Audio Dynamic Range – by Mike Higgins K6AER
What is you audio dynamic range? This mostly applies to SSB transmissions but could also apply to FM and AM as well. Simply put it is the difference between no modulation during key down and your modulation peak in dB.
Your dynamic range listed below will give you an idea on how your audio is perceived by the other contact.
- 10 dB, which is very harsh and tiring to listen too. Much background noise including fans, road noise, air-conditioning, dogs barking and in general background clutter noise. Your contact will ask for repeats a lot and in general your QSOs will be short.
- 20 dB, decent audio range with a little audio background noise. QSO’s will last longer. Very little repeats. Most stations fall into this category.
- 30 dB, your contacts will complement you on you audio, tonal quality aside; you will find folks will like to listen to your transmissions. Communications in weak conditions will be generally more successful.
- 40 dB, you are now into broadcast quality transmissions. This is not easy to obtain but with proper microphone techniques and mic gain settings most any transceiver can obtain this level.
- 50 dB, this is where you need to be if you plan on running a Linear Amplifier. With a +30 dB over S9 signal to your contact, your un-modulated signal will still be an S6 on their receiver. Poor dynamic range is the reason people ask if you are running a linear amplifier.
For FM you will need a deviation meter but with a good oscilloscope you could use the same method as you would use for AM. For AM you will need an oscilloscope to look at voltage level from no modulation and modulation peaks. For both FM and AM, this can be derived from a monitor receiver speaker output. SSB is much easier. Look at the peak signal as monitored from a nearby station. The difference in the peak reading to your modulating signal to the level received while not modulating is the dynamic range. If you have a lab grade watt meter you can look at the power output from the radio or amplifier. The formula is:
Log (power max/power min) x10 =DynamicRangein dB.
An example of a 1500 watt signal with a non modulation level of 100 mW is shown below:
Log (1500/.100) x10 = 31.76 dB
As you can see, 100 millawatts can transmit quite a lot of signal or noise. Some of this noise could be generated in the transmitter but generally it is from the microphone environment. To check you audio level, transmit into a dummy load and watch the output with no modulation. If you see a level indicated, turn you microphone gain down to zero. If the level drops to zero your microphone level is the problem with your low dynamic range and your audio environment.
Several things can be done to improve you dynamic range.
- Try to pick a quiet place for your station.
- Close the door to your shack.
- Use the microphone between 3 and 6 inches from your lips.
- Your ALC should read 10 dB or less.
- Avoid excessive compression. It is mostly microphone gain with a little filtering.
- Speak directly into the microphone, not on the side.
- Use a wind-screen (foam rubber) over the microphone.
- Be aware of cooling fan noise. Placement of fan related gear (amplifiers) is important.
- Use a suspended microphone. They pick up less desk noise and vibration.
- Avoid a room that has no rugs or drapes. Echoes don’t help and can make communication quality very poor.
- Make sure the TV and stereo cannot be heard.
These are the most prevalent items I hear being done in QSOs. If you’re mobile, roll up your window. Some FM mobiles have so much vehicle and wind noise their transmissions are unintelligible.
These are just a few suggestions on making your home station and mobile environment much more pleasant to listen to. Work with other hams for a critical ear. Now have fun.
Mike Higgins – K6AER