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
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:
> 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 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
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 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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