[OFARC] Tuning a Cobweb Antenna - need advice

[Don Davis]

Hi to All,
    Need your expertise and advice - I am in the process of tuning an MFJ 1836 cobweb antenna capable of 20M, 17M, 15M, 12M 10 M and 6M bands. I am using a telescoping mast mounted to the eave of a single story home.
 I followed the MFJ instructions for tuning the antenna about 7 feet above ground and obtained the lowest SWR possible for the center frequencies of the bands.
 However, when I installed the antenna on the mast and raised the mast about 20 feet above ground, the SWR readings for the center frequencies increased. The data is shown below. 
The center frequencies are the target frequencies desired; the resonant frequencies are the lowest SWR readings.
 I have a General license, so I am tuning for the SSB frequencies in the General bands. So, the questions are:
1. Should I stand on the roof and lower the mast to be able to adjust the bands for the lowest SWR readings? Or are the readings shown below "good enough"?
2. I have read that the cobweb is "omnidirectional". But somewhere I read it should be positioned for the broad area of the antenna to face North -South or East - West, depending on the desired transmission/reception???
Thanks for your reply,
Don KI5WWD

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|  | MFJ 1836 Cobweb Antenna 20 - 6M bands |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  | Antenna mounted 7 feet above ground for tuning using MFJ-259D antenna analyzer |  |
|  |  |  |  |  |  |  |  |  |  |
|  | General License |  |  |  |  |  |  |  |
| Band | Center Frequency |          SWR  |               Rs |  | Resonant Frequency |          SWR  |               Rs |
|  |  |  |  |  |  |  |  |  |  |
| 20M | 14.289 |  | 1.1 | 48 |  | 14.284 |  | 1 | 50 |
|  |  |  |  |  |  |  |  |  |  |
| 17M | 18.139 |  | 1 | 48 |  | 18.133 |  | 1 | 50 |
|  |  |  |  |  |  |  |  |  |  |
| 15M | 21.362 |  | 1 | 50 |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
| 12M | 24.96 |  | 1 | 54 |  | 21.951 |  | 1 | 50 |
|  |  |  |  |  |  |  |  |  |  |
| 10M | 29 |  | 1.2 | 42 |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
| 6M | 52.05 |  | 1.5 | 32 |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  | Antenna mounted approximately 20 feet above ground on telescoping mast. |
|  |  |  |  |  |  |  |  |  |  |
|  | General License  |  |  |  |  |  |  |  |
| Band | Center Frequency |           SWR |               Rs |  | Resonant Frequency |           SWR           |               Rs |
|  |  |  |  |  |  |  |  |  |  |
| 20M | 14.289 |  | 1.5 | 75 |  | 14.355 |  | 1.2 | 55 |
|  |  |  |  |  |  |  |  |  |  |
| 17M | 18.139 |  | 1.5 | 49 |  | 18.187 |  | 1.1 | 47 |
|  |  |  |  |  |  |  |  |  |  |
| 15M | 21.362 |  | 1.4 | 39 |  | 21.381 |  | 1.2 | 46 |
|  |  |  |  |  |  |  |  |  |  |
| 12M | 24.96 |  | 1.2 | 61 |  | 24.964 |  | 1.2 | 61 |
|  |  |  |  |  |  |  |  |  |  |
| 10M | 29 |  | 1.4 | 61 |  | 29.023 |  | 1.2 | 53 |
|  |  |  |  |  |  |  |  |  |  |
| 6M | 52.05 |  | 1.4 | 49 |  | 52.054 |  | 1.4 | 50 |
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|  |  |  | Band Plan for General License SSB |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  |  | 20M | 14.255 - 14.350 |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  |  | 17M  | 18.110-18.168 |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  |  | 15M | 21.275 - 21.450 |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  |  | 12M  | 24.930 - 24.990 |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  |  | 10M | 28.300 - 29.700 |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |
|  |  |  | 6M  | 50.1 - 54.0 |  |  |  |  |


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