G7FEK Limited Space Antenna

Given that I’ve now wound the balun that I wanted and it’s come up pretty well for a first attempt, I’ve finally started cutting the new antenna.

This one appealed to me for a couple of reasons.

  1. It’s small.
  2. It will do 80m, 40m, 30m, 17m, 15m and 12m without an antenna tuner if I cut it right.
  3. It will also do 20m if I add another semi-vertical wire that’s a quarter wavelength,

You can find out more about it here.

So today I

  • Cut the ladder line and the two horizontal sections.
  • Created a way of mounting it on the centre pole
  • Soldered the horizontal sections to the ladder line and secured this to my mount
  • Soldered a banana plug to the twisted ends of the bottom of the ladder line to go in to the balun,

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Above you can see all the bits that I’ve done today.

  • 24 feet of ladder line with the bottom twisted together plugged in to the balun that I made based on these videos.
  • The 8 foot and 38 foot horizontal sections connected to this cute little mounting point that I’ve constructed.

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Here’s the balun. It’s a nice fit into this box, though I still need to find something to attach to that nylon bolt to anchor it against the top so it’s not fully supported by the soldered wires to the banana sockets.

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It’s not as clear as I’d like but I’ve bolted together two cable mounts. One to slide down the pole and the other holding a cable tie looped through the two tent rope slides that the ladder lead and the horizontal wires attach too.

The horizontal leads are tied to the nylon slides so there is no tension on the soldered joints (I’ve learned this trick from my portable antennas). To stop the ladder line pulling through I’ve got three layers of heat shrink on the lead above the slides, as well as some cable ties to anchor it.

My aim here is to try to keep this as light as I possibly can.

You may notice that I’m using imperial measurements on this. I’m doing this as the conversions on the linked article just look wrong to me, so I’m going with the imperial lengths to start with. I will be tuning the horizontal sections once it’s up.

Next Steps

I’ve still got to cut the two counterpoises (~10 metres and ~20 metres) and put a banana plug on those for the balun.

The 40m/20m dipole is currently mounted on a 6 metre squid pole, set a bit under a metre above the ground. I’m not going to be able to use this pole for the G7FEK.

  1. It’s too short. I need about 7.4 metres
  2. It’s too flexible.

I’m going to fix my older 10 metre pole (thank you Haverford for the replacement section that I broke) and use it for the centre but only raised sufficiently far so that I can attach the balun to the pole at a usable height and then run the coax from there back inside.

Until I can get some 7 metre non-squid poles, I’ll attach the end to the 6 metre ones that I have been using portable.

Progress on Saturday September 26

I cut the counterpoises today (a little longer than  needed so they can be tuned). The 21 metre one may be a bit of a challenge and I suspect it’s going to have to turn at te fence line.

I’m now fully committed as I’ve taken down the poles and the 20m/40m dipole so I’m currently without HF at home.

Turns out that the lovely people at Haverford sent me three replacement segments so I’ve put those in, but I forgot that this pole has a tendency to like collapsing if it is vertical with no bend. I suspect that I’m going to be putting some tape at the segment ends to have it stay up.

I bought some more tent rope slides. I’ve slid one on to the longer horizontal segment so I can attach the 20m vertical segment a bit later on. I’ve put one also on each end of the horizontal segments I can use some 3mm cord to attach them to the end poles. I’ve not yet worked out how I’m going to do that attachment.

Anyway it’s starting to get dark here so I’m leaving any more until tomorrow.

Progress on October 7

Last night I managed to get it up in the air and run the counterpoises. A quick look at the antenna tuner showed that I was pretty good for 40, 30, 17, 15, 12, 10 & 6. The 80m leg was resonant around 3.3 MHz so will need a little trimming, but is still usable on 80m.

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Here is a good way to see that it’s exactly 7.4 metres up. The balun connects from teh ground. The ladder line is 7.4m.

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Looking towards the back yard from the 40m end. I decided to do a flagpole type set up so I can more simply raise and lower the antenna without having to take the poles down, as I’ve also duct taped the joins on the poles so they don’t collapse. I’m currently using my 6 metre poles for the ends. This is not really high enough as the antenna is supposed to be horizontal. I’ll get some 7 metre ones to replace them.

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Looking towards the 40m end from the other side of the centre pole.

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Looking towards the 80m end.  It’s anther of the 6 metre poles. I’ve velcrod it to a 130cm star picket near the fence.

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Another view looking towards the 40m end from the other side of the centre pole.

I still need to properly tune the counterpoise and the 80m segment, but it’s looking pretty good. I did a parks contact with Linda  (VK7QP) on 40m this morning using 50 watts. No RF floating around the office and it didn’t take out the VDSL.

I still need to add the extra vertical segment for 20 metres, too.

Progress on October 12

Even with the pole segments taped, I had the second top segment drop one in the wind. Fortunately, I still had the bottom-most segment still down so I was able to get it back up to 7.4 metres. Serendipitously, this now has the top of the antenna at a stronger part of the pole, so the 3mm cord I have running through the ring supporting the antenna is now functional without pulling the pole around.

I’ve taken some measurements at various frequencies before I start to tune this thing. Some nice surprises in there.

Frequency (MHz) SWR (x:1) Impedance
1.800 5.18 24.50
1.850 4.78 27.49
1.875 4.67 29.00
3.270 1.07 58.42
3.500 2.84 169.80
3.600 3.30 170.90
3.700 3.59 133.80
7.000 1.57 88.01
7.100 1.85 104.50
7.200 2.20 111.00
10.100 2.07 122.30
10.125 2.11 125.30
10.150 2.16 128.60
14.000 2.71 108.10
14.244 2.58 75.43
14.350 2.53 65.55
18.068 1.77 50.33
18.118 1.76 47.63
18.168 1.76 44.93
21.000 1.66 94.84
21.244 1.71 79.92
21.450 1.78 65.93
24.890 1.99 62.07
24.940 1.97 57.98
24.990 1.94 54.09
28.000 2.06 99.98
28.490 1.95 53.82
50.000 1.04 37.93
50.110 1.04 37.81
52.000 1.27 93.75
52.200 1.29 84.41

The real nice surprise is that even without the 20m segment, it’s quite usable on 20m. Also even though it’s around 5:1, the FT818, will work with this on 160m, even if it is hugely inefficient.

The next steps will be to look at tuning the counterpoises and then the 80m segment, as the 40 is pretty damned close to where it needs to be. It’s actually resonant at around 7.0MHz, perhaps a little shortening may not hurt.

I’ll continue to update this page as things progress.

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