| Build A 9 dB, 70cm, Collinear Antenna From Coax |
By N1HFX |
Recently the RASON technical committee was hard at work at the repeater site repairing our 2 meter repeater antenna. One of the members commented to me that I should write an article about collinear arrays so that we could all build our own. While it is not always feasible to home-brew a commercial quality antenna designed to take hurricane force winds, it is very feasible to built a collinear antenna for average use. This article describes a collinear antenna made from very inexpensive RG58/U coaxial cable and encased in PVC pipe.
Before we start building we need to cover some ground about the characteristics of coaxial cable. First remember that there is something called the velocity factor for coaxial cable. For RG58/U coax it is typically .66. This means that when we calculate the length of ½ wavelength in free space we need to adjust its size by multiplying it by the velocity factory. Simply put, RF slows down by the velocity factor when traveling through coaxial cable. All that aside now, lets calculate the ½ wavelength of RG58/U coaxial cable with a frequency of 444 Megahertz:
½ wavelength of coax = 300 / F / 2 * V
Where F = Frequency in Megahertz
V = Velocity factory of Coax
300 / 444 / 2 * .66 = .2229 meters or 223 millimeters
To allow for cutting the ends of our coax, we will need to add 8 millimeters to each ½ wave length for a total of 231 millimeters.To get started, we will need 8 half wave lengths (231 millimeters) of RG58/U coaxial cable to be cut and connected in the manner shown in Figure 1. First cut back 4 millimeters of the outer jacket, braid and dielectric exposing the center conductor as in Figure 2. Now cut back the outer jacket another 4 millimeters to expose the braid and push the braid back about a millimeter to prevent it from shorting with the center conductor. It is best to lightly tin the braid with solder at this point. Now solder each half wavelength as shown in Figure 1. Attach a few feet of RG58/U to the bottom of the array as in Figure 1 for feeding the antenna.
1/4 wavelength radiator = 300 / F / 4
Where F = Frequency in Megahertz
300 / 444 / 4 = .1689 meters or 169 millimeters
At the bottom of the array we will slide a 5/16 inch aluminum tube over the coax and crimp it to the braid of the antenna feed point only. If copper is used, it is okay to solder. The length of the tube is calculated as follows:¼ wavelength of tubing = 300 / F / 4 * V
Where F = Frequency in Megahertz
V = Velocity factory of Tubing. (Use .95 for 5/16" tubing)
300 / 444 / 4 * .95 = .1604 meters or 160 millimeters
Because a collinear antenna is hot with RF along the shield of the coax, it is necessary to prevent the RF from coming back through the coax. Slide three FT50-43 or almost any similar sized toroids over the bottom end of the coax as shown in Figure 3. The toroids should be placed about ½ wave length from the bottom of the array. Use the same formula for calculating a half wave length of coax. If you prefer, apply RF to the antenna at this point and slide the toroids up and down until minimum SWR is found. Tape the toroids to the proper point on the coax using electrical tape or similar means.
For final mounting, attach the antenna to a ¼" wooden dowel using tie wraps about every 3 inches. It may not be possible to obtain a wooden dowel for the complete length so attach two dowels together by using a 1 inch sleeve of 5/16" tubing and crimping the tubing at each end. Check SWR again to insure that no connections have separated or shorted. Carefully insert the coax and dowel assembly into several feet of ¾" PVC pipe for final mounting. Because of the tie wraps, it is not necessary to use spacers but may be necessary if larger size piping is used. Drill a hole for the coax at the bottom end cap and place an end cap on the top of the PVC. Do not cement end caps until the SWR has been doubled checked. Cement end caps and water proof coax opening on the bottom. Use whatever type of coaxial connector is desired on the bottom of the coax end but do not use RG58/U for your complete feed line. Use a low loss coax such as RG8/U for the main feed line to the transceiver. Don't forget to water proof all coax connectors.
If the eight ½ wave coaxial elements result in an antenna too long for your liking (over seven feet), then it is okay to use four ½ wave coaxial elements but the SWR may be slightly higher (Attach four ¼ wave vertical ground radials at the antenna feed point to help lower SWR.). If 9 dB gain is still not enough for you then increase the number of coax elements from eight to sixteen. You will probably need to attach guy lines to the antenna. Although only a 70 CM antenna was described in this article, the formulas can be easily calculated for the 6 meter, 2 meter or 1¼ meter bands. Millimeters were used for many of the measurements but can be converted to inches by dividing millimeters by 25.4 for those who are not familiar with the metric system. After installing one of these antennas, be prepared to hear stations and repeaters that you never heard before.
