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Scanner Antenna cable too long?
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You can get some "feed line loss" with a lot of excess cable. That means that reception might not be as strong as it would be if it were the exact length you need. Will you notice it with a scanner? I doubt it, but it wouldn't hurt to trim it to a closer length. It won't hurt a thing if you wrap the cable around the mast.
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50 yards is for the higher frequencies an long run, depending on thhee kind and quality of the coax.
If it is RG 58 and the frequency is 400 mHz then you add an extra 11.7 dB for every 100 feet of cable, meaning that you will have almost 2 S points lost
You have 50 yards, about 150 feet is 18 dB loss for thee extra cable, add the remaining cable length and you can figure it out for yourself what the attennuation will be.
Using RG 213 it is still 9 dB loss for the 50 yards alone.
So, question, what cable, total length of coax and what type of coax?
And 3 S points or 18 dB loss in reception is absolutely to be noticed...
50 yards is for the higher frequencies an long run, depending on thhee kind and quality of the coax.
If it is RG 58 and the frequency is 400 mHz then you add an extra 11.7 dB for every 100 feet of cable, meaning that you will have almost 2 S points lost
You have 50 yards, about 150 feet is 18 dB loss for thee extra cable, add the remaining cable length and you can figure it out for yourself what the attennuation will be.
Using RG 213 it is still 9 dB loss for the 50 yards alone.
So, question, what cable, total length of coax and what type of coax?
And 3 S points or 18 dB loss in reception is absolutely to be noticed...
Whoa...I thought it said 50' at first....50 yards is a lot. Most people just use regular RG6 or some other TV type coax for a scanner. If that's the case the loss is around 2db per 100ft at 100mhz and almost 5db at 400mhz. That extra length definately could make the difference between hearing a distant faint station and not hearing him.
Most antenna's and recievers are made for 50 Ohms coax.
Your 75 Ohm coax will hava an swr of 1.5 at both ends causing an little loss.
If you only wish to recieve on 150-170 mHz then little gain is to be expected by swapping the cable to RG 58.
Just an little gain can be had by using LMR 400, but on higher frequencies LMR 400 will show an bit better low loss.
50 Feet isn't that long, my cables for 2/70 are Ecoflex 15 , 1/2 inch very low loss coax, 75 feeet long an tad better as LMR 600, used to feed the 11 element Flexa yagi on 2 and the 23 element Flexa yagi on 70, and the Diamond X510N.
For the 5 element 6 meter beam it's Aircom Plus, like LMR 400, same cable is used for the Imax 2000, the Diamond scanner antenna used to feed the Ft100 for local repeaters, and the FD-4 OCF wiith added section for 160 meters.
Your antenna system is as good as the worst component.
73,
Your 75 Ohm coax will hava an swr of 1.5 at both ends causing an little loss.
If you only wish to recieve on 150-170 mHz then little gain is to be expected by swapping the cable to RG 58.
Just an little gain can be had by using LMR 400, but on higher frequencies LMR 400 will show an bit better low loss.
50 Feet isn't that long, my cables for 2/70 are Ecoflex 15 , 1/2 inch very low loss coax, 75 feeet long an tad better as LMR 600, used to feed the 11 element Flexa yagi on 2 and the 23 element Flexa yagi on 70, and the Diamond X510N.
For the 5 element 6 meter beam it's Aircom Plus, like LMR 400, same cable is used for the Imax 2000, the Diamond scanner antenna used to feed the Ft100 for local repeaters, and the FD-4 OCF wiith added section for 160 meters.
Your antenna system is as good as the worst component.
73,
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The differance between 50 and 75 ohms in a receiving situation is nothing. The antenna impedance will vary over a much wider range than that. RG-6 is not a bad cable and most certainly is better than RG-58 for the V/UHF bands. Keep the cable as short as you can however.
In short, don't worry about the 50/75 ohm "problem" as i said be4, it is just an small attenuation.
Depending on your antenna, discone, or otherwise, there will be more or less attenuation here because of the swr created by the antenna that is not spot on for the frequency where it is resonant.
An discone is quite broadbanded, and will have an wider usable frequency.
Here the swr stays low over an 1:4 frequency spectrum, and it'll even work in an 1:10 spectrum
Meaning, lower frequency 50 mHz will work fine up to 200 mHz, but can be used to 500 mHz, but the diagram then will shift unfavourably, i.e. downward tilt of the diagram.
Now you shortened the cable, more signal reaches your reciever, and the more you can recieve with less noise.
Have fun listening now
Depending on your antenna, discone, or otherwise, there will be more or less attenuation here because of the swr created by the antenna that is not spot on for the frequency where it is resonant.
An discone is quite broadbanded, and will have an wider usable frequency.
Here the swr stays low over an 1:4 frequency spectrum, and it'll even work in an 1:10 spectrum
Meaning, lower frequency 50 mHz will work fine up to 200 mHz, but can be used to 500 mHz, but the diagram then will shift unfavourably, i.e. downward tilt of the diagram.
Now you shortened the cable, more signal reaches your reciever, and the more you can recieve with less noise.
Have fun listening now