Discussion in 'Straight Keys - CW Enthusiasts' started by KB4MNG, Jul 1, 2019.
very good info! thanks
Exactly the same as a live audio setup. Effects are added to line-level audio before any amp or PA simply because at line-level, the audio signals can be mixed more precisely and it is easier to get the desired effect on one signal (whatever that is) without interfering with other signals. Line-level is a trimmer cap, audio level is an air-variable cap.
In a live audio setup, you start with a number of discrete signals (mics, instruments, recorded and/or generated SFX). With a good system, each signal can be equalized, compressed, gated, processed, etc., as desired - and THEN the various signals are mixed together to drive the amplifiers, PA, stage monitors, etc. There may be several different mixes going to different amplifiers.
In an HF receiver, you start with a bunch of signals all mixed together, plus noise, and one of the main jobs of the receiver is to separate the signal you want from all the others. What makes it even more of a sporting course is that the level of the various signals is all over the place, and has incredible "dynamic range". If we use the "6 dB per S-unit" scale, it is possible to want to hear a signal that is S1 which is surrounded by S9+40 dB signals - a difference of 88 dB or more.
The 1957 article by W1DX explains this very well.
73 de Jim, N2EY
That's exactly what a passive mixer does. The mixed and leveled output from the mixer then goes to powered speakers and monitors. The "several signals mixed together" are the channels of the board. From the channels, you can adjust effects, dynamics, isolation, compression, and anything else, first on the channel level, then to a lesser degree on the main output. The sound guy does a sound check on each instrument to dial in the channel, then on the entire group to mix the final output of all the channels together.
On drums (I'm most familiar with that) there are typically 5 mics. A drum has a resonant frequency, but also produces parasitic and sympathetic vibrations from the head and shell (unwanted overtones). Muffling the drum only goes so far, but at the board, adjusting high/mid/low settings make the resonant frequency pop right out. A lousy, poorly tuned drum can be made to sound pretty awesome. This is all done at line-level. A snare and bass drum are done the same way, but typically compression is added to level the signals, and you want to remove all reverb. All 5 channels come together at the board, where the volumes are adjusted to make all five mics sound like they are at the same level, the dynamic range is adjusted on the 5 channels to bring out whatever is desired. A dance band would want heavy bass, a jazz combo would want an even mix, etc. Then the output from all 5 channels gets mixed with the other channels.
The parallel is pretty clear....first you find the resonant frequency of the drum, and reject all of the other noise. You do that on multiple signals and put them together as one, at a common volume. Then the line-level mix is amplified at the speaker.
Oh yes.....I know.....
The point is that with a sound mixer, you start with individual signals and mix them together. With a receiver, you start with a whole bunch of signals all together and separate out the one you want.
Oh yes....I know...
The thing is, each of the 5 drum mics gets its own channel to the mixer. Each has its own filter and other settings. And in 99.99% of cases, the sound in each channel that you want is the loudest sound; the other unwanted sounds are weaker.
A receiver is VERY different.
You do that at the individual mic-channel level, before the other mics get mixed in.
Point is, the filtering is done as far from the speaker as practical. Same as in a receiver....
This is why the Southgate Type 7 is single-conversion, with the first IF crystal filter only two stages from the antenna.
73 de Jim, N2EY
Lose the fancy crap!
The old heads never owned that stuff, it wan't around, but they could do righteous CW work with poor signals.
Get yerself a good set of cans that aren't wide frequency. Several comm type fones can be had cheap on eBay.
The vy best filtering is in btween yer ears...
I know a lot of people always use a 200 or 500 Hz filter for CW, regardless of whether QRM is bad or not; but I generally only use them when trying to copy very weak or very fast CW in a crowded band. That way I hear the DX when it starts calling CQ 2 KHz away. The filter between my ears allows me to follow the station I am in QSO with and tune out everything else except a DX signal, something no other filter can do (for now, anyway).
Well...some of the old timers didn't have and fancy crap but the I.F. crystal filter has been around since the advent of the superhet.
People's eyes and ears do not all work the same way. I have to get past the little voices in my head before I can copy any CW.
I like to run narrower than 500Hz when there's lots of QRN too... AGC off eliminates the "pumping" of the crashes, just use RF gain
QSL on xtal filters. My R390 and 390a has them.
Those rigs work best using an Autek QF-1 or 1a audio filter I've found.
I have bad tinitus, multiple pitched tones in each ear 24/7.
Headfones are a vy big part of my receive arsenal here.