What Makes a Station Loud?
From The WB7TJD Wiki
Some pointers
Contents |
What makes a station loud?
As you listen to our repeater you will hear soft voices with no noise, LOUD voices, also without noise, and noisy signals where a LOUD voice may be too loud to achieve clear copy, and a soft voice may be lost in the noise.
Transmitter power
Transmitter power increases do not make the voice louder. Transmitter power increases will only quiet the static and noise associated with a weak or distant signal. Once the signal is being received at the repeater with full quieting, further power increases do nothing.
Audio power
Effects
A station with a LOUD signal, especially one that is three or more times as loud as the voice-identifier messages emitted by the repeater, will not sound their best, as they will cause people's squelch circuits to clip voice peaks if they are in an area where the repeater signal is relatively weak. Some radios have a tighter bandwidth filter than others, and LOUD voices will cause these radios to emit a distorted sound of the voice.
Soft voices, on the other hand, though fully quieted into the repeater, present challenges with mobiles traveling through noisy neighborhoods or areas of weak signal from the repeater. As the motoring ham passes the power substation on his right, that softly-spoken voice suddenly gets buried in a bunch of power line noise. A normal-level voice, approximately between one and two times the level of the identifier, will still be readable if the repeater can be heard at all.
Adjustments
Most FM rigs have no external microphone gain adjustment. Some older rigs tended to be set a little louder than average, and the single adjustment if you are told that you are too loud, that you can make is to increase the distance between the microphone and your mouth. Also, make sure that you are not talking loudly to compensate for noise around you.
If you have a soft voice on the air, you need to position the microphone closer to your face.
Optimum microphone positioning
The optimum microphone position is with the microphone resting against your cheek, angled so that you speak across the face of the microphone, not into it.
Then if that is too loud, back away from the microphone with the guidance of another operator on the air.
Internal adjustments
Starting with your microphone resting against your cheek as described above, adjust the internal mic gain potentiometer for optimum voice volume. If you are not ready to mess inside your rig, have a friend adjust it as you speak while someone is giving you critiques along the way.
The best adjustment you can make is to adjust the internal potentiometers on the printed circuit board inside your radio to ensure that microphone gain and deviation are not set too high, if you are comfortable with working inside your rig. Or let a more-experienced ham tackle the job.
The radio check
If one is looking for a signal report on an FM repeater, there are a few things to consider when offering one. Your S-meter, which reads incoming signal strength, is reading the strength of the repeater, not the user requesting the check. It will usually be a constant full-scale, no matter what kind of signal the repeater is hearing, because the repeater is transmitting a strong signal to you.
If you are not receiving a full-scale signal from the repeater, there is the possibility that you will hear noise on the repeater signal. You will hear this noise while the other user is transmitting, and while the repeater is still transmitting a carrier after the user quits transmitting. You will hear this noise when no one is transmitting into the repeater, when the repeater identifies. You will hear silence when the repeater is off, unless your squelch is standing open, in which case you will hear a loud roar.
If the user is not strong enough to hit the repeater with full quieting, you will hear noise on his signal in addition to any noise you have on the repeater signal at your location.
If the other user is running enough signal strength into the repeater to reach full quieting, any further increase in his power will not make any difference in audio quality. It will have no influence on your meter, as, remember, you are listening to the repeater.
No change in your transmitted power is going to make any improvement in your reception of the other user. Sometimes an outboard amplifier brick will contain a pre-amp that may improve your reception if the repeater signal is weak to you. You may be able to switch in the pre-amp independent of whether you use or bypass the output power boost. A pre-amp will increase the chance of receiver overload and reception of out-of-band signals, but can greatly improve a weak front-end's noise figure. Experience will determine which is best.
The user on the repeater will not boost his audio level with more transmitter power, or reduce his loud audio level by reducing transmitter power. This is controlled by his placement of the microphone relative to his mouth.
A loud user with a weak signal into the repeater may clip out of the repeater. What you will hear is a noisier signal with him present than without, and his voice goes silent, taking his noise with it on the peaks of his speech. You may even hear the courtesy tone or the repeater begin a voice ident and switch to Morse code. Other users will hear the same thing. Ask him to back off of the microphone. If he backs too far off, his voice may be lost in the noise while the repeater is being held open.
A loud user may cause the repeater to clip your squelch if you don't have a strong signal from the repeater. Other users may hear everything, and still others may hear the same as you. Try setting your squelch toward where the squelch opens with no signal to see if that resolves the problem. Then ask him to back off from the microphone.
Double distance, cut power density to ¼
The strength of an RF field around an antenna, the strength of sound waves into a microphone and the strength of the magnetic field around a power supply transformer are all affected by this rule of thumb: Double the distance and cut the power density by a factor of four. (Power density can be equated to volume, or loudness of sound, or intensity of light or other energy.)
Applied to setting your rig and power supply on the table, if you stack the two units together, you may experience hum in your transmitted audio. Place them twice as far apart, and experience ¼ the hum. Double the distance again and see a 16-fold decrease from the original problem. The power transformer's magnetic lines of force were inducing hum into your audio cabling.
Applied to speaking into your microphone, if you move your microphone to half the distance from your mouth, you quadruple the volume of your speech on the diaphragm of the microphone.
Applied to the placement of your antenna relative to your sensitive electronics, doubling its distance from an object will cut its signal field by a factor of four at the object's location. You may wish to raise the antenna to twice as high to distance it from surrounding rooftops, or you may wish to place it horizontally further away from something to reduce its impact.
Going one step further with the antenna, a vertical antenna is going to radiate most of its power toward the horizon. The higher the antenna's gain, the less power it will send skyward and it will concentrate it more toward the horizon, in all directions, unless you use a beam, which is then more efficient with its power by sending it all in one direction toward the horizon.
Considering that a high-gain antenna is sending its power toward the horizon, raising the antenna above objects is going to greatly reduce its impact on those objects moreso than on other objects on the same plane with the antenna. The power density rule still applies to objects on the same plane, as you move the antenna further away from them you see the four-fold benefit for every two times the distance that you locate it.
Objects directly below the antenna see far less energy from the antenna than objects at greater distance from, but on the same plane as, the antenna. But this is the result of the antenna pattern, which is focusing on the horizon. This is why an antenna placed high in the sky will actually cause less interference potential than one placed low.