<PAGE>
 
                                                                     EXHIBIT 4.6

           FILED
    IN THE OFFICE OF THE
  SECRETARY OF STATE OF THE
      STATE OF NEVADA

        APR 23 1998
       NO. C3741-84
           --------
      /s/ Dean Heller
DEAN HELLER, SECRETARY OF STATE

                  CERTIFICATE OF DESIGNATION, NUMBER, POWERS,
                    PREFERENCES AND RELATIVE, PARTICIPATING
                  OPTIONAL, AND OTHER SPECIAL RIGHTS AND THE
                  QUALIFICATIONS, LIMITATIONS, RESTRICTIONS,
                  AND OTHER DISTINGUISHING CHARACTERISTICS OF
                           SERIES B PREFERRED STOCK

                                      OF

                       U.S. DIGITAL COMMUNICATIONS, INC.

     The undersigned President and Secretary of this Corporation hereby certify 
that Board of Directors of this Corporation, pursuant to the authority expressly
vested in it has adopted the following resolutions creating a Series B issue of 
Preferred Stock:

     RESOLVED, that three thousand (3,000) of the ten million authorized shares 
of Preferred Stock of the Corporation shall be designated Series B Preferred 
Stock (the "Series B Preferred Stock") and shall possess the rights and 
privileges set forth below:

          A.   Par Value, Stated Value, Accretion Rate, Purchase Price and 
               -----------------------------------------------------------
          Certificates.
          ------------

               1.   Each share of Series B Preferred Stock shall have a no par
               value of and a stated value (face amount) of One Thousand Dollars
               ($1,000.00) (the "Stated Value").

               2.   The Series B Preferred Stock shall be offered at a purchase 
               price of One Thousand Dollars ($1,000.00) per share.

               3.   Certificates representing the shares of Series B Preferred
               Stock purchased shall be issued by the Corporation to the
               purchasers immediately upon acceptance of the subscriptions to
               purchase such shares.

          B.   Dividends.
               ---------

               1.   The Series B Preferred Stock will bear no dividends, and the
               holders of the Series B Preferred Stock shall not be entitled to
               the receipt of dividends on the Series B Preferred Stock.
<PAGE>
 
          C.   Liquidation Preference.
               ----------------------

               1.   In the event of any liquidation, dissolution or winding-up
               of the Corporation, either voluntary or involuntary (a
               "Liquidation"), the holders of shares of the Series B Preferred
               Stock then issued and outstanding shall be entitled to be paid
               out of the assets of the Corporation available for distribution
               to its shareholders, whether from capital, surplus or earnings,
               before any payment shall be made to the holders of shares of the
               Common Stock or upon any other series of Preferred Stock of the
               Corporation with a liquidation preference subordinate to the
               liquidation preference of the Series A Preferred Stock, an amount
               per share equal to the sum of (i) the Stated Value and (ii) an
               amount equal to zero percent (0.00%) of the Stated Value
               multiplied by the fraction N/365, where N equals the number of
               days elapsed since full payment for the shares of Series B
               Preferred Stock was deposited with the escrow agent for the
               offering of the Series B Preferred Stock. If, upon any
               Liquidation of the Corporation, the assets of the Corporation
               available for distribution to its shareholders shall be
               insufficient to pay the holders of shares of the Series B
               Preferred Stock and the holders of any other series of Preferred
               Stock with a liquidation preference equal to the liquidation
               preference of the Series B Preferred Stock the full amounts to
               which they shall respectively be entitled, the holders of shares
               of the Series B Preferred Stock and the holders of any other
               series of Preferred Stock with liquidation preference equal to
               the liquidation preference of the Series B Preferred Stock shall
               receive all of the assets of the Corporation available for
               distribution and each such holder of shares of the Series B
               Preferred Stock and the holders of any other series of Preferred
               Stock with a liquidation preference equal to the liquidation
               preference of the Series B Preferred Stock shall share ratably in
               any distribution in accordance with the amounts due such
               shareholders. After payment shall have been made to the holders
               of shares of the Series B Preferred Stock of the full amount to
               which they shall be entitled, as aforesaid, the holders of shares
               of the Series B Preferred Stock shall be entitled to no further
               distributions thereon and the holders of shares of the Common
               Stock and of shares of any other series of stock of the
               Corporation shall be entitled to share, according to their
               respective rights and preferences, in all remaining assets of the
               Corporation available for distribution to its shareholders.

