Wednesday, May 4, 2011

Tale of two antennas

My living room has two indoor antennas near ceiling height, one is near the windows and the other is near the door.  I put the door antenna in last, as a backup for 2nd tuner.  Then it turned out, that it actually seemed better (quite unexpected).  These have been there for several years now, unchanged.

To measure the two antennas this week, I moved Kenwood 600T into living room.  The 600T has a marvelous linear signal strength meter calibrated in 10dB increments.  From tests using a Sound Technology ST-1000A I can say the Kenwood meters are quite accurate, or at least quite linear (since my ST isn't calibrated recently either, and I don't have necessary impedance adapter for total accuracy).

So here are the measurements:

Living Room Door Antenna
88.3     60dB
90.1     43dB
91.7     47dB

Living Room Window Antenna
88.3     59dB
90.1     47dB
91.7     53dB

OK, now it looks like except for the tiny difference to 88.3, the window antenna is better after all.  But the problem is, 88.3 KPAC is my favorite station...

Now I am listening to KPAC, and on window antenna, and it probably isn't as good there.  The background hiss has turned slightly sizzly, and so has the omnipresent birdie (on all tuners to some degree except XDR-F1HD).

All the above stations are to the west, but possibly KPAC is more to the northwest than others, explaining why one antenna is better for some but not others (?).  All antennas are on the eastern wall of the room with same orientation, but perhaps the differences result from different sets of interfering objects.

I've also hooked up a 100Mhz oscilloscope to the scope outputs of the 600T.  The scope does not seem to reveal any meaningful differences...except that possibly the door antenna gives a slightly flatter and nicer trace on the screen than the window antenna.  All scope traces look reasonably good.  The cause of the birdie is not evident.  The best luck I've had with that was when I hooked up spectrum analyzer and observed small signal at 88.5.  There is nothing but noise at 88.5 using every tuner in my collection.

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