<PAGE>

                                                                   Exhibit 10.21

                           BRIDGE LOAN PROMISSORY NOTE

$3,000,000                                                      January 24, 2003

     FOR VALUE RECEIVED, AIRNET COMMUNICATIONS CORPORATION, a Delaware
corporation (hereinafter called the "Borrower"), hereby promises to pay, on May
24, 2003, or on such other date as the parties may mutually determine (the
"Maturity Date"), to the order of TECORE, INC. (hereinafter called the
"Lender"), at the Lender's principal address at 7165 Columbia Gateway Drive,
Columbia, Maryland 21046, the principal sum of Three Million Thousand Dollars
($3,000,000) or so much thereof as shall have been borrowed by Borrower during
the 120-day period following the date of this Note as set forth on Schedule A
attached hereto and made a part hereof, in lawful money of the United States of
America and in immediately available funds, together with interest thereon from
the date hereof, at a rate equal to Two Percent (2%) plus the "Prime Rate"
(defined below) in effect from time to time. The "Prime Rate" shall be the
"Prime Rate" quoted in the "Money Rates" section of The Wall Street Journal from
time to time. Interest on the unpaid principal amount of this Note shall be due
on the Maturity Date.

     This Note is subject to the terms of a Bridge Loan Agreement (the "Bridge
Loan Agreement") of even date herewith by and among the Borrower, SCP Private
Equity Partners II, L.P. ("SCP") and TECORE, Inc. ("Tecore"). This Note is
secured by collateral pledged by the Borrower to SCP and Tecore pursuant to a
Security Agreement of even date herewith by and among, the Borrower, SCP and
Tecore (the "Security Agreement"). All capitalized and undefined terms herein
shall have the meaning given them in the Bridge Loan Agreement or the Security
Agreement.

     Upon the occurrence of an Event of Default under the Bridge Loan Agreement
or the Security Agreement, the entire principal amount outstanding hereunder and
all accrued interest hereon, together with all other sums due hereunder, shall,
as provided in the Bridge Loan Agreement, become immediately due and payable.

     This Note is secured by and is entitled to the benefits of the Security
Agreement. In addition to the rights and remedies given it by this Note and the
Security Agreement, the Lender shall have all those rights and remedies allowed
by applicable laws, including without limitation, the Uniform Commercial Code.
The rights and remedies of the Lender are cumulative and recourse to one or more
right or remedy shall not constitute a waiver of the others. The Borrower shall
be liable for all commercially reasonable costs, expenses and attorneys' fees
incurred by the Lender in connection with the collection of the indebtedness
evidenced by the Note.

     To the extent permitted by applicable law, the Borrower waives all rights
and benefits of any statute of limitations, moratorium, reinstatement,
marshalling, forbearance, valuation, stay, extension, redemption, appraisement
and exemption now provided or which may hereafter by provided by law, both as to
itself and as to all of its properties, real and personal, against the
enforcement and collection of the indebtedness evidenced hereby.

<PAGE>

     All notices, requests, demands, and other communications with respect
hereto shall be in writing and shall be delivered by hand, sent prepaid by a
nationally-recognized overnight courier service or sent by the United States
mail, certified, postage prepaid, return receipt requested, at the addresses
designated in the Bridge Loan Agreement or such other address as the parties may
designate to each other in writing.

     This Note or any provision hereof may be waived, changed, modified or
discharged only by agreement in writing signed by the Borrower and the Lender.
The Borrower may not assign or transfer its obligation hereunder without the
prior written consent of the Lender.

     The term "the Borrower" shall include each person and entity now or
hereafter liable hereunder, whether as maker, successor, assignee or endorsee,
each of whom shall be jointly, severally and primarily liable for all of the
obligations set forth herein.

     If any provision of this Note shall for any reason be held invalid or
unenforceable, such invalidity or unenforceability shall not affect any other
provision of this Note, but this Note shall be construed as if this Note had
never contained the invalid or unenforceable provision.

     This Note shall be governed by and construed in accordance with the
domestic laws of the State of Delaware, without giving effect to any choice of
law provision or rule. Any controversy or dispute arising out of or relating to
this Note shall be settled solely and exclusively in accordance with the
provisions of the Bridge Loan Agreement and the Security Agreement, dated as of
even date herewith, which provisions are incorporated by reference herein as
though fully set forth.

     IN WITNESS WHEREOF, the undersigned Borrower has caused the due execution
of this Bridge Loan Promissory Note as of the day and year first herein above
written.

ATTEST:                             AIRNET COMMUNICATIONS CORPORATION



/s/ Stuart P. Dawley                By: /s/ Glenn A. Ehley   (SEAL)
--------------------                    ---------------------
                                        Glenn A. Ehley
                                        President and Chief Executive Officer

<PAGE>

                                   SCHEDULE A

     This schedule sets forth the principal amount borrowed by Borrower from the
Lender, up to the maximum amount set forth on the face of this Note.

<TABLE>
<CAPTION>
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                 Date                  Principal Amount             Signature of Authorized
                                                                      Officer of Borrower
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<S>                             <C>                                 <C>
January 24, 2003                $800,000
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</TABLE>