Why factory-set radio frequencies helped interception

How did factory-set, non-adjustable radios affect signals intelligence and counter-signals intelligence?

They hindered counter-signals flexibility but made signals-intelligence collection easier.

Older radios whose tuning was fixed at the factory were difficult to adjust in service. That limitation hindered counter-signals-intelligence work, while the predictable frequencies benefited signals-intelligence collection. The same inflexibility that constrained the operator could simplify an interceptor's task.