MFJ-1954 with base loading coil HF Antenna
When going portable in HF I usually use a simple wire dipole, 2x5m, for 20m up, and tune it with the Z817, but this setup goes only when trees are available to hang out my wires.
So for tree-less situations I decided to use a vertical antenna, and the primary key for this was the portability and backpack usage. MFJ-1954 telescopic whip, 3 meters (10 feet) long, was the best choice for that.
My interests in HF portable operation are 20m up bands, so with the 3m antenna I can cover 10 and 12m bands, and 20, 17 and 15m with a base loading coil.
The entire elements are hold up by a camera tripod, 1m height type, which I removed the mounting bracket for the camera, so the PVC pipe that support the whip, as described below, will thread in easily. With lambda/4 counterpoises, I managed to get good SWR, less then 1.5:1, on 20 to 10m bands. Anyway, because of the loading coil on 20-15m, radiation efficiency is less then a full length vertical.
A big building challenge was to find a way to mount the antenna to the tripod, along with the loading coil. The MHJ-1954 base thread is a little fragile, as I read the reviews on eHam.net, so I build a reinforcement from teflon, that will easily can be plug in and out to a PVC coupling, this one welded to a PVC pipe. A 2.5 sq mm wire is connecting the whip with the loading coil box.
I heated up at the stove the PVC pipe so that will thread in to the tripod extension.
For the base loading coil I choose to go with a Amidon T200-2 toroid. An air wound coil it would been the best solution, but space and building it were inconvenient.
Approximate coil inductances for a 3m long antenna, based on this calculations are:
20m – 4uH (18.5 turns on T200-2)
17m – 1.2uH (10 turns on T200-2)
15m – 0.5uH (6.5 turns on T200-2)
A 12 positions rotary switch is changing the coil taps. Fore more tuning possibilities, I have wired the toroid like so: 5, 6 and 7 turns for 15m band, 10, 11 and 12 turns for 17m band, and 16, 17, 18 and 19 turns for 20m. For 12 and 10m bands, the toroid is left in the air.
Two M6 bolts with butterfly nuts are used for counterpoises connection, and a SO-239 socket to rig/tuner. A DC plug is used to connect to the telescopic whip.
All the components fit to a Z-54 ABS box, from TME.
For transportation I used A/C pipes insulation. Goes nicely and protects also the antenna. Overall length of the whip collapsed is about 65 cm. All are easy to carry on a backpack.
So this is it. I made few QRP qso’s this summer with the antenna. I remember using it in IARU contest. Regarding how far it goes, it plays same like my dipole, I worked stations with 5W from Europe and some USA and JA. Hope from spring to test it in SOTA or WFF.