Just finished a long planned project to fix a feedhorn to an IBU single. Here is a comparison to an Opticum twin which according to my observations has a similar performance to the standard IBU. The reading were made 45 minutes apart so maybe the conditions had changed because I didn't see much difference using the metre up on the roof. Maybe the IBU pumps out more signal along the 20 m cable to the receiver where I made the readings.
16:22 (Opticum)
10714,H,21996,56,1 ;-70 dBm, 6.0 dB
10773,H,21997,56,1 ;-67 dBm, 4.7 dB
10803,H,21997,56,1 ;-67 dBm, 4.7 dB
10832,H,21996,56,1 ;-67 dBm, 4.7 dB
10921,H,21997,56,1 ;-64 dBm, 4.7 dB
10964,H,21996,56,1 ;-61 dBm, 7.7 dB
10994,H,21996,56,1 ;-63 dBm, 7.7 dB
11023,H,22996,23,2 ;-63 dBm, 6.9 dB
11053,H,21996,56,1 ;-67 dBm, 7.7 dB
11068,V,22996,23,2 ;-70 dBm, 4.7 dB
10729,V,22000,56,1 ;-70 dBm, 6.0 dB
10788,V,21997,56,1 ;-70 dBm, 6.0 dB
10818,V,21997,56,1 ;-69 dBm, 6.0 dB
10877,V,21996,56,1 ;-68 dBm, 4.7 dB
10906,V,21996,56,1 ;-68 dBm, 6.0 dB
11097,V,22996,23,2 ;-73 dBm, 4.7 dB
11127,V,21996,56,1 ;-76 dBm, 6.9 dB
17.05 (IBU)
10714,H,21996,56,1 ;-65 dBm, 6.0 dB
10773,H,21997,56,1 ;-63 dBm, 6.0 dB
10802,H,21997,56,1 ;-63 dBm, 6.0 dB
10832,H,21996,56,1 ;-62 dBm, 6.0 dB
10891,H,21996,56,1 ;-59 dBm, 6.0 dB
10920,H,21996,56,1 ;-59 dBm, 4.7 dB
10964,H,21996,56,1 ;-59 dBm, 7.7 dB
10993,H,21997,56,1 ;-59 dBm, 8.4 dB
11023,H,22996,23,2 ;-61 dBm, 7.7 dB
11052,H,21996,56,1 ;-64 dBm, 7.7 dB
10728,V,22000,56,1 ;-63 dBm, 6.0 dB
10787,V,21997,56,1 ;-63 dBm, 6.9 dB
10817,V,21997,56,1 ;-62 dBm, 6.0 dB
10876,V,21997,56,1 ;-60 dBm, 6.0 dB
10905,V,21997,56,1 ;-60 dBm, 6.0 dB
11067,V,22996,23,2 ;-64 dBm, 4.7 dB
11096,V,22996,23,2 ;-65 dBm, 6.0 dB
11126,V,21996,56,1 ;-69 dBm, 6.9 dB
The attached pix show the construction process and the final result in place. Next time round it will be easier - you learn from your mistakes after all. I'm not sure how crucial the length of the tube going down to the sensor from the feedhorn is - you don't have much control over that. I have installed a bit of aluminium pipe to make sure the diametre is constant the whole length. (Thanks to Steve for the tips on how to do this.)
The smaller dish is pointed at Intelsat 907 which I installed due to frustration with the low signal on 2E/F and to make sure I could watch the footy in HD (actually I'm not that bothered about that but I don't like it when scheduled recordings don't work).