Communicating Clearly

Communicating by radio is not always easy.  Distance between operators, propagation characteristics, the presence or absence of natural and man-made interference, antenna efficiency, antenna directivity, power level, configuration of each of the two radios, the accuracy of the microphone’s audio frequency response, the speed of speaking by the transmitting operator, and the clarity of enunciation by the transmitting operator all contribute to the ability of the receiving operator to understand the received audio signal.  Many of these variables are fixed for a given equipment installation, so that about all the transmitting operator can do to improve the receiving operator’s understanding of what he is saying is to optimize his transmitter’s configuration, use a good microphone, speak moderately slowly, carefully enunciate each word, use an appropriate amount of transmitter power and use the phonetic alphabet where appropriate.

The receiving operator can ensure against avoidable local noises in his shack, ensure that his rig is properly configured to maximize the understandability of the signals that are received, and use a good headset if doing so improves his understanding.  If the receiving operator suffers from some degree of hearing loss, a common enough problem for aging operators, then he should ensure he is wearing his hearing aids.  There are also some after-market products available that purport to shape the received audio signal to improve speech comprehension.

The energy spectrum of human speech is NOT flat.  It is biased toward the lower frequencies.  But speech comprehension is biased toward the higher frequencies where there is less speech power.  Moreover, audiologists report that effective speech comprehension requires 12 db excess over background interference.

To complicate the problem of communicating clearly via radio, few of us actually know how efffectively we are transmitting our audio signal, because we have not heard a recording of our own voice as received by another station.  We plug the transceiver in, follow the set up instructions, and set the microphone gain per instructions, and we mostly assume that the system is providing a good signal to the receiving operator.  Even if we receive a report that our signal has some defect, it’s difficult to take effective corrective action when there is no commonly understood descriptive language for the variety of problems that occur over the air.

The following are the author’s thoughts on improving radio communications effectiveness, and are a mixture of fact and opinion.  The reader is always invited to comment on what is said (see contact information at end).

Situational Awareness:  How the transmitting operator speaks should be responsive to how well the QSO is proceeding.  If the receiving operator reports 20 db over S9, and seems to follow the conversation with little trouble and few requests for repeats, then there is no need to make changes in the transmitting speech to improve received comprehension.  On the other hand, if the reported signal is weak, not much over the background noise level, there are frequent requests for repeating something, or you are having difficulty hearing the other station, then the transmitting operator should be mindful and alter his speech patterns to improve communications effectiveness.  Speaking more slowly, enunciating more carefully, using simpler conversational syntax, and using the phonetic alphabet are all effective actions.

Speaking slowly:  Comprehension of received speech is, to a point, inversely related to the speed of the speech.  We are all aware that some people routinely speak rapidly and others more slowly, and that is usually not a problem in normal face to face communications.  However, faster speaking tends to reduce comprehension over the radio, especially in the presence of interference.  The thoughtful transmitting operator will slow down his speech when faced with a problematic QSO.  He will also improve his enunciation, more carefully pronouncing each syllable.   Both of these actions can dramatically help the receiving operator.  A corollary to speaking slowly, is to be slow to start speaking so that it is clear that the transmitting circuits are functioning before speech commences.

Using Phonetic Alphabet:   The phonetic alphabet is designed to improve communications effectiveness under stressed conditions.  There is a single official phonetic alphabet but there is a wide variety in the actual phonetic alphabets that you hear over the air.  [Opinion Alert] Use of non-standard phonetic alphabets may retard communications effectiveness, instead of improving it, as the receiving operator is not ‘expecting’ the words he is hearing.  Use of ‘America’ instead of ‘Alpha’, ‘Yokahama’ instead of ‘Yankee’, ‘Kilowatt’ instead of ‘Kilo”, ‘Frank’ instead of ‘Foxtrot’, etc. have developed a following on the air, but the use of these non-standard phonetic substitutes add a further layer of signal conversion by the receiving operator before he knows what he has heard.  It is always better to use the standard alphabet.  This is particularly true when the phonetics used are cute word substitution for each letter (e.g. use of ‘Big Bad John’ for ‘BBJ’ is less likely to be understood by the receiving operator than the proper phonetics (‘Bravo Bravo Juliet’)

Microphone Proximity and Position:    The transmitting operator needs to maintain a consistent distance and position relative to his microphone in order to ensure a consistent pickup of his speech by his microphone.  This distance and position should be the same as that used when the microphone gain was set for the rig.  The operator who moves his head, or leans back in his chair while speaking, is producing a variable transmitted audio signal that is likely to contribute to reduced speech comprehension by the receiving operator.   I have heard Bob Heil [CEO Heil Microphones] say that the microphone should not be placed directly in front of the speaker’s mouth, but just to the side of the cone of emitted speech.  This reduces the likelihood that hard consonant sounds will overdrive the microphone.  All other things being equal, I have come to appreciate the fixed position that a headset boom microphone provides the transmitting operator, even though he moves his head or body position while transmitting the relative position of the microphone remains fixed relative to the source of speech.

