70cm and 2m antenna colocated issues?

[KG4GUF]

Hello all, I'm trying to expand my antenna system with a 70cm antenna. I already have a 2m 1/4 wave ground plane antenna bolted to the side of my desk. At one time, I had built a 70cm wire jpole antenna, but mounting this 4 inches from the 2m antenna didn't seem like a great idea to me if I wanted to maintain some semblance of omnidirectionalness, but how much would that really affect it? If it isn't much, then that basically solves the problem. But if it'd significantly alter the radiation pattern, then I'd like to know some other options. Is there a compact antenna design that works well on both bands? Most of the designs I've seen are quite a bit taller than I'd like to use since the tip of my ground plane antenna is already about half an inch from the ceiling. Here's a picture of my current mount if it helps any, I'd place the 70cm J-Pole about in the middle of the other half of the plywood that the ground plane is attached to.

Thanks for any help!
73 Matt

[KB4QAA]

Where to start?

Placing two antennas 4 inches apart will affect performance on both. Bad idea. Rule of thumb; place antennas at least 1/2 wavelength apart on lowest frequency. In this case 1 meter apart.

If you want a dual band antenna build or buy one. If you are using two radios, with one on each band, or a radio with a seperate port for each antenna, be aware that transmitting on 2m may desense the 440 receiver. This is a common issue for satellite ops. Typical solution is to use a filter or isolator.