Take off patterns for CB antennas we use.

[Marconi]

For a while now I have been checking some of my Eznec models to get the segmentation per inch close to the same for all models that I think are either set to specifications or close. I have them listed in the order of gain. You will note that all are mounted close to 32' feet to the feed point of the antenna except for two models, so some models will be at some disadvantage in the gain and angle category.

No matching device was included in any of these models. Only the Gain Master and the CF Dipole were isolated (ISO) from the mast and the separation is clearly visible in these models. Again, the Gain Master and the CF Dipole were the only antennas that had a feed point raised higher than the 32' foot feed point height compared to all other models. IMO this is to be taken as an advantage for the GM and the CFD, and the results will show to be more in the gain and possibly a little lower in angel at the maximum radiation lobe.

Also consider these factors in your evaluations for these models.

All antennas with parts of the antenna hanging below the typical 32' feed point height will show some less gain and angle effects as a result of being lower. This difference can be as much as 8' - 11' feet in height difference, where the gain and angle will benefit those with elevated feed points. The Gain Master and the Center Fed Dipole will both show these benefits by having higher feed points.

The AstroPlane and the New Top One's height to the hubs are 32' feet, but about 8'> hang down below the feed point. The model noted as "#1 .25 wave slanted radials RES 32'," the Merlin, and the Starduster model's each have radials hanging down about 7'+ feet below the feed points. This same idea might be considered as well...along with the A99/Imax that have slanted down radials that are effectively below their feed points about 5'-6' feet as well.

The file below is big and can take a few seconds to load.

View attachment CB antennas at 32' patterns.pdf

The model below is an antenna I built and designed using 102" SS whips. I use the hub from an A99 GPK, and a mobile mirror mount. I call this antenna my Marconi 5x.

Here I have set my Marconi 5x higher by 8' feet above the 32' foot hub to get the bottom of the antenna at 32' feet rather than its being at 24' feet. I've noted the elevation dimensions at the tip, the hub, and the very bottom of the antenna which again places the bottom of the antenna just as high as the bottom of the other antennas in this project.

Compare these results to a 5/8 wave that has a 22.5' radiator sitting on a 32' foot mast...where its tip will be at 54' 6", which still places the Marconi's tip 6' feet below the tip of the 5/8 wave tall radiator.

Is it surprising that this puts this little simple antenna right up there in the top of the big guns right below the Sigma4 and the New Vector 4000 models?

View attachment Marconi 5x 102'' w hub 40'.pdf

 

[Shockwave]

This makes it fairly easy to see that height above ground is the dominate factor in determining the TOA of the main lobe while the design of the antenna determines how much gain will be provided at that angle.

 

[Marconi]

This makes it fairly easy to see that height above ground is the dominate factor in determining the TOA of the main lobe while the design of the antenna determines how much gain will be provided at that angle.

Well Donald, I haven't tried to diagnose all this yet. The big job was trying to make sure that the models were pretty close in segmentation. I noticed this technique once in a article that Cebik published...where he gave enough data that I could actually duplicate his results. I just tweaked the segmentation values to get close to his results, and I began to see how he handled segments. I figured out with 500 segments available in my version of Eznec...that I can use the following scheme: wire length" / .25 in inches, wire length' / 3 in feet and everything works out pretty good.

Maybe I'll go back and do some free space patterns for all of these models, but with verticals models we don't see much ground reflection like Gary Wescom N0GW, suggested in his link on 211's thread on TOA.

He was also using horizontal models, and that might be confusing these guys if they try to interpret what his ideas are about and don't know there is a notable difference in patterns. I can't say Wescom is wrong, but horizontal patterns are entirely different in many respects from vertical patterns.

He is also discussing much lower frequencies for the most part, and IMO, operations there use different techniques to communicate, and some of that stuff does not directly relate to CBr's vertical polarity world...in a practical manner.

Just my thoughts on the subject, and I don't even like discussing TOA because the subject is so technical on the one hand, and then subjective on the other.

 

[Shockwave]

While the TOA will be different for vertical antennas, the effects of ground reflections on TOA is just as predictable as they are with horizontal antennas on HF. You'll notice all of your 32 foot models have a TOA within 2 degrees of each other. The small differences are related to the different centers of radiation these antennas have.

If your vertical antenna is placed one wavelength above ground on this band, you can expect a TOA around 9 degrees. If your horizontal antenna is placed at the same height you can expect a TOA around 14 degrees.

 

[W5LZ]

In general, meaning that it's nice to have, a low TOA is certainly not an absolute requirement for a 'good' antenna. Arriving signals do that arriving at a fairly large range of TOAs. Optimizing for the lowest one means that signals arriving at higher ones will not be heard as well. TOAs have been made into a false indication of how well things are going. Don't waste too much worry on it.
- 'Doc