please help me with my jumping script

when trying to make the player jump i ran into a problems with two code not agreeing to work together, here they are:
moving:

public class Controller2 : MonoBehaviour
{

    public float speed;

    private Rigidbody rb;

    private void Start()
    {
        rb = GetComponent<Rigidbody>();
    }

    private void FixedUpdate()
    {
        float H = Input.GetAxis ("Horizontal");
        float V = Input.GetAxis ("Vertical");

        rb.velocity = new Vector3 (speed * H, 0, speed * V);

    }

}

jumping:

public class Jumping : MonoBehaviour
{

    public LayerMask GroundLayers;

    public float JumpForce;

    private Rigidbody rb;

    private SphereCollider col;

    void Start()
    {
        rb = GetComponent<Rigidbody>();
        col = GetComponent<SphereCollider>();
    }

    void FixedUpdate()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            rb.AddForce(Vector3.up * JumpForce, ForceMode.Impulse);
        }
    }
}

Thanks in advanced

ps. i am new to unity and coding

Have you tried to simply retrieve the y velocity?

rb.velocity = new Vector3 (speed * H, rb.velocity.y, speed * V);