End Feed Half Wave
Started off with a "End Feed Dipole" ½ wave thing. Wanted it to do several bands at the the same time so I aimed for the popular SOTA bands of 12m, 20m and 40m. Some of the designs I have seen are for 10/20/40 as they are harmonicly related. KX4O did a forensic study of the Par Electronics End feed. See how I go!
Shamelessly stolen from KX4O website. I needed a starting point and it's as good as any.
I wound 0.5mm enamel coated wire on some 16mm conduit which has an OD of about 20mm. Started out with 55 turns and then removed turns till I got the inductance down to 26uH.
Made out of high pressure PVC pipe and end caps. Some brass bolts and wing nuts. Drill holes, solder wires onto brass bolts and push it all together.
I didn't have any 25mm toroids laying around. Only 12mm and 50mm. The 12mm with 0.5mm wire just wouldn't do the job. To many turns to get the job done on 40m and that would screw up 12m. So I moved over to a 50mm core and 1.7mm wire. 3 turns on the primary trifilar and 24 turns on the secondary to the EFD. Almost the same as the info provided by KX4O but thicker wire and larger core. So should handle higher power if I want to take it.
Testing and Building
Dug up some 1.5mm² wire I had laying around. Measured out just over 12m for the long bit and 3m for the short bit. Stuck an egg insulator on the end of the long bit. Strapped the choke across the egg insulator, threw a line in a tree and hauled it up. And started trimming. Final lengths with the 1.5mm² wire were 11640mm and 2670mm.
I have a nice air spaced variable cap from an old trannie radio and I hung this across the input to the balun. I tuned for minimum VSWR then measured the capacitance. 12m dipped at 190pF, 20m dipped at 255pF and 40m dip was at 505pF. So a compromise of 220pF was soldered in.
Replaced 1.5mm wire with flash wire from VK3PF which is much smaller (and lighter). And tuned all the lengths again. Final lengths are 11740mm and 3340mm. VSWR are: 12m=1.8:1, 20m=1.5:1 and 40m=1.5:1. This can be better if I can find some higher quality caps.
After my first activation I found how bad this antenna will perform if it's not hung up high enough. Also the "DX Wire" I have is (in my opinion) crap, insultulation cracks, once teflon is removed it has no strength. Maybe great for dipole but not for this. I'd rather carry the extra weight so I know I won't have any problems.
So a rebuild of the beastie out of 1.5mm². But the important factor is that the EDF is to be hung up the same way on site as I have done in testing. Having it sitting in a tree at a nice 80º it works great. Hung in trees that are only 5m high and the angle is below 40º is crap! So up went the squidie and built the new antenna based on that support only. Repeatable on site - no lost socks - no cut fingers - less swearing...
So now the choke is sitting at the highest point on the squidie, held in place by some 16mm conduit slid over the pole. The 40m top wire is tied off to somewhere away from the pole. 12m and 20m length is now up higher and straighter. A quick test with VK2HRX on a summit showed it works.
Just have a look at VK3PF's blog.... Liked the box with the tab idea so I did the same. Added a length of RG-62 inside the box with some ferrite beads slipped over it as a simple balun to keep antenna currents out of the cable.
Again from VK3PF's idea that he mentioned on the SOTA group. I will be using anderson connectors as the "switched" part of the antenna, so I got some nice green ones. And whilst in the local camping shop I found this paket of six "Dome Tent Plastic Sliders" for $5. How handy is that for the insulators between the switched bits? And there is enough in the paket for 4 bands. And so I made it for 12/20/30 & 40m.
Made a guy ring for the squidie from a 50mm conduit joiner. Slips down to the third pole and tied some rope around it.
So each set of dipoles was cut and tuned and the next band up was added. Quick and painless. And I found it works on 15m with no extra work needed. So that sweet.
And just for "shits & giggles" I tested were it works as an offset feed thing. Leave one side 40m and 12m on the other or one side 20m and the other 30m. Most of them were USELESS except for one....
Also have one of these tiny multiband mobile whips. Got it way back in 2000 when I did my bicycle tour of Japan as 7N2LCY. With an antenna base and a few radial wires it will make a handy GP for 15m and up. And 80m and 6m if I need to use those bands. Made the radial wires out of thin wire and store them in a sandwich bag and I just push them in with the "GND" connection on the outbacker.
Arrow Satellite Antenna
If I am asked for 2m or 70cm I can throw in the Arrow. 3 elements on 2m and 7 elements on 70cm.