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FW: [TowerTalk] Force12 C-31XR Tri Band Beam SWR

To: <towertalk@contesting.com>
Subject: FW: [TowerTalk] Force12 C-31XR Tri Band Beam SWR
From: n2tk@idsi.net (Tony kazmakites)
Date: Fri, 6 Aug 1999 11:53:31 -0400
This is forwarded from K3OO as to what he did to ix his C31XR


Hi Tony,

It appears that a lot of the folks I talk to have the same problem with 15m
resonance with the c-31xr.
I shortened my 15m driven element 4 inches per side.  If i were to do it
again i would only shorten it 3 inches per side.
By shortening the 15m driven element it also dropped the 20m resonant point
to the middle of 20m.
73,
Rick K3OO

>
>-----Original Message-----
>From:  owner-towertalk@contesting.com
>[mailto:owner-towertalk@contesting.com]  On Behalf Of K7LXC@aol.com
>Sent:  Wednesday, August 04, 1999 2:45 AM
>To:    k7jb@uswest.net; towertalk@contesting.com
>Subject:       Re: [TowerTalk] Force12 C-31XR Tri Band Beam SWR
>
>
>In a message dated 99-08-04 01:57:25 EDT, k7jb@uswest.net writes:
>> I just finished getting my Force12 C-31XR tri band beam up onto my 70'
>>  Rohn 45G tower.  If you own one of these antennas, I would like to hear
>>  from you as to the VSWR measurements you are getting.  Especially on 20
>>  and 15 meters.  The antenna specs posted on the Force12 web page:
>>
>>  http://www.qth.com/force12/index.htm
>>
>>  Indicate that the VSWR should be no greater than 1.7:1.  However, mine
>>  is more that this:
>>
>>  20 Meter Band:
>>  Frequency       Pf      Pr      VSWR
>>  14.000          300     50      2.37 out of spec
>>  14.050          300     45      2.26 out of spec
>>  14.100          300     40      2.15 out of spec
>>  14.150          300     30      1.92 out of spec
>>  14.200          300     20      1.69
>>  14.250          300     20      1.69
>>  14.300          300     20      1.69
>>  14.350          300     20      1.69
>>
>>  15 Meter Band:
>>  Frequency       Pf      Pr      VSWR
>>  21.000          300     30      1.92 out of spec
>>  21.100          300     40      2.15 out of spec
>>  21.200          300     45      2.26 out of spec
>>  21.300          300     50      2.37 out of spec
>>  21.400          300     60      2.61 out of spec
>>  21.450          300     65      2.74 out of spec
>>
>>  My antenna installer is growing impatient and is pressing me to get on
>>  with the completion of this installation.  So I am trying to gather
>>  actual info from other owners who have personal experience in measuring
>>  their C-31XR's results.
>>
>>  In addition, my antenna installer has gotten the same SWR measurements.
>>  So we are in agreement.  All of the suggested methods mentioned in the
>>  instruction manual have been tried by my installer and nothing has
>>  brought my VSWR measurements down to the Force12 specs for the C-31XR!
>>
>When the first of these antennas were shipped, there was a comment in the
>manual to take SWR readings at the end of 100' of coax. That comment has
>since been removed.
>The first one I installed was fine in the shack but just about
unmeasureable
>at the feedpoint. I would suggest using the shack as the measurement point;
>besides, we really on care about what the rig sees.
>The second one I installed was for our tribander comparison test. We never
>were able to get the 15M SSB SWR down but we didn't spend a lot of time
>farting around with it since it didn't affect the gain.
>Jerry, WB9Z, sent me the following message (which was posted and in the
>archives) about his experience:
>>> At 11:54 AM 7/1/99 EDT, you wrote:
>>In a message dated 99-06-30 23:31:44 EDT, you write:
>>
>>> Here's the 15 meter numbers:
>>>
>>>  20.785   1.6
>>>  21.010   1.7
>>>  21.100    1.9
>>>  21.200     2.5
>>>  21.250      2.8
>>>  21.300       3.0
>>>
>>>  VSWR on 10 and 20 doesn't go above 1.5  and the bridges stay solid
also.
>>>
>>Hi, Jerry-
>>
>>       Just got off the phone with you. Here's what our antenna test SWR
>was
>>like on 15M:
>>
>>21.025  1.4
>>21.125  1.7
>>21.225  2.2
>>21.325  3.1
>>21.425  4.1
>>
>>       It's not a lot different than what you've got. Like I said, Tom is
>the
>>only guy who can give you more help but changing the 15M driven dimensions
>>seems like an obvious place to start.
>>
>>     Don't forget that Tom had to make *many* compromises in designing
this
>>fine antenna so maybe the SWR on 15 is something you have to 'work
around'.
>>
>>Cheers & GL,  Steve    K7LXC
>
>
>>> Hi Steve:
>
>I have finished my work with the C31XR.
>I ended up taking 2 " off  of each 15 meter element half.  Since that the
15
>and 20 DE are coupled together, that  involved pulling both down.  We did
>that 5 times.  hi   See VSWR numbers below.
>To help eliminate that problem with the SWR bridge jumping around when
there
>is moving on the tower, either climbing around or just a little wind.  I
>added 2 insulators  to each element half between the 15 and 20 DE.  I used
>insulating materials from some old DB-212 low band loops, They side right
>over the tubing on the XR.
>That pretty much too care of that problem.
>These are the numbers using a MFJ-259B on the end of 250'  of LDF4-50A
>14.000   1.5
>      100   1.3
>      200   1.3
>      300   1.5
>      350   1.6
>
>
>21.000    1.5
>      100    1.4
>      200    1.4
>      300    1.6
>      350    1.8
>      400     2.2
>       450    2.4
>
>
>28.000 1.3
>      200     1.2
>      400     1.1
>      600     1.1
>      800     1.3
>29.000 1.4
>
>NOW,  maybe I should of took a little more off the 15 m DE,  but we were
>getting tired of jecking around with this G-dam thing and I was noticing
>some slight increase in reflected returns on 20.
>On 15 the return loss ended up a hell of a lot better than it came out of
>the box.   During IARU last weekend it seemed to play  pretty well.  I made
>1,908 Q's on SSB only.   Probably 30% were made using the XR.  >>
>Cheers & let us know how you do,    Steve     K7LXC
>
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