasing Line Length:\t\t"); ft_to_in(phase_line); } ------------------------------ Date: Mon, 9 Sep 1996 09:57:24 -0400 From: cooper@gmpvt.com (Tom Cooper) To: qrp-l@Lehigh.EDU Subject: [3845] re:EDZ antenna Message-ID: <199609091357.JAA27818@web.gmpvt.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" The Extended Double Zepp has a much narrower beam width than a 1/2 wave dipole, so you better get it pointed right. If your trees are in the right place, it is a good antenna for that weekly sked, but it isn't so swell for every day hamming. Tom WA1GUV ------------------------------ Date: Mon, 9 Sep 1996 18:46:58 PST From: wb2vuo@juno.com (William K Hibbert) To: qrp-l@Lehigh.EDU Subject: [3894] TANSTAAFL and Wire Antenna Message-ID: <19960909.184704.4319.0.wb2vuo@juno.com> One of my favorite terms I picked up from reading during my Pre-Teen and Teen years was "There ain't no such thing as a Free Lunch", abbreviated at TANSTAAFL. This is an accurate observation about the Universe in general, and definitely fits in the theoretical base of Antennas. The Extended Double-Zepp is a classical example of TANSTAAFL due to the relatively narrow pattern the antler displays. However, this tendency is NOT limited to the EDZ. If you take a "basic" dipole, and place another one in line with it, dividing the power evenly to the two antlers, you will end up with a Collinear array, which will show gain over the single dipole. It achieves this gain by taking energy from the "normal" pattern of the dipole, and combining it into a narrower pattern. My old "standard" ARRL "Antenna Book" shows the pattern of a "2-Element Collinear" to have a main (bi-directional) pattern with a beamwidth of about 40-degrees at the -3dB (half-power) points, this being the azimuthal pattern. The vertical pattern will be the same as a dipole at the same height above ground. The EDZ achieves its gain in the same manner, concentrating the energy into a narrower pattern, with the -3dB points at about 30-degrees. Other wire antlers have wider or narrower patterns, depending on the length, number of elements (or cells), etc, etc, etc... Even Yagis and Quads work in the same way, taking energy from where you don't want it and directing it where you do want it. I always like the "Searchlight" analogy, where one compares the illumination of a bare bulb compared to the illumination of the same bulb with a parabolic reflector. A flashlight will demonstrate this in your shack... "There Ain't No Such Thing as a Free Lunch"... but if you are willing to accept the inherent limitations, Lunch can be more interesting, and at a low cost, too! 72/73, Keith, WB2VUO, QRP-L #582 Trustee, KB2YTW/B 10 Mtr Beacon, (28.2860 MHz) "In the Depths of the Great Bergen Swamp...FN13ac" wb2vuo@juno.com ------------------------------