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| To: | "LF-Group" <[email protected]> |
|---|---|
| Subject: | LF: "Downward modulation" |
| From: | "Dick Rollema" <[email protected]> |
| Date: | Thu, 01 Aug 2002 10:31:37 +0200 |
| Reply-to: | [email protected] |
| Sender: | <[email protected]> |
|
To All from PA0SE Apparently my remark that the carrier of Droitwich goes downwards during modulation has caused confusion. I certainly did not mean "downward modulation" as we remember it from our AM transmitter days, an effect caused by insufficient drive, weak power supply or other shortcomings of the transmitter (or the operator...) The carrier of Droitwich and BBC World Service is normal as long as there is a modulating signal. But during moments of no modulation the carrier rises to a higher level. As soon as modulation reappears the carrier returns to its normal level. This can be clearly seen in the attachment to the reflector posting of 31/7 by Jim, M0BMU. I am sure this is done on purpose and not a matter of poor design, bad maintenance or incompetence of the BBC engineers. Dave, G3YXM, in his posting of 30/7 has told us that it is a feature of modern transmitters that can be used to preserve a silent background in the face of interference. I can understand that in connection with the BBC World Service but why it is applied to the 198kHz transmissions escapes me. 73, Dick, PA0SE |
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