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vk3juz您好，我也想与您讨论一下，
我知道您的说法不错，功放的操作手册也是这样写的。但我也不认为电子管功放不带天调，而且不能在swr大于3:1的条件下工作。因为那个pi网络就是天调了。所有功放都是为50欧姆负载设计的，因为馈线是50的，但是这不等于功放只能在额定负载下工作。请考虑pi网络的工作原理，见图。
pi网络可以被想象成两节反向对接的倒l网络，第一节可以把阻抗从高变低，第二节则可以由低变高。这就好玩了，极端情况下如果第一节的电容c1为0，整个pi网络就是低阻变高阻的单一倒l变换器；如果第二节的电容c2为0，那它就是高阻变低阻的倒l网络。如果其他情况，pi网络就能实现高变低、低变高或者等值变换。
由于电容、电感的调节范围有限，特别是c2往往会并联固定电容，这样才能更好地适配低阻抗负载，这就导致功放在不同波段的阻抗匹配范围不一样。尽管如此，功放在160米和10米之间的波段上匹配范围仍然远远不止3倍。有些，比如henry 3k，使用了变比很大的电容器，它的调谐范围就更宽。窄些的也有，比如al-1500，但我认为那是电容器的耐压不足造成的，包括屏极耦合电容也不足(如果没记错的话还不到5kv)。这也许才是al-1500容易打火的真正原因！
再谈匹配的概念，于此电路图说，如果通过调整c1、c2、l1+l2，我们获得了谐振的工作条件，并且屏极电流正常，那是不是说电子管工作在了正常的负载范围内？如果是的话，功放不就可以工作了吗？
那如果我们可以通过调谐这个pi网络让功放工作，那它是不是天调呢？
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bd1es您好，
您想讨论的is technical方面以后再说,在这主题上是求怎么正确使用方法.not technical.
从参与者呼号和提问上看他们都没有使用过或正确使用,包括您在内.我only想让他(她)们知道正确使用方法和保护方法而巳.他(她)们有呼号是业余无线电操作者,不一定要technical方面地东西,而technician不一定是业余无线电操作者,注意这是两个不同的操作介面.
如真喜欢technical请到echolink上找我面谈,下面一些才料供您参考.
73' see you next time on echolink
copy from bd4os
the history of 50 ohms
a lot of people ask, so here's the answer to the eternal question, "how did 50 ohms get to be the standard rf transmission line impedance?" here are a few stories. bird electronics will send you a printed copy of their version if you ask for it. this from harmon banning of w.l. gore & associates, inc. cable:there are probably lots of stories about how 50 ohms came to be. the one i am most familiar goes like this. in the early days of microwaves - around world war ii, impedances were chosen depending on the application. for maximum power handling, somewhere between 30 and 44 ohms was used. on the other hand, lowest attenuation for an air filled line was around 93 ohms. in those days, there were no flexible cables, at least for higher frequencies, only rigid tubes with air dielectric. semi-rigid cable came about in the early 50's, while real microwave flex cable was approximately 10 years later.somewhere along the way it was decided to standardize on a given impedance so that economy and convenience could be brought into the equation. in the us, 50 ohms was chosen as a compromise. there was a group known as jan, which stood for joint army and navy who took on these matters. they later became desc, for defense electronic supply center, where the mil specs evolved. europe chose 60 ohms. in reality, in the us, since most of the "tubes" were actually existing materials consisting of standard rods and water pipes, 51.5 ohms was quite common. it was amazing to see and use adapter/converters to go from 50 to 51.5 ohms. eventually, 50 won out, and special tubing was created (or maybe the plumbers allowed their pipes to change dimension slightly).further along, the europeans were forced to change because of the influence of companies such as hewlett-packard which dominated the world scene. 75 ohms is the telecommunications standard, because in a dielectric filled line, somewhere around 77 ohms gives the lowest loss. (cable tv) 93 ohms is still used for short runs such as the connection between computers and their monitors because of low capacitance per foot which would reduce the loading on circuits and allow longer cable runs.volume 9 of the mit rad lab series has some greater details of this for those interested. it has been reprinted by artech house and is available.
plus
the amplifier will comfortably deliver 1500 watts continuous carrier ("key down") into your antenna. its conservative rating of all components and efficient cooling system allows effective operation at this power level. with 2500 watts of total plate dissipation, the amplifier will operate well below the maximum power rating of the tube.
in order to achieve full output power, an input power of approximately 30 to 60 watts is required. if your transceiver delivers more output power, reduce the drive level. specially when operating rtty or any other continuous mode, reduce the drive level and let your transceiver run "cool" with less strain on its output components. amplifieris comfortable with all popular transceivers such as kenwood, icom, yaesu, jrc, tentec, etc.
the amplifieris has a very sophisticated tube protection circuitry, designed to protect against excessive plate current, screen grid current, screen grid voltage, bias voltage, overdrive, swr, etc. the tube is also protected from excessive temperature by continuously monitoring the airflow temperature. in case of any fault, the screen circuit further protects the tube and the power supply from a possible tube internal flash-over.
