RF microwave power.... Any HAM'ers help?

[MrMoMo]

Ok, so I do think I know a bit about electricity but this is beyond me.

I understand Ohms law, but there does not seem to be one for this.

Furuno Marine Radar, open array, rated at 4.5kW.

OK, 4.5kW = 4500W
Radar operates on 12VDC, draws no more than 10A, and this powers the display as well.

OBVIOUSLY, the antenna output in RF watts, are different watts than the electrical watts used to measure electrical power because...

12V @ 10A = 120VA =120W and you can't get power for free.

So, if this thing can only consume a MAXIMUM of 120W, how can we say that it puts out 4500W of RF? Is there a conversion for this somewhere? And how is a RF Watt defined? (obviously not a V x A thing) Like one RF watt = 10 electrical watts kind of thing.

Plus, if they are different, which they must be, WHY do we call them BOTH watts?

Now, from that, WHY do they rate it this way, when a regular Microwave oven, which also puts out microwave radiation, through a magnatron, is measured in Watt watts. Or are they measuring the power consumed here? (i.e. and 1100W microwave on full power CONSUMES 1100W of electrical power, not puts out 1100W of RF power)

The part that really blows my mind is how high that number is, especially since that is a relatively small radar. Furuno lists on their site, a 60kW 9' open array radar!!!! OMG!!

Just something that was tickling my brain, anyone care to explain?

 

[MrMoMo]

Whoever moved this here, thanks!! you did it faster than I could, I got booted off the internet....

 

[ParadiseCruiser]

MoMo -

I believe you have answered your own question here... you are comparing the proverbial apples v. oranges.

>> how is a RF Watt defined?

Many different ways. There are modes of RF radiation in continuous amplitude measured in watts, there are voice modulated amplitude modes measured as Peak Envelope Power (as in SSB) that are measured in watts, you have Peak Pulse Power - a pulsed form of RF (as in radar) that is measured in watts, and so on.

>> obviously not a V x A thing

Correct. None of these have anything at all to do with Ohm's law, and power consumption such as you have described.

>> WHY do we call them BOTH watts?

I give up. Why did the chicken cross the road? "There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy." Including the measurement of Radio Frequency waves.

Cheers, R -

 

[brew8]

The output power can be higher than you might think if it's peak power instead of RMS power(root mean square), a good gain antenna can give you a much higher ERP or effective radiated power, so a 250 watt radio with a high gain antenna can have an ERP in kilowatts, Cheers, Larry

 

[Doug_S]

Paradise Cruiser,

Great explanation. Couldn't have said it better myself.

KC6ZWY

 

[Kofoed]

Are they talking about ERP, effective radiated power? This applies, especially when using an anntenna with high directivity.

If they are using a dish, you can get WAY HIGH ERP compared to an isotropic radiator