Inside PVC Design Image:


This image was taken on 11/7/99 after 7 months of service.
 

Inside PVC Design Comments:

   Date:  Fri, 20 Aug 1999 22:42:27 EDT
   From: "Robert Glenn" <kf4pxz@hotmail.com>

Just a quick note to tell you how impressed I am with your simple, yet very
effective antenna design.  I have built two of them, and am using them on my
repeater.  I cannot afford high sites, but these antennae seem to make up
for that somewhat.  I have a split site set up (i.e. the rx & tx are in
different locations).  They out perform a db products 4 bay folded dipole
antenna that I have, and that's 6db gain.  I have given your antenna credit
on my page http://kf4pxz.members.atlantic.net and have a link in place back to the erie
co. races page, where I found the design.  Once again, thanks for the great
design.  73, RJ Glenn, KF4PXZ.


   Date: Wed, 12 May 1999 13:48:42 -0500
   From: Randy Albin <ralbin@trailmobile.com>

Hi Steve,

I built this antenna from another set of plans (someone must have copied yours - cant remember where I got this originally,
but instructions and specs were word for word) and had limited success with it.  When the wire is outside the PVC I can
tune it and come up with the following results for SWR.

145 mhz 1.5
146 mhz 1.3
147 mhz 1.4
148 mhz 1.5

Still somewhat narrow banded but acceptable.

When I feed it into the PVC pipe and perform the same tests I get:

145 mhz 2.0
146 mhz 1.6
147 mhz 1.9
148 mhz 2.1

This seems a bit high and is causing my radio to attenuate it's signal to prevent damage.

What were the results of your tests?  I am not sure what to change in order to bring things into line.  I have tried moving
the feedpoint up and down on the twin lead but cannot seem to improve matters by much.

Is there something obvious that I have overlooked?

What have I done wrong?

Randal R. Albin
Programmer/Webmaster
Trailmobile Corporation
ralbin@trailmobile.com
 

Sent:   Friday, May 14, 1999 7:53 PM
To:     Randy Albin

Randy,

I had SWR results like these at 5 Watts:
145.MHz 1:1.5 1/2
146.MHz 1:1.5
147.MHz 1:1.4
148.MHz 1:1.4 1/2
(I couldn't remember off the top of my head, so, I just went down to the radio room to check...)

I used a 50 foot section of new 50 Ohm coax.
Also, mounted the antenna on the roof, a top a section of 10 foot galvanized conduit, away from any metal objects.

Randy, how do you perform your SWR test?  The reason I ask is because, sometimes, when I do antenna tests to close to the
ground, I get false readings.  Also, if I'm to close to the side of a building or a car in the yard, the readings will be
off.

This antenna dose not work well at power levels above 7 watts.

Another thing that might throw off the match is how your mounting it to another object.  I attached my mast section to the
first 12 inches of the lower section of the antenna with 2 stainless hose clamps.

If this is not a help, this is what I would do.  Try to trim off a little of the top element, a few times.  This would
require de-soldering the small disk at the top, cutting off 1/4 inch, re-soldering, reassemble, and test....  The reason I
say this is that the "inside PVC" dose have an effect on the
wavelength of the antenna in such a way that it acts like it has been lengthened.  Shortening is a last resort, if nothing
else works.  Check the match with the antenna placed up high and away from everything first.

Good luck!

Steve  KB1DIG
 

   Date: Mon, 17 May 1999 08:57:10 -0500
   From: Randy Albin <ralbin@trailmobile.com>

Steve,

Thanks for replying.

I did perform my tests with the antenna's feed point only about 18 inches off the ground.  I suspended the antenna from a
tree and did my first tests and then when I fed it into the PCV pipe I guess that raised the feedpoint a few inches.  The
curious thing is that the conditions and location were the same each time.  The only difference was the PCV.

I am only using 5 watts power...I guess I just need to try raising the antenna a little...

Thanks for your help.
 

Randal R. Albin  KB9PWJ
Programmer/Webmaster
Trailmobile Corporation
ralbin@trailmobile.com