Sorry to hear of your HF SSB difficulties. There’s been loads of good advice on this thread! I don’t have an FT-817/818 but I do use a uBitx transceiver, which is similarly low powered and even more basic. I’ve used a simple link dipole (actually it started out as a single band 40m dipole, then I made ~10m extensions to bring it to resonance on 80m. So now it’s a 2 band link dipole. ) and as long as I put out a spot or two I’ve always managed to qualify my summits (so far, thanks to the dedicated chasers).This is in Aus though - might be different in the UK.
I think that’s how it works, but I’d say it should work fine at least on 40m, as even if the coil of wire is lossy, on 40m there won’t be much coiled up.
But the main reason for this post is to agree with the previous posts that the antenna SWR may well be the problem. It sounds like a bit of experimenting with the antenna and SWR meters (external and built in) may be a good idea. As has been mentioned, a basic analyzer would be a help.
Obviously, I don’t know what your meter at home is, but
(A) if it’s not a cross needle type meter, is it calibrated properly?
(B) are you reading the right scale? Sounds obvious, but it’s not sometimes and
(C) they’re not always accurate.
I have an MFJ tuner with a built in cross-needle meter and if I set up the tuner to read 1:1 SWR on the built-in meter, the SWR at the rig is often around 3:1… I’ve found this with different antenna, feed lines, and so on, and have confirmed the accuracy of the rig’s meter several times with my analyzer. I probably could recalibrate it but it doesn’t worry me too much.
But if the SWR is up, the rig will not only cut back the power to protect it’s finals, but there’ll be reduced power transfer to the antenna as well. I’ve seen this quite dramatically with my uBitx - it’s got no SWR protection, so it will try to output full power in to any load, until the smoke comes out, anyway… but I’ve had reports of my signal dropping fairly dramatically when the antenna is mismatched.
Just a few thoughts - which probably doesn’t add much to the previous posts…