4 ms·
Home TV coax has a characteristic impedance of 75ohm. If you just plug consumer devices in directly you will get a pretty significant SNR loss from reflections
by q3k 7y ago
Home TV coax has a characteristic impedance of 75ohm. If you just plug consumer devices in directly you will get a pretty significant SNR loss from reflections and other impedance mismatch effects.
- EarthIsHome 7y agoSure. But I would bet that most Wi-Fi access points use a 50-ohm system. (Plus, the connectors on a home tv coax cable probably won't mate with the router connectors.) If you want to use a 75-ohm cable, you'll have to use impedance converters to convert to 50 ohms. Bottom line: just make sure the components you're connecting in your system are properly matched to avoid a lot of reflections and power loss.
- kazinator 7y ago> If you want to use a 75-ohm cable, you'll have to use impedance converters to convert to 50 ohms. ... says the article, clearly.
- dboreham 7y agoThis confused me but I think you mean "Most WiFi Access Points use a..."?
- EarthIsHome 7y agoThanks! Corrected
- kps 7y agoDoesn't everyone have a stash of old 10base2 cables? The idea of running a network over them is strangely appealing.
- segfaultbuserr 7y agoImpedance matching is overrated, the return loss of 50-ohm into 75-ohm is 14 dB, or a VSWR of 1.5:1, it means a low reflection, in practice the return loss is even better due to the loss in the cable. Also, unlike some digital systems that are expected to operate in a controlled environment, Wi-Fi is designed to work with multipath interference, so running Wi-Fi over 75-ohm coax can already get better SNR than running it over-the-air, so matching is not always necessary. You can always add one at the last step if it turned out to be necessary.
- superkuh 7y agoThe mismatch loss between 50 and 75 ohm cable is 0.4 dB (or ~5%). It's not really significant unless you're doing small signal work (which wifi isn't) or if you're doing high powered work where 5% loss heats the coax (which wifi isn't).
- himinlomax 7y agoWouldn't there be a problem with reflection? Attenuation is not the issue here, reflecting even a fraction of a strong enough signal could potentially even be destructive for the device. It's possible though that WiFi devices, particularly those with coax ports, have protection against this.
- superkuh 7y agoStanding wave ratio would be 1.5. Peak powers under 1 watt (and probably under 600mW). The transmitter is going to be fine.
- baybal2 7y agohttps://www.soontai.com/IMPEDANCE-CONVERTER.html https://www.soontai.com/IMPEDANCE-CONVERTER.html