A 6m Feed-point Choke Using RG8 Mini
Whilst testing various chokes with the VNA, you find yourself destroying quite a few meters of coax in the process. It’s like wind it ‘long’ and then trim back until you find the sweet spot. As you can see below, the graveyard for this length of RG8 Mini came when originally creating a 10m choke using the same piece of RG8 Mini.
After trimming back the original coax, I found a couple of good solutions that would work well for 6m aficionados. The former used was 68mm PVC ‘FloPlast’ drainpipe which is commonly used here in the UK and very inexpensive. Outlets such as Wickes and B&Q currently stock it.
I ended up winding 7 turns of RG8 Mini around a small section of the FloPlast pipe. The nice thing about this coax is that it’s very flexible but will withstand much more power than standard RG58. I’ve tested it at 1kw without any issues.
As you can see from the above image [click it for hi-res PDF], at 6m the choking impedance is between 7000 and 8000 ohms – so very useful. When testing I actually found higher choking impedances using a fibreglass former of 2 inches – but then fibreglass is more expensive and not everyone would potentially have any lying around in their workshops.
For those interested, when using a 2 inch fibreglass former [2.5mm wall] the amount of turns changed to ‘9’ [using the same coax length] and achieved a choking impedance in the region of 10,000 ohms. You can’t really go wrong [and it’s QRO handling of course].
Cheap and easy. Makes a great choke for the 6m band.
