Web Updated;
06/07/2011
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Settings Chart, 4 Band rotary dipole.
| BAND | Centre Freq | Positive Arm (Coax Centre) | Negative Arm (Coax Braid) | ||
| Coil Tapping Point | Telescopic Sections | Coil Tapping Point | Telescopic Sections | ||
| 40m | 7.120 | 8 | 6 | 8 | 8 |
| 20m | 14.200 | 3 | 5 | 2 | 7 |
| 15m | 21.185 | 1 | 2 | 1 | 9 |
| 10m | 28.4 | 1 | 3 | 1 | 1 |
General Notes:-
Every aerial built will vary, this depends upon manufacturing and height of operation.
This is a guide based on my own aerial and should not be relied upon before confirming a safe operating VSWR.
If your radio has a built in antenna (tuner) matcher, you may be able to use the whole band width.
At the time of writing I have not resonated the aerial for 30m or 17m but the construction WILL be capable of tuning to these frequencies. I will update the site when completed.
Once a basic resonance has been achieved, minor band centre adjustment can be made by retracting or extending the +ve Whip. Depending on the band in use this may be as little as 15mm Adjustment.
It is necessary that the antenna is not perfectly balanced with the same whip
and tapping points each side.
This imbalance changes the impedance by offsetting the feed point within the
wave form creating additional z ohms and matching to the radios required 50
Ohms.
The aerial will not tune to 6m as it is physically too long, with both fly leads left off I guess you could force an ATU to match the length but performance will suffer. If I had made the two 25mm dia arms less than 1425mm each it would have reached 50.125 Mhz, but I predominantly wanted 40m and was concerned that shortening the arms would result in more turns on the coil and hence more loss!
The number of telescopic whips shown DOES NOT INCLUDE THE FIXED SECTION to the coil former, hence a value of 2 means two sections slid out and NOT two sections showing!
If this is not clear please email me for further advice.
Have fun! 73 de Graham