Quote:
|
The page in question is confusing (IMHO) and seems to mix a bunch of different issues together. I was trying to understand which bits of that page are inherent to the combiner and which were part of the particular setup he was describing.
|
I also find that page confusing, and I have been doing antenna experiments since I was 8 years old when I built my first crystal set radio. I'm now 82, still studying antennas, have been a radio amateur (ham) since the early 50s, having built many ham antennas, and have been making tests and measurements with antennas for digital TV since 2008.
My McAfee security software tells me to stay away from that page, so I look at the Google cache version instead. I previously used the Norton security software that let me look at hdtvprimer pages.
On that page Ken Nist KQ6QV is talking about "How to combine antennas that point in different directions" but starts his explanation with a splitter and then makes a conclusion about a splitter in reverse used as a combiner. He then states there is a loss of 3 dB.
I found it difficult to make that leap to the conclusion that he did because when the two antennas are aimed in different directions, the same signals from each antenna arrive at the combining point with results that vary because of differences in amplitude and phase.
He does go on to state
Quote:
|
(It will be explained later that when the two antennas are pointed at the same TV station, the reflected currents subtract to zero, and as if by magic, the 3 dB combiner loss turns into a 3 dB gain.)
|
I have found, by actual measurements with a signal level meter, that when two identical antennas aimed in the same direction are combined with a splitter in reverse, the gain can be as much as 2.5 dB. When the two antennas are aimed in different directions, the results can not be predicted. Some channels survive the combining, and others are lost.
The discussion is still going on by people that are smarter than I am:
Thread
http://www.digitalhome.ca/forum/186-...rm-fields.html
relevant posts begin here at post #14 between holl_ands and K6STI and continue on page 2 of that thread
http://www.digitalhome.ca/forum/186-...ml#post2629098
Their discussion is about two antennas aimed in the same direction, but the two antennas are not in a uniform signal field because of trees in the signal path, which is a problem similar to combining two antennas aimed in different directions.
holl_ands is a communications engineer who is an expert in computer modeling and K6STI is a ham who designs computer modeling software for antennas. As Jeff Dunham's Peanut says sometimes the discussion goes "woosh" right over my head.
Rather than argue about it endlessly, I prefer to make some measurements to find out for myself, as the link in my signature says.