(Compiled from inquiries made to the TopBand Reflector and private communications)
Two Wire Beverages:
I use 2 wire beverages with good success. Mine are 580', 12" spacing, and average about 8' or 9' off the ground.I always wound my own transformers. This year, I tried the K1FZ matching and termination transformers. I don't know why, but they perform much better than my own units. I would advise using a termination transformer on the distant end. . . it will help you get optimum front/back. The spacing is not real critical. If it varies somewhat, it's no big deal. Good luck and 73. . . Dave W0FLS >1)Use an end termination transformer (wind my own) or just ground/float the >far end? I recommend the termination transformer because you will get better F/B if it's done correctly. Simply grounding one wire will work but not as well. >2)Okay to let the spacing vary a bit (6 - 12 inches) with the tree trunk >diameters? Yes, some variation is OK but try to keep the variation gradual over distance. Sharp changes create impedance "bumps" which are not so good. >And any other comments/advice would also be warmly received ;-) Be sure that the unused feed is always terminated (dummy resistor, etc.). The power in that feed has to be dumped somewhere or else it ends up going back down the Beverage and into the other feed as an unwanted signal. Also, it's a good idea to measure the SWR with an antenna analyzer (MFJ259 or whatever) and trim the impedance matching transformers for lowest SWR. 73, John W1FV > 1)Use an end termination transformer (wind my own) or just ground/float > the far end? By all means, use the reflection transformer! Establish a good ground at both ends with ground rods or equivilent. I like 1-inch copper pipe, since every copper-plated ground rod I've ever installed has rusted through the ccopper in short order. You can wind your own transformer: it's a simple process. > 2)Okay to let the spacing vary a bit (6 - 12 inches) with the tree trunk > diameters?Yes, but try to keep the run in a straight line. If you are going to use trees to support the wire, consider nailing or screwing crosspieces made from 2x2 lumber (15-18-inches wide) at constant heights from the round, and with notches at the top to retain the wire. You can space them 12" - 15" for 160, and the wire can be pulled tight when resting unrestrained in the notches. We've never used trees as supports: we fabricate "Beverage Poles" out of 2x2 poles, with a 15-inch crospiece at the top (with notches). I use an auger bit to dig 2-inch holes 18-inches deep in the yard, and support the poles in these holes. My Bevs come down in the Spring, and when we were doing the W8LT 160M Contest efforts, we had a large open field to navigate for our long Bevs: no trees to use! 73, Jeff Maass Buy a 1/4 mile roll of 17 Gauge Aluminum Fence wire from your farm supply store. This wire has extremely low weight per length and can be stretched very tightly. I suspect it would need only 2 intermediate supports between the ends (i.e about 200' per span). Build 2 supports with the desired wire spacing and perhaps one intermediate spacer for each span (i.e. 3 total). I don't have the formula in front of me but I guess 3-4" spacing would be in the ballpark for 17 Gauge wire to be around 4-500 ohms. You can connect Cu to Al wire easiest if you use twist electrical connectors with a dab of Noalox inside each. I would slope each end of the wires down to a stake and stretch it as tightly as I could. This should allow you to need only 2 intermediate supports with very low sag. One set of spacers between supports would then make 100' spans without any physical spacers, but if you stretch the wire very tightly I suspect there would be little variation, even in a brisk wind. Hopefully someone will calculate the exact spacing for #17 wire to yield 400-500 ohms, but I'm guessing 3-4" should be fairly close. The key to all of the above is stretching the wire VERY TIGHTLY! 73, Bill W4ZVUsing Ladder Line for the Beverage Wire:
I've heard it mentioned a couple of times by guys on the reflector and ON4UN briefly alludes to constructing a 2 wire Beverage using 450 ohm transmission line (pp 7-22 and 7-23 of his book). I thought this might make installation a lot easier if I could scrounge up the wire. If there is a technical down side to using such closely spaced conductors, I'd appreciate hearing from any knowledgable folks. Ladder line works fine. The only disadvantages are cost and wind loading. However, two parallel number sixteen copperweld wires cost about 5 cents per foot of antenna. Now figure out how you would make spacers, and how long it would take to install the antenna using each system! You could also use 300 TV twinlead. I've used 450 ohm line for all my two wire Beverages since the early 70's. For me, the extra cost is offset by the ease of construction. There are no electrical disadvantages when using close spaced wires, other than some slight deterioration of termination in wet weather with plastic "ladder line". As a matter of fact, I don't believe there are any real advantages to using modest or wide spaced conductors in two-wire Beverages. As a general rule, the closer and more evenly the wires are spaced the better the antenna behaves. That's because it is easier to keep the standing waves off the line, making termination better over a wider frequency range. Think of the wire as serving two functions, as an antenna with the wires tied in parallel and as a transmission line to reach the far end. Anyone who understands transmission lines would never use a very long, wide-spaced, line (more than a few thousandths of a wavelength spacing) because they know it would be a very poor transmission line. The longer the line the more critical the spacing is. 73, Tom W8JI I wrote an article in the early 80's describing how to use coax, twin lead, or any other transmission line to make a Reflection Beverage. I had a similar article in Communications Quarterly. The point of both was you could use almost any transmission line if impedances of transformers were adjusted. Certainly that would apply to coax, although you would have to be careful about voltage distribution at each end. I have used 300 ohm twinlead and 450 ohm ladder line with equally good results, and coax wouldn't be a problem either. On 160 meters (or anywhere below UHF) virtually all transmission line losses are related only to conductor resistance...not the dielectric. Keeping that in mind, any thin small conductor could be both electrical and mechanical problems. 