Exhibit B JOINT FILING AGREEMENT The undersigned hereby agree that the Statement on Schedule 13G with respect to the Common Stock of Numerex Corp. and any further amendments thereto executed by each and any of us shall be filed on behalf of each of us...

Exhibit B

                             JOINT FILING AGREEMENT

     The undersigned hereby agree that the Statement on Schedule 13G with
respect to the Common Stock of Numerex Corp. and any further amendments thereto
executed by each and any of us shall be filed on behalf of each of us pursuant
to and in accordance with the provisions of Rule 13d-1(k)(1) under the
Securities Exchange Act of 1934, as amended.

     This Agreement may be executed in separate counterparts, each of which
shall be deemed an original, but all of which shall constitute one and the same
instrument.

Dated: February 27, 2009

                                            POTOMAC CAPITAL MANAGEMENT LLC

                                            By:   /s/ Xxxx X. Xxxxx
                                                  ------------------------------
                                                  Xxxx X. Xxxxx, Managing Member

                                            POTOMAC CAPITAL MANAGEMENT INC.

                                            By:   /s/ Xxxx X. Xxxxx
                                                  ------------------------------
                                                  Xxxx Xxxxx, President

                                            XXXX X. XXXXX

                                            By:   /s/ Xxxx X. Xxxxx
                                                  ------------------------------
                                                  Xxxx X. Xxxxx