It was late Bob, so I could have made a mistake in what I was trying to say. I agree the model without radials is not a sound design and the pattern shows that at the bottom of the radiator. IMP the exception could only be if the Imax/A99 tuning device is able to decouple the antenna from the support and the feed line in some modest way...that helps prevent what we see in the non-isolated model I posted. I'm just not convinced that an Imax/A99 is not the exception I noted above. I know our I-10K will not work worth a hoot unless we have nearly full 1/4 wave radials on it, no-way-no. Something is making the difference.
The idea I was intending to make was that the typical .625 radiator need radials if isolation was expected to work, or else the real Imax/A99 has some innate ability to help decouple the antenna from the mast, and if there were a feed line added to the mix, we'd have to add a choking device of some type, and that probably goes without saying.
The particular model you reference here was added as a comparison to the non-isolated no radial model only. I was thinking to show what could happen if the antenna was adequately decoupled in some way, similar to what I think the Imax/A99 tuning device can do, thus we don't need radials or isolation. This is not to say that isolation might not improve performance in some way, but that we see the Imax/A99 working good enough all the time, and when I tested my A99, I didn't see enough obvious difference to matter. I think I was talking you through my experiences at the time, via emails back in early 2011. That was when I got frustrated and accidental threw away all of my work notes and reports for my A99.
I agree, isolation alone without radials is probably not a good solution, just like your test have shown.
Can you give me some details of what you tested an how? I asked in my post above how the radials were done and what kind of antenna was being tested. Was that test the MultiMode antenna setup that is similar to the A99? I want to see if horizontal radials vs. slanted radials makes a difference. I might try again to model the feed line too, but I don't think I can do a choke.
This is off this subject a bit, but somewhere recently I think I posted a model of an Imax/A99 with various angles of degrees for the radials here on the WWRF.
That was an idea I got from a discussion on Cooper's Forum, of all places. At the time I was also checking out the report on the subject that Tech 833 did sometime back on the Imax with a GPK added. The models I made as a result seemed to support his idea that radials at 30* degrees showed a nice improvement over radials slanted at 45* degrees, the traditional angle most used, and similar results with horizontal and steeper angles of 20* degrees did not show to be working nearly as good as the 30* degree angle. For some time I doubted his report, but these models support his findings.
