[Towertalk] Re: 15M on C31XR

[Jan Erik Holm]

Do I get this right, the C31XR doesnīt work out of the box?
 From the below it seems to me that the C31XR needs to be
rebult to work properly.
Itīs been stated on this reflector over and over again that the
Force12 antennas are "the best in the world" (my own interpretation),
now if you have to rebuld it to get decent SWR it seems to me
that you certainly donīt get what you pay for.
My feeling is that a expensive product like this shouldnīt need to be
fiddled with, correct me if Iīm wrong.

Jim SM2EKM
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Bob Henderson wrote:

>Dink
>
>I have a C31XR up at about 70 ft fed with three seperate feeders.  Each
>antenna is fed with 50m of HD100 coax and each has a choke balun of 12 turns
>of coax with a piece of 6 inch dia plastic water pipe as a former so the
>turns don't bunch up.
>
>SWR on all bands is at 1.1:1 or better at my chosen centre frequency.  These
>are 14100, 21200, and 28200.  These c/f give me good swr across CW and
>sideband segments.  To achieve this I removed the tips from the 15m
>element,added extra length to the 20m element and used hairpin matches on
>all three driven elements.  These took some fiddling with to achieve best
>effect.
>
>The above swr readings were taken with the feeders to the other two yagis
>open circuit.  Any kind of load placed across the 20m coax whilst using 15m
>messes up the SWR on 15m.  This has caused me a problem in my SO2R set-up
>which I have worked around by putting a 15m parallel tuned circuit in series
>with the 20m feed.  I used a small L and big C to minimise the effect on my
>20m SWR.  It's a compromise but it does work.
>
>With good choke baluns on each driven element I have found SWR to be
>substantially independent of feeder length.  That is with 50m and longer
>feeder I haven't tried with feeders shorter than 50 metres.
>
>BTW You did remove the tips from the 15m elements didn't you?  The 15m
>elements as delivered are too long for the separate feeders option.
>
>I have added a Cushcraft XM240 at about 85 feet (turned 90 degrees to the
>C31XR) and I have inverted vee dipoles for 160m and 80m hung just below the
>C31XR.  None of this seems to have had a materially adverse effect on swr or
>performance of the C31XR so far as I have been able to judge.
>
>I hope this helps.
>
>73
>
>Bob 5B4AGN
>
>
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