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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%。