从矿石收音机到边带电台 第06章 [复制链接]

1. chapter 6, harris

crystal sets to sideband
(c) frank w. harris 2006, rev 10

chapter 6

building a homebrew qrp

among the guys i work, qrps seem to be the most common homebrew project, second only to building antennas. therefore this chapter describes a simple qrp design i have settled on. i use my qrps as stand-alone transmitters or i use them to drive a final amplifier to produce higher power, 25 to 100 watts.

it’s true that before you build a transmitter you’ll need a receiver. unfortunately, a good selective, all-band ham receiver is complicated to build and most guys don’t have the time and enthusiasm to do it. (see chapter 13.) on the other hand, chapter 7 describes building a simple, 5-transistor 40-meter receiver that i have used with the qrp below to talk to other hams. this simple receiver will work best during off hours when 40 meters isn’t crowded. it can also be used to receive morse code for code practice.

the qrp transmitter shown on the left is designed exclusively for 40 meters, (7.000 to 7.300 mhz.) the twelve volt power supply comes in through the pig-tail wire on the right. the telegraph key plugs into the blue marked phono-plug socket on the right of the aluminum heat sink. the antenna output is the red-colored socket on the left end of the heat sink.

a 40-meter qrp module.

the transmitting frequency of the qrp module is controlled by a quartz crystal. that’s the silver rectangular can plugged into the box on the right front. the knob on the far right is a variable capacitor for adjusting or “pulling” the crystal frequency over a range of about 3 khz. as we shall explain in chapter 10, variable frequency vfos that can cover the entire band are hard to build. i don’t recommend starting out with a vfo. you need success, not frustration.

start simple

the easiest qrp is just a crystal-controlled oscillator. it usually has one to three amplifier stages to raise the power to between 1/2 to 5 watts. this will get you on the air quickly. unfortunately crystal control means you must order $18 custom crystals for your favorite frequencies in each band. because the oscillator only has a very narrow tuning range, you can usually only call cq (calling any station). as luck would have it, it always seems as though the other fellow calling cq is just out of your crystal range.






1. chapter 6, harris

从矿石收音机到边带电台
(c) frank w. harris 2006, rev 10

第6章

做一个自制的qrp

  在和我一起干的人中，qrps似乎是最普通的自制项目了，排第二的就是做天线了。因此，本章描述了一个我完成的简单的qrp设计。我使用我的qrps作为单独的发射机，或者我使用它们来驱动一个终端放大器以产生更高的功率，达到25-100瓦。

  事实是，在你做一个发射机之前，你将需要一个接收机。不幸的是，一个选择性良好的全波段火腿接收机做起来复杂，因此，大多数人没有时间和激情来完成它。（参见第13章。）另外一方面，第7章描述了做一个简单的、使用了5个晶体管的40米接收机，我用下述的这个qrp同其它火腿交谈。当40米波段不拥挤的情况下，这个简单的接收机在业余时间将会工作得最好。在练习收发报的时候，它也能够被用来接收莫尔斯代码。

  左图所示的qrp发射机专用于40米波段，（7.000到7.3000mhz）。12v的电源由右边的引线送入。发报键插入蓝色标记的唱机插头插座里，在右边的铝散热片上。天线输出端为红色的座子，在散热片的左边。

一个40米的qrp模块

  qrp模块的发射频率由一个石英晶体控制。那是银色的长方体罐子，它能够被插入右前方的盒子里。最右边的旋钮是一个可变电容，用来调节或者“拉”晶体频率，使其达到大约3khz范围。我们将会在第10章来解释它，但是能够覆盖整个波段的可变频率vfos很难做。我不推荐在一开始就使用vfo。你需要的仅仅是成功，但不是失败后的沮丧。

简单地开始

  最简单的qrp仅仅是一个受控的晶体振荡器。它通常有一个到三个放大器级，来升高功率为1/2到5瓦。这将会使你开播的进展更快。不幸的是，使用受控晶体就意味着你必须订购$18的定制晶体，在每一波段为你想要的频率。因为晶体仅仅只有非常狭窄的可调范围，你也许通常只呼叫cq（呼叫任意电台）。碰巧，似乎是总有其它同道中人，刚好在你的晶体范围之外呼叫cq。

0602



2. chapter 6, harris



the transmitter “mainframe”

the transmitter “mainframe” you could use this bare-board little transmitter just as shown above. however, it will be more convenient to mount it in a larger chassis equipped with an on/off switch, pilot lights, an antenna relay, and other niceties. my whole transmitter assembly is shown below.      

the transmitter “mainframe” is a box to contain your transmitter modules. the large meter at the upper right indicates the current drawn by the final amplifier. it's helpful to know how much power the transmitter is consuming. the switches and lights on the lower left are the main power switch and the transmit/ receive switches. there are also led lights to indicate which switches are active. the large red button is a “spot” switch. with the spot switch engaged, the qrp oscillator may be tuned to another station without actually transmitting. how big you make your mainframe depends on your plans and ambitions. as you can, see, i had really big plans. by the time you add multi-band capability, a vfo, power supplies, and single- sideband capability, even a large box may be too small. my previous mainframe was too small so i made this one extra large to eliminate crowding.

