8 GHz dual mode feed

thingiverse

Version 1.0 ! This is a low noise dual mode used feed for 8 GHz weather satellite reception. Theoretically, best f/D is ~0.4 when lowest NF LNA are used, but max efficiency is at f/D~=0.6 so it might be suitable for offset dishes as well. The 3D print consists of the base, the waveguide and the dual mode section which are connected with screws. Two waveguide sections have been included: one for linear polarization and another one for both RHCP and LHCP polarizations on separate SMA connectors. This work has been based on the W2IMU/N2UO 23cm design found here: http://ok1dfc.com/EME/technic/septum/N2UO%20opt.pdf. After printing, it has to be painted with a conductive paint and then electroplated in a bath. It is absolutely important the resulting surface to be as smooth as possible. Roughness will result in losses so patience when sanding/smoothing will pay off ! I used PLA and smoothed it with sandpaper starting from grit 500 up to 2000. Conductive paint and plating solution used were bought from https://www.tifoo.de/ Painting has to be carefully done paying attention not to leave any blank areas. If ABS/ASA are used I guess the smoothing process can be expedited in acetone vapors or the like. The final efficiency of the feed depends on surface roughness and the presence of any non-plated gaps. Notes: 1) You could try scaling it in the slicer to make e.g a feed for 10 GHz! 2) For 8 GHz SMA probe length inside the waveguide is 7mm . The dimensions of the block where the SMA sits had been adapted so that no tuning is necessary when these connectors from Kuhne are used or the equivalent Amphenol 132147 e.g from Mouser leaving just 7 mm inside the waveguide. These connectors are about 17.8mm long and the Teflon section is about 15mm. 3) The Teflon section in the waveguide needs to be cutoff. 4) The Teflon section in the SMA block can be painted and plated to avoid having to rely on the plating inside the hole. 5) The SMA connector itself can even be soldered onto the plated feed !!! Obviously, it is not as robust as on a feed of metal but should be good enough for fixing it once with an SMA torque wrench. Don’t push it too much though