                                      -2-
<PAGE>
 
               2.   A merger or consolidation of the Corporation with or into
               any other corporation, or a sale, lease, exchange, or transfer of
               all or any part of the assets of the Corporation which shall not
               in fact result in the liquidation (in whole or in part) of the
               Corporation and the distribution of its assets to its
               shareholders shall not be deemed to be a voluntary or involuntary
               liquidation (in whole or in part), dissolution, or winding-up of
               the Corporation.

          D.   Conversion of Series B Preferred Stock.
               --------------------------------------

               The holders of Series B Preferred Stock shall have the following 
conversion rights:

               1.   Right to Convert.  Fifty percent (50%) of each share of
                    ----------------
               Series B Preferred Stock shall be convertible, on the effective
               date of registration and at the Conversion Prices set forth
               below, into fully paid and nonassessable shares of Common Stock
               and the remaining fifty percent (50%) of each share of Series B
               Preferred Stock shall be convertible on the forty-fifty (45th)
               day after the effective date of registration at the Conversion
               Prices set forth below (sometimes referred to herein as
               "Conversion Shares").

               2.   Mechanics of Conversion.  Each holder of Series B Preferred
                    -----------------------
               Stock who desires to convert the same into shares of Common Stock
               shall provide notice ("Conversion Notice") via telecopy
               (facsimile) to the Corporation. The original Conversion Notice
               and the certificate or certificates representing the Series B
               Preferred Stock for which conversion is elected, shall be
               delivered to the Corporation by international courier, duly
               endorsed. The date upon which a Conversion Notice is received by
               the Corporation shall be a "Notice Date."

     Upon receipt by the Corporation of a facsimile copy of a Conversion Notice,
the Corporation shall immediately send to the holder, via telecopy (facsimile), 
a confirmation of receipt of the Conversion notice which shall specify that the 
Conversion Notice has been received and the name and telephone number of a 
contact person at the Corporation whom the holder should contact regarding 
information related to the conversion. The Corporation shall use all reasonable 
efforts to issue and deliver within three (3) business days after the Notice 
Date, to such holder of Series B Preferred Stock at the address of the holder on
the stock books of the Corporation, a certificate or certificates for the number
of shares of Common Stock to which the holder shall be entitled as aforesaid; 
provided that the original shares of Series B Preferred Stock to be converted 
are received by the transfer agent or the Corporation within three (3)

                                      -3-
<PAGE>
 
Business days after the Notice Date and the person or persons entitled to 
receive the shares of Common Stock issuable upon such conversion shall be 
treated for all purposes as the record holder or holders of such shares of 
Common Stock on such date. If the original certificate(s) representing the 
shares of Series B Preferred Stock to be converted are not received by the 
transfer agent or the Corporation within three (3) business days after the
Notice Date, the Conversion Notice shall become null and void.

          3. Lost or Stolen Certificates. Upon receipt by the Corporation of 
             --------------------------- 
          evidence of the loss, destruction, theft or mutilation of any Series B
          Preferred Stock certificates (the "Certificates") and (in the case of
          loss, theft or destruction) of indemnity or security reasonably
          satisfactory to the Corporation, and upon surrender and cancellation
          of the Certificates, if mutilated, the Corporation shall execute and
          deliver new Series B Preferred Stock Certificates of like tenor and
          date. However, the Corporation shall not be obligated to re-issue such
          lost or stolen Series B Preferred Stock Certificates if the holder
          thereof contemporaneously requests the Corporation to convert such
          Series B Preferred Stock into Common Stock, in which event the
          Corporation shall be entitled to rely on an affidavit of loss,
          destruction or theft of the Series B Preferred Stock Certificate or,
          in the case of mutilation, tender of the mutilated certificate, and
          shall issue the Conversion Shares.

          4. Conversion Dates. The shares of Series B Preferred Stock shall
             ----------------
          become convertible into shares of Common Stock at any time commencing
                                  ------
          (i) the effective date of a registration statement covering the
          Conversion Shares and (ii) forty-five (45) days after the effective
          date of registration of the shares to be converted (referred to as a
          "Conversion Date").

          5. Conversion Formula/ Conversion Price. Each share of Series B
             ------------------------------------
          Preferred Stock shall be convertible into the number of shares of
          Common Stock in accordance with the following formula (the "Conversion
          Formula"):


          [(.00) x (N/365) x (1,000)] + 1.000
          -----------------------------------=
                  Conversion Price

where,

       N=  the number of days between (i) the date that, in connection with the 
         consummation of the initial purchase by holder of shares

                                      -4-
<PAGE>
 
               of Series B Preferred Stock from the Corporation, the escrow
               agent first had in its possession funds representing full payment
               for the shares of Series B Preferred Stock being converted, and
               (ii) the Notice Date.

