I have had very good success using wideband transformers, as Brian suggests.
If you use the configuration shown in Figure 2 here: you can get good results out to several hundred MHz. I use something like this in series with the CATV box to minimize the hum from the power leakage on the CATV feed. In that case, it's a 75 Ohm application and it was pretty flat to 1 GHz. Using a balun at the input and another at the output helped. The transformers shown in the attachment worked pretty well, with one "turned sideways" to use as a conventional flux coupled transformer.
Clarke
