Jeff here is my model of the V4K with and without a choke to stop current from flowing on the feed line and/or mast. This model of the V4K is made using what I call a "Simulated Feed Point." This means I simply placed the FP at a point on the model's mast near the bottom where I find 50 OHM's. This is similar to how the gamma taps into the radiator and IMO this is not direct feeding the antenna.
PDF #1
1. this model is in Free Space (FS). 1st page shows the Main Control screen which indicates, at the bottom, the Average Gain Report for this model. It shows AG = 0.999, which indicates the model is reliably accurate. The other 3 images are the antenna view in FS, the free space pattern with the max gain & angle noted, and the feed point match condition for the model. I add this version of the model as a control to help maintain accuracy when I finally place this model over Exnec's idea of Real Earth, which simply adds back the losses and the mast to the real Earth model.
2. I added the mast connected directly to the base of the antenna. This model is the V4K with the mast 4" inches below the base of the antenna to add CMC isolation (ISO). The model has no choke, and instead requires an insulator to deal with the current on the radiator like Henry discusses. The model shows an image in the antenna view. I also add a close up view of the cone area including the location of the feed point (O) up above the base of the antenna where I found 50 OHMs. Next image shows the pattern and the max gain/angle, next is the image of the wires used to make the model, and last shows the feed point impedance values and SWR.
3. shows the same model as #2 with no isolation (ISO) and instead uses a simulated choke at the top of the mast to deal with the CMC currents.
PDF #2
1. shows the V4K antenna with out ISO or a choke. I forgot to include this model above. It shows how bad the CMC can be for this model. IMO, this is what Henry was talking about when he discussed the CMC issues.
2. is an unrelated V4K model I had on file. Jeff, per your request I added 4 horizontal 109" radials about 12" inches below the base of the antenna. This model also has the feed point located at a 50 OHM point near the bottom of the radiator, but the model is a bit different in other minor ways, even though the matching results are similar. Jeff, I also added overlays of the various patterns in the PDF files, so you can more easily compare these effects.
Thus far I don't see any of these modifications to the models making a notable difference, one way or another. IMO, I don't think these variations are the same mods as Donald is suggesting, mods that will make a big difference 50 miles away. I'm hopeful that maybe he and/or Homer can give me some dimensions that supports their observations and experience.
