Calibrating weather radar
 

I have always wondered how a weather radar is calibrated.Is it done on the aircraft or on a test bench and should it be re calibrated if the radome is changed?

From a Line Engineering point of view, arrives pre-calibrated from workshop, just slam the various bits in and function test.
Radome exactly the same just hang it on and function. Most problems with a dome are only detectable at range in the air.

How are they calibrated before they leave the manufacturer then,and how do you build into the calibration process a 20 year old radome that has probably been repainted four or five times?

Radomes are stripped and inspected before repainting. Scheduled maintenance includes using a test meter to check for moisture ingress. Moisture is plotted and for minor defects, the contaminated area repaired before repainting and return to service. In the event of major repairs, radomes are sent out to specialist centres that can perform attenuation testing after the repairs are completed.

Radar equipment is calibrated on the bench in accordance with the overhaul manual, prior to certification and return to service.

The Weather Radar equipment, like all other equipment installed in a commercial transport aeroplane, is built to a standard (TSO or Technical Standard Order) and certified to meet those specific measurable standards. Whether it is brand new from the manufacturer, or returning to service after repair or overhaul, all equipment is tested against the certified design standard prior to release to service.

(The above comments apply to commercial air transport operations under an AOC, that must comply with an Approved Maintenance Programme. I can't speak directly for General Aviation, but their requirements are similar.)

Blacksheep, how eloquent, you obviously do not have my terse engineering prose !
I wrote a tale about visiting a fleet of 1-11s in Nigeria all of whose Wx Radars were "weak returns" and were all radomes eroded and full of moisture. I recommended replacement but on they flew until the "C" checks in the UK when they were grounded.
Drunk I forgot to send it.

Surely not!!
 

WHAT?!!! Nigerians bending the rules?!! Surely not!!:ok:

Bending is not my word of choice, ignoring would be.

ANTENNA
 

Blacksheep, you are right.
But if you are working in a company, with different type
of aircraft , with the same type of radar installed,
you jack it up to 0-level and adjust antenna
stabilization. According the AMM.

Most of the stabilisation set-ups with which I'm familiar (Boeings & Fokker)are done against Vertical Gyro or IRS reference attitude with no need to jack the aircraft to zero/zero. The topic though, is more about receiver sensitivity and the possibility of variations or attenuation of the returns due to differences between radomes.

Yes
 

Yes, the thread is about radomes.
But the first question was about "adjustment"
Yes, the vertical gyro gives attitude reference to the antenna.
0-Flight attitude is different between a bell-212 +
Fokker 50 .
The gyro does not know, where its installed.
That explains the antenna-adjustment.
Its not interesting, to see, how the weather is in "outer space"!

Part of my job when I worked at Hatfield was the testing of Radomes for signal attenuation. most repaired radomes actually had less signal loss as a rule than new ones.

When I was referring to calibrating of the radar in my original post I meant calibrating the radar image and gain on board the aircraft.The radar in my aircraft is stabilized by the IRS.

Radar Calibration
 

The automatic gain and image are calibrated on a bench in a repair shop or repair station using special test equipment. If you mean some field adjustments (e g manual gain control, contrast etc.) then this information can be found in a flight manual.

The first question was about calibration, which in electronic equipment generally refers to adjustments of scale, gain or sensitivity.
The antenna is stabilised to operate in the true local horizontal plane and operates to that datum regardless of aircraft attitude. Working from that datum, the antenna may be tilted manually (both above and below the horizontal plane) by the pilot, in order to examine the weather ahead and within the scanning arc of the antenna. When tilted up, the weather radar would indeed be examining "outer space" as you put it, but in doing so will detect any weather between the aircraft and the rest of the cosmos.

Adjustment of antenna stabilisation comes under what airflorida1 correctly describes as "field adjustments".