That would have been Sporadic E ("E skip") which is not related to Sunspot numbers or solar flux. In fact, I always found a slight inverse relationship - Es tends to be better in Sunspot minimum years.

When you say 45 degrees, is the ladder line angled down towards one end of the G5RV - kind of passing underneath the antenna wire? That would not be ideal, but not the end of the world. If it's angled at 45 degrees but still 90 degrees from each wire, then it's absolutely fine. I hope you see what I mean - describing stuff in three dimensions is not easy ;-)

73, Paul G4IJE.

Thanks for all the good ideas guys. I'll let you know how I get on.

73, Paul G4IJE.

Many thanks for the information. All very helpful indeed. It seems I need to buy a few more 61 cores - I have just two at the moment. It looks like designing a balun that will cover 7 to 50MHz with decent performance is not trivial.

Thanks again for your very detailed response.

73, Paul G4IJE.

I guess a current balun would be preferable. I don't have any other cores but I would be willing to invest in some. The 100 watts would be mostly SSB but I do like a bit of SSTV which I run at about 70 watts or so with 100% duty cycle for up to 2 minutes.

Any further assistance would be greatly appreciated.

Thanks and 73, Paul G4IJE.

Many thanks for that Steve - way beyond the call of duty :-)

Any suggestions where to go with this idea? The antenna looked excellent for the few minutes before I fried the Hari balun and I would really like to get it working properly.

I have just built an OCF dipole (AKA "Windom") and I need a 4:1 balun that covers 7 to 50MHz. I briefly used a Hari 4:1 balun (made in Germany) but I managed to fry it with 100 watts on 6 metres. After putting up the antenna this afternoon, I did a quick SWR check on the four bands it covers and was delighted to find everything exactly as per the EZNEC prediction. I found some Sporadic E on 6 metres and worked HA8EK on the first call. Great! It works! Unfortunately that quick exchange of 5/9 fried the poor balun (to be fair, it was only specified to work up to 30MHz), so now I need to build a better one.

I have some FT140-61 ferrite cores which I'd like to try. Searching the internet reveals many similar designs based on bifilar windings around a toroid. There seems to be some debate above whether it's worth reversing the winding. Also most designs are for 3.5 to 30MHz. Is it worth using a few less turns for a design intended for 7 to 50MHz? What wire gauge would be appropriate for 100 watts? Reverse the winding halfway or not bother? I plan to check the "match" by using a 200 ohm load and measuring SWR but some suggestions for a starting point (wire gauge, number of turns etc) would be appreciated.

73, Paul G4IJE.

I've just ordered a couple of FT-140-61 toroids to play with. Lots of balun designs out there in internet-land, but does anyone have a tried-and-trusted design that covers 7 to 50MHz?

OK, that's pointed me in the right direction, although that particular model is too big, heavy and expensive for my purposes. I'll look for ferrite-based solutions rather than powdered iron.

Thanks.

I'm thinking of building an OCF dipole (Windom) that should work on 7, 14, 28 and 50MHz. Any suggestions for a suitable 4:1 balun? Most designs based on T200-2 toroids seem to be for HF use. What happens if that type of balun is pushed to 50MHz? Does it become lossy? Power levels will be 100 watts max.

You could check for losses with a power/swr meter and a dummy load but from your description they will probably work fine for jumpers etc at moderate power levels on HF.

Thanks - that is similar to what I have in mind.

I am planning to build a trapped dipole for 20 and 40 metres using coax traps made with RG58/U cable. It would be helpful to know what wire lengths to use as a starting point, to reduce the cut-and-try experiments to a minimum. I know the LC ratio of the traps (L=1.425uH, C=87.8pf) so can I use that to get a ball-park figure for the outer (40m) wire lengths?

The "58" would suggest that it is similar to RG58/U - or at least that's what the manufacturer is trying to imply. What's the OD? Is it tinned or copper braid? Stranded inner? What does the dielectric look like? How does the braid density compare to genuine RG58/U? Strip some back and compare it with photos of RG58/U. Some cheaper copies of coaxial cable use less braid than the genuine part and are a bit more lossy, but may be perfectly usable for modest runs at HF.

Is it the same on all bands? It might a filter issue. And you've definitely measured something nearer 100 watts in the past, using the same meter, cables, dummy load etc, that you are using now?