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## Topband: A wee bit more on power coupling

 To: Topband: A wee bit more on power coupling btippett@alum.mit.edu (Bill Tippett) Thu, 09 May 2002 14:44:13 +0100
 ```N4ZR wrote: >Well then, I guess I share Tom's confusion. You did state that verticals would be the antennas of choice in NA and EU, based on the amount of insertion loss for a dipole. It seems reasonable to ask, "-24 dB compared to what?" Or asking the question the other way round, what would be the insertion loss of a vertical at the same locations? Compared to the dipole's normal pattern. This is why power coupling loss must be considered as only one component of the total pattern. To compare a vertical and horizontal antenna, you need to do compute total system gains including pattern gain over the actual ground conductivity and at actual takeoff angles, and then superimpose the power coupling loss on the horizontal and vertical antenna patterns. Bob did give coupling loss by TOA for vertical polarizations here: http://lists.contesting.com/pipermail/topband/2002-May/014848.html but I haven't seen the equivalent by TOA for horizontal polarizations. I'm not going to do this but here's what you need to do to compare antennas: 1. Model a vertical over actual ground conductivity (near and far fields). 2. Model a dipole over the same and at the actual height. 3. Choose a common takeoff angle (this is very important!) 4. Add the vertical coupling loss in the direction of interest (North) to the vertical at the selected takeoff angle. 5. Add the horizontal coupling loss in the same direction and at the same takeoff angle for the dipole. 6. Compare the two models. Here's the problem as I see it. A low dipole has its TOA peak at 90 degrees and a decent vertical has its TOA peak around 20 degrees, so the antennas are VERY different in TOA patterns before you even take power coupling into account. The main question in making any comparisons is to choose the takeoff angle to W8 or VE3. I would guess 30-40 degrees but I really have no idea, and without choosing the correct takeoff angle, any modeling comparisons are meaningless. If you could estimate the correct angle, it should be possible to compute #6 above and do some actual on-the-air tests after Tom reorients his 300' dipole from broadside E/W to broadside N/S! :-) 73, Bill W4ZV ```
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