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Subject: [TowerTalk] CUSHCRAFT 40-2CD HELP
From: (Bill Hider, N3RR)
Date: Wed, 10 Jun 1998 14:20:34 +0100

You don't say how high or whether the step ladder is made of wood or not. I
suspect it is wood, since the results are FB from my experience. You don't say
how high your antenna will eventually be on your tower. You also don't say to
what Cushcraft spec you tuned the antenna (CW, MID, PHONE, etc).

Anyway, someone suggested that you point the antenna straight up and measure it

again.  That method will work well and give you an excellent reference as to
what the performance will be in the air at a height of 1/4 Wavelength (70 ft)
or higher.

I have built and installed two of the 40-2CD antennas.  Both antennas were
built to the CW dimensions in the installation manual. Both have been tested
pointed straight up, in the clear, suspended by ropes, as well as horizontally
balanced on non-metallic saw horses about 4 feet off the ground.

The vertical tests gave "final-height" results that very closely resembled
Cushcraft's SWR charts in their installation manual.

The sawhorse tests gave results very similar to what you are getting!!  The
resonant frequency of the antenna will rise when the antenna goes up in the
air.  The SWR will improve as well!!

Finally, I have found that by using the Cushcraft "book values" in the
installation manual, you should be in fine shape once the antenna is up in the
air.  Again, I am assuming the final hieght will be 60 - 70 feet or so. It will

work fine at 50 feet too, it just may have better SWR and pattern a little bit

Summary: If you can't test it more before you put it up, you should be fine,
based on the limited info in your post.

BTW, I also added mechanical strengthing to both of my 40-2CDs using the W6QHS
modifications per several QST articles of the early 1990s.

Visit my website to get an ariel view of my installation and a look at the
engineering that goes into a single op contest station design:


Bill wrote:

>      We acquired a used 40-2CD (40 meter 2 element yagi) and wanted to test
>      it out after assembly.  Assembly went fine after putting on some new
>      hardware.  We tried testing it on a step ladder just to see if it was
>      in the ballpark.  Turns out that the resonant freq is at 6.90 MHZ, and
>      above 3 to 1 SWR in the ham band.  I know it's close to the ground,
>      but what else can be done before putting it up?  Is this normal?  Any
>      other way to test it?  Is following the Cushcraft assembly
>      instructions dimensions usually close to being correct once it's up?
>      Any help appreciated.
>                              73 Denis, W4DC
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