![]() ![]() If your analyzer displays the SWR as infinity or off-scale, the loss is too low to measure. If you only have a SWR value, you can calculate it from the SWR value using the following formula or any purpose-made calculator: Remember, the return loss is the coax loss applied to the signal twice, so divide the dB value by two. the higher-end RigExpert models do) then you can use that value. If your antenna analyzer directly reports return loss (e.g. Since cable loss is frequency-dependent, set the analyzer's frequency to the highest frequency you plan to use (which should have the most loss), or whichever frequency you wish to measure at. In this configuration the return loss (amount of power not reflected back to the analyzer) the analyzer measures will be equal to twice the loss in the cable (because the signal bounced back, so it went across the entire length of the cable twice). Hook it up to the analyzer with the other end not connected to anything - this unterminated end will reflect the signal back almost perfectly. If you have or can borrow an antenna analyzer, you may be able to use it to measure the actual loss in a piece of coax. Loss when receiving matters only if the incoming signal is so weak that the limiting factor is not noise picked up by your antenna but noise internal to your receiver or leaking into it from nearby sources. Loss when transmitting means you're wasting that fraction of your transmitter's power - if the current result is adequate for the contacts you want to make, then don't worry about it, but if the loss is significant then improving the coax is overall cheaper and more efficient than getting a bigger amplifier. Just multiply/divide to find the actual loss for your length.īut be sure to think about whether you actually care about the loss: If you look at the manufacturer's datasheet for the coax (you should be able to look it up from the printing on the side of the cable, if any) will give a table or graph of loss in dB per 100 feet (or some other such standard length) versus frequency.
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