Flat coax

[brainfarth]

I've tried to find some flax coax cable on the net with little luck other than the foot long pieces you stick in your window. I need a piece at least 10' long, and preferably 25' in length. Does anyone know where I can get one from, or one that I can construct myself? Or is it possible that I can modify an existing cable that is capable of transmitting the frequency required for a cable box? I have purchased 25' HDMI cables for 14 bucks on ebay that I could put coax ends on.
Any help would be appreciated.
-Mike

[sanlyn]

HDMI cable is not coax. It is twisted-pair stranded-core Ethernet wire adapted for a/v use. Cable coax is RG-6 18g solid-core cable with RF screw-on connectors. Offhand I don't have a ready source, but I've seen flat RG-6 and RG-59 all over the 'net. Stay away from RadioShack and BestBuy. Their cheap, over-priced RG-6 is not up to spec.

[brainfarth]

HDMI cable could be coax IF it is capable of carrying the frequencies that a cable box requires. I dont mind chopping up some cables, if I knew they could deliver the frequencies okay. Radioshack and bestbuy do not have anything even remotely close to what I am looking for, so buying their stuff is not an issue. One would think that people would have a need for something of this nature.

[SirLurksAlot]

welll actually, in theory, any 2-wire 'cable' with an impedence of 75 ohms will work. however, it's not really that simple. HDMI cables definitely don't qualify nor does any sort of twisted-pair, and have considerable signal losses at cable tv frequencies. loss per foot can also matter a great deal. unless you can afford to waste time and $'s on experimenting, why reinvent the wheel?

coax (or co-axial cable) is coax because there is a center conductor that is completely surrounded by an outer conductor (shield). this creates a set of characteristics that MOST applications calling for coax-type interconnecting wire require. this doesn't describe HDMI cables...neither style of cable can be used in place of the other, except in very limited and specific circumstances.

also, ratshack cable is no more a crap-shoot than almost anyone elses cable. i've sweep-tested miles of coax (literally), some of it ratshacks, and it was fine. i encourage the poster claiming it fails spec to be specific about what spec it fails.

brainfarth, you mite look for some 75 ohm twinlead (which can sometimes be found in a shielded configuration). this is likely what is being sold as flat coax. it -should- be really inexpensive, try a ham radio shop/supplier. they use that stuff a fair amount. after you figure out how to attach an F59 connector (i assume that's what you'll need) to a flat cable, you'll be set.

hope this is helpful!

[sanlyn]

SirLurks, if you thought your ratshack cable looked "fine", you can use anything. Why pay their high price? Go to HomeDepot. I threw mine away. Too much transmission noise.

HDMI is 100-ohm cable.

[Cornucopia]

Coax is round for a reason - consistent, good EMI/RFI and other electrical noise rejection (even shield coating all around and equivalent diameter = best cancellation). Of course, engineers created this for this reason (but assuming longer-run use).

For shorter run use, I guess you could substitute by using Cat5e/Cat6 with converters on both ends (lots of studios do that).

Scott

[SirLurksAlot]

SirLurks, if you thought your ratshack cable looked "fine", you can use anything. Why pay their high price? Go to HomeDepot. I threw mine away. Too much transmission noise.

HDMI is 100-ohm cable.

Well, I'm sure bad hunks of coax exist. I've had to trash a full 1000' spool of Times Microwave LMR900 coax. and it doesn't get much better than LMR, generally. I refered to sweep-testing, which is how pro's verify the spec-compliance on large runs of the stuff. If you were getting a high-noise level when using ratshacks stuff, you most likely got some that had a splice in it (or had poorly attached F59's). This isn't uncommon at all. All mfgrs of coax do some splices during spool-filling, as needed to fill the 'last spool' of the run when they come up short. <shrugs> I've used a LOT of coax over the past 40yrs, both for receive-only situations (like TV) and for Kilowatt+ transmission of RF. While ratshacks stuff is far from my first choice, it's worked fine with 2 exceptions..both splice related.
Still not sure what spec you referred to, but from yor comment, I assume you're talking about shielding. Standard for RG6, RG59, and RG11 is 95% shield coverage. RS coax absolutely meets that spec. Not flaming ya bud...just pointing out the verifiable facts in hopes of limiting confusion and myth propagation.

