Earlier in my post #32, I did not try an match the models and I noted the models showed fair matches with near perfect Average Gain results. IMO it likely would matter little if I got them to match. However, DB made a point that his models were all matched and also showed very good AG results. Thus I matched my two Sigma4 and two NV4K...both with and without horizontal radials added in my attempt to respond to JAF0 question about adding radials to his Vector...in light of the discussion.
I mentioned earlier that my models showed the Sigma4 responded nicely when adding radials, but my New Vector 4K just showed mediocre gain. My V4k model without radials showed better gain results and about matched the S4.
Since Henry's report came up in discussion on the Avanti Sigma 4, I decided to consider both designs per the dimensions I had available.
File 1. shows an overlay of the pattern for the 4 models in the order of maximum gain. The models are at 36' feet to the feed point and set with Ground Description set to medium (0.001, 5), or very poor: cities, industrial per Eznec software.
My model was set a 27.205 MHz. When I attached the mast to the antenna mount the model went a little capacitive...showing a reactance -5.757 ohms at the feed point. This made the radiator short and thus raised the resonant frequency to 27.30 MHz. I did not tune this out of the model. The model shows a bandwidth of 1.30 MHz at the feed point. When I tuned the reactance out of the model the BW did not change, but the antenna was resonant at 27.205 MHz as a result.
File 2. is a model of my Sigma 4 with my idea of a gamma match in Free Space. It shows the Average Gain results and all models show near perfect AG at or near = 1.
File 3. is a model of the Sigma 4 noted in File 2, however it is over Real Earth. It too has three horizontal radials mounted at the base of the 16.5" mounting bracket. I added the mast to the antenna, but it is isolated (ISO) 4" inches at the base of the mounting bracket.
File 4. is the same model as #3 above, but the antenna is not ISO from the mast. This model shows no indications of Common Mode Currents on the mast as does the other model that is ISO. The gain with the no ISO did drop a little however. The match changed very little.
To check if the length of the mounting bracket made a difference in the gain and/or match, I set the 3 horizontal radials 1.00" inch below the hub and the gain dropped from 5.44 dbi at 8* degrees to 4.84 dbi at 8* degrees. The SWR match with the horizontal radials set 16.5" inches below the hub dropped from 1.116 ohms to 1.147 ohms when set at 1" inch instead.
Thus, I think W8JI and Henry might arguably be correct in suggesting that radials will help the gain a little when added to the Sigma 4, but according to my models here...this does not seem to apply to the New Vector 4K with its larger radial cone. Only some real good real-world testing will prove one way or the other. That said, Henry reported on the Sigma4 and I'm not sure about the source of information given by W8JI on this design.
