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G3RUH 60cm dish and patch feed



Graham Shirville wrote:

I put up one of RUH's wok dishes and patchfeeds on my tower to replace the old X9 2 metre antenna that was there.
With a DB6NT preamp I can hear the noise floor of the transponder and lots of earth noise. Unless you want to hear the noise floor at very high squint angles there is no purpose in making it bigger.

Wayne replies:

THANK YOU very much for the first report of quality transponder reception using the G3RUH 60cm dish and patch feed.  I was hoping that a 60 cm dish would be satisfactory when used with an optimized feed and a low-noise preamp.  I sure haven't heard the noise floor with my 2x3 foot TranSystem BBQ dish and modified AIDC converter.

The prevailing wisdom on amsat-bb seems to be that the lowest-cost solution for good AO40 transponder reception is to use a 3-foot or larger solid dish.  This neglects the fact that a 3-foot (or larger) dish requires a very robust mounting structure to withstand even moderate winds.  And that cheap lightweight rotors are not suitable for such a large wind load.  My situation may be somewhat unusual, but my existing satellite antenna array is on a rooftop tripod with lightweight az/el rotors.  Here are the two upgrade paths for me:

1. Buy a 3-foot (or larger) dish, more rugged rooftop structure, G-5500 rotors, and use my existing downconverter.  Total cost would be at least US$700.  Reception would be truly awesome if I also added a DEM preamp.

2. Buy the G3RUH 60cm dish, patch feed, and a DEM preamp.  Use my existing TranSystem downconverter, roof tripod, and lightweight az/el rotors.  Total cost will be about US$400.

I have just about convinced myself that I would be better off with a small-but-optimized setup rather than a larger less-optimized setup.  Any comments or suggestions?

A final couple of question for Graham Shirville:

1. Did you mount the patch feed as pictured on the G3RUH web site?  Or did you route the 3 support arms to the edge of the dish?  That should improve the performance by producing less "shadowing".

2. How far away was AO40 when you heard the transponder noise floor?

Wayne Estes W9AE


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