Need advice: fuzzy/blurry/snowy/static picture on recently purchased 7800

Hi!  I recently purchased an Atari 7800 on Ebay.  Unit came with an existing RCA cable.  Had to purchase a power supply separately.

I purchased 1 of these to connect the unit to my LCD TV:

http://www.amazon.com/Intellivision-Colecovision-Adapter-VINTAGE-WITHOUT/dp/B0028MXOF6

After making the proper connections, I get a fuzzy picture similar to the first picture at this link:

http://www.atariage.com/forums/topic/173539-the-atari-7800-displays-a-blurry-image/

I made sure that the RF channel output on the Atari 7800 matched the same analog channel on the TV.

What can I do to improve the signal output?  Could I be dealing with a bad RCA cable?  Should I buy an RF demodulator (or find an old VCR) to try?  Or, did I simply just purchase a defective unit?

Thank you to all replies.