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 Working Out Frequency
 Novice From United Kingdom, joined Aug 2012, 90 posts, RR: 0Posted Sat Sep 22 2012 12:21:54 UTC (3 years 8 months 6 days 8 hours ago) and read 3324 times:

 The following are the typical specifications for an airfield surface movement radar: Frequency 10000 MHz PRF 15000 pps Pulses length 0.05 usec Beam width 0.4 Aerial rotation 60 to 75 RPM What it is i'm having problems understanding what frequency is an understanding it in the above stance, i can understand the PRF of 15000 as it has a pulses every 0.05 useconds that ties in with 15000 pps. The definition of frequency is that it is the number of complete waves passing a fixed point in one second, denoted by the symbol f and usually expressed as Hertz. Though from the above specifications i would of thought this would of made sense for the pulses has there is a complete pulses every 0.05 microseconds, i just don't understand this 10000 MHz and how it ties in with the rest of the specification, can anyone understnd?
 Jetlagged From United Kingdom, joined Jan 2005, 2620 posts, RR: 25 Reply 1, posted Sat Sep 22 2012 18:09:47 UTC (3 years 8 months 6 days 2 hours ago) and read 3238 times:

 You need to differentiate between the concepts of radar frequency and the pulse repetition frequency. The radar waves have a frequency of 10,000 MHz. This is transmitted as a series of pulses. In this case there are 15,000 pulses per second and each pulse is 0.05 microseconds long. You can calculate from the PRF that the time between the beginning of each pulse is 66.67 microseconds. So the pulses are very short compared to the time between them. Taking the speed of light as 300 million m/s, each pulse would be 15m in length. The wavelength of the radar is 0.03m, so there are 500 wave oscillations in each pulse. If the radar was continuous wave, with no pulses, it's frequency would still be 10,000 MHz. So frequency and PRF aren't directly related.
 The glass isn't half empty, or half full, it's twice as big as it needs to be.
 Novice From United Kingdom, joined Aug 2012, 90 posts, RR: 0 Reply 2, posted Sat Sep 22 2012 19:57:11 UTC (3 years 8 months 6 days ago) and read 3211 times:

 Hi Jetlagged Sorry but i'm still stumbed by this, i work out at it being 6.6 microseconds based on there being 100000 microseconds in a second thus 100000 divided by 15000 equals 6.6? and i would also like to know how you came up with 15m length based on the speed of light of 300000000 m/s? Thanks for you help Novice
 David L From United Kingdom, joined May 1999, 9645 posts, RR: 42 Reply 3, posted Sun Sep 23 2012 02:26:26 UTC (3 years 8 months 5 days 18 hours ago) and read 3149 times:

 Quoting Novice (Reply 2):i work out at it being 6.6 microseconds based on there being 100000 microseconds in a second

Ah... but there are 1,000,000 (one million) microseconds in a second. A microsecond is one millionth of a second.

 nomadd22 From United States of America, joined Feb 2008, 2142 posts, RR: 0 Reply 4, posted Sun Sep 23 2012 05:42:40 UTC (3 years 8 months 5 days 15 hours ago) and read 3111 times:

 I'm not sure what you're trying to figure out here. You have a 10,000 mhz carrier wave making .05us long pulses 15,000 times a second. That means each pulse is 500 cycles long and you have one every 67us. (1,000,000/15.000) Jetlagged didn't say a wavelength was 15M. He said it was .03m. Wavelength is just is just 300.000.000 divided by the carrier frequency.
 Anon
 David L From United Kingdom, joined May 1999, 9645 posts, RR: 42 Reply 5, posted Sun Sep 23 2012 10:39:45 UTC (3 years 8 months 5 days 10 hours ago) and read 3041 times:

15m is the pulse length expressed as a distance.

You know the pulse lasts 0.05 microseconds (0.00000005 seconds) and travels at a constant 300,000,000 metres per second.

Distance equals velocity multiplied by time, so 300,000,000 x 0.00000005 = 15 metres. That's the distance between the front of a pulse and the back of the same pulse.

 nomadd22 From United States of America, joined Feb 2008, 2142 posts, RR: 0 Reply 6, posted Sun Sep 23 2012 13:01:41 UTC (3 years 8 months 5 days 7 hours ago) and read 3020 times:

 Quoting Novice (Thread starter): i just don't understand this 10000 MHz and how it ties in with the rest of the specification, can anyone understnd?

As far as the original question, nothing really "ties in" with anything. Just about any of those specs can change without affecting the others.

 Anon
 ferpe From France, joined Nov 2010, 2809 posts, RR: 60 Reply 7, posted Sun Sep 23 2012 13:54:47 UTC (3 years 8 months 5 days 6 hours ago) and read 3007 times:

 Non French in France
 Novice From United Kingdom, joined Aug 2012, 90 posts, RR: 0 Reply 8, posted Sun Sep 23 2012 16:23:48 UTC (3 years 8 months 5 days 4 hours ago) and read 2986 times:

 Thanks for helping me out with that wealth of information guys, i have learned a lot on radars, frequencies, wavelengths and pulses that i simply wouldn't of grasped with reading it from a book! Cheers
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