感度測定
受信機のレストアが終わると感度を測ってみたくなるのが人情。 セットアップはSGとパソコンによるオーディオアナライザ。
FRG-7 (xi)
Sensitivity Measurement
Sensitivity Measurement
The photo left shows my setup for sensitivity measurement, using an SG and an audio analyser software making use of PC audio facility.
これが使用したオーディオアナライザソフトの画面。 efu氏作成のWaveSpectraというオーディオFFTソフト。 結構有名なのでご存知の方も多いと思う。 実にコンパクトかつ軽快で色々設定もできるので便利に使わせてもらっている。 S/N比を計算して表示してくれるので、感度測定が非常に楽に行なえた。 オーディオ用途なので、デフォルトではfsが48kHz, 即ち帯域が24kHzと広すぎるので、fsの設定を22.05kHz,即ち11kHz帯域にして測定した。 これを見ると、もう一つ下のfsの11.025kHzで良かったのかも知れない。まぁ、バンド外のノイズが十分落ちていて変なビートも無いので良しとした。
I used this free audio analysing software named 'WaveSpectra' published by Mr 'efu' here in Japan. This is basically a FFT analyser and have a functionality of working out S/N which is very handy for sensitivity measurement. Its default fs is 48kHz, which is a bit too wide for this purpose so I went for fs=22.05kHz option, which is still a bit too much and should've gone for 11.025kHz. However, the outband noise shown is small enough and there's no outband beats disturbing the measurement so I gave it a go anyway.
全周波数範囲、各MHzの中心でのFRG-7の感度の測定結果。 各測定周波数がxx.52MHzと少しズレているのはxx.5MHzピッタリに出るビートの影響を嫌ったため。 結果は、予想通りというか、自身の使用感とも、巷の意見とも一致する、バリバリの高感度である。 5MHz以下、それも中波でほんの少々落ちるが、それでも、十分過ぎる程の感度である。 当然スペックの2uVは全周波数でクリアしている。 昔の機械にしてはハイバンドの感度低下も無く、むしろハイバンドで元気なのは以外だった。
The overall sensitivity of this FRG-7 measured is, as expected, quite high, and backs up real operating feel of it. It shows a bit of degradation below 5MHz, esp on MW band but still far more than enough, and still maintains its specified sensitivity, 2uV. What is unexpected was the fact that it maintains good sensitivity on higher band, which is extraordinary for the receiver at that time.
以前から中波で感度ムラがあるような気がしていたので、これも測定してみた。 確かに低い方で落ちているが、3dB程度である。 多分、調整前の2ndLOのレベルがこのバンドでは風前の灯であったのが原因と思われる(だから(un)LOCKランプがなかな消えなかった)。 調整後のこの結果に有意差があるかどうか微妙なところ。
I measured this sensitivity deviation in MW band because I have had a feeling that MW has patchy sensitivity. As shown left, there's certainly a degradation on lower frequency but only 3dB or so, and I'm not sure if it's any significance at all. Most likely the reason I experienced patchy sensitivity on MW was that output level of 2nd Lo was way too low because of its BPF off-tuned (that's the reason why (un)LOCK LED hardly turned off).
ついでに15MHzでVFOの端から端までの範囲での感度のムラを測定。 これは、以前、VFOが800kHz以上でかなり感度が悪くなっていたため。 すでに第一IFのパスバンドがズレているのが原因だと判明しており、再調整済、また、2nd IF トラッキングも再調整したので、左のように殆ど有意差は無くなったことを確認できた。
I also checked in-band sensitivity deviation on 15MHz, because I used to experience sensitivity degradation on band edges higher than 800kHz on VFO reading. The cause of this has already been identified as 1st IF passband slippage, and already been re-aligned as well as 2nd IF tracking so I confirmed this problem's gone, as the plot on left shows.
I used this free audio analysing software named 'WaveSpectra' published by Mr 'efu' here in Japan. This is basically a FFT analyser and have a functionality of working out S/N which is very handy for sensitivity measurement. Its default fs is 48kHz, which is a bit too wide for this purpose so I went for fs=22.05kHz option, which is still a bit too much and should've gone for 11.025kHz. However, the outband noise shown is small enough and there's no outband beats disturbing the measurement so I gave it a go anyway.
The overall sensitivity of this FRG-7 measured is, as expected, quite high, and backs up real operating feel of it. It shows a bit of degradation below 5MHz, esp on MW band but still far more than enough, and still maintains its specified sensitivity, 2uV. What is unexpected was the fact that it maintains good sensitivity on higher band, which is extraordinary for the receiver at that time.
I measured this sensitivity deviation in MW band because I have had a feeling that MW has patchy sensitivity. As shown left, there's certainly a degradation on lower frequency but only 3dB or so, and I'm not sure if it's any significance at all. Most likely the reason I experienced patchy sensitivity on MW was that output level of 2nd Lo was way too low because of its BPF off-tuned (that's the reason why (un)LOCK LED hardly turned off).
I also checked in-band sensitivity deviation on 15MHz, because I used to experience sensitivity degradation on band edges higher than 800kHz on VFO reading. The cause of this has already been identified as 1st IF passband slippage, and already been re-aligned as well as 2nd IF tracking so I confirmed this problem's gone, as the plot on left shows.
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