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With all the leftover wiring is it best to cut it and put a new end on or just coil it up and put it neatly away? I have alot of leftover wire on my gmr18hd radar, vhf, and Garmin 4212......cut/splice or coil it?
Thanks,
Brice
I always leave extra cable in case of future problems etc. That said, I would cut off large excess of power supply cables but when it comes to the radar and transducer cables I would coil them and leave alone.
VHF cables are easy to make the length you want as they usually come without the connector soldered on in the first place. But here again leave some extra for future problems.
Coiling "radio" wave type cables (VHF, radar) has two affects, one is bad, and one is good. However, BOTH of them on our size boats and in the amount of cable we are talking about (maybe 10' extra, coiled 2, 3 or 4 times in a circle) have VERY little affect, so I would not worry about it.
But the non-technoical (dumb guy: that's me!) explanation is this:
1. Bad: Coiling the cable can create inductance, just like the inductance that makes an electric motor work (an electric motor is simply a wire coiled around a magnet, the inductance makes it spin). The inductance can degrade the signal by "stealing" power from it. So, if you coil enough vhf cable for example, at the right size coil, you can actually lower the output power of radio (because some of the power is lost in the cable). But again, the amount we are talking about here is almost not measureable.
2. Good: Coiling the extra cable can solve rf noise problems on your radio sometimes. If you are getting noise from a motor neat the cable for example (humming, buzzing, fuzzy sound when the motor is on), coiling the cable can sometimes reduce this noise, but at the same time, your also getting some of #1.
My take on it, if you can solder and put ends on the cables (it's not that hard!), then cut them to lenght. BUT, leave enough extra length for "later"(a foot or 2), YOU WILL NEED IT (aka a guy named Murphy!). If cut to length, it will be cleaner looking, you will not have heavy coils of cable bouncing around possibly putting pressure on your connections, you will not have cable tangled up behind the helm.... and yo uwill not have the possbile loss affect os #1 above. BUT, if you are not handy, forget it, and coil it up, tuck it away somewhere and go fishing!!
I was going to wind all my extra cables over a big reel, but now i'm worried. What would happen if two rf cables are wound together? Am I right in assuming that CAT 5 twisted pair will probably not cause a problem in that bundle? I know enough to keep them away from AC wiring, but how about battery cables?
__________________ If it ain't broke, I haven't played with it.
If coiling a coaxial transmission line affects the flow of current inside the transmission line, could you please explain how the transmission line knows it is coiled? Does the transmission line also know if it makes a 90-degree bend to the right? To the left? To the current flowing inside a coaxial transmission line, there is no sense of the shape of the transmission line. That's why it's a transmission line and not a circuit element!
Coiling a coaxial transmission line does not create any inductance in the transmission for the transmission line current flowing inside it.
Coiling a transmission will create an inductance to currents flowing on the outside of the transmission line, but those are not the transmission line currents flowing inside the transmission line. They can be stray currents created by external fields. In general it is beneficial to coil a coaxial transmission into a small solenoidal coil as it creates a radio-frequency choke which helps to suppress the flow of stray antenna currents on the transmission line and to isolate the transmission line from the antenna.
The VSWR on a transmission line is not affected by the length, except for the influence of loss in the line itself. The VSWR is determined by two factors:
--the characteristic impedance of the transmission line
--the characteristic impedance of the antenna
Neither of those change when you change the length of the transmission line. Any measurement of VSWR change with transmission line length change that might be seen is generally due to poor directivity in the measuring device and the influence of antenna currents flowing on the outer skin of the coaxial transmission line which the measuring device has inappropriately allowed to affect the measurement.
"VHF antenna wire" (coaxial transmission line) is not RADAR waveguide, so advice directed at the installation of RADAR waveguide is not particularly applicable to a coaxial transmission line in the VHF region. At microwave frequencies there may be considerations on bend radius for the waveguide which limit the installer from making small coils or sharp bends.
Interesting explanation, it sounds like you have an understanding of basic coil theory (inductance), however it seams you are lacking in antenna theory which is applicable at VHF frequencies. BTW I am a EE. Changing the length of a transmission wire can (and does) change the resonance of the frequencies residing on the wire. You can easily reduce the efficiency of the antenna by changing the wire length.
Installing electronics "TO CUT OR NOT TO CUT?" 
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