small logo SETI League Technical Manual -- Block Diagram

RF Cables

Copyright © 1999 by H. Paul Shuch, Ph.D.
Executive Director, The SETI League, Inc.
PO Box 555, Little Ferry NJ 07643
email n6tx @

The most common SETI station configuration would place the microwave receiver, signal analysis computer and related accessories inside the house, with the antenna and LNA mounted outside, some distance away. To connect the two halves of a SETI station, we use an RF cable.

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 in the 1.4 to 1.7 GHz region of the spectrum typically used for amateur SETI. 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); follow the LNA with a satellite TV line amplifier; 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 Andrew Heliax ® (which can cost upwards of tens of dollars per meter).

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