[TowerTalk] Force12 C-31XR Tri Band Beam SWR
K7LXC@aol.com
K7LXC@aol.com
Wed, 4 Aug 1999 02:44:49 EDT
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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