I modified my redundant Decca aerial because of poor reception - the results were marvellous. Berthed in Cherbourg last year able to get Radio 4, Solent, Clasic FM on the FM range as well as Radio 4 Long Wave.
...me too! I took my old Decca aerial off, then thought that it may be good for the radio, and immediately stuck it back on. Works great, looks the part.
It's forever getting into photos though. Here it is coming out of the balding head next to the white Navtext aerial...
I made a dixplexer may years ago to use a 1W 2m (144mHz) amateur radio tx/Rc using the car whip antenna. The only effect was slight reduction in signal strength to he AM band of the car radio when transmitting otherwise it was perfect.
I recall that the design used two tuned circuits to block out the 2m transmission from the wrong Rc and to match the Tx to the antenna.