AngularJS ham radio required

I have the following HTML, I need to select radio select. Not sure how to do this in AngularJS.

<div class="form-group">
    <label class="control-label pull-left"><small>Type of M (<i>check one</i>):</small></label>
    <div class="col-md-5 pull-left">
        <label class="radio-inline pull-left">
            <input type="radio" name="radio" ng-model="m.pr.MType" value="PrRep"> PrRep
        </label>
        <label class="radio-inline pull-left">
            <input type="radio" name="radio" ng-model="m.pr.MType" value="LProd"> LProd
        </label>
    </div>
    <div class="input-group col-md-3">
        <div class="input-group-sm">
            <label><small>Prod LNum</small></label>
            <input type="text" class="form-control" id="provProdLNum" ng-model="m.pr.prodLNum" ng-required="m.pr.MType != 'PrRep'" />
        </div>
    </div>
</div>

      

        
        
        
      

    

I've tried this:

<input type="radio" name="radio" ng-model="m.pr.MType" value="PrRep" required> PrRep
<input type="radio" name="radio" ng-model="m.pr.MType" value="LProd" required> LProd

      

        
        
        
      

    

and this:

<input type="radio" name="radio" ng-model="m.pr.MType" value="PrRep" ng-required="m.pr.MType != ''"> PrRep
<input type="radio" name="radio" ng-model="m.pr.MType" value="LProd" ng-required="m.pr.MType != ''"> LProd

      

        
        
        
      

    

Not sure which is the correct one to use here ...