As the previous post pointed out, loss occurs two different ways.
The first is - the frequency it is being used on. If you are going to use a coax on 11m ('CB') as opposed to 6m ('Ham'), then there will be more db loss when using the same cable on 6m than 11m. 6m is 50mhz, and the cable requirements are higher; 11m is ~27mhz and the requirements are not as demanding. But that depends.
The second form of loss occurs over the length of that cable. There is far more loss @ 100 ft than there is at 50 ft. Gets pretty bad @ 300 ft. That depends on coax quality . . .
Now between the freq used AND its length - is REALLY how one calculates loss. To consider the MOST important factor that plays upon previous factors - is the QUALITY of that cable being chosen. High end cable may have an initial high price; but it lasts longer (better UV protection) and has less loss.
For a 200-300 ft length being used on ~27mhz, the db loss can become a serious factor. Losing 6db's on receive is the same as losing one whole S-unit. If you have 2 S-units of static coming in to your radio's receive - and the signal loss is 1 S-unit from the cable alone - then the transmitting station needs to be three S-units or higher hitting your antenna just to hear him. Only 25% of the output power is getting to the antenna too. We are talking about the poorer quality cable here - BTW.
Not a smart DX plan - IMO. SO your antenna with really high gain may not see much of a difference - but it is still being affected somewhat. If your antenna is less than optimal, then it is taking a nice bite out of your station's effectiveness. For best results, use no more length than you need, making as straight as shot as possible with some extra length for 'wiggle room' in the shack.
Same is true for transmit on the same coax. It can cut down the real power output from your station considerably.
There is no 'perfect coax' either. They will all have various degrees of loss. The better coax will surely cost more than the 'truck stop special' stuff that CK mentioned. In fact, it can get downright expensive depending on what you choose. If you have to use a long piece of coax; expect a real loss of receive and power output - or pay the price and buy the better stuff.
Below is a link to a coax calculator. Plug in the values for frequency, length, SWR, coax type/brand, and power - and it will calculate the power loss and receive db loss. I have found it invaluable. After using it, I decided that 50 ft of Belden 9913 'Flex' coax on 27.205mhz using 75 watts output and a SWR of 1.2 was outstanding and acceptable. Only 6 watts of transmit loss and 1/3 of a db of receive loss (or 1/18 of an S-unit BTW). Outstanding. It cost about $65; but for the length and small amount of loss, it is excellent. So is LMR-400; it is very close to the same specs and is just as excellent. Holds more than 500 watts - if that is what you need to know.
Just for laughs, use the coax calculator and use the 'Tandy' ('Radio Shack') brand of RG-58.
Talk about loss - lol (approx 25% or more - if greater than 50 ft).
"Junque".
Coax Calculator
The first is - the frequency it is being used on. If you are going to use a coax on 11m ('CB') as opposed to 6m ('Ham'), then there will be more db loss when using the same cable on 6m than 11m. 6m is 50mhz, and the cable requirements are higher; 11m is ~27mhz and the requirements are not as demanding. But that depends.
The second form of loss occurs over the length of that cable. There is far more loss @ 100 ft than there is at 50 ft. Gets pretty bad @ 300 ft. That depends on coax quality . . .
Now between the freq used AND its length - is REALLY how one calculates loss. To consider the MOST important factor that plays upon previous factors - is the QUALITY of that cable being chosen. High end cable may have an initial high price; but it lasts longer (better UV protection) and has less loss.
For a 200-300 ft length being used on ~27mhz, the db loss can become a serious factor. Losing 6db's on receive is the same as losing one whole S-unit. If you have 2 S-units of static coming in to your radio's receive - and the signal loss is 1 S-unit from the cable alone - then the transmitting station needs to be three S-units or higher hitting your antenna just to hear him. Only 25% of the output power is getting to the antenna too. We are talking about the poorer quality cable here - BTW.
Not a smart DX plan - IMO. SO your antenna with really high gain may not see much of a difference - but it is still being affected somewhat. If your antenna is less than optimal, then it is taking a nice bite out of your station's effectiveness. For best results, use no more length than you need, making as straight as shot as possible with some extra length for 'wiggle room' in the shack.
Same is true for transmit on the same coax. It can cut down the real power output from your station considerably.
There is no 'perfect coax' either. They will all have various degrees of loss. The better coax will surely cost more than the 'truck stop special' stuff that CK mentioned. In fact, it can get downright expensive depending on what you choose. If you have to use a long piece of coax; expect a real loss of receive and power output - or pay the price and buy the better stuff.
Below is a link to a coax calculator. Plug in the values for frequency, length, SWR, coax type/brand, and power - and it will calculate the power loss and receive db loss. I have found it invaluable. After using it, I decided that 50 ft of Belden 9913 'Flex' coax on 27.205mhz using 75 watts output and a SWR of 1.2 was outstanding and acceptable. Only 6 watts of transmit loss and 1/3 of a db of receive loss (or 1/18 of an S-unit BTW). Outstanding. It cost about $65; but for the length and small amount of loss, it is excellent. So is LMR-400; it is very close to the same specs and is just as excellent. Holds more than 500 watts - if that is what you need to know.
Just for laughs, use the coax calculator and use the 'Tandy' ('Radio Shack') brand of RG-58.
Talk about loss - lol (approx 25% or more - if greater than 50 ft).
"Junque".
Coax Calculator
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