I’m trying to build a compact EFHW for SOTA and base QRP operations. Inspired by @HB9EAJ’s description and @HB9BCB’s answers on this forum, I want to make it multi-band (I was also a HB3 operator for a few years ). Most descriptions I see online use wires 20m or 40m long. For my use case, I’d like to use something 10m or shorter and 10-20m bands. It’d be nice to have 40m and also some of the intermediate bands (17m, 15m, 12m) but if the design doesn’t allow those bands, that’s fine. My main constraint is the antenna length.
I understand it is possible to use shorter antenna wires together with a loading coil to make it resonant on lower bands, but I was not able to find a good description for different use-cases or the theory behind this. Again, most online descriptions are for 40m or lower bands and I’m not sure if the inductance values and pigtail length (the part of the wire from the coil to the end of the antenna) can be applied to other antennas. For a 10m wire, or a 5m wire, what kind of loading coil would be needed, and what are the lengths of the main wire and the pigtail?
Thanks for the reply @9A3IV ! Could you please describe the table: what do the values in the cells indicate (pigtail length, loading coil length, inductance, or something else) and what is “Draadlengte”? And what does material 43 mean? I am using a 49:1 UnUn (cc @OE5JFE). Are the values in your reply valid in this case?
The page here >Coil-Shortened Dipole Antenna Calculator < while not directly answering your query, may give some further reading/thoughts around loading/trapping which can be carried over to an EFHW antenna.
There is a little equation at the bottom of the page if you need to melt your brain…
Maybe the “coil shortened vertical” page on the same site is a better match?
KK6JFD, I have built the same antenna as OE5JFE referred to; it will work on 40/20/10 as described. Using 5 meters of wire will just not work on 20M unless you use a loading coil - which may not work well for the 40M capability. Cut the 20M section (begin with 33’ of wire) and tune, then add coil and about 8’ of wire and tune for 40. Done - then check 10M and it should work okay at 2:1 SWR or less.
Here is a link to the PackTenna 49:1 EFHW which shows you how to make this work.
This is a very easy ask.
The beauty of a simple EFHW is that you can just wind out the amount of wire you need, leaving the rest on the winder (with a clove hitch).
If you wind out ~10m of wire , you will have 20 & 10; ~15m → 30,15,10; ~7.5m->15; 8.5m->17. 6m->12
The trick here is to mark the lengths for each band e.g put a marlinspike hitch in the wire with a matchstick or bit of weed whipper nylon.
For very short wires (e.g. 10m) it is very easy to get up and change links, so a linked EFHW would be a good choice for you. (it is a bit of a pita when you have to walk down a 40m wire)
I would start with a ~20m wire for the 40m band with links for 30m, 17m,15m,12m. Now you just roll the wire out to the band that suits you best, and use the links to select which bands work with those lengths. Your default is to run out 10m of wire and use links for 17,15,12