AMERICAN EUROCOPTER AS350-B1 HAD AN NMAC WITH ANOTHER HELI.

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I WAS FLYING THE ABOVE DESCRIBED HELI. I HAD BEEN MAINTAINING L-HAND ORBITS OVER THIS SAME LOCATION FOR OVER 20 MINS. I WAS TUNED TO LAX HELI FREQ 119.8 AND WAS TALKING TO SAME HAVING BEEN CLRED INTO CLASS B WITH LAX. I ALSO WAS MONITORING 123.02 (LOS ANGELES HELI'S ADVISORY FREQ) GIVING POS RPTS. WHILE OVER SAID LOC; I HEARD HELI 1 AND HELI 2 (COMMERCIAL HELIS) REQUEST TO TRANSITION NBOUND 110 FREEWAY (CLASS B) WITH LAX. LAX TWR CLRED BOTH AND ALSO ASKED ME IF I HAD VISUAL. I ADVISED 'AFFIRMATIVE; WILL KEEP VISUAL SEPARATION.' AT THIS TIME I ACTIVATED MY LNDG LIGHT AND TAXI LIGHT (ALREADY HAVING A LOWER AND UPPER STROBE ON AND HAVING ON MY ANTI- COLLISION LIGHT AND POS LIGHTS ON). APPROX 2-3 MINS LATER; I HEARD A THIRD HELI; HELI 3; ADVISE HE WAS 'EBOUND TO 10 FREEWAY AT LABREA' (APPROX 4 MI FROM MY LOCATION). HELI 1 AND HELI 2 WERE FLYING IN THE VICINITY OF LOS ANGELES CIVIC CENTER (CLOSE TO MY LOCATION) AND I THEREFORE KEPT MY LNDG AND TAXI LIGHTS ON FOR ADDITIONAL VISIBILITY AND GAVE A POS RPT ON 123.02. WHILE CONTINUING L-HAND ORBITS AND ON A HDG OF APPROX 270 DEGS; I OBSERVED AN ACFT EBOUND 10 FREEWAY AT APPROX 930 FT MSL. THIS ACFT WAS APPROX 30 FT ABOVE (VERT); 0 FT (HORIZ) AND APPROX 150 FT AHEAD AND CLOSING. AT THIS TIME I IMMEDIATELY REDUCED COLLECTIVE PITCH AND BANKED L (LARGER ANGLE) TO AVOID A MIDAIR COLLISION. AT THIS TIME I TURNED BACK NBOUND AND OBSERVED THE ACFT TO BE A HELI AND BELIEVED IT TO BE HELI 3. I THEN INQUIRED ON 123.02 IF HELI 3 HAD OBSERVED ME OR HEARD MY POS RPTS. HELI 3 ADVISED THAT HE HAD TO MAKE AN EVASIVE MANEUVER AND DID NOT SEE ME UNTIL JUST PRIOR. HELI 3 ALSO ADVISED ME THAT HE DID NOT HEAR MY POS RPTS. I FILED AN NMAC RPT WITH HAWTHORNE FSS AND ALSO NOTIFIED LAX TWR SHIFT SUPVR OF THE ABOVE INCIDENT. SUGGESTION: OUR HELIS HAVE TO BE AT LOWER ALTS IN ORDER TO BE ABLE TO PERFORM THEIR MISSION. COMMERCIAL HELIS DO NOT. I SUGGEST THAT THESE OPERATORS BE ENCOURAGED IF NOT MANDATED TO FLY AT HIGHER ALTS IN METROPOLITAN AREAS SUCH AS LOS ANGELES.