Good afternoon everyone. Is there a guide anywhere on what cable I could safely use based on the length?
I will be operating on 462mhz at up to 50w, but with antennas at various distances. I was wondering if there was any sort of guide so I don't have to ask every time.
For example: My friends car will need 25ft of cable, her house will need about 40ft of cable, and my house will need about 75ft of cable. I know that i can use RG58 for shorter runs, but at what point should i use lower loss cable, and what should I use?
This is a good place to start:
Coax Loss Calculator
Enter your coax length, frequency (462MHz), load SWR (use 1:1 for now), and your power in from the transmitter. What it will give you is the matched loss, the SWR loss (will be the same as the matched loss if you use 1:1 SWR), total loss in dB and the power out, as seen at the end of the coax.
Keep in mind that some of the cables listed under the coax choices are 75Ω, and some of them are odd types that can be difficult to find.
Don't get hung up on any one type, either. I know some hobbyists seem to be under the impression that LMR-400 is the be all, end all of coax, it isn't. For long lengths, you may need something better.
Also, make sure you consider your budget. While it's nice to design everything and be super concerned about the power out at the antenna, you often don't need much actual power if you have a good antenna system. Remember that antenna gain will boost performance, so make sure to figure in your antenna choices.
I've had situations where 50 feet of RG-8 was all I had and I needed a radio working. People will claim that RG-8 isn't "good enough" for UHF. Truth is, it worked just fine for what I needed. Keep your expectations realistic, and don't get too hung up on the numbers.
As for vehicle installs, RG-58 works just fine. It's a heck of a lot easier to route. I've got about 50 800MHz radios running in mobile applications with RG-58. At 800MHz, the coax losses are a lot greater than at 462MHz, and all these radios work fine.