PERFECTING THE X-POL - PERFECTLY CENTRED ELEMENTS, COAX EXIT ROTATION AND NON-METALLIC H-FRAMES
If you want an X-pol Yagi and wish to maintain the software predicted noise figures (G/T) the ONLY way this can be achieved is with perfectly centres X and Y planes. If the elements in each plane are off-set or even have a matching section (such as a T-match) extend into the opposing plane, pattern distortion and noise figure degradation WILL occur. It does not matter what you read or see if noise figures on paper, those models did not include the off-set!
Some customers take the advice and do things right, Constantin, KG6NK is one of those guys. We built his 4 x 22el 144MHz low noise LFA Yagis with perfectly centred, thru-boom elements and he built an H-frame to support the system completely from fibre glass. Simply adding a small piece of fibreglass to the ends of metallic supports does not cut it, the remainder of the metallic tube WILL conduct and WILL degradation performance. Constantin had excellent results with his 2 x 22el built this way so decided to upgrade to 4 and the installation is almost done!
Almost there! a 4 x 22el X-pol low noise LFA Yagi system with perfectly centred elements with just cables to connect, at KG6NK
All coax cables, when completed will exit the rear of the antennas and the forward-most coax cable / ferrite choke is curved and has a rotational exit from the feed point in order there are no, flat surfaces (coax cable is metallic too!) in order to minimise any potential interaction.
When investing in VHF/UHF systems for low noise applications, particularly EME, it is important to do it right, not what best works for mass production purposes. Ensure you get antennas manufactures the best way to ensure excellent results. If this sounds like the way you want to have your EME system configured, let us know and InnovAntennas and we will give you all the help and advise you need, post and pre-sale.
X-pol Configuration Check List:
• Perfectly centred elements with no off-set (particularly important on 70cms)
• Absolute minimal contact with any element (no feed point boxes or structures)
• Rotational exit of coax/balun from the feed point
• Rear exit of all coax cables
• Rear Splitter mount to hold splitter rearward for minimal coaxial runs (in photo)
• Non-metallic H-frame
Of you want the best in low noise Yagi replication – look no further than InnovAntennas
Photo: Almost there! - Constantin sent us this photo of his system almost ready to go. Next step, cable connections and finalisation!
Justin, G0KSC - InnovAntennas