It probably works because both are yagi antennas pointed in exactly the opposite directions. The front to back rejection of each antenna is enough to prevent out of phase cancellations to occur. Just a guess.
...or to the same direction but at different bands (e.g. VHF + UHF)
This should be considered as a 3rd scenario that easily and successfully done all the time using a UVSJ combiner. Same direction, different direction for each antenna doesn't matter, it still works as you noted.
The linked article refers to two dissimilar antennas linked by #12 AWG electrical wire that looks like it is still in the original 2/3 conductor sheath. #12 AWG electrical wire is a disaster at TV frequencies. It's nowhere near the correct impedance, will have excessive SWR and may have dielectric losses.
That article is a perfect example of how not to install two antennas. The two antennas are dissimilar, too close together, not joined properly and pointed in different directions. The poster just got lucky and probably benefits from having strong, non-interfering signals in both directions.
p.s. I can get two channels with a paper clip. It doesn't mean it's a good TV antenna.
Did a search of the Forum, and couldn't find much about using wire instead of joiners/combiners? TY.
I can confirm that the concept works. I took two, silver sensor antennas - mounted with an electrical junction box on a pole (I've seen them mounted individually on a pole as well), one pointed north and one pointed south, and then combining the two with a simple splitter in reverse, then fed to a satellite multiswitch. Works great - I get signals from both directions, and the feed is available anywhere I have a satellite drop, via a mixer-splitter.
It is fairly easy to connect two Identical Antennas pointed in Same Direction [cable lengths must be SAME Length] or Different Directions using a standard RF Splitter, as a Combiner connected in reverse [RF Combiner Mod]. However there is a 0.5 to 1.5+ dB LOSS in the RF Combiner due to Internal Loss as well as Gain, Phase and SWR Mismatch in the Ferrite Hybrid Transformer inside the RF Combiner: Antenna Comparisons, Antenna Reviews, DIY Antenna Modifications, HDTV Antennas
It is NOT easy to design an interconnecting Harness using JUST Bare Wire (see for example my HHH or HVH, designed via Computer Optimization Software).....and is even more difficult using off-the-shelf 300-ohm Twinlead Transmission Lines (or typically better 450-ohm Ladder Line), since you can ONLY adjust the Length and NOT the Impedance [needed to turn it into an Impedance Transformer]....and there is high Loss when Wet/Snow/Ice.
In my HHH (Holl_ands Horizontal Harness) and HVH (Holl_ands Vertical Harness), the Optimizer finds not only the Optimum Total Length (must be MORE than the given Stacking Distance), but also the Variable Impedance (separation distance between the Harness Wires) of the Transmission Lines....both of which are significantly affected by PROXIMITY to all of the OTHER Wires in the Antenna (and vice versa).
If you make RANDOM choices, you're going to get RANDOM results, incl. the likelihood of poor SWR and possibly Gain Drop Outs on some Frequencies....
However there is a 0.5 to 1.5+ dB LOSS in the RF Combiner due to Internal Loss
this is true only if power combiner/splitter has isolation between ports, as in https://en.wikipedia.org/wiki/Wilkinson_power_divider
if no isolation (not a Wilkinson type, or frequency differs from wilkinson design frequency) - half of signal will go to port and will be radiated by second antenna
"if no isolation (not a Wilkinson type, or frequency differs from wilkinson design frequency) - half of signal will go to port and will be radiated by second antenna"
So if half of the signal goes out the other port to the antenna, is this not a loss?
And my old (Mar 2009) Summary of Low Loss Wilkinson Stripline Couplers....note only Partial Band Coverage for most but not all Couplers. Typical Internal Loss is 0.2 to 0.5 dB, irrespective of whether 2-Port, 4-port or whatever. Frequently used to sum Multiple Output Stages in an RF Amplifier, so may or may NOT be suitable as a Low-Loss Combiner....so check with manufacturer: https://www.avsforum.com/forum/25-hd...l#post16072450
In a Ferrite Hybrid Transformer [typical Cable Splitter/Combiner], internally there is a 75-ohm Load Resistor connected to the port "D", also called the DIFFERENCE PORT. As illustrated in App. Note M586 Figure II (first entry), when there is a Phase Difference between the two Input Ports, internal Port "D" dissipates the "Difference". And the "3 dB" Combining Gain (less Internal Losses) is ONLY realized when Input Signals are EQUAL, with the difference being dissipated in the Internal Load Resistor on Port "D"....see MACOM App Note M561.
Power coming in on one port and going out the OTHER is measured by the ISOLATION Spec...which is quite high in ALL of the above Splitter/Combiners....incl. Wilkinson. I don't know of any of THESE types that have significant energy going from one Input Port to another.
That is true only for combining in-phase equal-magnitude signal (i.e. using phased array of N antennas pointed to the same transmitter).
If second port has zero signal (hence this antenna is pointed in different direction), this zero-voltage cannot prevent energy flow (no port isolation)
Combining 2 antennas from 2 directions using a reverse splitter return a loss of 3-4 dB on each antenna's signal. But would it be possible to pick up the signal from one antenna and retransmit it at low power over-the-air in front of the other one ?