It worked! Using TV TwinLead for Cable Television

[speedqueen]

So I can rearrange the living room to accommodate the Christmas tree later this month I will have to run a cable through two aligned cold air return grates. The problem was that the cable wouldn't fit, so I had the idea to see if I could use two 300 to 75 ohm reverse balons and a length of 300 ohm Twin Lead that could fit between the slats of the air return grate. Theoretically it should work, but I had my doubts as to whether TwinLead could handle the large bandwidth used by digital cable. In the dry run(stringing the TwinLead across the living room) it worked flawlessly and even worked for on demand services.

Here is proof, also this is my "new" TV set, a late '70s Zenith ChromaColor II. It replaced a '90s rear projection set.

 

[speedqueen]

Almost forgot,

Major credit to Dwight(OldTvMan) for replacing the red gun potentiometer on the set.

 

[washman]

digging that old school console TV

 

[panthera]

Cool TV!

For such a short run, I don't see why it wouldn't work.

 

[kb0nes]

Certainly no reason it wouldn't work, twin lead has MUCH lower losses then a coaxial line. The transformers would be the only possible problem since their frequency range could be the limiting factor. Cable TV signals are generally pretty hot so I would expect it to work though.

The only fly in the ointment is that twin lead is far more likely to radiate RF. This is especially true if the balance of the line is upset by metallic objects near where it is run. Coax relies on shielding to prevent radiation, twin lead relies on phase cancelation of equal and opposite conductors to not radiate. This was the reason that twin lead died off when cable came in. Cable companies have to maintain a level of shielding performance so as to not interfere with radio services. Any leakage likely will never be known to you, but other licensed services could be impacted.

 

[rp2813]

Phil, is that why it used to be advised when stringing twin lead to give it a twist every several feet, or was that more about preventing signal interference?

 

[kb0nes]

Ralph, the twist was to give it better wind characteristics. I think it eliminated flapping.

There are versions of twin lead feeders that have "windows" cut out of the web. This is mostly done to prevent the line loss from increasing when the cable is wet or iced up. To a degree the windows reduce wind load related problems too.

The thing that was often (wrongly) done with twin lead was to neatly tape it to the metal mast, this really upsets the balance of the line. Of course most twin lead is just bringing in a receive signal so the line doesn't really radiate. It would probably make the line more receptive to receiving RF interference from nearby transmitters though, i.e. wrongly acting as an antenna.

I still use 450 ohm windowed twin lead (Ladder Line) for some 7Mhz shortwave antennas. The losses of parallel feeders like this are WAY less then coax, but they are a pain to route away from metal, shouldn't let them lay on the ground etc. but the low losses are still an advantage. In general I like coax though.

 

[cfz2882]

cool old console TV

I have my 1982 zenith"space command"in DD use as my main TV-a 1982 RCA selectavision CED disc player and a 1989 Mitsubishi VCR sit on top DVDs play on the 2010 Panasonic 42" plasma. Family TV~1977-79 was a 1968 RCA console(round face PX)that worked good until about the 10yr mark then began to break down every few weeks:after about 4 repair episodes,was junked:using a large resistor salvaged from the set for another project,discovered the resistor was burnt out...

 

[rp2813]

That is so Gift of the Maggie about the resistor.

 

[cfz2882]

yeah,that was a bummer to find the bad resistor after the set was junked-there was other heat related damage in the set elsewhere from some hot-running tubes and badly placed hot resistors.I would love to have that RCA today,and would relocate some of those resistors/upgrade to higher wattage to reduce damaging heat.The '68 console was all tube,but a 1976 all transistor RCA also had heat damage at the 10yr mark from some hot-running components-I was going to add a fan to that set,but the TV quit on me and I could not find the problem back then.My early '80s RCA sets have been much more reliable.BTW,that big '68 console had a 6x9"speaker in each end-very good sound