          Conversion
          Price =        Discount Price or the Ceiling Price, whichever is less,
                         but in no event shall the Conversion Price be less than
                         the Floor Price.

          Discount
          Price =        25% of five (5)-day average Closing Bid Price for the
                         Corporation's Common Stock immediately before
                         Conversion Date.

          Ceiling
          Price =        100% of Closing Bid Price for the Corporation's Common 
                         Stock the date of Closing.

          Floor Price =  $.50 per share of the Corporation's Common Stock with
                         the agreement to adjust the floor should the
                         Corporation's Common Stock trade less than $.50 per
                         share for five (5) consecutive days prior to the
                         conversion dates herein. The adjusted floor shall then
                         be the lowest Closing Bid Price for the Corporation's
                         Common Stock during such five (5)-day period.

     For purposes hereof, the term "Closing Bid Price" shall mean the closing 
bid price for the Corporation's Common Stock on the NASD Electronic Bulletin 
Board, or if no longer traded thereon, the closing bid price on the principal 
national securities exchange on which the Common Stock is so traded. The holder 
shall be entitled to an additional discount privilege equal to one percent (1%) 
per month, or fraction of a month, from the time of closing until the Conversion
Date for any conversions thirty (30) days after the Conversion Date and one-half
percent (1/2%) per month or fraction of a month for any conversions thereafter 
("Additional Discount").

               6.   Automatic Conversion.  Each share of Series B Preferred
                    --------------------
               Stock outstanding on May 1, 2001 automatically shall be converted
               into Common Stock on such date in accordance with the Conversion
               Formula and the Conversion Price then in effect, and May 1, 2001
               shall be deemed to be the Notice Date with respect to such
               conversion.

                                    - 5 -                 
<PAGE>
 
     7.  No Fractional Shares. If any conversion of the Series B Preferred
         --------------------
         Stock would create a fractional share of Common Stock or a right to
         acquire a fractional share of Common Stock, such fractional share shall
         be disregarded and the number of shares of Common Stock issuable upon
         conversion, if the aggregate, shall be the next higher number of
         shares.

     8.  Reservation of Stock Issuable Upon Conversion. The Corporation shall at
         ---------------------------------------------
         all times reserve and keep available out of its authorized but unissued
         shares of Common Stock, solely for the purpose of effecting the
         conversion of the shares of the Series B Preferred Stock, such number
         of its shares of Common Stock as shall from time to time be sufficient
         to effect the conversion of all then outstanding shares of the Series B
         Preferred Stock; and if at any time the number of authorized but
         unissued shares of Common Stock shall not be sufficient to effect the
         conversion of all then outstanding shares of the Series B Preferred
         Stock, the Corporation will take such corporate action as may be
         necessary to increase its authorized but unissued shares of Common
         Stock to such number of shares as shall be sufficient for such purpose.
     
     9.  Adjustment to Conversion Price.
         ------------------------------

           (a) If, prior to the conversion of all shares of Series B Preferred
           Stock, the number of outstanding shares of Common Stock is increased
           by a stock split, stock dividend, or other similar event, the
           Conversion Price shall be proportionately reduced, or if the number
           of outstanding shares of Common Stock is decreased by a combination
           or reclassification of shares, or other similar event, the Conversion
           Price shall be proportionately increased.

           (b) If, prior to the conversion of all shares of Series B Preferred
           Stock, there shall be any merger, consolidation, exchange of shares,
           recapitalization, reorganization, or other similar event, as a result
           of which shares of Common Stock of the Corporation shall be changed
           into the same or a different number of shares of the same or another
           class or classes of stock or securities of the Corporation or another
           entity, then the holders of Series B Preferred Stock shall thereafter
           have the right to purchase and receive upon conversion of shares of
           Series B Preferred Stock, upon the basis and upon the terms and
           conditions specified herein and

