Different Elements in Receive Chain. Dish Parabola Feed LNBC RF Cable Divider Receiver

Transcription

1 Art of Dish Tuning

2 Indian Curry Little bit of Technical & More of Practical Layman Dialogue Mainly aimed for Grass-root level Dish Tuning Not a Conventional Kind of Lecture. More of Interactive Kind of Session. Please add to the information wherever anybody Can. Lets Have a Question Session First

3 Different Elements in Receive Chain Dish Parabola Feed LNBC RF Cable Divider Receiver

4 Most Important Elements of Receive Chain Dish Parabola (Its Pointing) Feed & its various Nuances Motorized Dish Set-Up is a must for Proper Alignment & upkeep Polarization should also be motorized Dish should have good Azimuth & Elevation Markers

5 Dish Parabola Bulls Eye-Hit -12 db Elevation Plan For hitting the unique peak knowledge about approximate levels to be received is important

6 Dish Parabola Down link C/N o = EIRP + G/T C/N = C/No -10Log(BW if ) Signal Level = for 19 dbw Beacon Received on SA 19 dbw 196dB 48dBW EIRP Space Loss + Gain of Antenna + 60 db 10 db 8dB Gain of LNBC Cable Loss Divider 1-2 db loss Connector loss = -59 dbm

7 Most Important & Most Neglected Element of Receive Chain Feed Its polarisation Its positioning (position & verticality) Feed reflector mismatch (Beamwidth) Feed reflector mismatch (VSWR) Use standard good feeds, Chaparral etc.

8 Feed Polarisation Linear Polarisation a) Horizontal b) Vertical Circular Polarisation a) LHCP b) RHCP Feed Polarisation should Match with Received Signal Polarisation

9 Feed Focal Point Location f = D 2 16x f Calculated focal point D Diameter of Dish x depth of dish parabola

10 Feed Focal Point Location focal point D f d

11 Feed Typical example for 6.3 m ECIL Dish Dia of Dish D Depth of Dish x = 633 cm = 97 cm Through Calculation Focal point of dish f = 258 cm f/d = 0.408

12 Feed Dish & Feed f/d (Beam-width) Most dishes have f/d between 0.27 & 0.45 Calculated f/d for our ECIL dish is The f/d of your dish & feed should match for maximizing the received signal Over illumination or Under illumination deteriorate the G/T of the dish Mismatching the f/d between the dish & feed can cause losses of 2 db or more

13 Feed f/d (Beam-width) Sliding Direction Scalar Ring x Feed-Horn

14 Feed f/d (Beam-width) f/d x (mm) f/d x (inch)

15 Feed Dish & Feed Mismatch (VSWR) VSWR of Feedhorn Effective increase in LNBC temp. ( K)

16 Feed Figure of Merit (VSWR) (50 K) (25 K) / 0.98 T K = T(antenna + feed) + T(LNBC)/G(feed) System Noise + Temp. T(receiver)/{G(LNBC) + G(feed)} = 75.5 K (14.06 db K) Now for 25 K increase in temp. of LNBC due to mismatch = 101 K (20.04 db K)

17 Instruments-Gadgets Spectrum Analyser 4:1 divider with dc pass Small Rf cables with f-type, N-type Connectors Adaptors Spirit level Plumbline For the first time only Measuring Tape Azimuth Elevation Meter

18 Aligning Your Dish for Alignment Take your dish to total vertical position i.e., looking towards sky. Use spirit level to position Measure the diameter of the dish at least from two directions at right angles Check the diameter at two three positions Measure the depth of the dish parabola Calculate the exact theoretical focal point

19 Aligning Your Dish for Alignment Check the centering of your feed through plumb-line & spirit level You can also use other rough methods if you don t have spirit levels or plumb-line or you want to check when your dish is inclined. Adjust the feed so that it is at the focal point

20 Measurement Set-up Spectrum Analyser 1:4 divider with dc pass Analog Satellite R cvr V A A/V Mon DC Pass

21 Seeking your Satellite Basic Requirement Must know the beacon frequency of your satellite Its better to know the EIRP & typical received C/N at a particular place with a particular sized dish to see whether it matches with your results Polarisation of beacon & your feed should be known Polarisation of actual signal to be received & your feed should be the same Should know the Azimuth & Elevation required for your satellite

22 Seeking your Satellite Establish the setup for measurement/alignment Connect satellite receiver, spectrum analyser through power divider. Have a picture mon. for satellite confirmation Point the dish in the direction of the satellite Use Azimuth-Elevation meter or other reference View whole transponder on the SA Align your dish to start getting different Carriers on SA

23 Seeking your Satellite Maximizing Set your SA to view Beacon frequency with total span less than 5 MHz First ensure that you are on main lobe About 12 db down peaks should be received on either side in azimuth & elevation Maximize the beacon by alternate Azimuth- Elevation alignment & then Pol. adjustment Put the SA in dual active & max Hold mode Further maximize the beacon signal

24 Seeking your Satellite Fine Tuning Now reduce the span per division to about 15 KHz RBW to about 300 KHz or around VBW to 100 Hz or less Put the SA in dual active & max Hold mode Now further maximize the beacon signal Also adjust polarisation to get maximum signal

