[TowerTalk] XM240

[Bill Parry]

Howdy Doug,

I only got one response but I did it anyway. I bought some RG11 coax and a
double female coax connector here locally, looked up the VF of the coax,
measured the length, and put it in line. (I wish I had used RG6 now.) I
hooked it up and it DIDN'T work...I was very surprised!

I thought it might be sensitive about where in line I put it, so I moved it
so that it was as near my amp as I could and it DID work. I can't find my
info with the original SWR! My 80 M 75 ohm coax is connected directly to the
80 M sloper... that's probably the best place to put it.

SWR Now:

7.0	1.6
7.05	1.0
7.1	1.4
7.15	1.8
7.2	2.5

The lowest SWR is about 50 KHZ lower than it was. This is a real gain for
me. I don't really care about 40M phone and if something is really important
there, I can just remove the 75 ohm coax (its inside the shack!) My Alpha
87a loves me again because I don't have it fault every time I go to 40 from
another band anymore. 

I know that I didn't really "fix" anything but my amp is fooled into
thinking the SWR is lower and that's good enough for me. The antenna already
worked well. 

Since I originally put this out on TowerTalk I am going to send a copy
there. I hope you don't mind.

Good luck

Bill, W5VX


>-----Original Message-----
>From: Doug Renwick [mailto:ve5ra at sasktel.net]
>Sent: Monday, July 09, 2007 11:09 AM
>To: 'Bill Parry'
>Subject: RE: [TowerTalk] XM240
>
>Bill,
>
>Did you ever get any responses?  Did you try it and if so what were your
>results?  I have a XM240 and like you would like to 'broaden' it.
>
>Doug
>
>
>Subject: [TowerTalk] XM240
>
>I am really tired of the Steppir stuff...let's talk about something
>else.
>
>I have a 2 element Cushcraft XM240. It has been up for about 5 years at
>about 40 Meters high and has always been a fine antenna. I have had one
>problem with the antenna. I set the point at which I have the lowest SWR
>at
>about 7.075. I knew that the antenna was fairly broad and I wanted to be
>sure that the SWR was OK in the CW band. I didn't realize the SWR curve
>was
>not going to be symmetrical and the SWR was going to rise very quickly
>toward the bottom of the band. As a result the 2:1 points are about
>7.020
>and 7.285. The antenna still works nicely in the 7.000 - 7020 range but
>it
>creates problems with my amplifier.
>
>I have always just put up with this, the antenna works well and I am
>certainly capable of retuning the amp. A friend was over the other day
>and
>suggested putting a 1/4 wave section of 75 ohm coax inline at the shack
>to
>broadband what the amp sees. I was amazed that I hadn't thought of this
>before. I have a full size 80 sloper from the top of the tower and I did
>this very thing to it. It works fine and the SWR is good across the
>entire
>band.
>
>So the question is:  Are there any drawbacks to using this procedure on
>a
>yagi? I have lost my notes on the exact frequency that I would chose to
>cut
>the 1/4 for...(yes I know I need to include in the velocity factor.) I
>assume that I would choose +/- 7.025.
>
>It is definitely not worth the time and expense of taking the antenna
>down
>to lengthen the driven element a few inches!
>
>Any thoughts?
>
>Bill, W5VX
>
>
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