Case Studies
Interfacing to Offset IF Radar Altimeter
The customer is using an offset IF radar to map forest terrain density. The equipment will be mounted in an aircraft, which will also be carrying a Global Positioning System (GPS) for reference.
The plane will fly at an altitude of 10,000 feet. A 512ns radar pulse will be sent out and a return pulse will be received about 20uS later, from which 10,000 samples will be acquired. After the pulse is received, there will be a relatively long re-arm time of about 250 to 300 uS for the radar.
The goal is to minimize the amount of data acquired so that each pulse and return can be digitized and processed before the next set of data arrives. This experiment will require the highest sample rate possible while maintaining a high Pulse Repeat Frequency (PRF).
GAGE'S SOLUTION
The solution to this problem is the CompuScope 8500, which can capture data at 500 MS/s and can transfer data at up to 100 MB/s over the PCI bus.
On the CompuScope 8500, the time it takes to acquire one sample of data is calculated as 1 sample ÷ 500 MS/s or 2 ns. As waves travel at a rate of 1 foot per nanosecond, the distances can be resolved within 2 feet.
The card will be equipped with 128 Kilosamples of on-board memory (the minimum for this card), which is more than enough for the customer's sampling requirement.
The card will also include the Gated Digitization option (to ensure data is only collected when necessary, as explained below) as well as the External Clock option (for synchronizing the CompuScope 8500 with the customer's radar system).
The initial burst from the radar will take 512nS. The radar interface controls the gate, which will ensure that samples are collected only when it is high.
The next 20uS are the send and return time for the pulse. Data is not acquired during this period of time as it is of no interest to the customer. Also, this 20us of data would only waste valuable time later on when transferring data to the PC.
When the data is ready to be captured, the gate is brought high and the capture begins.
The data is then transferred to the PC, and the card is re-armed for another capture.
This method fulfills the customer's time requirement, and in fact there will be another 100-150 uS left over before the next pulse comes in.
To ensure proper gate synchronization, Gage will also provide a synch out signal called the Gagebus Clock. This signal will allow the customer to synchronize the primary data latch clock with their gate signal to ensure that there will be no jitter due to an asynchronous gate.
PRODUCT RECOMMENDED
CompuScope 8500 with 128Kilosamples of on-board memory
with External Clock, Gate option, and special Gagebus clock out option
This application note is provided "as is" without any warranties of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability or fitness for a particular purpose. Gage Applied Technologies further does not warrant the accuracy and completeness of the material contained herein. Gage Applied Technologies may make changes to this material, or to the products described in it, at any time without notice.
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