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A doubling of power expressed in decibels is nominally 3 dB. If each antenna is identical and receiving identical amounts of signal power and in matched phase and you can combine the outputs of each without loss then the combined power of the two would be 3 dB greater than one antenna alone. In practice, that's a lot of 'ands' in a row... 2 to 2.5 dB net gain is considered a good result.
I can't see you achieving reliable reception from Seattle... there's the primary problem of extremely weak signals compounded by co-channel and/or adjacent channel interference in most cases. Then there are no doubt some FM signals that would be potential sources of harmonic interference.
You need to be able to add the noise margin of the signal in the air together with the net gain of the antenna minus any balun and cable losses ahead of any active device such as a preamp. (Amplifier gain does not add to the antenna gain, because it amplifies noise received by the antenna while adding some of it's own noise. If the antenna can't get the job done, an amp won't fix it.) If the number is positive, you are getting to a point that may produce reception. But the NM figure listed in your report does not account for the effects of co-channel, adjacent channel, FM or any other source of interference. Also, at that distance, atmospheric conditions are going to govern a great deal of the path. As a result you're going to see a wide range of path loss variation as the weather changes. Sometimes the atmospheric conditions will be in your favor... but at least as often, not. On any given day the real and predicted NM on such a path could differ by well more than 10 dB.
If you still want to try, I'd get a big 7-69 combo or a big UHF panel and H-VHF Yagi... A preamp that tolerates strong signals and an FMI filter.
Winegard HD7698P and Antennacraft HBU-55 are a couple of combos to look at.
The DB8E + Y10713 pair is a another off the shelf solution for entry level DX'ers.
Another option is to roll y'er own... The GH10N3 comes to mind... and then there is the stuff of legend, the Rhombic.
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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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Last edited by GroundUrMast; 5-Sep-2014 at 12:42 AM.
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