[Elecraft] Miniature self-supporting HF antennas

[Rick M0LEP]

(Consolidating replies to a couple of messages here...)

The object of my exercise was not to measure the exact losses in the 
loading coil, nor to determine why it made such a poor antenna, but to 
determine which antenna would work best for the appropriate bands from a 
SOTA summit.

The antennas under consideration were the loaded vertical (adjustable 
for all the bands required), a link-dipole (covering bands up to 15 
metres), and various mono-band elevated ground plane verticals (one for 
each band from 20 metres to 10, though only 12 and 10 aren't covered by 
the dipole). I'd taken the loaded vertical on a couple of activations. 
One had been a reasonable activation (14 contacts on bands between 40 
metres and 12 metres) and one had been a struggle (just 4 contacts, 
enough for the points, in over an hour and a half of calling on HF 
between 60 metres and 12 metres, with me resorting to CW for the last 
contact), but on both I'd noticed the reports I was being given were 
lower than I'd have expected.

My friend could only help with the lower HF bands, so I have more 
confidence in those tests, and I wasn't expecting the loaded vertical to 
shine when compared to the dipole, but the magnitude of the difference 
was surprisingly wide. To give myself a baseline expectation I'd first 
tried contacting him with my (then) main 27ft tall vertical (which had 
some top-loading and a feed-point ATU), both with my main rig and the 
KX3 I planned to use to test the portable antennas. Somewhere I had 
detailed notes of all the numbers, but I can't find them. However, the 
QSOs are also in my log, and with the main rig at 100 watts we reported 
5 and 9 both ways. With the KX3 at 10 watts we reported 5 and 7 both 
ways. I then took the KX3 outside to test the portable antennas, using 
it at the same 10 watt level. The best QSO on the loaded vertical has me 
giving him 5 and 1, and he giving me 3 and 1. On the dipole the log says 
5 and 9 both ways. Some of that will be down to radiation pattern, 
height above ground, and so on, but it confirmed experience from the 
second summit mentioned above. Clearly, if I want to make contacts on 
the lower HF bands then the dipole is a far better bet.
 
For the higher bands I had to rely on RBN and any contacts who happened 
to answer, so the comparison's a bit harder to quantify exactly. (RBN 
skimmers don't report every CQ, so you have to play games changing 
frequencies, and waiting, in order to get enough coverage.) However, as 
best I could figure, the loaded vertical was well down on the un-loaded 
mono-band ones as well as on the link dipole. Again, height above ground 
level will have had some effect. The loaded vertical has its own little 
tripod, so isn't far off the ground. The others all rely on telescopic 
fishing poles, so they're at least a few feet higher off the ground.

In all cases the loaded vertical was worst, in some cases by a very 
large margin. At best (on 10 metres, which was clearly its best band) it 
was only 6dB or so so down on the elevated ground-plane vertical. That 
could be down to elevation, radials, the loading coil, or all three.

I'd rather over-optimistically hoped that the self-supporting loaded 
vertical (total weight 1.5kgs) would do the SOTA job nicely. The dipole, 
a couple of verticals for the bands the dipole doesn't cover, pegs, 
guys, and a short (6 metre) telescopic pole weigh 2kgs in total.

For SOTA purposes the loaded vertical was not worth carrying despite its 
(mostly) glowing reviews on eHam. Sure, I've made a few contacts with it 
from SOTA summits, so it wasn't totally useless, but the alternatives I 
now take are far better.

Next time I'm tempted to make a link-dipole I'll make sure it has 
additional links for 10 and 12 metres so I can save myself the weight of 
the elevated ground-plane verticals I usually carry for those bands.

On 21 Jul 2015 Wes N7WS wrote:
> If so, you are not determining the effects of loading coil loss

On 21 Jul 2015 Mel, K6KBE wrote:
> does not tell you why one works better that the other one.

-- 
73, Rick, M0LEP   (KX3 #3281)