Saturday, 16 July 2016

Vertical antenna rebuilt

I collected all the neseccary ingredients for this simple upgrade from Alu tape antenna to Cu tape antenna. Now, this monday was the right time and coorperating weather to disconnect te vertical and rebuilt it with the I-max 2000 as base. Before I started I made a photo from the field strength at the shack on 15m I expected a increase with the "new" antenna. I was wrong but I think I know why. More about that later.



When I had the old antenna down to dismantle I now had the possebility to inspect it closely. Actually in 7 years time it had been damaged so much that there were holes in the insulation especially at the top part. Even the copper wire was broken at one point. The antenna obviously suffered a lot from the weather.

 It is a miracle I still could make DX with this antenna even with QRP! Since there were holes there was water inside which resulted in heavy corrosion of the tape were it touched the copper wire. Of course I know copper and aluminium are not good together when air can reach it. But since a aluminium wire was hard to find I had no choice. At least it did hold for several years.

I dismantled the antenna and built the "new" one. The I-max is a very flimsy antenna compared to the size. Actually I hope it holds this winter and with the large winds that always come up once or twice a year.

Anyway, the tape was applied on the antenna and just to be shure I taped a copper wire on the first layer of tape again. Everything was taped in with insulating tape. That's a lot of tape isn't it ;-)


Actually everything went smooth. Till I had to fasten the radials again, it started to rain. Rain is something we get a lot this year. It is probabely a forecast that the next half of the summer will be very dry, we'll see. Back in the shack I noticed SWR on all bands was close to perfect and below 1,5:1. Looks good, so now a look at the field strength meter on 15m. The needle dropped? Strange I expected a improvement. I moved the field strength meter away from the radio and it went "dead" no reading at all. I probabely measured a radiating coax cable? Or I measured radiating radials as the old vertical was in such bad shape that it almost couldn't radiate anymore? If anyone knows better?

Well, I'm just a antenna experimenter. I like to experiment with unconventional designs. I don't know much about antenna theory and certainly am not a antenna expert. Actually I'm just doing it for fun, to learn something from it and hopefully it works out. I tested the antenna in the afternoon and noticed I was spotted in Paraquay on 17m and in the USA on 20m. Received stations from Japan on 20m. I made some contacts on 20, 17, 15 and 10m and it all works fine. Propagation was not that good at the start of the week I think. I used PSK and JT digimodes for the test. Listening on SSB before going on digimode I heard nothing on those bands! A strange experience!

I had some time to do more tests in the next few days and was not disappointed although propagation was rising. A amazing 17m JT65 QSO with BD0AAI from China wednesday evening into a dark path doesn't happen to me often. His signal was very good actually, could it be longpath? At the same time there were conditions to South America, excellent signals from that part of the world...Thursday evening I read PC4T's post about the quote from K2WH "bands are only dead if you believe they are". So I started calling with JT65 on a "dead" 10m band and immidiatly got response from IZ2NAB and later from UB6AAK. Signals were weak but it was not bad for a dead band. Again confirmation that the antenna works especially for weak signal communication, something I really love in this hobby.

At the moment I only tested with digimode. Through the week I have been listening on SSB but hardly heard any interesting (DX) station although digimodes showed propagation was there. I probabely have to wait for a nice contest to really test the antenna out. The results so far are promising. Of course it is not as good as a (3 band or more) directional antenna. I think it can be compared with a endfed antenna although this one can match to about 50 Ohm everywere from 1,8 - 30MHz, a real multiband vertical.




3 comments:

  1. Hallo Bas, mooi stukje vakwerk geleverd. Lijkt mij nog al een klus om ca. 7m te ommantelen met koperfolie. Het is mij niet duidelijk of je nu nog een blanke draad er langs getrokken hebt en op de folie hebt gesoldeerd.
    Dat de veldsterkte volgens de meter minder is, kan er inderdaad op duiden dat de oude antenne slechter gewerkt heeft. De tijd zal het leren. Ik ben benieuwd naar de verdere resultaten. Op het eerste gezicht werkt het uitstekend. 73 Hans, PE1BVQ

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    1. Hallo Hans, voor alle duidelijkheid heb ik de tape niet gewikkeld. Het is 1 strook over de volledige lengte. Daarop heb ik een afgestripte 2,5mm electriciteitsdraad gelegd en die met wat stukjes kopertape hier en daar vast gezet. Daarna alles omwikkeld met gewone zwarte isolatietape. De afgestripte draad is niet helemaal afgestript, heb over ongeveer 40cm de isolatie laten zitten om het geheel nog aangesloten moest worden op de tuner. Ik eb niks gesoldeerd, al had dat misschien nog iets beter geweest. Het had wel mogelijk geweest. 73, Bas

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    2. Sorry, voor de type foutjes in bovenstaande. Inderdaad is duidelijk te merken dat het stralingsdiagram anders is. Heb wel het idee meer zwakke signalen te kunnen horen met digimode. Helaas vang ik ook meer QRM, dat is natuurlijk wel een negatieve bijkomstigheid. 73, Bas

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Thanks for your comment. Bedankt voor je reactie. 73, Bas