键伍工程师谈TH-F7（附原文）
BA4IN 译
2001年第十期日本<<CQ HAM RADIO>>杂志有一篇关于键伍手机双段对讲机TH-F7的文章，在日本以外销售的机器型号为TH-F6A，这两者主要的不同之处在于TH-F6A内置一个可在220MHz发射的频段，而TH-F7没有。这篇文章是参与TH-F7设计的两位键伍工程师的一席谈话。
TH-F7突出的特点是：
1、使用本机锂电池输出5W功率；
2、使用了大容量电池，可长时间工作；
3、在不同的频段或相同的业余频段，可以同时接收两个频率；
4、可以在很宽的频率范围内使用SSB/CW方式接收信号。
TH-F7设计方案中最富有挑战性的是如何把这么多功能集中放到一个小型手持机中，在设计的初期就把机器的尺寸被定为首要因素，为达到此目的，采用了如下关键技术：
1、TH-F7使用了两块，每块6层的电路板，并且采用了小体积的贴面封装元件，称之为“1005”(体积1*0.5mm)。
2、TH-F7使用7。4V锂电池及分立件的场效应管(2SK3476)做功放。从手持对讲机角度看，镍镉电池要好于锂电池，但TH-F7选择了后者，是因为锂电池有容量大的特点。
3、TH-F7有六个前端及放大器，分别是：
100kHz-10.1MHz，
10.1MHz-50MHz，
50MHz to 108MHz，
108MHz to 265MHz，
265MHz to 600MHz，
600MHz to 1.3GHz。
此外它还有两级覆盖100KHz--1300MHz的接收宽带放大器。
在设计中最困难的工作是对机器散热的处理，加在末级FET功放管上的工作电压，在使用本机电池时是7。4V，使用外接电源时是13。8V。工作时FET散热片上的温度可能会上升到100摄氏度，不能简单地使温度通过机壳散热，如果这样做，温度太高，使用者怕是无法拿在手中。末级功放的效率在40-50%，其余部分最终变成热量散发，大约有6W，这是没办法的事情，TH-F7只能尽可能地减少其它电路部分的散热。TH-F7有一个过热保护电路，当温度超过极限时，功率最低会降到0.5W。当使用外接电源时，大约连续发射3分钟后温度保护电路动作，发射功率下降，使机器通过空气散热。功率从5W降到2W对降低过热效果不明显，所以选择从5W降到0.5W。
在健伍公司的产品中，TH-F7是第二款具有宽带接收功能的手持收发(对讲)机，第一款型号是RZ-1。
在144M和430M对讲机中增加1.2G频段是很困难的，如果这样做，电路上需要专门用于1.2G的滤波器和发射功放管。
原文：
Interview with Kenwood engineers
The October issue of Japanese CQ Ham Radio Magazine has an article on Kenwood handheld transceiver TH-F7. It also is selling as TH-F6A outside Japan. The major difference between the is TH-F6A has 220MHz buit-in, but TH-F7 does not. The article is an interview with two Kenwood engineers who were the members of the TH-F7 development. It of course is written in Japanese. Here is my English summary for non-Japanese HAMs.
The outstanding features of TH-F7 are:
1. 5W output power with the lithium-ion stock battery
2. Long run using the large-capacity battery
3. Dual receive in two different bands and in the same amateur band (144 or 430).
4. Wide band receiver with SSB/CW capable.
The most challenging job in the TH-F7 project was to have all the features above built into the small hand held size. To tell the truth, the size was defined at the very first phase of the development. The key technologies that made those features possible are:
1. TH-F7 has two six-layer PCBs, and uses tiny electronic parts of surface mount type, called 1005 ( 1mm x 0.5 mm).
2. TH-F7 has employed a 7.4V lithium-ion battery and a discrete FET power amplifier (2SK3476). From the hand held transceiver perspective, Ni-Cd battery is superior to Li-ion battery, but TH-F7 has selected the latter because of the larger capacity.
3. TH-F7 has six RX front end amplifiers for 100kHz-10.1MHz, 10.1MHz-50MHz, 50MHz to 108MHz, 108MHz to 265MHz, 265MHz to 600MHz, and 600MHz to 1.3GHz. It also has a second wide-band amplifier covering 100kHz-1.3GHz.
The most difficult work during the development was the heat management. The drain voltage of the final TX FET is either 7.4V with the stock battery or 13.8V with the external power supply. The temperature at the heat sink of the FET rises as high as 100 degrees C. The heat cannot simply be diffused to the body, because, if done so, the user would not be able to hold the radio. The efficiency of the final amplifier is 40 to 50 percent. The loss, which eventually is dissipated as heat, is about 6W. There is no way to get around to it, so TH-F7 has to keep the heat generated by the other parts as small as possible. TH-F7 has a heat protection circuit, which gets the output power down to 0.5W when the temperature exceeds the threshold. Approximately three minute continuous TX with an external power supply might trigger the automatic power down, though it depends on the atmosphere temperature. Since the power down from 5W to 2W does not help preventing overheat, it jumps from 5 to 0.5W.
The TH-F7 is second hand-held transceiver with wide band RX in the Kenwood product history; the first one was RZ-1.
It is difficult to include 1.2GHz in addition to 144 and 430MHz (Japanese version does not have 220MHz). To have 1.2GHz, the filters and TX power transistor dedicated to 1.2GHz should be needed.