TV coax cable for guitars?

[Hal]

ok question #1 - what does the impedance rating on TV cable mean?  

#2 - mouser has some TV cable wire, 100% foil shield coverage, for $30 for 100 feet.   I know it won't be as flexible as guitar cable, but I want it to make pedal hookup wires.  Is there any reason this wouldn't work?

[davebungo]

At the frequencies we're talking about I think it will work fine for short patch cables.

[petemoore]

Solid core stuff?
 Thing is if its solid core, it's really meant to have that fitting at the cable end, soldering this to anything that flexes it, like 1/4'' plug, will tend to break the core wire.

[Hal]

pete - good point.  Yea, this was solid core.  I think they might have some stranded core, though.  I gotta check.

but what does the impedance mean ?  That still puzzles me.

[mlabbee]

I'm not exactly sure, but my guess is that impedance is relevant to television transmission because they have very high frequencies (much higher than guitars?)

[Hal]

well, see, whats strange is that the impedance is 75 ohms.  Not 75 ohms per foot or something like that.  Its not a "resistivity" kinda thing.  Yea, I understand that it causes imdance to signals in the 100mhz range, but I don't see how _any_ length of cable has 75 ohms of impedance.  Weird.

[niftydog]

it's actually a transmission line - somewhat different to just a cable. The characteristic impedance of 75ohms is typical of modern video systems. It's not in ohms/foot because it's actually an impedance (imaginary component), not a resistance( real component). Impedance in this case is probably mostly due to the characteristics of the dielectric (the stuff between the core and the shield)... difficult to comprehend I know, but trust me!

Far too complex to go into detail here, suffice to say that if you're interested, a google search on "transmission line" and "imaginary algebra" will tell you more than you ever needed to know on the subject.

It'll work, video cables are rated for around a 5Mhz bandwidth. Solid core is definately no good and often the shield is impossibly thick and very hard to solder.

[Peter Snow]

Another type of coax that works is thin ethernet cable that was popular for local area networks (RG58?) in the early days. I picked up a whole sh*t-load of the stuff out of the dumpster when we switched to UTP CAT5 at my workplace many years ago. Still got tons of it in my basement. Both solid core and stranded core were available and I have used both for guitar cords and patch cables.  However the bending radius is far less than modern coax designed for audio purposes - specially the solid core.
An added bonus is that it is teflon coated so I can keep playing even if the building is burning down. Mmm... maybe I should ask BB about that :roll:  

Cheers,

Peter

[Paul Perry (Frostwave)]

The WORST cable in the universe (for audio purposes) is the two pair phone cable with shielding and an intense blue plastic jacket that you find in skips.
It is so microphonic that you can use it for a bass drum by plugging one end into an amp & tapping your foot on it (TRUE!)
Do not ask me how I know this :oops:  :x

[nooneknows]

I've always used RG58 for guitar cables, and I can say they're very clear, the only complain is about the mechanical characteristics (they're stiff).
capacitance is low and they have a very good dielctric. They're also very cheap.
With certain guitar rig you could find them a little too bright, but it's just a matter of taste.
(the nominal impedance is meaningful at very very high frequencies only)

[Hal]

I looked through the catalog again.  There is some stranded wire, but nothing quite as cheep as the $30 for 100 feet.  Argh.  I'll probably buy one big one and cut it down.

As for plugs, i'm looking at these: http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=352344&e_categoryid=329&e_pcodeid=01701

I love the switchcraft 228 plugs, but they're too expensive for this!  Does anyone know anything about these?

[bigjonny]

I use solid-core double-sheilded/double-insulated video cable for some of my rig â€" works great.  But, yes, you cannot go bending it like crazy.  However, suffice it to say using it for hookups between pedals (as Hal proposed) is a more than acceptable proposition if you velcro you pedals to a common board (plank?).  As long as those cables stay put (for the most part), they will do their job just fine.  For more “mobile” connections, use stranded.

[Boofhead]

TV cable usually works fine.  As others have already mentioned the solid core stuff breaks, the stranded core stuff works great.  The braided shield types are far better than the foil types but they aren't easy to find these days.   The important cable parameter is the capacitance per meter (or foot) and this is usually low on TV cable.  TV cables don't often specify capacitance per meter.  Basically the cable capacitance loads down pickup and you lose highs.  It's the total capacitance which matters so as the cable lengths increases capacitance becomes more important to control.

As for the meaning of (characteristic) impedance of a cable, it's not a simple thing to understand from a laymans point of view.   It comes under the heading of Transmission-lines.  A cable has capacitance and inductance these affect the signals transmitted over the cable - the cable acts like a filter and presents a varying load impedance.   It so happens when the load at the far end of the cable is terminated with a resistor that matches the characteristic impedance of the cable then at the input end of the cable the load looks like a perfect resistor  ie. the effect of the cable has totally disappeared.   That is why RF people go to so much trouble with matching and SWR'ing.

For audio impedance matching is fairly useless.  Also most loads are high impedance  - you will never get a cable made to match such high impedances.   Basically low level audio signals see cables as a capacitor.  For speakers the inductance becomes more of an issue.

Contrary to what people think the transmission line effects are not confined to high frequencies.   The transmission line effects become a problem when the length of the cable is longer than the wavelength of the signal - for TV that's about 1m, since cable runs are generally > 1m it's a problem.    Power systems which operate at 50Hz or 60Hz are prone to transmission-line effects, the reason is because power systems have extremely long cable runs.