                                   -6-     
<PAGE>
 
                    in lieu of the shares of Common Stock immediately
                    theretofore issuable upon conversion, such shares of stock
                    and/or securities as may be issued or payable with respect
                    to or in exchange for the number of shares of Common Stock
                    immediately theretofore purchasable and receivable upon the
                    conversion of shares of Series B Preferred Stock held by
                    such holders had such merger, consolidation, exchange of
                    shares, recapitalization or reorganization not taken place,
                    and in any such case appropriate provisions shall be made
                    with respect to the rights and interests of the holders of
                    the Series B Preferred Stock to the end that the provisions
                    hereof (including, without limitation, provisions for
                    adjustment of the Conversion Price and of the number of
                    shares issuable upon conversion of the Series B Preferred
                    Stock) shall thereafter be applicable, as nearly as may be
                    practicable in relation to any shares of stock or securities
                    thereafter deliverable upon the exercise hereof. The
                    Corporation shall not effect any transaction described in
                    this subsection unless the resulting successor or acquiring
                    entity (if not the Corporation) assumes by written
                    instrument the obligation to deliver to the holders of the
                    Series B Preferred Stock such shares of stock and/or
                    securities as, in accordance with the foregoing provisions,
                    the holders of the Series B Preferred Stock may be entitled
                    to purchase.

                    (c) If any adjustment under this subsection would create a
                    fractional share of Common Stock or a right to acquire a
                    fractional share of Common Stock, such fractional share
                    shall be disregarded and the number of shares of Common
                    Stock issuable upon conversion shall be the next higher
                    number of shares.

               10. Redemption Privilege. The Corporation shall have the right, 
                   --------------------
               in its sole discretion, to redeem in whole or in part any shares
               of Series B Preferred Stock submitted for conversion. The
               redemption price per share of Common Stock after conversion of
               the Series B Preferred Stock shall be calculated as 133% of the
               face value plus any accrued Additional Discount.

          E.   Voting. Except as otherwise provided below or by the General 
               ------
          Corporation Law of the State of Nevada, the holders of the Series B
          Preferred Stock shall have no voting power whatsoever, and no holder
          of Series B Preferred Stock shall vote or otherwise participate in any

                                      -7-
<PAGE>
 
            proceeding in which actions shall be taken by the Corporation
            or the shareholders thereof or be entitled to notification
            as to any meeting of the Board of Directors or the shareholders.

     Notwithstanding the above, Corporation shall provide holders of the Series
B Preferred Stock ("Holders") with notification of any meeting of the
shareholders regarding any major corporate events affecting the Corporation. In
the event of any taking by the Corporation of a record of its shareholders for
the purpose of determining shareholders who are entitled to receive payment of
any dividend or other distribution, any right to subscribe for, purchase or
otherwise acquire any share of any class or any other securities or property
(including by way of merger, consolidation or reorganization), or to receive any
other right, or for the purpose of determining shareholders who are entitled to
vote in connection with any proposed sale, lease or conveyance of all or
substantially all of the assets of the Corporation, or any proposed liquidation,
dissolution or winding up of the Corporation, the Corporation shall mail a
notice to the Holders, at least ten (10) days prior to the record date specified
therein, of the date on which any such record is to be taken for the purpose of
such dividend, distribution, right or other event, and a brief statement
regarding the amount and character of such dividend, distribution, right or
other event to the extent known at such time.

     To the extent that, under Nevada law, the vote of the Holders, voting
separately as a class, is required to authorize a given action of the
Corporation, the affirmative vote or consent of the Holders of at least a
majority of the shares of the Series B Preferred Stock represented at a duly
held meeting at which a quorum is present or by written consent of a majority of
the shares of Series B Preferred Stock (except as otherwise may be required
under Nevada law) shall constitute the approval of such action by the class. To
the extent that under Delaware law the Holders are entitled to vote on a matter
with holders of Common Stock, voting together as one (1) class, each share of
Series B Preferred Stock shall be entitled to a number of votes equal to the
number of shares of Common Stock into which it is then convertible using the
record date for the taking of such vote of stockholders as the date as of which
the Conversion Price is calculated. The Holders also shall be entitled to notice
of all shareholder meetings or written consents with respect to which they would
be entitled to vote, which notice would be provided pursuant to the
Corporation's by-laws and applicable statutes.

          F. Protective Provisions. So long as shares of Series B Preferred
             ---------------------
          Stock are outstanding, the Corporation shall not, without first
          obtaining the approval (by vote or written consent, as provided by
          law) of the Holders of at least seventy-five percent (75%) of the
          then outstanding shares of Series B Preferred Stock:
              
                                      -8-
<PAGE>
 
               (a) alter or change the rights, preferences or privileges of
               the Series B Preferred Stock so as to affect adversely the
               Series B Preferred Stock;

               (b) create any new class or series of stock or issue any
               capital stock senior to or having a preference over or parity
               with the Series B Preferred Stock with respect to dividends,
               payments upon Liquidation (as provided for in Section B of
               this Designation) or redemption, except for a class of stock
               approved by WS Marketing & Financial Services, Inc. d/b/a
               SMS Capital Services, or increase the number of authorized
               shares of Series B Preferred Stock or change the Stated
               Value thereof;

