[K3] [Elecraft] Rx/Tx equalization band selection

[Jim]

Low order distortion

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
Sent: Sunday, August 24, 2008 6:28 PM
To: Barry N1EU; elecraft at mailman.qth.net
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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