RF meter with input noise suppression
View Patent ↗The invention provides a handheld RF meter with an improved isolation from EMI. The meter incorporates an interference barrier comprising a connecting cable and one or more ferrite cores possibly having different impedance characteristics.
1. A meter for monitoring an RF signal received from a network cable, comprising:
a casing;
a printed circuit board (PCB) disposed inside the casing, the PCB having RF circuitry for monitoring the RF signal;
an input RF connector affixed to the casing for receiving the network cable,
a connecting RF cable extending between the input RF connector and the PCB for providing the RF signal to the PCB; and
a first ferrite core coupled to the connecting RF cable so that the connecting RF cable passes therethrough, for attenuating interference signals transmitted via a conducting sheath of the network cable.
2. A meter according to claim 1 , further comprising a second ferrite core coupled to the connecting RF cable so that the connecting RF cable passes therethrough.
3. A meter according to claim 2 , wherein the first and second ferrite cores are designed to cumulatively provide at least 200 ohm impedance for interference signals in a frequency range from 50 MHz up to 1 GHz.
4. A meter according to claim 2 , wherein the first and second ferrite cores have differing frequency responses.
5. A meter according to claim 2 , wherein the first ferrite core has an impedance that peaks at about 250 MHz and the second ferrite core has an impedance that peaks at about 750 MHz.
6. A meter according to claim 2 , wherein the first and second ferrite cores are disposed at the ends of the connecting RF cable.
7. A meter according to claim 2 , wherein the connecting RF cable is connected to the PCB via an internal RF connector having a ground portion in direct contact with a ground plane of the PCB.
8. A meter according to claim 1 , wherein the first ferrite core is held in place with a heat shrink tube.
9. A meter according to claim 1 , wherein the connecting RF cable include RF connectors attached at the ends thereof.
10. A meter according to claim 9 , wherein the connecting RF cable is at least 8 cm long.
11. A meter according to claim 9 , wherein the connecting RF cable is between 8 cm and 12 cm long.
12. A meter according to claim 1 , wherein the connecting RF cable is fully internal to the casing.
13. A meter according to claim 1 , wherein the network cable is a coaxial cable of a cable TV network, and the RF signal is a cable TV signal provided therein.
14. A meter according to claim 1 , wherein the connecting RF cable comprises a coaxial cable.
15. A meter according to claim 1 , wherein an impedance of the connecting RF cable is substantially 75 ohm.
16. A meter according to claim 1 , wherein the casing is sized to be held in a human hand.
17. A meter according to claim 1 , wherein the first ferrite core comprises Nickel Zinc Ferrite material.
18. A meter according to claim 1 , wherein the first ferrite core has an external diameter about 8 mm, internal diameter about 4 mm, and a length about 12 mm.