               (c) do any act or thing not authorized or contemplated by
               this Designation which would result in taxation of the
               holders of shares of the Series B Preferred Stock under 
               Section 305 of the Internal Revenue Code of 1986, as
               amended (or any comparable provision of the Internal
               Revenue Code as hereafter from time to time amended); or
               
               (d) enter into a merger in which the Corporation is not the
               surviving corporation; provided, however, that the
               provisions of this subparagraph (d) shall not be applicable to
               any such merger if the authorized capital stock of the
               surviving corporation immediately after such merger shall
               include only classes or series of stock for which no such
               consent or vote would have been required pursuant to this
               section if such class or series had been authorized by the
               Corporation immediately prior to such merger or which
               have the same rights, preferences and limitations and
               authorized amount a class or series of stock of the
               Corporation authorized (with such consent or vote of the
               Series B Preferred Stock) prior to such merger and
               continuing as an authorized class or series at the time
               thereof.

     G. Status of Converted Stock. In the event any shares of Series B
        -------------------------
     Preferred Stock shall be converted as contemplated by this Designation,
     the shares so converted shall be canceled, shall return to the status of
     authorized but unissued Preferred Stock of no designated class or series,
     and shall not be issuable by the Corporation as Series B Preferred Stock.

                                     -9-  
<PAGE>
 
               H. Taxes. All shares of Common Stock issued upon conversion of 
                  -----
               Series B Preferred Stock will be validly issued, fully paid and
               nonassessable. The Corporation shall pay any and all documentary
               stamp or similar issue or transfer taxes that may be payable in
               respect of any issue or delivery of shares of Common Stock on
               conversion of Series B Preferred Stock pursuant hereto. The
               Corporation shall not, however, be required to pay any tax which
               may be payable in respect of any transfer involved in the issue
               and delivery of shares of Common Stock in a name other than that
               in which the Series B Preferred Stock so converted were
               registered, and no such issue or delivery shall be made unless
               and until the person requesting such transfer has paid to the
               Corporation the amount of any such tax or has established to the
               satisfaction of the Corporation that such tax has been paid or
               that no such tax is payable. The Corporation shall adjust the
               amount of dividends paid or accrued so as to indemnify the
               holders of Preferred Stock against any withholding or similar tax
               in respect of such dividends.

          FURTHER RESOLVED, that the statements contained in the foregoing 
resolutions creating and designating the said Series B Preferred Stock and 
fixing the number, powers, preferences and relative, optional, participating, 
and other special rights and the qualifications, limitations, restrictions, and 
other distinguishing characteristics thereof shall, upon the effective date of 
said series, be deemed to be included in and be a part of the certificate of 
incorporation of the Corporation pursuant to the provisions the General 
Corporation Law of the State of Nevada.

Signed on April 21, 1998.
          --------

                                               /s/ Robert J. Wussler
                                               ---------------------------------
                                               ROBERT WUSSLER, President
                                               U.S. DIGITAL COMMUNICATIONS, INC.


                                               /s/ [ILLEGIBLE]
                                               ---------------------------------
                                               Assistant, Secretary
                                               ---------
                                               U.S. DIGITAL COMMUNICATIONS, INC.



                                     -10-
<PAGE>
 
STATE OF MARYLAND       )
                        )ss.
County of  Montgomery   )
           ----------

     On April 21, 1998, before me, the undersigned Notary Public, personally
              --
appeared ROBERT WUSSLER, known to me or satisfactorily proved to be the person 
whose name is subscribed to the foregoing instrument, and acknowledged that he 
executed the same in the capacity and for the purposes therein contained.

     In witness whereof, I have hereunto set my hand and official seal on the 
day and year first above written.


                                       /s/Patricia Dennis
                                       ------------------
                                       Notary Public

My Commission Expires:

        9/12/01
 ---------------------


                                     -11-
<PAGE>
 









                                                 ------------------------------
                                                        STATE OF NEVADA
                                                       Secretary of State

                                                 I hereby certify that this is a
                                                 true and complete copy of
                                                 the document as filed in this
                                                 office.

                                                           APR 24 '98

                                                         /s/Dean Heller 
                                                           DEAN HELLER
                                                       Secretary of State 
                                                 
                                                 By D. Farmer
                                                    ---------

                                                 ------------------------------

                                     -12-