# Calculating attenuation of coax cable run

This question is related to my question about long-distance Ethernet.

I discovered the Netsys NH-310C, a reasonably-priced device for converting Ethernet to coax for long-distance runs. The manufacturer provided an attenuation/bandwidth chart to determine the maximum expected bandwidth at various distances, as well as the user manual, which indicates the frequencies utilized by the device are in the 12 MHz to 44 MHz range (on page 5).

I am looking to use this cable. Attenuation per 100 feet is specified as: 1.60 dB for 55 MHz signals and 0.58 dB for 5 MHz signals. So I assume the attenuation for 44 MHz signals is somewhere between these values, probably around 1.4 to 1.5 dB per 100 feet.

Here is the diagram showing approximately how the cable will be run, underground in 1/2" PVC conduit, with pull points along the run, requiring couplers.

I'm trying to determine if I am calculating the attenuation value correctly for the cable, and also how to calculate the value for couplers/splitters. Here is what I have so far:

• Total cable length: ~2200 feet
• Splitter (tee) needed: 1
• Couplers needed: 2

• Cable attenuation (max @ 44 MHz): 22 x 1.5 = 33 dB

• Splitter attenuation: ???? ________
• Coupler attenuation: ???? _______

How to determine the splitter and coupler attenuation values? The specs I am finding are related to cable TV channels (in the 200-300 MHz range) so they list much larger attenuation than would be encountered at 44 MHz.

From the specs I have given, does this setup look reasonable? Do you think the signal levels are suitable to provide approximately 100 Mbit operation (i.e. in the Green link quality section) per the manufacturer's spec?

It was suggested by the Netsys engineer that I could add active amplifiers if needed. However, I only have power available at each building. No power available at the connection points between.

• I didn't see your original question. I really think wireless will work better. I know you don't have line of sight. But if you use 900 MHz, and look for a high spot that can see both buildings or almost see them, you can put a solar and battery powered repeater at that location to establish a reliable link. The wired connection is going to be way more expensive. Ubiquiti radios are relatively cheap and somewhat reliable. Two km is not a long haul for these radios, especially if you get a high gain antenna. Jun 9, 2015 at 6:50
• Two Ubiquiti Rocket M900 radios and two 900 MHz Yagi antennas (also from Ubiquiti) and I bet you can get a link through the trees. The 900 MHz band is somewhat able to penetrate foliage. This setup can reach 20 km with line of sight. I believe it is possible it may make 2km without line of sight, and if not, like I said, you may be able to find a high point to install an off-grid repeater. Jun 9, 2015 at 7:02
• Thanks @mkeith but both areas are in trees - there is no way for wireless to be suitable. I was really asking for advice on the attenuation factor of the coax cable run in this question, to determine if it's within manufacturer's spec. Jun 9, 2015 at 12:51
• I assume the insertion loss of the couplers will be insignificant compared to the loss in the 2000 foot cable run. The splitter, since it literally splits the power will have at least 6 dB of loss. I don't see how an amplifier would work in this application. Amplifiers only provide gain in one direction, but all three points, A, B and C will have to transmit and receive, right? The user guide mentions a max speed and a max distance but does not say that they are possible simultaneously. C may end up with very poor bandwidth. Jun 10, 2015 at 4:55
• It is really NOT my intention to beat a dead horse. But another option that would work is to use 900 MHz off-the-shelf radios (rocket M900), but link them together with cable in conduit exactly as you plan. You would need 50 Ohm cable with total loss between A and C of less than 100 dB at 900MHz. I think it is possible to find such a cable, but cost may be quite a bit higher than the RG6 you linked to. Jun 12, 2015 at 20:43