Fig. 4 - Conversion Points
A. Use a dremel tool with a carbide bit that looks like an end mill, cylinder shaped. Carefully cut the waveguide hole out to the vias. Don't cut the vias off but nicking them won't hurt. Don't worry about saving the old PC board probe, you will attach a new one as the original is too short.
B. Cut a piece of brass 12 by 3 mm. solder it in place so it extends short of the center of the wave guide hole.
C. The parallel coupled filter must be modified. You could scratch the copper off and extend the trace with a piece of copper so there is no filter. I choose to build a new filter to gain a little advantage from adjacent transmission on the other end of the 10 gig band. Image is not a concern as the only signal there are the very weak from satellites. On the other hand, when you are ready for a long haul, the extra 3 db of LNA noise from the image is meaningful considering the price of x-band power devices for your transmitter.
Fig. 5 - Parallel Coupled Filter Modification
I used a couple of thin copper strips 2 by 10 mm to cover the ends of the original filter. Use bits of #28 to extend the feeds. This filter is matched at quarter waves and on centers so the feeds and elements have to form symmetry. If you plan on modifying the filter rather than bypassing it, you will need to take measurements as movements of less than a quarter of a millimeter have a powerful effect on the band pass. Black traces are the original and the blue is added material.
Fig. 6 - The Other Probe
For the other polarization, unsolder the probe and pass it through the component side of the board. Just resolder it back to the solder side of the board and it will be about the right length for ten gigs. This is the input point I used for the test setup while the probe is removed. I soldered a very close trimmed coax to the ground and this point. Because there is bias voltage for the first amp at this point you need a cap or dc block on the input line.
Fig. 6 - Case milling
First I cut the old waveguide and horn off as close to the case as possible with a sawsall. I then drilled the case with a 3/4 inch drill. The milling for the new wave guide was done by hand with a dremel tool. If you are unsure of yourself, you can take this to a machine shop and they will probably do it for the fun of it. I cut enough material to make a tight fit with the copper water pipe. You will need to solder a small piece of brass in the waveguide that duplicates the original to separate the polarizations for the receiver.
Fig. 6 - Waveguide attached
This is a good start for the first time out. I was able to get pretty close to the sensitivity of the original at 12 gigs. Because I maintained reception of both polarizations, I'll be able to experiment with multiple signals on the same path. Field tests are next. After I'm done with local test and if I put this receiver up permanently, I'll worry about weather proofing it. I also need to optimize a horn before then.