1970年代初頭、周波数カウンターは高価な上に重くて大きくて、誰もが所持できるようなものではありませんでした。その後ロジックICやLED表示器の急速な進歩で自作も容易になりましたが、まだ高価だったTTLを沢山使うブレッドボードづくりに気が乗らず、自分は二の足を踏んでいました。
1977年に秋葉原の亜土電子が三菱電機のIILを使ったワンボードのカウンターキットFC-355Dを発売。IIL (integrated injection
logic) ICには分周／カウンター、デコーダ、LEDドライバが全部入っている上、TTLコンパチで動作する点も魅力で、基板のサイズもキット価格も手ごろだったからすぐに買い求めたものです。
このICには入力信号の周波数から特定のオフセット値 (例えばIF周波数455kHz)を減算して表示する機能が付いており、「Radio counter」と称してこれをPRしていました。これはリグの周波数読取り精度向上を望む多くの方から注目されたと思います。アマチュアの自作機器への応用例も雑誌に掲載されたりしました(※1)。同時期にミズホ通信が類似のカウンター基板を発売
(※2) したことも記しておきます。
たった5桁のカウンターながら、VFOの作り込みではその威力を存分に発揮しました。回路定数決定や温度補償のためのデータ取りには真に大助かりで、TX,
RX-002に展示したリグの周波数安定度は、そのお蔭でVYFBに作り込みができました。
これを「自作」と呼べるか疑問になるほど簡単なキット品ですが、当時果たした役割が大きかったのでここに展示することに致します。
これは余談ですが、製作当時にJJYで較正した基準発振の10MHzを今回43年振りにチェックしたところ、その誤差は40Hz だったので少し感動しました。製作は1978年。
（※1） CQ ham radio Mar.1979 p267-279, “1200MHz SSB transceiver” Yoshiro
Mataka/JA4BLC.
（※2） Ham journal No.14 (1978) p79 “frequency displaying with M54821P Mitsubishi
IIL” JA1AMH.
Five digits frequency counter, 100Hz～30MHz, Zin 1MΩ, sensitivity≧30mVrms,
frequency offset function included (for a super-het radio receiver), DC8～10V
200mA
In the early 1970s, frequency counters were expensive, heavy, and large,
and not something that anyone could afford to own. After that, with the
rapid progress of logic ICs and LEDs, it became easier to manufacture a
frequency counter, but I was reluctant to make a breadboard that used a
lot of TTL, which was still expensive.
In 1977, Ado Electronics, located in Akihabara, launched the FC-355D, a
one-board counter kit using Mitsubishi Electric's IIL. I was attracted
to the IIL (integrated injection logic) IC because it contained all the
functions of a frequency divider/counter, decoder, LED driver, and it was
TTL compatible. The size of the board and the price were affordable, so
I immediately bought the kit.
This IC had a function to subtract a specific offset value (ex. IF frequency
455 kHz) from the input signal frequency and display it, and the manufacturer
called it a "radio counter" to promote it. I think this attracted
the attention of many amateurs who wanted to improve the frequency reading
accuracy of their rigs. An example of its application to an amateur's home-built
rig was also published in a magazine (*1). At the same time, a similar
counter board was put on the market by Mizuho Tsushin (*2).
Although it was only a five-digit counter, it showed its full potential
in making a VFO of good stability. This is such a simple kit that I wonder
if it can be called "homebrew," but I put it here because it
played a significant role at the time. (It was really helpful to get data
for determining circuit constants and temperature compensation, and the
frequency stability of the rig exhibited in TX, RX-002 was built into VYFB
thanks to it.) This is an aside. I checked the reference oscillator of
10MHz, which was calibrated with JJY at the time of manufacture, for the
first time in 43 years, and was a little impressed to find that the error
was only 40Hz. This was assembled in 1978.
（※1） CQ ham radio Mar.1979 p267-279, “1200MHz SSB transceiver” Yoshiro
Mataka/JA4BLC.
（※2） Ham journal No.14 (1978) p79 “frequency displaying with M54821P Mitsubishi
IIL” JA1AMH.
Five digits frequency counter, 100Hz～30MHz, Zin 1MΩ, sensitivity≧30mVrms,
frequency offset function included (for a super-het radio receiver), DC8～10V
200mA
