Condxが悪いと1KW出しても不感なのに、状態が良い時は微弱電波で遠くまで届いてしまうというのが電離層伝搬の不思議さです。2021年はサイクル25が上昇し始めたので、others-014に展示したST-BY機能付き可変ATTを小出力の7MHz送信機に取り付け、数mW出力でQSOにチャレンジしました。
7月に入り、500mW→50mW→10mW、と徐々に出力電力を下げながら交信テストを行い、8月には5mWで川崎市多摩区と、3.5mWで宮城県宮城郡とQSO。そのあと送信機出力を200mWに絞り、23dBのATTをかませて目標の1mWまで出力を低減しました。忍耐強くチャレンジを続けた結果、9月11日0143UTCに7M1ANM/1安藤さん（埼玉県狭山市移動、当地松本市から直線距離で135㎞）から応答をもらい、ランダム交信が成立したものです。
こちらが受け取ったレポートは驚いたことに599で、後日受け取った安藤さんからのメールによれば、Sメータは7～9振っていたとのこと。一方松本で受信した安藤さんの信号強度は65dBμV（59+25dB）ほどでした。当日のイオノグラムを見ると、伝搬はEスポ電離層によるものだったようです。回線計算は、伝搬が松本→狭山の片方向に10dBほど有利なもので、電離層の反射効率は30%以上だったことを示唆しています。
実のところ、8月から9月10日までの1か月間で1mWに応答があったのはたった一度だけ、それも“QRZ？”。1mWは受信機の局発電力にも満たないレベルなので、やはり難しいチャレンジでした。
QRPは我々を謙虚にしてくれますが、それがあまりの低出力になると、全く歯が立たなくて卑屈になってしまいます。それで嫌になって止めちゃったら、話はそれでおしまい。モチベーションを維持しながら十分エンジョイするには、1mW出力の専用送信機を新たに作るよりも、例えば1mW～数100mWの間で（連続或いはステップ状に）スムースかつ正確に出力可変できるようにすることを優先すべきです。
これは自分の感想ですが、ベストな空中状態と相手局に恵まれれば、恐らく500μW以
下でも電離層反射のランダムQSOは可能だろうと思います。
CW QSO of ionospheric propagation on 40m with one milli-Watt output as
a tiny peanut (mosquito) whistle.
The wonder of ionospheric propagation is that when the condition is bad,
it doesn't go across even if it's running kilo-watt, but if the condx is
improved, very QRP radio wave can reach far distance. In 2021, as Cycle
25 began to rise, I installed the variable ATT with stand-by function exhibited
in "Others-014" on my QRPP 7MHz transceiver and challenged myself to make QSOs with
a few milliwatts output.
In July I was QRV while gradually lowering the power from 500mW to 50mW
to 10mW, and in August I made a QSO with JA1/Tama-ku, Kawasaki City with
5mW output to the antenna and with JA7/Miyagi-gun, Miyagi Prefecture with
3.5mW. After that, I reduced the power to the target power of 1mW by using
the ATT mentioned above in combination with the transceiver while reducing
the output power to 200mW or less, and as a result of my perseverance and
challenge, I got a call back from Syuich Ando/7M1ANM/1 (portable Sayama
City, Saitama Prefecture, 135km from Matsumoto City of my QTH) at 0143UTC
on September 11, and succeeded in random QSO. To my surprise, the report
I received was 599, and according to an e-mail received later from Ando-san,
the S-meter was swinging from 7 to 9. On the other hand, the signal strength
of ７M1ANM/1 received in Matsumoto was about 65 dBμV (59+25 dB). The ionogram
of the day shows that the propagation was due to Sporadic-E ionosphere.
The line calculations suggest that propagation was about 10 dB in favor
of one direction, Matsumoto to Sayama, and that the ionospheric reflection
efficiency was over 30%.
As a matter of fact, in the 30 days from August to September 10th, my 1mW
sending was replied only one time, and that was "QRZ?” Random QSO
with 1mW which is less than the local oscillator power of a receiver was
still quite a challenge. QRP humbles us, but when it gets too low-powered,
it becomes utterly toothless and demeaning. If we get sick of it and stop,
that's the end of the story. Rather than building a new dedicated transmitter
of 1mW output, we should prioritize making it possible to vary the output
power (continuously or in steps) smoothly and precisely between 1mW and
several hundred milliwatts, for example, in order to maintain motivation
and have enough fun.
This is just my opinion, but if you are lucky enough to have a good condx
and a partner station, it is probably possible to make a random QSO with
ionospheric reflections with 500μW or less.
CW QSO of ionospheric propagation on 40m with one milli-Watt output as
a tiny peanut (mosquito) whistle.
