This is forwarded from K3OO as to what he did to ix his C31XR
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.
>[mailto:firstname.lastname@example.org] On Behalf Of K7LXC@aol.com
>Sent: Wednesday, August 04, 1999 2:45 AM
>To: email@example.com; firstname.lastname@example.org
>Subject: Re: [TowerTalk] Force12 C-31XR Tri Band Beam SWR
>In a message dated 99-08-04 01:57:25 EDT, email@example.com 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:
>> 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
>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
>> Just got off the phone with you. Here's what our antenna test SWR
>>like on 15M:
>> It's not a lot different than what you've got. Like I said, Tom is
>>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
>>fine antenna so maybe the SWR on 15 is something you have to 'work
>>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
>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
>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
> 100 1.3
> 200 1.3
> 300 1.5
> 350 1.6
> 100 1.4
> 200 1.4
> 300 1.6
> 350 1.8
> 400 2.2
> 450 2.4
> 200 1.2
> 400 1.1
> 600 1.1
> 800 1.3
>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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