The Band Optimized Log Periodic Dipole Array (BOLPA) is the brain child of Justin Johnson G0KSC and is the combination of multiple 3 element monoband Log Periodic Arrays on one boom. It has long been known that the Log Periodic can provide directional performance over a very wide range. Some years ago, Justin G0KSC decided to experiment with narrow-band Log Periodic Arrays to ascertain if additional performance (in terms of Front to Back ratio (F/B) and forward (Gain) could be achieved. Justin established that with just 3 tightly packed elements, excellent F/B and gain could be achieved across the whole of the amateur bands within a very short boom length. At the same time it can deliver a 50 Ohm feed point impedance rather than the more traditional 200 Ohm. To give an example of size, one of these 3 element monoband Log Periodic Arrays for 20 Meters would sit on a boom a little over 6’ in length
The BOLPA is a combination of 3 element monoband Log Periodic Arrays upon the same boom. The BOLPA 13 being 3 elements on 20m, 15m, 10m and 6m. In this antenna, 12 Meters is a bonus band, it is delivered between the 3 elements for 15 Meters and the 3 elements for 10 Meters almost by accident. A small amount of optimization of the spacing between the 15 Meter 3 element cell and that of the 10 meter cell finalized the performance. With 17 Meters, a little more work was needed. The 20 Meter, 3 element cell was shifted back along the boom. This allows for an additional single element to be placed between the 20 Meter 3 element cell and the 15 Meter 3 element cell. Only the width of this single 17 Meter element and the position of the 20 Meter cell and 15 Meter cell (along the boom) were optimized to achieve excellent performance.
This revolutionary antenna consists of 6 trapless monoband logs on a single 30` boom and 13 full size elements.
- Computer optimization gives full monoband gain and front-to-back ratio on every band. Exceptional flat in-band impedance eliminatis transmitter re-tuning.
- Operate six bands: 20,17,15,12,10, and 6 meters with a single direct 50 Ohm feed. Easily handles far more than the full legal power limit.
- No 4:1 balun, no matching devices, no traps, no coils -- super low losses.
- At least 3 full size elements are active on each band. 24 ft. turning radius, 30 ft. boom, 36 ft. longest element. 160 lbs.
- Operate 6 bands simultaneously. Perfect for multiband SDR recievers.
The addition of the 17 Meter band element did more than just provide excellent performance on 17 Meters. It provided an additional ‘illuminated’ element on 20 Meters so that 4 elements are active on 20 Meters, rather than just 3. The same applied on 15 Meters where the single 17 Meter element was now able to be used as a ‘reflector’ type function for 15 Meters. This allowed all 3 of the elements in the 15 Meter cell to be optimized for maximum gain and F/B resulting once more in another band with 4 active elements.
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