Topband: Elevated resonating radials question - A35MT

[Tomas Magyla]

Season's Greetings to everyone!



Many thanks for QSOs with A35MT on the Top Band before and during the CQ WW
CW 2007 Contest.

I had some pretty sad experience with elevated radials, below is the
question I wanted to ask (sorry for long introduction).



For the expedition I needed a simple vertical to cover 160m, 80m and 40m
bands. A modified Battle Creek Special wire version was constructed, with
elevated radials, tuned to resonate on appropriate band, and two traps. On
160m band the antenna worked as Inverted L, with 40m and 80m coaxial traps
acting as "extension" coils. On 80m and 40m bands the antenna worked as a
quarter-wave vertical, due to the traps "cutting-off" the rest of antenna.
After a few nights of work before the contest, I have decided to operate
SOSB on 80m, as the response I was getting on 160m band was pretty
disappointing: some of the stations who could hear me 579 on 80m band when
QSY-ed to 160m, could not hear me at all.


Due to my travel arrangement I had to leave A35 very early Monday morning –
the contest was not over yet (A35 local time = GMT+13 hrs). To minimise the
amount of the remaining disassembling and packing work for Monday morning,
so that to spend more time at the radio in the morning, I have dismantled
beverages, dipoles and have taken off 160m and 40m band radials from the
vertical, leaving only 4 elevated radials on 80m band. I did not expect 160m
and 40m resonating radials to influence the performance on 80m band. I was
not equipped nor had time to compare the field strength on 80m band without
160m and 40m radials. On the other hand, the SWR and Z curve taken with
non-professional Vector Network Analyser convinced me everything was within
the acceptable limits.

However, from the response during the second night operation, I've got an
impression that resonant 160m and 40m band radials did have a significant
influence to antenna performance on 80m band. Or was it just because that
the number of elevated radials used was very small – 12 radials for 40m, 4
for 80m, and 2 for 160m. Other expeditions seemed to have good success
operating with only 2 elevated radials on 160m?



I was interested to know whether anyone has had a similar multiband vertical
experience such that (absence of) resonating radials on one band would
significantly impact antenna efficiency on the other band, or was this just
a wrong impression I've got. Did anyone had any field measurements taken?



73 de VK2CCC (ex LY1F)



P.S. If you'd like to read A35MT story:



http://www.qrz.lt/ly1df/A35MT_eng.htm