transmitter mainframe

hf construction methods – building your own circuit boards

back in the vacuum tube days we built hand-wired hf transmitters. inside they had long wires running every which way. however, transistors generate high power with low voltage and big currents. as a result, the inductance of the wiring must be kept as low as possible. this means you must build with a circuit board or the transmitter simply won’t work.      

for example, once i connected an output lead from a 21 mhz (15 meter band) transistor power amplifier to the base of the next stage with a bare wire 4 inches long. if this had been a vacuum tube circuit, this wire coupling would have worked well. but with high current transistors, the wire acted like an rf choke. that is, the wire blocked current flow as if it were an inductor. sliding an oscilloscope probe along the wire, i could see an 80% drop in drive voltage from the output of the first amplifier to the base of the next stage. in contrast, a wide circuit trace printed on a circuit board acts like a coaxial cable and has very low inductance. with a pc board the same drive to the next stage can be nearly 100%, not 20%.






2. chapter 6, harris



发射机“主机”

  你能用这个由裸板做的小发射机，如上所示。但是，如果把它装在一个大底盘上，配备了开关、指示灯、发射天线与其它部件，使用起来就会更加方便。我的整个发射机组装后如下所示。

  发射机“主机”是一个容纳你的发射机模块的盒子。右上方的强度计指示终端放大器的电流。它有助于了解发射机的功率消耗。左下角的开关与灯，是主电源开关与收/发开关。也有led灯，来指示哪个开关合上了。大的红色按钮是一个“触点”开关。如果它在忙，表明qrp振荡器可能已经调谐到另外一个没发射电台。你的主机的大小取决与你的计划与雄心。正如你能看见的，我有一个大计划。那时，当你增加了多波段、vfo、电源、ssb，当初的大盒子也显得太小了。我先前的主机太小了，因此，我做了这个超大的主机来消除拥挤。

发射机主机

hf的制作方法——做你自己的电路板

  回到真空管的日子里，我们做手持hf发射机。机内每一路都有长线。然而，晶体管产生了高功率、低电压与大电流。结果是，接线的电感必须尽可能小。这就意味着你必须做一个电路板，否则发射机就不能工作！

  例如，我曾经使用了4英寸长的裸线，连接一个21mhz（15米波段）晶体管功放与下一级的基级。假如是真空管电路，这段导线连接将会工作良好。但是，由于使用了大电流晶体管，它就像一个rf扼流圈。换句话说，它就像一个电感阻塞了电流。用示波器的探针在上面滑行时，我能看到有80%压降，从第一个放大器的输出到下一级的基极。相反，印刷电路板上的宽线的表现就像同轴电缆，感抗非常低。使用pc板，同样能够将近100%地驱动下一级，而不是20%。

第0603页

3. chapter 6, harris



if you have already developed your own method of making printed circuit boards, you may skip ahead. but if you have never done this before, read on.

making prototype rf circuit boards

pc board tools and materials

i usually use double-sided printed circuit (pc) board material such as radio shack part # th 276-1499a. this board has layers of thin copper bonded to both sides of a 1/16 inch fiberglass sheet. i only solder components to the surface of one side. the solid surface of grounded copper on the opposite side provides distributed capacitance over the whole circuit. i believe this gives extra stability and works like as a grounded shield to prevent radiating signals to whatever circuits might be adjacent to the bottom of the board.

traces on a pc board act like transmission lines

a transmission line, such as the coaxial cable that delivers your tv signals, is remarkably efficient. as explained in chapter 4, the wire in the center of the coax acts like a distributed inductance that rings with the distributed capacitance between the center wire and the outside insulation. in other words, a coaxial cable is a distributed lc circuit and does not dissipate the voltage and the energy as you would otherwise expect. in fact, the energy losses that do occur are only the heating losses in the insulation and the simple resistance losses that happen in copper wire.      

a two-sided circuit board can be designed to act like a circuit wired with pieces of coax. the circuitry is mounted on one side of the board while the other side is ground. each trace has a small amount of inductance and each trace has a proportional amount of capacitance with the grounded copper on the far side of the board. the result is that signals are almost unchanged as they travel along the traces of a circuit board. it would be interesting to build the exact same rf power amplifier on single-sided and double-sided boards and compare the difference in performance at hf frequencies. i’m convinced double-sided is far better, but i've never done a controlled experiment.

in microwave printed circuit boards the traces are deliberately designed to act like transmission lines for the particular frequency that is being used. the precise, optimum dimensions for these “microstrip” traces can be calculated for maximum performance. fortunately for us, high frequency circuit boards like ours don’t have to be designed with so much care.

etched circuit boards  

there are at least four ways to make homebrew rf boards. originally i tried etching “real” printed circuit boards with ferric-chloride solution. it’s slow, messy, and lots of work. etching boards is an art that isn't easy to master. you may under-etch or you may over-etch, often on the same board! if you succeed, you’ll have a result close to a commercial product. unfortunately, when you use a circuit layout from an arrl handbook or qex magazine, you are making the assumption that you can buy all the exact parts the author used. good luck! the parts you can actually buy may not fit on the board. i found that the worst limitation of etched pc boards was that i couldn’t build and test my circuits one transistor stage at a time. if i needed to add another component or add another amplifier stage, i had no room for it. the key to success in homebuilding is building and testing one small circuit at a time.






