I know I probably need to build a Moxon antenna for SOTA activations on 6m but these are not the easiest things to make so as an interim I thought I would make up a Slim Jim antenna for 6m.
Built to these dimensions the SWR was around 1.7:1 so I shortened it in stages, eventually ending up with an overall length of 4155mm and a VSWR of about 1.3:1. I didn’t try altering the feed point locations but I suspect you might be able to get it lower if you did.
Using a NanoVNA I was very surprised to see how narrow the band is over which it will work.
I aimed to tune it as close to the FT8 frequency of 50.313MHz as I could get.
Slung from a 6m fishing pole it is probably a bit close to the ground so I did some tests with the pole sticking out of the skylight from the top of my house. The results were encouraging. I managed a few actual QSOs on 6m and amazingly PSK Reporter showed my signal was picked up from the Cape Verde Islands which at just over 4,000 km I think must be a double skip - which isn’t bad for 10W.
What it doesn’t seem to work on is CW. I could hear no signals and the RBN network didn’t report any activity from me.
I just need to try it out from the top of a SOTA summit next. Being vertical it probably won’t be heard by many in the UK but it seems to work when given a boost by ES.
It would appear to be fine to me… it covers the CW, SSB and FT8 frequencies at a perfectly acceptable SWR. It needs to be much higher than on a ground mounted 6m mast however. Otherwise it will be a cloud warmer. It will still work but not as well as when well clear of the ground.
You may find mileage in making an endfed 1/2wave dipole (aka Flowerpot) and a 1/4wave ground plane and comparing the 3 of them. You should be able to make a 1/4wave GP for 12m and change the top section for a shorter radiator for 10m and again for 6m. That would give you three antennas for the Summer SpE bands. As we move over the coming years into better F2 propagation they’ll serve you well though as we get to when 12/10 and 6 are seriously open, your Moxon will be worth having.
Thank you and yes, a bit more tinkering required. A 1/4 wave ground plane sounds interesting.
I tried a 30m centre-fed dipole which at 5 half wavelengths was supposed to be suitable for 6m but I couldn’t get any joy out of it.
I may be being unfair about CW, there wasn’t a lot of activity on 6m CW on RBN and I suspect the stations close to me and likely to be in range had horizontal antenna.
A classic 1/4wave GP has a 1/4wave vertical radiator and 3 1/4wave radials sloping down at 45degrees. Do the maths to get the actual wavelength but 24.91MHz is sort of the middle of 12m band and a 1/4wave there is 3.008m. It will be different in practice as the insulation and end-effects will alter the length. 4 lengths of 3m wire, radiator to centre, radials to screen of coax to radio. A 12m 1/4wave fits perfectly on a 5m pole. In my case, the 3 radials end in small Bulldog clips and they clip to each mast support guy rope. The radiator is attached to the top. Do some Pythagoras and trig to work out how to get 45degs with your pole and guys. Measure and snip to get a match you can live with.
Now take a 1/4wave for 10m. 28.3MHz is mid way between CW and SSB and 1/4wave is 2.625m. Cut a new radiator and leaving radials in place, trim for best match. Swap between radiators for 12/10m operation. You could put a link in to alter the length but in my case, getting to the link is the same effort as swapping the top. Repeat for 6m.
By the time you’re at 6m the Moxon will be better as it is steerable. But 6 pieces of wire, the longest being 3m to give 3 bands is a bargain to me.
That’s sounds interesting. I could perhaps build it around a PL259 socket which would take a banana plug for the different radiators. I also seem to recall the radials only need to be at least a 1/4 wavelength and can be longer so one built for 12m would do shorter wavelengths - must check on that!
Last year I bought an MFJ 6m J-Pole to pair with my Yaesu VX-7r and used it to make some contacts in the VHF contest and on summits. When I put it on an analyzer, I found it was resonant way above the 6m FM range, so I moved the feedpoint down and got it sorted out. Next time out, there was an opening and I made a contact some 300 miles away while activating a summit.
But, that thing was way too bulky, so I homebrewed a 6m EFHW. So far, I’ve only made a few contacts (one about 60 miles away, the other in the 30s), both on summits. I can’t say it works better or worse than the j-pole, but it’s much more compact, about the same size as the HT with the radiator wrapped around the transformer.
It is quite bulky but rolled up can be strapped on the outside of a rucksack - but an antenna made from wire will always be much more compact and this may be the way to go.
Yup, that’s an option too. I built my EFHW because I sometimes take a radio on activities that preclude a pack with the antenna strapped to the outside (running, biking, etc).
My approach to 6m /P is rather rough and ready - I have a 2m dipole where the elements can be swiveled together for packing, so I got two lengths of stiff wire with alligator clips to clip to the ends of the dipole to bring it to resonance on 6m, I’ve had good results with this during several Es openings but haven’t encountered one on a summit yet!
This is the base zoomed. If you look at the pole from the bottom up, there is a black spring clip used to hold the feeder to the mast and stop it blowing in the wind. Next there is a piece of brown plastic which is the guying collar slipped over the pole and stopping at the bottom section approx 1m up. You can see 3 green Nylon cords coming out which attach to tent pegs. If you keep looking up you come to the three radials made from grey wire. Each is angled down at about 45deg. They join together at a crocodile clip. The other ends terminate in a pink bulldog clip stolen from my wife’s pen and paper drawer! These just clip to the guy cords. At the top of the picture you can see a BNC plug with green strain grommet on the end of about 3m of RG58. This connects to a BNC socket. The crocodile clip connects to the socket flange for the radials. There is a Lucar connector to the centre pin. The radiator has the other Lucar spade and it runs ups to the top of the pole.
Here is a zoom on the connector. You can see (just!) the three grey radials coming together ending at the clip connecting to the outer, the green strain relief grommet and the silver of the BNC flange socket and the white 1/4wave radiator running up the pole. The RG58 feeder drops down by the pole. A yellow elastic cord toggle holds the joint between the radiator, radials and coax snug against the pole.
The advantage of all this is the antenna can be deployed in moments. Hang the radiator over the pole, attach feeder, clip in place, attach radials croc clip, stretch radials out to each guy and clip. Unroll feeder to operating position. Job done… work DX
Andy, very helpful, thank you. Does the clip carrying the radials just clip to an exposed bit of braid near the top connector? I was thinking of attaching them permanently but it will be much easier to deploy and put away if they were easily detached and then rolled up seperately.
There’s a bit of old RG58 screen that was soldered to the flange, about 5cms I think. It’s flexible so it wont snap or fatigue off and the clip goes to it. Neither the bulldog clips or crocodile clip are super strong so if you pull too hard on any wire then the clips come undone saving you snapping anything.
I’ve always had antennas dismantle into several pieces so they are easier to deploy and pack away without long lengths getting tangled.
