Member - Roachie replied:

Mate, I've never had any problems with one interfering with the other. Don't currently have an AM. However, until I move my HF antenna down the rear end, it was right beside the UHF on the bullbar and the phone antenna is only about 2 feet away too.
They are all doing different jobs (ie: different frequencies) so shouldn't be any problem......somebody with more expertise might think differently.
Just my experience.

Bonz (Vic) replied:

I asked this qn ages ago as I wanted to put both AM and UHF antennas beside each other on the LHS of the bullbar. I was told that they do degrade each other in the plane where one antenna interferes with the other, and in the end I put the AM on the RHS with a dock smith bonnet bracket, solved the worries

Rick Blaine replied:

I have done some practical work with antennaie of late and found that it was well worth the effort to mount it on my roof... performance is UNBELIEVABLE...e.i. Canberra/ Yass/ Bredbo. They both need an "independant" ground plane if they are to work at their peak, the am car radio wont worry because its recieve only and the UHF will recieve without any worries but UHF transmition will be degraded by having another antenna in its ground plane. Speaking of UHF arn't there some morons on channel 7. I used to fit radios to the spooks cars and did we have problems with covert antennas... some times 200 metres was all they were good for...hmmmm a long time ago in an era best forgotten...