Calibrate WX Radar

Discussion in 'Avionics and Upgrades' started by Sluggo63, Jul 24, 2021.

  1. Sluggo63

    Sluggo63 Pattern Altitude

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    Do/can avionics shops (or regular mix shops for that matter) check the tilt calibration on weather radars? I have a Sperry/Primus-200 unit that functions, but it seems that I need to have the tilt way too far up to not paint ground returns. I know and have used the tilt formula up high in the FLs to position the beam on other radars, but it doesn't seem to be working down low where I'm flying in the Seneca.

    TIA
     
    Last edited: Jul 24, 2021
  2. Jim Carpenter

    Jim Carpenter Pre-takeoff checklist

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    Not trying to be snarky, but, does it matter? It's all relative, 5-up, 5-down, whatever, unless you somehow don't have full range. (Kind of like the old "This one goes to eleven.")
     
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  3. Sluggo63

    Sluggo63 Pattern Altitude

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    I understand. I don't know if I have full range. To get what I think is an acceptable tilt, I have it +10, which seems high. Granted, all my other radar experience has me in the FLs where the tilt is -1. I figured it would be higher down low, but I didn't think it would be that much higher. I just ordered James Barr's book, Airborne Weather Radar: A User's Guide, and I'll go through that first. Next time I"m over some flat land I'll try to get a good look at where I get ground clutter and work the equation from that.
     
  4. Arnold

    Arnold Cleared for Takeoff

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    When I flew the Shorts that amount of tilt would have gotten my attention, except on the ground. May be wroth a look. Are the manuals still available?
     
  5. Jim Carpenter

    Jim Carpenter Pre-takeoff checklist

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    Looks like you could get the manual from Essco:
    RCA - Primus - Honeywell - Sperry Primus 200 Color Radar 1979 System D — Essco Aircraft
    It does sound like maybe out of whack somehow. Assuming you have a 10" antenna (normal for small twins), with a level aircraft, you'd want center of the beam to be (roughly) zero, with the cone of the beam maybe 5 deg above and 5 below. If you paint ground on the screen at nautical miles equal to height in 1000s AGL, that should be bottom of beam down 10 deg., meaning center would be 5 deg. down from zero. So, yeah, let's say at 5000 AGL, you have to tilt up according to your knob scale, 10 degrees to get a ground paint at 5nm, that does seem a bit far out of adjustment. (I'm guessing here, didn't stay at a holiday inn,, don't play one on tv, etc.)
     
  6. Rockymountain

    Rockymountain Pre-takeoff checklist

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    I suspect given the age and size of that radar that what you are looking at is an actual beam width far wider than the theoretical beam width. The scatter and side lobes are likely reflecting back. While perhaps not worthless, I would suspect the radar is very very suboptimal by todays standards. The small aircraft radars continue to get more powerful with tighter measured beam widths. The new solid state, flat plate Garmin 70, 75 and 80’s are impressive. Not sure I would waste any money on the legacy stuff. If you have the room and money to upgrade, especially if you fly in an environment where you depend on radar.
     
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  7. Sluggo63

    Sluggo63 Pattern Altitude

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    That's a very good point. I'm probably used to a much more "robust" radar and need to recalibrate my expectations as to what this one will provide for me.
     
  8. martym

    martym Pre-takeoff checklist

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    Yes. The antenna may need to be shimmed. It needs to be fairly accurate to properly evaluate wx echos. Best time to do it is when the plane is up on jacks so it can be easily leveled.
     
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  9. martym

    martym Pre-takeoff checklist

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    Well, I could have saved you $9.95 or whatever they charge for that book now. I'm sure he meant well but that book is pretty light on technical information. You will learn a bunch more useless acronyms which serve no purpose.
     
  10. ROBERT DAVISON

    ROBERT DAVISON Filing Flight Plan

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    Sounds like the issue is likely an antenna mounting issue as mentioned by a previous poster, the radar unit is likely mounted so that it is pointed slightly nose low in level flight attitude. Try shimming and see if it helps your tilt angle issue.
     
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  11. Sluggo63

    Sluggo63 Pattern Altitude

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    I wish I only paid $9.95. Now I'd be embarrassed to tell you what I actually paid... :mad:

    YGTBFKM ;)
     
  12. Sluggo63

    Sluggo63 Pattern Altitude

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    Thanks, guys. The plane is going in for annual next month. I'll have the shop look at that.