i have the radioshack sputnik antenna in my small field with with 120 feet of coax cable and two connecters the tracks are about 6 miles from my house and i have it about 15-20 feet in the air should i mount it higher or in my attic also where i have it at they are some trees near it also it is on a plastic pole bolted on to a metel pole by 3 ubolts
railroad monitering
- Thread starter j611thebullet
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it is rg58 and i just noticed that the cable had some cuts and one part was splitting
also how much further should i go up
To add to what Dave said, RG58 is only practical in the mobile where length doesn't exceed 18 feet or so, or for frequencies below 30MHz and lengths 50 feet or less. That having been said, a Sputnik is one of those no gain antennas so you're looking at signal loss no matter what you do so to minimize it you should use low loss coax (don't ask, your answer is all over the forum) and as short a length as possible. That leaves the attic, right?
Since your 120-foot run of RG-58 is already split, and there is a lot of loss, even at RR frequencies, I think that replacing it with at least common RG-6 cable would be the first thing I'd do for a low-budget improvement.
What can help is to search for
coax cable loss calculator
where you enter the cable type, frequency, and the length of the run and it will calculate it for you.
For instance, the Times Microwave coax cable loss calculator shows that with 120 feet of RG-58, and at 150 mhz, there is 7db of loss, which means you only have about 20% of your antennas original signal strength at the end of the coax! Switching to common RG-6 only has a total run attenuation of 4.2 db. That's a little more than half - a good improvement over losing 3/4 or more of the energy with your RG-58. Probably even more with damaged/corroded connectors, split jackets that have sucked up moisture, etc.
Only mount the antenna as high as is safe for number 1. You don't want it falling onto electrical lines, nor breaking property or injuring people if it comes down. And the higher you raise it, the more signal loss in the cable you will have.
So nobody can really tell you for sure - you'll have to experiment.
Generally, if I had the option of running only an attic antenna that was SAFE, vs some rickety unsafe mount up high, take the attic option. Run the lowest loss coax you can.
What can help is to search for
coax cable loss calculator
where you enter the cable type, frequency, and the length of the run and it will calculate it for you.
For instance, the Times Microwave coax cable loss calculator shows that with 120 feet of RG-58, and at 150 mhz, there is 7db of loss, which means you only have about 20% of your antennas original signal strength at the end of the coax! Switching to common RG-6 only has a total run attenuation of 4.2 db. That's a little more than half - a good improvement over losing 3/4 or more of the energy with your RG-58. Probably even more with damaged/corroded connectors, split jackets that have sucked up moisture, etc.
Only mount the antenna as high as is safe for number 1. You don't want it falling onto electrical lines, nor breaking property or injuring people if it comes down. And the higher you raise it, the more signal loss in the cable you will have.
So nobody can really tell you for sure - you'll have to experiment.
Generally, if I had the option of running only an attic antenna that was SAFE, vs some rickety unsafe mount up high, take the attic option. Run the lowest loss coax you can.
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intrepid97
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How well would LMR-400 work?
Some good advice is to take a look at a coax characteristics table. It lists the various sizes of coax and the amount of loss they have at various frequency ranges. That table gives loss in dB's, which are sort of complicated units of measure. 3dB means either a 50% loss or gain, as a reference. Fractions of dB are almost meaningless unless they add up to a sizable 'chunk'. The same size coax will have less loss at HF and will have more loss at VHF and higher. As frequency increases so does the amount of loss, absolutely normal. Pick a coax size/type that fit's you needs... and wallet.
Antenna 'gain'.
Gain is a reference, or comparison to a standard antenna. The 'standard' antenna is a 1/2 wave length. That doesn't mean that 1/2 wave length antenna is the best, it's only an industry 'standard' way of measuring things. A 1/4 wave antenna has less gain that a 1/2 wave and a 5/8 wave has slightly more gain than a 1/2 wave. They also have differently 'shaped' radiation patterns, so selecting one that fit's your needs is the 'key' to which would be best for you.
The one thing that can mean better reception at VHF than almost anything else is antenna height. The higher the better! You also have to balance that with what's practical for you. Not just in height, but with the length of the feed line and the associated losses. I wish I could have all of my antennas at a 1/4 mile high. But... I'm not going to hold my breath, you know? Do what you can do and then quit worrying about it. Oh, and an outside antenna is always better than an inside antenna, almost. That deals with what may be obstructing the signal getting to the antenna.
About that LMR-400 coax. Yes, it will definitely be 'better' than RG-58. Too many variable involved to say how much better, but it'd be better anyway ($$$).
Have fun.
- 'Doc
Antenna 'gain'.
Gain is a reference, or comparison to a standard antenna. The 'standard' antenna is a 1/2 wave length. That doesn't mean that 1/2 wave length antenna is the best, it's only an industry 'standard' way of measuring things. A 1/4 wave antenna has less gain that a 1/2 wave and a 5/8 wave has slightly more gain than a 1/2 wave. They also have differently 'shaped' radiation patterns, so selecting one that fit's your needs is the 'key' to which would be best for you.
The one thing that can mean better reception at VHF than almost anything else is antenna height. The higher the better! You also have to balance that with what's practical for you. Not just in height, but with the length of the feed line and the associated losses. I wish I could have all of my antennas at a 1/4 mile high. But... I'm not going to hold my breath, you know? Do what you can do and then quit worrying about it. Oh, and an outside antenna is always better than an inside antenna, almost. That deals with what may be obstructing the signal getting to the antenna.
About that LMR-400 coax. Yes, it will definitely be 'better' than RG-58. Too many variable involved to say how much better, but it'd be better anyway ($$$).
Have fun.
- 'Doc
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