I'm thinking of upgrading my present green screen radar to a new version and started to look at specs at which point I realized I have no clue what some of the ratings mean. Specifically, I am interested in a more precise distinction between a 2kw and 4 kw array. My present 2kw 16 mile rated radar draws a little over 10 amps at 12v when transmitting - obviously this isn't transmitting a 2 kw signal. At that power draw, it's more like 100 watts erp. I guess I have 2 questions: 1. What exactly does the radar power advertized as 2kw actually mean?, and 2. Would it be a valid assumption that a 4kw radar transmits twice the signal of a 2 kw unit? thanks in advance Don
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Radar KW
Your questions and confusion are very similar to mine until recently. As I understand it, the way they get 2KW of power out of 12V and draw 10 amps rather than 167, is by a transformer that converts the 12V to a much higher voltage (like 200V in the amps x volts = watts equation, assuming 100% efficiency.) The light dawned on this for me when I was working on the radar dome and made the mistake of touching a lead at the dome which still had voltage in it from a charged capacitor, even though the power to the unit was shut off. ZAPPP!!! It sure made me jump! And no, I was lucky, it didn't blow out any diodes in the radar, or in me, although my wife might argue otherwise.
Your questions and confusion are very similar to mine until recently. As I understand it, the way they get 2KW of power out of 12V and draw 10 amps rather than 167, is by a transformer that converts the 12V to a much higher voltage (like 200V in the amps x volts = watts equation, assuming 100% efficiency.) The light dawned on this for me when I was working on the radar dome and made the mistake of touching a lead at the dome which still had voltage in it from a charged capacitor, even though the power to the unit was shut off. ZAPPP!!! It sure made me jump! And no, I was lucky, it didn't blow out any diodes in the radar, or in me, although my wife might argue otherwise.
It's the Peak Power of the radar! 
The 2 kW or 4 kW is the radar's peak power. A modern radar sends a pulse signal. The energy transmitted is called the "Duty Cycle" which is the "Pulse Width" (PW) times the "Pulse Repetition Rate" (PRR). Sometimes they give the "Pulse Repetition Time" (PRT) which is the inverse of the PRR or they state it as "Pulse Repetition Frequency" (PRF) which is the same as PRR. The Duty Cycle is equal to the average power used divided by the "Peak Power". Think of the radar's duty cycle as a musical note generated by a trumpet. The musical note generated by the trumpet will have a specific tone and duration. The musical tone is based on the note you are blowing and how long you are blowing it. You can blow the note softly or really loud; the musical note and duration of that note doesn't change, only the loudness changes. The louder the tone generated, the further the tone will carry and be reflected back. If you look different radar manufacturers, a 2 kW unit from one manufacturer can sometimes use as much power as a 4 kW unit from another manufacturer. The height of the antenna also affects the distance the signal can be sent and be reflected back. The radar horizontal distance in nautical miles is 1.25 times the square root of the antenna height above the water. Fair Winds, Clyde Radar formulas http://www.tpub.com/content/neets/14191/css/14191_47.htm
The 2 kW or 4 kW is the radar's peak power. A modern radar sends a pulse signal. The energy transmitted is called the "Duty Cycle" which is the "Pulse Width" (PW) times the "Pulse Repetition Rate" (PRR). Sometimes they give the "Pulse Repetition Time" (PRT) which is the inverse of the PRR or they state it as "Pulse Repetition Frequency" (PRF) which is the same as PRR. The Duty Cycle is equal to the average power used divided by the "Peak Power". Think of the radar's duty cycle as a musical note generated by a trumpet. The musical note generated by the trumpet will have a specific tone and duration. The musical tone is based on the note you are blowing and how long you are blowing it. You can blow the note softly or really loud; the musical note and duration of that note doesn't change, only the loudness changes. The louder the tone generated, the further the tone will carry and be reflected back. If you look different radar manufacturers, a 2 kW unit from one manufacturer can sometimes use as much power as a 4 kW unit from another manufacturer. The height of the antenna also affects the distance the signal can be sent and be reflected back. The radar horizontal distance in nautical miles is 1.25 times the square root of the antenna height above the water. Fair Winds, Clyde Radar formulas http://www.tpub.com/content/neets/14191/css/14191_47.htm
Another way to
lookat this is on flash units for cameras. Many flash units are sold interms of watt-seconds. Thus the 500 watt-second flash that happens in 1 millisecond delivers the energy of a flash of the same light energy as a 500 watt light exposed for one second. The radar pulse may have an energy of 4 kw but a duration of only a few microseconds and is repeated several times per second. The time for a radar pulse to travel 1 mile and return is 12 microseconds so the pulse must be short.
