Which cable to choose, 50 or 75 Ohm?

Which cable to choose to connect the antenna to a router or modem, with a characteristic impedance of 50 or 75 ohms? In disputes on this issue, many spears have already been broken. On YouTube, on forums, in some articles convincing arguments are given by supporters of both the first and second options. Whose point of view is correct? In such a situation, it is sometimes difficult for a radio amateur, and even more so for a man far from radio engineering who makes a DIY antenna, to make an aware choice. This article is intended to help him in this...

Foremost, we note that the numbers 50 and 75 did not appear by chance. Theorists make it simple prove by formulas that the impedance of 75 ohms is optimal for receiving equipment, and 50 ohms is optimal for transceiver. Since our modems and routers are transceiver devices, the 50 Ohm standard has been adopted for them. At the same time, we immediately note that the end-to-end use of a characteristic impedance of 50 ohms for antennas, connectors and cables is in this case the most optimal. At the same time, provided that a high-quality cable is used, there will be minimal losses both for reception and especially for transmission and, accordingly, maximum speeds. In addition, 50 ohm connectors are usually much better quality than "TV" 75 ohm connectors, have lower losses and are more reliable. An antenna with such connectors does not need service and repair for quite a long time.

It would seem that the answer to the question posed at the beginning of the article is unambiguous, if not for one "but". The question is the cost of 50-ohm cables and connectors. The fact is that a high-quality 50-ohm cable, such as 5D-FB or RG8, is several times more expensive than available 75-ohm cables, and the cost of high-quality 50-ohm N-connectors is ten times higher than the cost of 75-ohm F-connectors.In addition, 75-ohm cables and connectors can be found in any market, and for 50-ohm cables you often have to go to distant lands. The affordable 50 ohms RG58 can't be considered high quality, as it's thin and has unacceptable attenuation, as we've talked about many times before. So the question arises, is it possible to use affordable inexpensive 75 ohm cables and connectors with 50 ohm equipment? After all, if you made a 4G MIMO DIY antenna from improvised materials, then it doesn't befit to pay several times more money for cables and connectors than you spent on making this antenna. Of course, there are some anonymous for whom the process is more important than the result, and they are ready to spend all their time and resources on it, but the majority still think rationally. Calculations and direct measurements show that the use of 75-ohm cables and connectors is quite acceptable. Mismatch loss in this case will be minimal if you make a 75-ohm high performance antenna with an SWR of no more than 1.5. Then, when connected to 50-ohm equipment, the SWR will be slightly more than two, which is quite acceptable. Compared to an ideal 50-ohm path, only the outgoing speed is noticeably reduced, which for most users does not really matter, since the incoming speed remains almost the same. Replacing a thin 50-ohm RG58 with an affordable 75-ohm RG6 is not only acceptable, but also highly desirable. Do not forget that the cable loss depends on its length, so the problem discussed here usually occurs with a feeder length of more than 5 meters. The longer the feeder, the greater the loss in it and the greater its cost. With short feeders, you can neglect both and freely use the RG58.

If you buy a ready-made assembly from the manufacturer and financial issues do not play a role for you, then you need to choose an assembly with 50 ohm high-quality connectors and cables. In this case, you get an ideal option not only in terms of technical parameters, but also in terms of reliability and fault tolerance. If the assembly with 75-ohm cables and connectors allows you to save a lot of money and this is important to you, then this option is quite acceptable. Do not believe any radio engineers who claim otherwise. But you need to understand that in this case, the manufacturer is also trying to get his share of the margin. You need to make sure that all the saving money don't go into his pocket, otherwise you are simply deceived. But in the case of a home-made antenna, the making of which is aimed primarily at saving money, a 75-ohm assembly is not only acceptable, but also more preferable in terms of technical and economic balance.

Related links:

• 50 Ohm vs. 75 Ohm: Which is Best For You?
• The Reasons for 50 Ω and 75 Ω Transmission Lines—And Why You Should Choose Carefully;