Core RC, Code Radio issue

[Tobamory]

Just some advice needed. bought the 69.99 code radio and receiver but had issues since I moved outdoors, with reception, ive tried 2 receivers, and rebinding etc, works ok close to me, ive even installed a new aerial but if I get to the other side of the track its intermittent and I get twitchy controls. aprox 20m

I got the the 2nd race with a diff receiver from my 2wd and it worked as I popped it on the grid but not when I was on the stand. 5m

I gave up. im thinking faulty radio, but wondered if anybody had any ideas if this was common for this radio, or any settings I could look at, batteries say strong.

I think im going to buy a spectrum anyway and have the shop take a look at this one,
thanks