Atari 800XL RF cable (and I/O cable availability?)

David Griffith dgriffi at
Fri Jan 23 00:34:49 CST 2015

On Fri, 23 Jan 2015, tony duell wrote:

>> 1) When hooking this up to a TV via the RF input - is there any "magic"
>> involved, or will a suitable braided co-ax TV cable with a phono connector
>> added at the Atari end do?  I know it "works" because I lashed one up
> Maybe... The modulator output is nominally 75 ohm, and should be linked to
> such a piece of coax. European TVs have a 75 ohm aerial input, often on what
> we call a 'Belling-Lee coax socket', so it's just a cable. US TVs, I am told, may have
> either a 75 ohm coax input, often on an F connector, or a 300 ohm balanced input
> (for parallel twin feeder cable) on a pair of screw terminals. For the former, just
> connect it up. For the latter you may need a matching transformer, aka a 'balun'
> (BALanced to UNbalanced converter). I am pretty sure you can buy these, but
> it must be possible to wind one if you can get a suitable core
> The European switch box is just a switch. The US one I have somewhere has
> screw terminals for the aerial input, a bit of twin feeder for the output and
> IIRC a phono socket for the computer RF input. There is a balun inside.
> The switch is special too. It is designed to minimise RF leakage from the 
> computer to the aerial, since linking an aerial to the computer modulator
> output would make a very low power TV transmitter. How far it would be
> detectable I do not know, but the FCC (or whoever) take a dim view of 
> such things.

Doing such a thing would have an appreciable chance of causing damage to 
the modulator because it's feeding into something that's probably not 
tuned to precisely the right frequency.  Antennas designed only to receive 
tend to be very poor for transmitting.

David Griffith
dgriffi at

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