lookat this is on flash units for cameras. Many flash units are sold interms of watt-seconds. Thus the 500 watt-second flash that happens in 1 millisecond delivers the energy of a flash of the same light energy as a 500 watt light exposed for one second. The radar pulse may have an energy of 4 kw but a duration of only a few microseconds and is repeated several times per second. The time for a radar pulse to travel 1 mile and return is 12 microseconds so the pulse must be short.
My answers ...
1. What exactly does the radar power advertized as 2kw actually mean? The power level of the transmitter is actually 2kw. It is only turned on for a microsecond or so at a rate determined by the range setting. On low range settings the pulse rate is (or should be) higher than the long range settings which are lower. That depends on the design of the unit of course but is important in that the sensitivity of the unit is higher with more pulses to look at. You might want to look at the power drain and see if it increases on the shorter ranges. It should since an increase in the pulse rate increases the power consumption. You can also probably hear the pulses if you put a detuned AM radio next to the scanner when it is on. It is probably a few thousand pulses per second which you can hear easily. There are sometimes options which allow you to look at a longer distance on the high range scale and in effect slew (shift) the display forward. That requires slowing the pulse rate which will decrease the sensitivity and thus the ability to see a small target. Again you can watch the power drain and see if that is what it is doing. If this slewing option is a jumper setting within the unit, it may affect the sensitivity on all ranges and would be a good thing to check out if you set it that way permanently. 2. Would it be a valid assumption that a 4kw radar transmits twice the signal of a 2 kw unit? Generally speaking, yes. The antenna of a 4kw unit is usually bigger, too, so it will be more sensitive just from that difference. The antenna size is usually more important than the transmitted power. My advice is to put the scanner as high as practical on the mast for more range and do not ever put it at eye level as it will cook the color detecting parts of your eyes over time.
1. What exactly does the radar power advertized as 2kw actually mean? The power level of the transmitter is actually 2kw. It is only turned on for a microsecond or so at a rate determined by the range setting. On low range settings the pulse rate is (or should be) higher than the long range settings which are lower. That depends on the design of the unit of course but is important in that the sensitivity of the unit is higher with more pulses to look at. You might want to look at the power drain and see if it increases on the shorter ranges. It should since an increase in the pulse rate increases the power consumption. You can also probably hear the pulses if you put a detuned AM radio next to the scanner when it is on. It is probably a few thousand pulses per second which you can hear easily. There are sometimes options which allow you to look at a longer distance on the high range scale and in effect slew (shift) the display forward. That requires slowing the pulse rate which will decrease the sensitivity and thus the ability to see a small target. Again you can watch the power drain and see if that is what it is doing. If this slewing option is a jumper setting within the unit, it may affect the sensitivity on all ranges and would be a good thing to check out if you set it that way permanently. 2. Would it be a valid assumption that a 4kw radar transmits twice the signal of a 2 kw unit? Generally speaking, yes. The antenna of a 4kw unit is usually bigger, too, so it will be more sensitive just from that difference. The antenna size is usually more important than the transmitted power. My advice is to put the scanner as high as practical on the mast for more range and do not ever put it at eye level as it will cook the color detecting parts of your eyes over time.
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