how pass textbox server control value by anchor tag querystring

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ASP.NET4

<script language ="javascript">

function getPnr()
{
var txtval = document.getElementById('TextBox1').value;
document.getElementById('a1').href="/KB/answers/default.aspx"?param1=" + txtval ;
}

</script>

And anchor tag ...........

<a class="menu-root " id="ancher"   önclick='getPnr()' href ="#" rel="lyteframe" rev="width: 500px; height:200px; "
                            style="font-family: arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;  overflow:hidden; ">
                              GO</a>

But in aspx page querystring not find the value which is passed by textbox.
Please correct my code