3. chapter 6, harris



  假如你已经知道怎么做pcb了，那就可以跳过本节。但是，如果你从来没有做过，就请继续阅读。

制作rf电路板的原型

做pcb所使用的工作和材料

  我通常使用双面pcb材料，例如：无线电小零件#276-1499a。这种板是1/16英寸厚的玻璃纤维板，两面都有薄铜层。我只在一面焊元件。反面的接地铜，它为整个电路提供分布电容。我坚信，这将会提供额外的稳定性，它就像接地屏蔽，可以阻止辐射信号干扰任何接近于底板的电路。

pcb上的导线就像传输线

  一条传输线，就像同轴电缆，可以非常有效地传输tv信号。如第4章所述，同轴电缆的中心线就像分布电感，它被中心线与外包绝缘皮之间的分布电容套住。换句话说，同轴电缆就是一个分布式的lc电路，它不会损失额外的电压和能量。事实上，能量损失在所难免，绝缘产生的热损失，简单的铜线电阻损失。

  双面电路板能够被设计成同轴电缆那样好。电路只布在板的一面，另外一面为地。每条线路都有一点电感，每条线路都和反面的地铜产生相应的电容。结果是，当信号沿电路板上线路传输时，几乎不变。在hf频率，用单面板和双面板来做严格相同的rf功放以比较性能差异，这是非常有趣的。我深信双面板表现优越，但我没有做对比实验。

  微波pcb上的走线，会为所使用的频率而特意地把它设计为传输线。确切地，会为这些“微波传输带”线的最优的性能而计算它们的最优尺寸。幸运的是，像我们所使用的这些高频电路板，不需要如此精心地设计。

蚀刻电路板  

  自制rf板至少有4种方法。最初，我试验了使用氯化铁方案来蚀刻“真正的”pcb。这个过程非常缓慢、肮脏，且工作量大。蚀刻电路板是一门不容易掌握的艺术。你可能会蚀刻不足或者过度蚀刻，通常，在同一块板上，这两种情况都会发生！假如你成功了，你将有一片接近于商品pcb的成品。不幸的是，当你使用在一本arrl手册或者qex杂志上的电路原理图的时候，你会做出如此假定，你能买到同作者所使用的完全一样的部件。祝你好运！实际上，你能够买到的部件很可能不适合这块板。我所发现的最坏的局限是，如果使用蚀刻法做pcb，我就不能一次一个晶体管级地构造与测试我的电路。假如我需要添加另外一个部件或者增加另外一个放大器级，但是我没有给它预留空间！自制成功的关键是，一次只构造并测试一个小块电路。

第0604页


4. chapter 6, harris



gouged pc boards

my favorite method for making rf boards is carving them into a bare, two-sided pc board with a small wood-carving gouge. the gouge is a chisel with a cupped end, perhaps 1/8 to 3/16 inch across. i got mine from brookstone tools.      

notice the cupped end of the wood-carving gouge

two small wood-carving gouges
this qrp board was made with “gouged board” construction. nearly all of the visible copper is "ground." the aluminum angle on the right serves a heat sink for the output transistor.

when you push the gouge along the board at a high angle and twist your wrist back and forth, the gouge carves out a little trench through the copper. hint: keep your elbow high and the gouge won’t skate across the surface and into you hand. ouch! obviously two “trenches” can isolate a strip of copper that serves as wire or “trace.” often i just isolate little islands of pc trace onto which i solder short component leads. i usually solder components to the surface, rather than drilling mounting holes for each lead.






4. chapter 6, harris

用圆凿刨pcb

  我做rf板的最喜欢的方法是，使用一把小木凿，在一块裸露的双面pcb上通过雕刻来完成它。这种凿子的尖端有凹陷，大约为1/8-3/16英寸。我用的是从brookstone工具店买的。

注意木凿子的尖端

两把小木凿子

  这块qrp板是使用“凿板”法做的。几乎所有的可见铜皮都是“地”。右边的直角铝板是输出晶体管的散热片。

  向前扭动你的手腕，当你大角度地沿板推动凿子时，就会在铜皮上挖出一条小沟。注意：抬高你的肘子，这样凿子就不会误伤你的手。（如果不慎被划到，那将会很）痛！明显地，两条“沟”能够隔离出铜线或“铜路”。通常，我只在焊接小元件的引脚的地方，隔离出小块的pc路。我通常是在表面上焊接元件，而不是钻孔安装。

好文章，顶！