Hardware Contributions to Speech Comprehension:  On the transmitter end, poor speech comprehension at the receiving end can be caused by excessive, or insufficient, microphone gain, excessive speech compression, and improper setting of microphone equalizers in newer digital rigs.  While transceiver user manuals give instructions for setting these features, they tend to be general (e.g. “the meter needle should not exceed the blue band on the meter”, or “set the adjusting knob to between the 9 and 12 o’clock positions”, or “the setting is too high if the ALS LED lights up”).  The problem with these adjustments is that as operators we have no easy way to determine the overall effect on our transmitted audio of these settings after we make them.  Even if we have friend who will describe back to us our audio quality, those descriptions are difficult to translate into meaningful terms and tend to become reports of either ‘OK’ or ‘doesn’t sound quite right’.  The most valuable tool to personally assess the effect, that changing the transmitter’s settings has, is to hear an audio recording of one’s own signal, and then notice the changes that various settings have.

Microphones:  The microphone is probably the single most critical piece of hardware that directly relates to quality of speech comprehension.  While we spend upwards of several thousand dollars on a transceiver, amplifier, and auto tuner, and possible on a tower and antenna, we do not seem to spend as much effort or money on selecting our microphone.  Microphones can run the gamut from excellent to very poor and we have no easy way to assess the effect that our microphone has on speech comprehension at the receiving end unless we get recordings of our transmitted signal. 

A microphone, which may seem like a very good price bargain, may degrade your communications effectiveness.  There is a lot of literature in the public domain describing the qualities of a good microphone but I have developed the opinion that above all else, the microphone must provide a strong audio frequency output across the audio spectrum between 500 Hz and 2.4 kHz.   Frequency responses going higher than 2.4 kHz are acceptable but the microphone should not produce audio below 300-500 Hz because it is wasted energy that does not contribute to speech comprehension but consumes a fairly large part of the transmitted power envelope. 

A microphone that is good on an ICOM, may not be good on a Yaesu, and vice versa, due to differences in the transceiver’s microphone power circuit and the transceiver’s microphone input circuitry.   If possible, get a report or an audio recording, using the microphone that you will use on the air.

Microphone Gain Setting:  The microphone gain setting establishes the degree to which the microphone’s audio input signal modulates the transmitted RF signal.  Microphone gain can degrade communications effectiveness by being set too low or by being set too high.  Overdriving a microphone can create RF clipping and cause splatter of the transmitted signal, degrading both the specific transmitted signal and the ability of operators to hear other traffic in proximity of the transmitted frequency.  However, most operator manuals have cautions against overdriving the microphone gain and experience to date is that I have not often heard microphones with gain set too high.  It seems that far more signals are under driven than are over driven. 

We have all heard signals in which the RF was very strong (59 or better), had good excess over background noise, and still the audio signal was ‘weak’ and hard to understand.  These signals need additional microphone gain.  We can contrast that to other signals that had RF levels at or close to the background noise level and yet their audio had strength and punch that far exceeded that of their S-meter strength.

Digital Signal Processing:  Modern transceivers generally include DSP circuits that eliminate background noise static or notch out tones due to operators tuning up on frequency.  However, these DSP circuits do incrementally degrade the accurate reproduction of the received audio signal.  While increasing the DSP noise level cancelation setting may continue to reduce the background noise level, it also increasingly degrades the received audio signal.  There is a trade off to be considered between the improved readability of the audio signal due to reduction of interfering noise level, and the reduction in the readability of the audio signal from increasingly high settings of the DSP noise cancellation circuit.  These DSP circuits should be set to match the actual on-air conditions and not left at a high level that was once appropriate.  To a much lesser extent, notch circuits may be deactivated in hard to hear situations in which there is no on-air tuning interfering with the received signal.

VOX Circuits:  Voice operated transmission (VOX) circuits allow for hands free voice transmission, otherwise bypassing ‘Push-to-Talk’ circuits, and are a substantial convenience to a busy transmitting operator.  However, VOX circuits can be problematic to the receiving station if they are not properly set up, or are used in inappropriate background noise environments.  VOX circuits can be well set up and provide very effective service, but it can also be difficult to determine if they are improperly set.  VOX circuits have to be set to determine the level of sound at which they will commence transmitting and how quickly they will drop out.  This sets up a trade-off between losing starts of sentences, or words, before the VOX engages, and having the VOX trigger due to background noises in the shack (phone, XYL, coffee cup placed on table, etc.) and interrupt reception during the receive portion of a QSO.   While overly sensitive VOX settings will become apparent to the operator during the receive cycle, insensitive VOX settings are not as obvious to the transmitting operator unless the other station in the QSO reports clipping of his sentences or words.  One potential way to avoid use of VOX circuits, while still gaining the benefit of ‘hands-free’ activation of transmitting circuitry, is to use a foot treadle for PTT activation.

R. A. Goodwin 
N4HCI 
Bobgn1@cox.net 

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