How to output just raw json from my Joomla controller for Ajax requests?

I want to create a Joomla json response for an Ajax request. So, I followed the instructions here: JSON Responses with JResponseJson

I implement the following code in my controller:

use \Joomla\CMS\Response\JsonResponse; class RamControllerAjax extends JControllerLegacy { public function capitals() { try { $country = JFactory::getApplication()->input->get('country'); if ($country == 'UK') $capital = 'London'; elseif ($country == 'Spain') $capital = 'Madrid'; else $capital = "I don't know"; $capital_json = json_encode($capital); echo new JsonResponse($capital_json); } catch(Exception $e) { echo new JsonResponse($e); } } } 

When I call it with the URL: http://joomla_clasificados/index.php?option=com_ram&task=ajax.capitals&country=UK

I receive the correct json response:

{"success":true,"message":null,"messages":null,"data":"\"London\""} 

But inserted in the middle of a normal Joomla page. Like this:

What I want is the json response alone. I tried some changes in the URL, like:

http://joomla_clasificados/index.php?option=com_ram&task=ajax.capitals&country=UK&format=json

that gives me the error:

Invalid controller: name='ajax', format='json' 

Same thing with format=raw variant.

What I am doing wrong ? How could I get only the json response?