Posted by
Jim-168 on
Aug 24, 2008; 11:01pm
URL: http://elecraft.85.s1.nabble.com/Rx-Tx-equalization-band-selection-tp779103p780325.html
Low order distortion
-----Original Message-----
From:
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[mailto:
[hidden email]] On Behalf Of Jim Brown
Sent: Sunday, August 24, 2008 6:28 PM
To: Barry N1EU;
[hidden email]
Subject: Re: [K3] [Elecraft] Rx/Tx equalization band selection
On Sun, 24 Aug 2008 14:41:54 -0700 (PDT), Barry N1EU wrote:
>Why is 50hz important if it is completely outside the passband? +/-16dB at
>50hz has zero effect on rx or tx in the K3.
Don't be so sure that there's no effect. It's important that when this
undesired low frequency energy is produced by the mic, it is not carried
through AUDIO path where it can trigger limiting, create distortion, or even
cause overload. On the air, especially during contests, I hear lots of low
frequency trash on SSB signals, most of it room noise.
In general, if the desired bandwidth of a system is limited, as ours is, the
modulating signal (in this case, microphone audio) should be bandwidth-
limited as early in the signal chain as practical. Many good mics have
built-in high pass filters or low-frequency roll-off filters. When I'm
mixing live program material, whether music or speech, I ALWAYS use a good
high pass filter on every microphone preamplifier. With most musical
instruments, it's set near 200 Hz. With instruments like a bass or bass
guitar, I'll move it down to 40 Hz or so.
73,
Jim Brown K9YC
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