Hi John,
yes South Herts DAB doesnt make it over to your side of Herts very well, though I was able to listen to it in the car well in Potters Bar and even on Cattlegate Road but once I had got to Crewes Hill it had gone.
You should be able to hear London N on 9B well now, it the strongest DAB signal where I am in the Lea Valley near Herts/Essex/London border. I too can get Jackie on FM and all the DAB muxes that you get apart from South Herts and Kent.