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New DSP Family
innovative technology to keep you a step ahead
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Application Note
Copyright © 2016 Trilithic, Inc. All Rights Reserved - 062816-REV1 Specifications are subject to change without notice. Please contact your sales representative for further information.
Tracking LTE and Off-Air Digital Ingress Tech Tips
IntroductionMost technicians are familiar with using the spectrum analyzer in a signal level meter to check existing wiring in a home for ingress. This test is almost always part of a home-certification program and consists of disconnecting the drop from the tap, connecting the drop to the meter, and looking back at the house for any energy in the 5 MHz to 110 MHz range. Since the home has been disconnected from the plant, there should be no signal on the coax. If there is, it is an indication there is an issue somewhere in the existing wiring that needs to be tracked down and corrected.
A similar test can also be used to track down ingress issues from cell phone towers and off-air digital TV stations. If you are experiencing issues with downstream channels and there are cell phone towers or a strong off-air TV station nearby, the issue could be related to ingress. Just checking for ingress in the return path may not detect ingress in the higher frequencies. Impairments in coax can act like antennas. Just as different types of antennas are better at some frequencies and not others, different impairments in coax can be better “antennas” at some frequencies and not others.
With the full spectrum analyzer in the DSP family of meters, you can easily check for ingress caused by cell phones and TV stations. This feature is standard in the 1G DSP and the 720 DSP, and is an inexpensive option in the 360 DSP and 180 DSP.
innovative technology to keep you a step ahead
www.trilithic.com
innovative technology to keep you a step ahead
www.trilithic.comPage 2
New DSP FamilyApplication Note
Tracking Down IngressBelow is an example of LTE interference using a 360 DSP meter:
You will notice that we have set the Mode to Start/Stop and have set the Start frequency to 700 MHz and the Stop frequency to 800 MHz. (Note: You may have to set the Stop frequency to 800 MHz first, if it is below 700 MHz.) In this example, the detector is set to Average. You can also use the Maximum setting for a peak-hold trace.
You can also clearly see some cell phone signals in the 730 MHz to 740 MHz area. If the issue is visible at the tap, go to the ground block. If it is not visible at the ground block, then you likely have a bad drop. If it is visible at the ground block, then just work your way through the home until the impairment is found.
innovative technology to keep you a step ahead
www.trilithic.com
innovative technology to keep you a step ahead
www.trilithic.com Page 3
Application Note New DSP Family
For Additional Help, Contact Trilithic Applications Engineering 1-800-344-2412 or [email protected] or www.trilithic.com
Lastly, below is an example of an off-air TV station:
In this example, we have changed the Start/Stop frequencies to 650 MHz and 700 MHz. There is an off-air TV station broadcasting at 677 MHz and it is clearly visible, along with another at 659 MHz. We have also set the Detector to Maximum to display the live trace and the peak hold trace.
As we have shown, the full spectrum analyzer feature in the DSP family of meters can help you easily and quickly identify and track down issues caused by cell phone towers and TV station transmitters.
