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                                                                   EXHIBIT 10.21

                          THIRD AMENDED LOAN AGREEMENT

     WHEREAS, on the 25th day of October, 2000, STILLWATER NATIONAL BANK AND
TRUST COMPANY OF STILLWATER, OKLAHOMA (hereinafter referred to as the "Bank")
and WESTWOOD CORPORATION, a Nevada Corporation (hereinafter referred to as
"Westwood"), TANO CORP., a Louisiana Corporation (hereinafter referred to as
"TANO"), NMP CORP., an Oklahoma Corporation (hereinafter referred to as "NMP"),
and MC II ELECTRIC COMPANY, a Texas Corporation (hereinafter referred to as
"MCII"), (collectively Westwood, Tano, NMP and MCII are hereinafter referred to
as "Debtor") entered into a Loan Agreement (hereinafter referred to as the "Loan
Agreement"), wherein the Bank agreed to enter into a revolving loan agreement
whereby the Bank would loan to the Company up to TWO MILLION EIGHT HUNDRED
THOUSAND and NO/100 DOLLARS ($2,800,000.00) for the purpose of financing the
Company's ongoing operations, which agreement was evidenced by a Renewal and
Amended Revolving Promissory Note of even date therewith ("Note"); and

     WHEREAS, on June 25, 2001, Bank and Debtor entered into an Amended Loan
Agreement whereby the parties amended the Loan Agreement by, among other things,
extending the Maturity Date and increasing the rate of interest contained in the
Note and;

     WHEREAS, on December 19, 2001, Bank and Debtor entered into a Second
Amended Loan Agreement whereby the parties amended the Loan Agreement by, among
other things, extending the Maturity Date and increasing the line of credit
available to the Debtor to THREE MILLION EIGHT HUNDRED THOUSAND and NO/100
DOLLARS ($3,800,000.00) and;

     WHEREAS, the parties wish to make further adjustments to the lending
arrangements between the parties, including increasing the line of credit
available to the Debtor to FOUR MILLION FIVE HUNDRED THOUSAND and NO/100 DOLLARS
($4,500,000.00).

     NOW, THEREFORE, in consideration of the mutual promises herein contained,
the parties hereby agree to amend the Loan Agreement in the following respects:

     1.    Paragraphs 1.1, 1.1 (a) and 1.1 (b) of the Loan Agreement are amended
to read as follows:

           1.1    Subject to the terms and conditions of this Agreement, Debtor
           shall have the right from time to time, prior to the "Termination
           Date" (defined below), to borrow and, upon repayment, reborrow from
           the Bank amounts not at any one time in the aggregate principal
           balance exceeding the lesser of: (i) the Borrowing Base determined as
           of the date of borrowing; or (ii) Four Million Five Hundred Thousand
           and No/100 Dollars ($4,500,000.00) (hereinafter referred to as
           "Revolving Loan"). For these purposes:

                  (a)  "Termination Date" means July 15, 2002.

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               (b)   "Borrowing Base" means, as of any given date, the sum of
               the following factors: (1) seventy-five percent (75%), or at the
               Bank's sole discretion any lesser percentage designated upon
               forty-five (45) days notice, of Eligible Trade Accounts
               Receivable of TANO, MC II and NMP; plus (2) fifty percent (50%)
               of the value of the inventory of TANO, MCII, and NMP, not to
               exceed Two Million Four Hundred Thousand and No/100 Dollars
               ($2,400,000.00).

     2.    Paragraph 1.2 of the Loan Agreement shall be amended to reflect that
the "Renewal Note" which is defined in that paragraph refers to the Third
Amended and Restated Revolving Promissory Note between the parties dated of even
date hereof in the original principal amount of Four Million Five Hundred
Thousand and No/100 Dollars ($4,500,000.00).

     3.    This Loan Agreement shall be further amended to provide that upon the
execution of this Third Amended Loan Agreement, and as a condition precedent
thereto, the Debtor shall pay to the Bank a Loan Fee of One Thousand and No/100
Dollars ($1,000.00).

     4.    Except as may be amended herein, the terms and conditions of the Loan
Agreement remain in full force and effect.

     IN WITNESS WHEREOF, this Agreement is executed this 15th day of March,
2002.

                                  "BANK"
                                  STILLWATER NATIONAL BANK AND TRUST
                                  COMPANY, STILLWATER, OKLAHOMA


                                  By:   /s/ Joe E. Staires
                                     ----------------------------------------
                                     Joe E. Staires, Senior Vice President


                                  "COMPANY"
                                  Westwood Corporation, a Nevada corporation


                                  By:   /s/ Ernest H. McKee
                                     ----------------------------------------
                                     Ernest H. McKee, President

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                                     TANO Corp., a Louisiana corporation



                                     By:   /s/ Guy Hardwick
                                        ---------------------------------------
                                        Guy Hardwick, President



                                     NMP Corp., an Oklahoma corporation



                                     By:   /s/ Ernest H. McKee
                                        ---------------------------------------
                                        Ernest H. McKee, President



                                     MC II Electric Company, a Texas corporation



                                     By:   /s/ Ernest H. McKee
                                        ---------------------------------------
                                        Ernest H. McKee, President

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