The SETI League, Inc., a membership-supported, non-profit {501(c)(3)}, educational and scientific organization Searching for Extra-Terrestrial Intelligence

Ask Dr. SETI ®

Chapter 6: Technology

Choosing RF Cable

Dear Dr. SETI:
What exactly is RF Cable and where do I get it? How much $? What length before signal degradation using 12' dish and other "standard" SETI stuff (ICOM receiver, GaAs MMIC LNA)? Thanks, a fellow student and I (btw, we are League members) are setting up a system and have had NO experience with this...
Adam (student)

The Doctor Responds:
Welcome to The SETI League, Adam. We appreciate your support, and participation.

RF stands for radio frequency. The cables we use are usually coaxial (ie, "coax" cable), and we prefer those with low loss at radio (specifically microwave) frequencies. The stuff used for cable TV is cheap (pennies per meter) but pretty lossy at 1.4 GHz. The kind you buy for, say, CB radio antennas is a little better, and a bit more costly. If you have a local Radio Shack store or similar, you can probably find what they call low-loss coax -- it's larger (perhaps 1 cm diameter) than the CB or TV type, costs maybe a dollar or more per meter, and may go under such part numbers as Belden 9913, RG-8 Polyfoam, etc. It may take special connectors (the ones most of us use are called "Type N"), which require some experience to properly install.

For any type of coax, the longer the lossier. So we try to keep our antennas near the radio room. If this is not practical, we can do several things: use more gain in the preamp (to boost the weak signal before it suffers cable loss); mount the whole receiver, or just the downconverter, outside on the dish (pumping a lower frequency through the cable is more efficient); or use specialized cables such as hardline or heliax (which can cost upwards of tens of dollars per meter).

You and your classmate might want to scour the campus for (1) an electronics or ham radio club, or (2) an Electrical Engineering major, or fellow student who happens to be a radio amateur. They might be willing to collaborate, and it sounds as though you could benefit from some experienced helpers. Good luck!

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