"Back in the day" (pre-1965ish) most TVs didn't have 75-ohm antenna inputs - just a pair of screws on an insulated block for twin lead. "Rabbit Ears" back then used twin lead for that reason. Outdoor antennas for TV used twin lead (300 ohm "ladder line").

Twin lead is maligned by many (non hams) for lack of understanding. For low loss at VHF/UHF it simply cannot be beaten, particularly for its low cost.

The problem with twin lead is that the impedance is very easily disturbed by nearby metal objects (the mast on which the antenna is mounted) hence the need for (at least) six-inch standoffs to keep the cable away from the mast on its way down to the house. Getting it through the wall is another set of problems.

Hence the development of the 300-ohm to 75-ohm balun adapter. Transformed the parallel feed (twin lead) to a coaxial feed (which is much easier to bring through a wall since the shielding inherent with coax cable handles the problem). Another balun at the TV (remember, this is back in the day) got you your twin-lead pigtails and a return to the balanced line 300-ohm cable those TVs "expected."

So along came some brainiac who figured that building a balun drive point on the antenna itself would eliminate the need for the twin lead altogther, bringing us to the abomination known as 75 ohm coax cable for long runs from the antenna right to the TV. Good "on paper" but lousy in practice since just about *all* consumer grade 75 ohm coax is ***garbage***. At runs over 25 ft it starts getting horribly "lossy" unless you are using quality cable (hard to find in most locales and very expensive to the homeowner who just wants to "hook up the TV."

In ham radio, we jump for joy at the prospect of "finding" spools of cable TV aluminum jacket hardline (75 ohm) since that stuff is (almost) as good as it gets for low-loss. There are better. They are usually at least a half-inch (or more) thick, difficult to handle mechanically, and an absolute pain in the ass when you go to install a connector on it. So the cable TV hardline is a "gold mine" to the VHF/UHF ham (6m through 1,296 Mhz). Low loss; easy to "find"; easy to handle; and most ham rigs handle 75 ohm without breaking a sweat (the 50 ohm ham rig, particularly in the period 1970-1995, is a myth - those things handled everything from roughly 40 ohms to roughly 100 ohms without a problem - that's why they had all those *tuning* controls!).

Enough for now....

--K2NE

What is this mysterious "TV antenna" of which you speak? Some sort of newfangled way of transmitting video wirelessly?

I think most folks had their first introduction to 300-75 ohm baluns when they got their first VCR. Twin lead was still widespread back then, and you needed one on each side of the VCR connection, which had only 75 ohm antenna connections. There was a flat style balun for the TV side, and an elbow style balun for the antenna connection. A few years later, everyone got cable and it became pointless.

And it took at least another 15 years before the consumer electronics industry realized that, perhaps, putting line inputs for audio and video on *every* television is maybe a good idea after all.

Speaking of ancient computing ... Commodore 1701 monitors with Y/C inputs even in the early 1980's ... for the win! Built like tanks and had a great picture.


I may have mentioned this before ... on my commie I separated out the luminance pin from the video connector (ok I could have done this with a stock cable and just used one output, but I was a broke high school kid and I had DIN connectors and a soldering iron already on hand!) and ran it to a monochrome monitor. I used that for clear 80-column text while BBSing, and a color TV for games and other graphics. Quite a nice rig :)


And yes, before cable came to town, we had an antenna on the roof with twin lead. It was installed like 99% of the homes in the world ... screw the cable onto the two terminals, drop it carelessly down the roof, and find a place to get it through the wall without doing too much damage. Like 99% of the homeowners in the world, my dad wasn't a ham operator.

Back in NJ many years ago my next-door neighbor wasn't a ham radio operator either. But he took great pains to explain the advantages of twin-lead to me (the ham operator) and how to properly mount it, route it, and keep it relatively "safe" from the "attacks" of weather.

No ham operator.
Ph.D. in Electronics Engineering, though... <evil grin>

2015-05-03 01:31 from ax25 @uncnsrd
Subject: Re: Interview with author/futurist Arthur C. Clarke, from an AT&T-MIT

1976

Arthur C. Clarke.  Probably made some of the computing world
possible.  He might not have, but probably did.  Imagination is a
powerful thing.

1945
Same guy - A. C. Clarke
October 1945
"Can Rocket Stations Give Worldwide Radio Coverage?"
A treatise on the use of geosynchronous orbit satellites for radio relay.
Source: Wireless World; October 1945

Now this is just getting stupid.

[ http://www.commodoresmart.com/?kid=6CHC4 ]

The latest group of people to get their hands on the Commodore brand have decided to offer a brand new version of the Commodore PET.

It's an ordinary Android smartphone that says "Commodore PET" on the bezel.
That's all. Nothing else.

I hope it has Bluetooth; I want to hook it up to my IMSAI Car Stereo.

Awwww... IG.... and here I thought you would have an Altair Car Stereo.
Disappointed I am.

Will the phone have a chicklet keyboard too??

No, and that's why it doesn't deserve the name. It's the same generic touchscreen phone everyone else makes. I would have liked a phone with a nice keyboard on it :)