It's a spoke. In this case, it's highly likely to be a Soviet era SA2 'Guideline' Surface to Air Missile search radar. It's frequency is very similar to that of airborne weather radar which is why it shows up so often over Eastern Europe and the Middle East.
And does it make them easy for the enemy to spot? Sure does! In a battle, lighting up someone like that is a sure fire way to get an anti-radiation missile like HARM or ALARM to heading your way. These home onto the transmissions. This would make you switch off the radar, or lose it. But switching off the radar may not help either. The British ALARM missile climbs to height and pops out a parachute if it loses the signal. When the radar fires up again, off it goes again!
And of course, being able to receive radar transmissions is a useful defencive aid. If you're in a transport aircraft for example, recieving transmissions from enemy radars is a good cue to be somewhere else!