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Subject: Re: relationship b/w dB and frequency

Date: 08/02/01 at 9:23 PM
Posted by: John Dunn - Consultant
E-mail: ambertec@ieee.org
Message Posted:

In Reply to: relationship b/w dB and frequency posted by abbas on 08/02/01 at 6:45 PM:

Hello, Abbas.

I'm going to speculate a bit, but we may be able to get somewhere.

A specification like -5 dB at 60 MHz probably means that some device's output or signal gain is 5 dB less than that same device's property at some other frequency. For example, a low pass filter could be rated for - 5dB at 60 MHz with respect to some lower frequency like, say, 1 MHz. Conversely, for a high pass filter, that - 5dB at 60 MHz might be with respect to properties at maybe 500 MHz.

The dual specification of -2dB at 6 MHz and -30 dB at 12 MHz is simply a more specific statement. It provides not just one datum for the device's response, but two.

The terms "symmetrical and asymmetrical RF inputs" are not familar to me, but perhaps they refer to "balanced and unbalanced RF inputs". In that case, a "balanced" input would be something like a 300 ohm ribbon line which has a balanced or symmetrical structure of its two conductors with respect to ground where an "unbalanced" input would be a coaxial cable input.

As far as such terms possibly being applied to modulated signals, the only thing I can think of that they might pertain is the vestigial sideband modulation used in NSTC television transmission.

Good luck.

John Dunn - President
Ambertec, Inc.

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