Hi Lee,
Just a couple quick suggestions/comments, you'll surely get many more.
If you have or can get an antenna analyzer, try it right at the antenna,
without the coax. Lossy coax will show a lower, not a higher SWR, but there
may be some other problem.
Depending on height, a dipole may have an impedance closer to 70 Ohms than
50, so you may be seeing some of that mismatch to the 50 Ohm coax..
Can you lower your 80 Meter dipole and test with it down? That seems more
likely to be a possible interaction than the tower.
I agree that you should be able to obtain a better match than 1.8:1, but you
may not ever find that "perfect" match you are looking for.
Just my .02,
73 - JC, k0hps@amsat.org
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Lee Buller
Sent: Thursday, June 01, 2006 7:26 AM
To: TowerTalk Reflector
Subject: [TowerTalk] Liberal Arts Question on Dipole Antennas
Ladies and Gents....
Recently, I had to replace my 40 meter dipole (more of an Inverted-Vee)
antenna because the coax center lead had broken off the. The dipole worked
OK, but I was never really sure that I liked it. What is there not to like
about a dipole antenna? (I sure I get some wise cracks here). The dipole
did not seem to have a resonate point. It was below 1.8:1 on CW and was
about 3:1 on SSB. So, the antenna was long.
The new antenna, using a Budwig connector this time, shows the same
characteristics. I cut the the antenna at 66 feet and I made sure that both
sides of the antenna were the same length....33 feet. The antenna is
mounted at 45 feet using a bracked that runs through the tower. The antenna
in question is on the east side of the tower while an 80 meter antenna is on
the west sime of the tower mounted on the same bracket. The feed points are
about three feet apart....on seperate coax feeds.
The end of the Inverted-Vee on 40 comes down to about 20 feet off the
ground...while the 80 meter antenna ends about about 12 feet off the ground.
The 80 meter antenna is in a straight line, while the 40 meter antenna has a
slight VEE to to the tie points. So it has VEE to the the east....and a Vee
down. This is hard to explain in words. I hope you experts get this.
The new antenna was failry good on SSB but not great ... about 1.8. I
attached two test leads to each end and the antenna show that it was at 1.8
on CW...around 7.025. It seems that the test leeds were too long and now it
is resonate below 7.0.
But, there seems to be a crazy problem that I cannot get the anntenna any
lower than 1.8 to one....thinking that there should be a length in there
that should be "perfect." I cannot find the "perfect point" which I would
like to have around 7050.
Reading the Antenna Handbook...this antenna is working as stated although
I did not anticpate the length of an inverted Vee to go longer. I've read
the articles, but it seems there is something wrong with the antenna.
Is there an interaction between the tower...the 80 meter antenna...the Vee
to the east?
Is the coax bad? IT has been up there for quite some time and it was used
at another location before I put it up here.
Comments, flames, postulations, editorials, and pontifications are all
welcome. They might show on my web pate later on....so...you have been
warned.
Thanks for the discourse on a simple dipole
Lee Buller - K0WA
In our day and age it seems that Common Sense is in short supply. If you
don't have any Common Sense - get some and use it. If you can't find any
common sense, ask for help from somebody who has some common sense.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|