DE N1HFX
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哈罗CQ火腿社区 > 火腿技术区 > 天线
棒子天线的一种新的结构认识！
建立 A 9 分贝、 70 cm, 在同一直在线的天线从哄
被 N1 HFX
最近 RASON 技术委员会在重复的人在工作中很难位置修理我们的 2 公尺重复的人天线。对我批评的成员之一我应该写一个文章有关在同一直在线的排列以便我们全部可以建立我们自己的。它不总是能实行的到家-酿造酒商业的质量天线设计拿飓风力量风, 它非常能实行到建造一个在同一直在线的平均用的天线。 这一个文章描述一个在同一直在线的天线从非常廉宜的 RG58/U 同桥电缆制造而且在 pvc 装入管。
以前我们开始建筑物我们需要到掩护一些地面大约同桥电缆的特性。 首先记得有某事为同桥电缆打电话给速度因素。 因为 RG58/U 哄它典型地 .. 这方法当我们计算长度 ? 波长在自由的空间我们需要调整它的大小藉由藉着速度工厂乘它。 只要简单地放，当旅行过同桥电缆的时候，射频根据速度因素减慢。 所有的旁白现在，让计算那 ? RG58/U 同桥电缆的波长用 444个百万赫之的频率:
? 波长哄 =300/ F/2* V
哪里在百万赫之的 F= Frequency
V= Velocity 工厂哄
300/444/2*.=. 公尺或 223 毫米
考虑到切断那结束我们的哄, 我们意志需要把 8 毫米加入每个 ? 为总数为 231 毫米的波长度。
拿开始, 我们意志需要 8 一半 RG58/U 同桥电缆的波长度 (231 毫米) 是削减和连接以在图 1 被显示的样子. 第一削减向后地暴露中心领导者的 4 毫米的外部夹克、辫子和电介体当做在图 2. 现在削减向后地外部的夹克另外的 4 毫米暴露辫子和推辫子背面大约一毫米阻止它短那中心领导者。 它是最好对轻轻的锡此时用焊接剂的辫子。 现在焊接剂每个一半如图 1 所显示的波长. 附上 RG58/U 的一些脚到那底部排列当做在图 1 为饲养天线。
现在它的时间把另外的元素加入那顶端和底部在同一直在线排列。 首先增加一 ? 波元素到那顶端如图 3 所显示的天线. 使用 #16 固体电线或相似的和焊接剂它只有对中心领导者。 长度那 ? 波元素是有计划的依下列各项:
1/4个波长暖器炉 =300/ F/4
哪里在百万赫之的 F= Frequency
300/444/4=. 公尺或 169 毫米
在那底部那排列我们意志滑一 5/16 寸铝管在那之上哄和卷缩它对天线饲养的辫子点只有。 如果铜被用，它对焊接剂是好。 管的长度是有计划的依下列各项:
? 装管的波长 =300/ F/4* V
哪里在百万赫之的 F= Frequency
V= Velocity 装管的工厂。 (使用 . 为 5/16" 装管)
300/444/4*.=. 公尺或 160 毫米
因为一个在同一直在线的天线向前很热具有射频那盾那哄, 它对避免射频而言是必需的从来临向后地完成的那哄。 滑三 FT50-43 或几乎任何相似的按规定尺寸制作环在那之上底部结束那哄如图 3 所示. 环应该是放置有关 ? 波长度从那底部排列。 使用计算的相同的公式一一半的波动长度哄。如果你偏爱, 此时应用射频到天线而且上下地滑动环直到最小量 SWR 是发现。 音带环到那适当的点在那之上哄使用电的音带或相似的方法。
在完成在同一直在线天线的基本集会之后，在地板上用天线应用很少的射频或地面。 相对地低点 SWR 应该是此时观察。 SWR 将会是非常低的一经天线是装在那空气。 如果 SWR 是大超过 2-1 横过那整个的乐团, 一个连接可能分开或短发生。 它意志是必需品到正确的问题以前进行。 在善行 SWR之后是获得, 地方热收缩装管向前所有的连接或外套紧紧地以电的音带。
为结局架设，附上天线到一 ?" 木制的合钉使用领带外套有关每一 3 寸。 获得一个木制的合钉可能不是可能的为那完全的长度如此藉由使用 1 寸一起附上二个合钉袖 5/16" 装管而且在每个结束卷缩装管。 检查 SWR 再保险没有连接有分开或短。 小心地插入物那哄和合钉集会进入一些脚之内 ?" 结局的 pvc 管架设。 因为领带外套, 它是不必需品到使用取间隔的装置但是可能是必需品如果大的大小吹笛被用。 钻孔机一个洞为那哄在那底部结束无边帽和地方一结束无边帽在那之上顶端 pvc。 做不水泥结束无边帽直到 SWR 有是两倍检查。 水泥结束无边帽和水证明哄第一次的在那之上底部。 使用任何的类型同轴联编者是需要在那之上底部那哄结束但是做不使用 RG58/U 为你的完全饲养线。 使用一低点损失哄如此的当做 RG8/U 为主要的饲养线对无线电收发机。 不要对水证明忘记全部哄联编者。
如果那八 ? 波同轴的元素造成对你的爱好 (超过七尺) 是太长的一个天线, 然后它是好到使用四 ? 波同轴的元素除了 SWR 可能些微地是比较高的 (附上四 ? 波垂直的地面径向在天线饲养点到帮忙低的 SWR.)。 如果 9个分贝仍然得到对你是不充足的那么增加那数哄元素从八到十六。 你意志或许需要附上人线对天线。虽然只有这 70 CM 天线在这一个文章中被描述，公式装于罐头容易地有计划的为 6 公尺, 2 公尺或 1? 公尺乐团。 毫米是二手的为多数测量但是能是转换到寸被分度毫米 25.4 为不对公制的系统感到熟悉的人。 在安装这些天线之一之后, 是准备听到车站和重复的人你从不听到以前。
DE N1 HFX
自己制作时，第一段1/4和最后一条1/4视情况可以去掉，这两段是用来做阻抗匹配的