73, Tom W8JI Since a beverage antenna is carrying no current, ohmic losses aren't really a factor. You could use #30 wire if you could ever get it to stay up! Anyway, 18 gauge should be fine. However, if it's soft copper it will stretch and may break under weight of ice and snow (particularly when combined with wind). Copperweld would be a much better choice (mechanically speaking). I use #18 military surplus telephone wire (steel) which I buy in one mile spools from Fair Radio Sales of Lima, Ohio. It's made to be stretched and really holds up well to the Iowa winters. It comes as a pair of wires so I have to pull them apart which is kind of a pain. . . but it's good wire and the price is right. 73. . . Dave W0FLS I am using two wire bevs made from 450 ohm PVC covered ladder line. Here's what I know about it: 1) It is convenient to run out - more so than with normal two runs of say #`14 THHN stranded at say 2-3 foot spacing. 2) I am told it is SLIGHTLY less efficient than a two wire at 2-3 foot spacing 3) It's use requires a feedpoint matching xfmr with its output impedance made for 450 ohm ladder line RATHER than the 600-800 required for the two #14 wire variety. 4) Similarly, the reflection xfmr required at the far end must also be customized for 450 ohms as well. I have two such bevs made from 450 ohm ladder line I purchased at RADIOWARE (Craig Clark at 1 800 950-WARE) The CUSTOM feedpoint and REFLECTION xfmrs I had made for me by Clark Electronics (K1FZ). These cost $129 and $99 respectively - you can reach Bruce K1FZ at k1fz@agate.net Good luck 73 JEFF I have 4 beverages constructed with the 450 ohm ladder line, and they work just fine. I have also made one out of RG-58 coax, which also works just fine. Remember, on a single wire beverage, that there are two signals present at all times. One from the front direction, and the other from the rear. You could run a coax feed to both ends, and have a bi-directional antenna, just by hooking one or the other to your transceiver. or you could use 450 ohm ladder line to send the far end signal to the near end. Thus, between either conductor of the 450 ohm ladder line to ground, you have one signal, and between the two conductors, is the other signal. This allows you have both near and far signals at one end, at the same time. Proper transformers (2) at the near end and a single 1:1 transformer at the far end should do the trick. I have several twists in the ladder line, every few feet, as this makes it less susepticle to the wind. The two wire beverage has two modes, first the antennas mode (same as a single wire beverage, both wires have front and back signals present), and secondly, the transmission line mode (the two wires in the ladder line carry the far end signal to the near end). Any trnasmission line can be used for a beverage, 50 ohm coax, 90 ohm coax, 300 ohm TV twin-lead, 450 ohm ladder line, 600 ohm ladder line, or a pair of open wires of any spacing. The only difference is the matching transformer requirements. Hope I have helped you understand what I am trying to get across. 73 & DX, Dick - N6FF >In my limited understanding of >terminating the far end - I though a transformer was necessary when the >characteristic antenna impedance differed from 450 ohms. ] A transformer is ALWAYS necessary. >ON4UN gives the impedance of a 2m high ladder line Beverage at 424 >and 449 ohms respectively using 450 and 300 ohm ladder line >Wouldn't it then be possible to dispense with the > transformer at the far end and use a simple open/short circuit termination? Nope, won;t work for crap. That ground one wire idea makes no electrical sense at all. 73, Tom W8JI A procedure I use for "tweaking" the reflection transformer is to adjust the turns ratio until the SWR in the reverse direction at the receiver end is flattest. By flattest I mean that SWR exhibits the smallest variations up and down over a wide range of frequencies, and not necessarily the lowest SWR. With an antenna analyzer like the AEA or MFJ, sweep the frequency from 1.8 to as high as 10 MHz and look for the SWR to change the least over this entire range, not just inside the amateur bands. This procedure usually gets you very close to the optimum. 73, John W1FV I've been involved in re-doing the low band antennas at KC1XX the last few months in preparation for the upcoming contest season. I helped install four 2-wire Beverages which use the K1FZ KB-2 feed box. The 160, 80, and 40 meter stations will be using the Beverages. I have to agree the performance and construction quality of Bruce's boxes are excellent. Also, Bruce has been very good about providing "tech support" for his products. For those of you doing 2-wire Beverages, he also now has a reflection transformer product, the KB-3. In general reflection transformers will give you much better F/B than simply tying one of the wires directly to ground, which is what most people do. At KC1XX we saw a big improvement in performance when we changed over to reflection transformer terminations (our own homebrew units) for all the Beverages. BTW, I have no commercial interest or affiliation with K1FZ. 73, John W1FV
N1EU Postscript I've installed a pair of two wire Beverages using 450 ohm 18AWG copper-clad ladder line and they work fine. However, significant improvements have been made over the last 3 years as a result of changes to the reflection and matching transformers. The first transfomers followed the designs I found in several of the popular books. The new transformer followed the design presented by W8JI in Communications Quarterly, Spring 1997. Signal level, f/b ratio and SWR all improved. More information on the transformers I wound can be found here. |