PA8W Amateur Radio

            Wil, PA8W,  E-mail: PA8W@upcmail.nl             
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Good SSB audio quality on reception


A short note on the  reception audio quality:


Of course reception audio quality is very important as well. 
You need a good speaker to reproduce the spectrum running from 100Hz to 3,5kHz at least, with a good flat frequency response. And, this speaker should be well aimed to the listener. 
This is where lots of compact transceivers go wrong. 
My IC746Pro for example, has a speaker in the top side. 
This is killing for a good frequency response. 
Especially the higher frequencies will be radiated in the wrong direction, since they are quite directive.
I solved this by putting a 20x20cm aluminium reflector screen over the speaker, in a 45 degree angle, so that the sound is reflected forward. This gives me the full spectrum of the speaker, and therefore a consistant audio quality.

An excellent external speaker can be homebrew very easily:
Take a small loudspeaker out of a speech dedicated application, such as one out of a 100V church column.
They are fine speakers for our application, and often in 8 ohm impedance (without the 100V transformer)
Put it in a small enclosure out of MDF, plywood or chipwood.
When connected to a radio, you will notice a boomy sound coming out of it,
caused by the self-resonance of the speaker-cabinet system.
Now fill the enclosure with lots of sound absorbing material such as BAF, sheep wool, or other fibres.
It may be necessary to pull a piece of stretch cloth around the speaker chassis, to prevent absorbing material to enter the chassis, and lean against the back side of the paper cone.
Now, filled with absorbing material, the speaker will have lost its excessive low end, and perform very well for communications purposes.
Make sure it is well pointed towards your listening position, for the best, consistant audio. 

By far the best way to operate is to wear really good headphones.
 Period.
Keep your audio level within healthy limits though.
I use Koss UR-30 headphones, which have a pretty flat frequency response.
Using the Koss UR-30, you will hear how many Hams with Extended SSB spill a lot of power in the 100Hz region or even below.
It looks like they try to compensate for the bass roll-off that most communication receivers display.
This of course is a totally useless approach; do you think the BBC back then would add extra low end to compensate for the poor bass response of the popular small transistor radios? Absolutely not.

I know however of measures that were taken in the USA sound studios where big hits were born: 
In the final mixing stage, a recorded song was played back over a reduced bandwidth speaker to simulate AM car radio quality.
The song would have to sound fine over this poor speaker, because back then, music was very likely to be appreciated mostly during very long car drives over the American highways, totally out of range of the weak local FM radio stations.
If a song couldn't be enjoyed over a AM-speaker, it would never have become a real bestseller!

Testing your receiver's audio response:
There's a simple way to test the frequency response of your entire receiver chain.
Just put up a small local RF signal from any source and tune your radio to it in SSB mode.
Rotating the dial of your radio, you will hear the sinusoidal tone of that signal.
Turn the dial towards a lower pitch until it becomes just too low to hear. Try to get a "zero beat".
Read the zero beat frequency from your display. Now turn the dial slowly towards a higher pitch until the volume drops at the high end (often around 2,5kHz) Note this frequency as well.
Ok, repeating this frequency sweep, listen carefully for increasing or decreasing volume on your speaker. 
Any big peak or notch is bad news, and should be investigated.
It will generally be caused by a poor speaker or poor listening position. Again good headphones will take care of this.
Small ripples within + and - 3dB are quite normal, and a slightly raised level towards the high end is quite normal as well.
 The frequency response of your SSB filter is showed by your S-meter; small fluctuations again are normal, but in this measurement they will not result in ripples in your audio, since your automatic gain control will smoothen this automatically.
Fluctuations of more than 6 dB on your S-meter will however be degrading your audio in normal operation and are therefore not ok!

Some of the newer generation transceivers use DSP-based SSB-filters which can be user-modified. 
If it offers the choice between hard knee and soft knee filters, be sure to choose soft knee; a steep, hard knee filter will show much more ringing effect which is really unpleasant and may cause listening fatigue much faster.)

Consistancy  
Consistancy by the way is very important for the ears (or brains!) ability to get used to a type of sound which is likely to be far from perfect, while refining its skills of speech recovery in difficult conditions. 
As this is a process that takes some time to refine itself, you don't want to confront your brain with constantly changing acoustic conditions. 
Don't underestimate the power of your brain as a signal optimizer!
So if your stations sound quality on receive is ok, try to stick to the existing setup.
This will give your brains the necessary time to get used to, and adapt to the situation.
Only then your brains capability as a signal optimizer will come to full development.

 


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