Another daft aerial question

[Paul]

The only daft question is the one that's not asked!

Yes you can, and yes you'll have to SWR it.
The plate, the bigger the better but ideally no less than 1.5m square. It should be 2.5 meters but that's all your roof space gone in one hit.

Having said that, you could mount it on a biscuit tin. It's going to be better to buy (I hate that word) a hole mounted aerial base. Drill the biscuit tin and mount it in the middle Solder onto each corner the thickest wire you can get and run it out in a star fashion from the biscuit tin edges each "leg" a minimum of 2.5 metres. That way the long wires become part of the aerial (aka radials).

I'm guessing you'll extend the coax with a long patch lead into a room.
Always use proper uhf connectors and as this aerial will be a "tad twitchy" to SWR, the extension cable should be in multiples of 3 metres.

For peace of mind, fit a TVI filter in the line.

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Don't mount it too close to your cold water tank or electrical wiring.