25 Seeking your Satellite Measurement Set RBW to 10 KHz VBW to 10 Hz or 30 Hz (for best averaging) Now measure the relative C/N Add 40 db to get the received C/N o Match with the expected C/N o If results Match Bingo You have hit the Bulls Eye

26 Final Touch Store the setting of spectrum analyser, for fine adjustment by anyone at a touch of a button. With Site-Master take Distance to Fault Signature of the cable (50 ohms), to notice any cable-connector related problems Seal the connector at LNBC end. Forget Your Input Signal Worries

27 Alignment with Waveform Meter Coarse Alignment by Picture monitor View a blank line in the vertical mode Put the waveform meter in 5 mode Tune the Dish to minimize the noise Now detune the satellite receiver by 1 MHz Again tune the dish Further detune the satellite receiver by 1 MHz Again tune the dish Repeat the above steps to get maximum alignment

28 Tit Bit Advices Check Whether Your Receive system is 50 Ω or 75 Ω RF Cable used is preferably RG 11 for 75 Ω systems. Connectors are properly connected Most Neglected. Have your best technician to make the cables. Properly tie the RF cables at LNBC & IRD ends so as not to stress the LNBC & IRD mounted connectors and also use proper gauge GI wire for cable support. The cable used should not be rolled or have any deformities, that will result in generation of noise Preferably use N type connector. For F-type connectors use fixed central conductor type connector. Wherever commercial IRD is used, check the audio impedance. Generally it is K Ω unbalanced. Match it to 600 Ω balanced, using transformer or some ckt.

29 Tit Bit Advices Make Back Plate for Commercial IRDs, using standard N- Type, BNC & XLR Connectors.You can use S-Band R cvr Back-plate Touch up the receive dish at-least once in two months. You can store the setup for various dishes in the spectrum Analyser & then anybody can do the alignment. Use divider to distribute the signal of the dishes If dish is motorised then it is okay, otherwise walkie talkie or remote handset telephone can serve the purpose.

30 Frequency (MHz) Cable Losses RG Attenuation (20 )] in db/100m Drop Cable RG RG Trunk Cable HR-540 Series 7.12

31 Beacons Beacon Frequency (MHz) EIRP (dbw) Pol. INSAT 3C Cir. INSAT 2E Cir IS PAS Hor. Thaicom Ver.

32 Look Angles Sat. Long. Long: Lat: Az El Rajasthan Ajmer C E IS PAS Thai Barmer C E IS PAS Thai

33 Look Angles Thai PAS IS E C Jaipur Thai PAS IS E C Bundi Pol.off El Az Lat: Long: Sat. Long.

34 Look Angles Thai PAS IS E C Jodhpur Thai PAS IS E C Jaiselmer Pol.off El Az Lat: Long: Sat. Long.

35 Look Angles Sat. Long. Long: Lat: Az El Pol.off Uttar Pradesh Agra C E IS PAS Thai Allahabad C E IS PAS Thai

36 Look Angles Thai PAS IS E C Bareilly Thai PAS IS E C Banda Pol.off El Az Lat: Long: Sat. Long.

37 Look Angles Thai PAS IS E C Kanpur Thai PAS IS E C Gorakhpur Pol.off El Az Lat: Long: Sat. Long.

38 Look Angles Thai PAS IS E C Lucknow Thai PAS IS E C Lakhimpur Pol.off El Az Lat: Long: Sat. Long.

39 Look Angles Thai PAS IS E C Mussourie Thai PAS IS E C Mau Pol.off El Az Lat: Long: Sat. Long.

40 Look Angles Thai PAS IS E C Delhi Thai PAS IS E C Varanasi Pol.off El Az Lat: Long: Sat. Long.

41 Log Calculations db Tips

42 Log Calculations ± 3 db db Tips multiplying/dividing power by 2 ± 6 db multiplying/dividing power by 2 2 = 4 i.e., every increase of 3 db multiply by 2 ± 10 db multiplying/dividing by 10 ± 20 db multiplying/dividing by = 100 i.e., every increase of 10 db multiply by 10 0 dbm means 1 milli-watt 0 dbw means 1 Watt dbw = 30 dbm (as 1 Watt = mW)

43 Log Calculations db tips ± 1 db multiply/divide by ~1.26 ± 2 db multiply/divide by ~1.58 ± 3 db multiply/divide by ~2 ± 4 db multiply/divide by ~2.51 ± 5 db multiply/divide by ~3.16 ± 7 db multiply/divide by ~5 ± 8 db multiply/divide by ~6.3 ± 10 db multiply/divide by 10

44 Power Levels db tips multiply/divide by 2 multiply/divide by 3 mul/div by 4 (2 2) multiply/divide by 5 mul/div by 6 (2 3) multiply/divide by 7 mul/div by 8 (2 2 2) mul/div by 9 (3 3) mul/div by 10 (2 5) ± 3 db ± 4.77 db ± (3+3 = 6) db ± 7dB ± ( = 7.77) db ± 8.45dB ± (3+3+3=9) db ± ( = 9.54) db ± (3+7 = 10) db

45 Log Calculations Examples 43 db = = db = = =500 or = = ~ 500