About Sound Range Frequencies
For the convenience of communication, we will introduce the concept of the frequencies of the transmitted signal, break the entire frequency range of the signal into three parts:
- Low frequency – frequencies from 60 to 200 Hz;
- The average frequency is 200 to 1500 Hz;
- High frequencies are 1500 to 3000 Hz.
In the entire sound spectrum of frequencies there are very important areas and individual frequencies, which are responsible for the quality transmission of speech and vice versa make in voice broadcasting unnecessary to us the sound of deafness, promiscuity, grinding, ringing and so on. In general, by and large one of our main tasks is to form a signal with “correct” levels at certain frequencies. Otherwise, all the trouble happens.
So, we pay special attention to the following frequencies:
- Low frequency. Here I want to stop in more detail. Very important frequencies, this is a range of 80-130 Hz. It is these frequencies in the voice of the operator that create a pleasant warm “home” sound. But at the same time, going forward, I note that one of the main errors encountered is excessive strengthening of these frequencies. This can not be done, otherwise at weak levels on the receiving side will hear only hooting, with almost no informativeness in the signal. As experiments show, the signal level at these frequencies should not exceed 15-20 dB in relation to other frequencies of single-lane signal. In addition, most of the transmitter’s energy is spent on the transmission of these frequencies. What happens with the wrong formation – we shake the power, and in the end we are not accepted!
Next is a very important frequency of 160 Hz. It is in this section of the vocal spectrum that the deaf sound of the signal is hidden or as the sound is said. 160 Hz try to cut immediately available methods, for this usually apply the appropriate filter in the equalizer with high goodness, say 1/3 octave.
It’s a very important point. To keep the frequencies beautiful and deep on the air, it is necessary to form a signal to the transmitter modulator at least with a double reserve on the bandwidth. That is, if we want to qualitatively transmit frequencies of 60-130 Hz, the spectrum of frequencies in the forming ACH equalizer should start at least from the frequency of 30-75 Hz. Otherwise, unnatural sounding at low frequencies is provided. The same applies to high frequencies, high-quality sound at frequencies 2500-3000 Hz should be provided with the appropriate band of equalizer in the area of 5000-6000 Hz, otherwise the high frequencies will sound lifeless, soft and the whole signal will sound “flat” and inexpressive. In literature, this is due to the concept of phase distortionofs of sound, but we will not discuss these serious issues now.
- Average frequency. A very important range in the speech spectrum, which is responsible for intelligibility, informativeness and individuality of voice. The naturalness and basis of the voice spectrum form frequencies of 250-500 Hz. Sound engineers call these frequencies the voice base.
Here you need to certainly strive to withstand a fairly even characteristic of the ACH. The 700-1200 Hz frequencies are another very important range. As the statistics show, most people have a characteristic failure in the voice at a frequency of about 700-900 Hz. This disadvantage will have to be compensated by the equalizer. If there are large failures at these frequencies (15-20 dB) the voice of the operator becomes, as noted by many radio amateurs “gun, this is especially noticeable when listening to such a signal when the narrow band of the receiver is turned on (2400 Hz and below). However, it should be noted that at large levels (10 dB or more) in relation to the neighboring frequencies in the ACH signal frequencies 1000-1500 Hz will create an unpleasant “metal” sound.
- High frequencies. These frequencies have little effect on speech intelligibility, but give it a characteristic juicy and bright sound of consonants and sizzling sounds in the voice of the operator. Everything here is quite simple, with a relatively even ACH in the range of 1500-3000 Hz form a small rise (2-3 dB) at frequencies 2400-2700 Hz.
That’s about it.
Taking into account the above, we define the requirement for transmitting equipment. And there are two main ones.
The first is that the transmitter must provide the necessary 60-3000 Hz bandwidth in SSB mode.
The second is not to make additional non-linear distortions in the signal, when the compressor is turned off, which occurs when the mixers and the end cascade of the transmitter are not working properly.
At the first request, everything is solved relatively simply. Modern digital transivers tend to have a fairly wide allowable bandwidth. The stated transmission bands in transmission mode are usually 100-3000 Hz (different manufacturers have a non-essential setting). But the peculiarity of the work of digital filters of the main selection of modern transmitters is that with the use of the equalizer it is easy to form a signal at a level of -6 dB with a low frequency of up to 50 Hz without noticeable non-linear distortions. A little more complicated is the issue with the transmission of trebles. Based on their same features, it should be noted that in most of the produced transcomputers, digital filters are very susceptible to the formation of distortions at high frequencies with even a slight pumping of the signal in this area. This is especially evident in the transceivers produced by YAESU and KENWOOD. Conclusion – the formed signal should have from this point of view corresponding to the Ach.
To meet the second requirement, you need to make sure that the exit cascade and the PA board driver are operating in the standard EV modulation mode for SSB. As practice shows, this requirement for a large number of trans-believers produced by manufacturers is not met. Sometimes you have to increase the values of the initial rolls in the weekend cascades of the transmitter 2-3 times. And here is the undisputed leader of the firm YAESU. To be honest, I don’t really understand this energy saving policy. Much less often there is a problem with the incorrect operation of transmitter mixers. Their optimal performance is primarily influenced by the levels of signals sent from heterodines and support generators. With the appropriate measuring technique and amateur radio skills, these issues are relatively simple.
With analog transceivers, the task is complicated only by the fact that not all transceivers have the opportunity to include a high-quality broadband quartz filter in the transmission mode. For obvious reasons, the use of piezoceramic filters and EMF filters in analog transivers to form a high-quality SSB is not discussed within this topic, as these requirements are very high. This is primarily a rectangular filter ratio (no worse than 1.5), bandwidth (at least 2.8 kHz at -6 dB) and unevenness in the transparency band (no more than 3 dB). Given all this, you can focus on the use of quartz filters such as:
ICOM FL-96, FL-257 (at 455 kHz).
INRAD (under a specific transiver INRAD releases an appropriate filter with a band of 2800 Hz).
Here is an approximate list of trans-believers, leading manufacturers’ firms, which can be recommended without significant refinements to solve our problems:
– KENWOOD TS-850, TS-870S, TS-950SDX, TS-200
0- ICOM IC-746PRO, IC-756PROII, IC-756PROIII, IC-7600, IC-7700, IC-780
0-YAESU FT-1000MP, FT-1000MARKV, FT-1000FIELD, FT-950, FT-2000, FT-5000, FT-9000
.- FlxRadio Systems SDR.