The Ø1/2" Absorptive ND Filters are mounted in SM05 series lens tubes, the Ø25 mm Metallic and Absorptive ND Filters are mounted in SM1 series lens tubes, and the Ø2" absorptive ND filters are mounted in SM2 series lens tubes. Refer to the Specs (Reflective) and Specs (Absorptive) tabs above for detailed information about the filters included with each kit. Thorlabs' Reflective and Absorptive Neutral Density (ND) Filter Kits offer our most popular filters prepackaged in convenient metal storage boxes. Labeled Inserts Hold Filters Securely in Storage Box.Mounted Versions are Housed in Labeled SM Threaded Lens Tubes.10 Filters Included with Optical Densities from 0.1 - 4.0 (12 Filters from 0.1 - 5.0 for the NEK02).Ø1/2", Ø25 mm, Ø2", or 2" x 2" Absorptive ND Filters Available.Ø1" Mounted Reflective (Metallic) ND Filters Available.It uses 6mm aluminium tube for the radials, 4mm brass tube for the driven element and is built around an N-Type chassis socket mounted to a 40x40mm aluminium square, held together with rivets.
The next two images show one I built for the 70cm band. I use one at home on 70MHz, click here to see construction details and more images. They are very forgiving due to the low impedance feed. I have made quite a few of these antennas over the years with good results. (42° is the theoretical perfect angle for 50Ω feed, but who’s measuring!) For VHF and below, as the elements get bigger, some more structured design is needed.Ī quarter wave monopole mounted against a perfect ground will have an impedance of around 36Ω but by bending the radials down at an angle of 45°, we increase this to around 50Ω whilst at the same time lowering the radiation angle more towards the horizon. These antennas can easily be built for UHF or above by using a chassis mount N-Type (or SO-239) connector, some solid wire and solder. You could cut a little on the large side and trim the antenna for best match at your desired frequency if you have the equipment. The velocity factor is set to 95% which should be fine for most people. This is a true unbalanced antenna, with a feed impedance of around 50Ω and therefore a great match to 50Ω unbalanced feedline.
There are usually four radials, three being a minimum, but you could use up to six. The radiating element is a quarter wave (λ/4) and the radials are 12% longer. Ahh, the good old quarter wave ground plane! This calculator can be used to design a Quarter Wave Ground Plane antenna, with radials.
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