VA3TO PORTABLE MICROWAVE EME

1.8m Portable Microwave EME Project
ala OK1DFC ( pictured above)
Work In Progress.

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Elevation Pendulum | Azimuth Pulleys

6cm Feed Probes | 6cm Feed Septum | 6cm Feed Completed

9cm PA Input | 9cm PA Output

After succeeding at 2m and 23cm EME I wanted to try it on the higher microwave bands so I decided to focus on the 6cm and 9cm bands to start.

Dish:
My neighborhood is filled with mature trees and my backyard does not have much visible moon time from any single spot so I chose to build a portable dish that I can move around to avoid trees or bring to other operating locations. I just happened to have a new in the box 1.8m solid prime focus dish that I acquired a few years ago that's identical to the one OK1DFC uses so I studied his portable tripod arrangement and approxmated the design using photos on the web. I drew up the triangular plates for the main structure and round dish support plates in AutoCad and had a local company cut them using a waterjet system.

Tracking:
A RazTrack tracking system designed by Gary N8CQ will be used. It's a great little standalone touchscreen system based on the Raspberry Pi. It can work with a variety of sensors including US Digital A2 encoders or less expensive MAB25/MAB28 absolute encoders along with Gary's MAB/MPU boards to simulate the "SEI" serial bus protocol.
The Elevation sensor was constructed based on this paper by JH1KRC Gravity Detector . It uses a weighted pendulum riding on ball bearings with an MAB28 absolute encoder mechanically coupled to it.
For the Azimuth I designed a pair of pulleys in Solidworks and had them 3d printed in plastic. The cogged teeth of the pulleys were designed to use a standard and readily available GT2 belt, so it will never slip. One pulley slips over the 2" mast (driven by an Alpha Spid rotator) and is held into position with a pair of set screws. The other pulley fits onto the position encoder, secured with a single set screw. Both pulleys are the same diameter for 1:1 position sensing. The sensor pulley will be mounted to the middle plate on the main structure.

Feedhorns:
I acquired a 9cm septum feedhorn but thought I would try my hand at building one for 6cm. After a bit of research I chose to build a Septum feed according to SM6FHZ and SM6PGP's document A Novel 5 Step Septum Feed Suite . I followed the design precisely and cut and filed 3 different stepped septums before I was satisfied with one. The milling maching that I have access to was not capable of radiusing the brass connector saddles so I had them done by a local machine shop. Once I had all the pieces I carefully soldered it all up using the gas stove in the kitchen. Skip, VE6BGT happened to be in the process of testing some microwave feedhorns that he had built. He had a signal generator and network analyzer and went through the trouble of making up a test jig. He kindly offered to check mine for me so I boxed it up and sent it to him. With some minor adjustment of the probes he was able to attain a Return Loss of -29 dB with isolation of 21 dB. Pretty darned good !

Power Amplifiers:
I bought a couple of 9cm Toshiba UM2683B amplifiers and I decided to combine them for some decent EME power. These amplifiers are rated for 25W but capable of producing 65~70w each with a modification seen in this document by DL7YC 40 More Watts at 3400 MHz . I used a standard passive Minicircuits splitter on the input and I ordered a Hybrid Ring Coupler from HamDesign for the output. I measured and cut the input and output semi-rigid lines to be equal lengths but I put an SMA line adjuster on one input line to allow me to fine tune any small imbalance in phase. Each amplifier is mounted to a thick base finned aluminum heasink and the whole assembly is held together using sheet aluminum. The PA assembly has a fan on each end (push/pull) to keep the Class A amplifiers cool. I have a DB6NT/Kuhne 100w 6cm power amplifier so I'm all set for TX power on both bands.

This project is presently on hold.

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