Hope this helps!

[sanlyn]

Some people see no difference. Some people don't care. If I were among those two demographics, I could have saved time and money.

I'm surprised you work with wire but think that the only "spec" is shielding. Anyway, it doesn't matter so much, just to my own eyes and ears. The last time I had to string some extra cable, I found a site that sold per-foot the same cable my cable company uses. Choice cable publishes its specifications, in the box, in catalogs, or on their website. The specs include more than shielding. Cheap wire has high capacitance, high inductance, high alloy content, junk tin connectors (gold plated sometimes, but still junk)-- and, as you mention, splices. I'm not their target buyer.

[SirLurksAlot]

Some people see no difference. Some people don't care. If I were among those two demographics, I could have saved time and money.

I'm surprised you work with wire but think that the only "spec" is shielding.
The specs include more than shielding. Cheap wire has high capacitance, high inductance, high alloy content, junk tin connectors (gold plated sometimes, but still junk)-- and, as you mention, splices. I'm not their target buyer.

Ok. I believe i referred to sweep-testing. Apprently, you don't knowm what that is or what it reveals about coax.

I mention shielding -only- because you stated you had noise issues with RS coax, That is often (almost always) a shielding issue. I was responding to your statement only. I never said nor suggested shielding as the only important spec.

As far as "high inductance and high capacitance" is concerned...if either is 'off' to a signifigant degree, the impedence is also going to be off. Just the sorts of things sweep-testing is intended to reveal.

Also, when Rf in the range used for cable TV is passed thru a conductor, most of the signal is flowing on the skin of the conductor, almost none in the deeper parts of the conductor. Gold plating reduces the the resistance 'seen' by the signal, as the signal is flowing primarily thru the gold, not the tin under it. To be honest, TRUE high-quality connectors are silver-plated tin or zinc. Gold isn't as good, but is used despite its higher cost becaues it's prettier and draws the uninformed (tarnished silver is ugly, but conducts every bit as well as untarnished silver does). And while nickel plated zinc (or brass, which is sometimes used as well) looks better than pure tin, the difference in electrical resistance amounts to milliohms. A differnce that is impossible to measure in terms of signal-loss.

Some folks just see differences because they expect to, due to having been misinformed by 'experts'. Try checking with actual RF engineers (and i don't mean cable company employees) as all I've told you is common knowledge in the field. There is a big diff between opinion stated as opinion, and opinion stated as fact. All I've said can be verified in any college level RF engineering text dealing with transmission lines and terminations. You might want to read up on the subject of sweep-testing and what it does for us, as well.

It can't hurt to know as much as we can about our favorite hobby/field!

[sanlyn]

Yes, I know what sweep testing is, and I've had some of my cable choices tested by a techs at WNET (Monster's top-pricved coax turned in a nominal impendance o5 35ohms and had higher inductance than their subwoofer cable, BTW). But I don't sweep test everything, haven't strung a piece of coax in 20 years, and never intend to again.

Proposal: You use what you want, I'll use what I want, and the O.P. can make up his own mind. But anyone who tries to tell me that RatShack CATV coax doesn't look like crap is blind as a bat. Enjoy.

[pandy]

HDMI have 100Ohm impedance (100 ohms ±15%) - coax usually have impedance bellow 100Ohm - typical coax used for home RF is 75Ohm.

You can buy "flat cable feed through window frame" like this

http://www.conrad-uk.com/medias/global/ce/9000_9999/9400/9410/9410/941065_AB_00_FB.EPS_1000.jpg

http://www.dipolnet.de/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d271.../E/8/E8234.jpg

however as You see this is not coax cable but cable with impedance close to 75ohm flat enough to pass trough frame... this mean that shielding is not consistent over whole line and it can eventually pick up some interferences.