Dave wrote:
Hey starman,
I am still trying to digest the material on the website you listed. I even found another website that referrences this one, and has pictures. I am
still not clear on the purpose of the 30turn/10turn matching transformer
inside the shielded box. What does this accomplish that a 300/75 ohm
matching transformer between 300 ohm twinlead and 75 ohnm coax would not?
The homemade matching transformer described on the website(s) is
designed to work best at shortwave frequencies and AM(MW) too. A generic
TV transformer (balun) is intended for a higher range of frequencies and
usually doesn't work well below about 10-Mhz. The TV ferrite core is
made with a material that operates best at TV frequencies. The website
mentions removing the core from a TV balun for making the shortwave
transformer but I recommend getting a type '43' material for the core.
You can try a TV balun to see how well you receive the lower shortwave
bands. It will almost certainly not perform well on the AM broadcast
band. However as someone mentioned, this could be an advantage if you
have a lot of strong AM stations in your area that interfere with
shortwave reception.
Also I am planning on grounding the shield of the coax to a grounding stake at the "base" of the antenna, as soon as the coax comes near enough to the ground to do this. How can I do better than that, for a ground?
The low noise antenna on the website is the best way to achieve a good
RF ground for an inverted-L (random wire). This is because the antenna
end of the coax is located close to the ground. Otherwise you should
ground the shield of the coax when it first comes near the ground. This
will require the grounding block I mentioned in the previous post.
I do appreciate your patience.
"starman" wrote in message
...
Jim Williams wrote:
If I run a wire out the window to a tree near the house, do I also
need to run a ground wire to the ground outside?
Does an outside wire perform better if it's grounded or is it a safety
precaution (or both)?
It's mainly a safety issue, since you can't make a good RF signal ground
for the type of antenna you're considering (random wire or inverted-L),
*unless* you use the technique on the following website:
http://www.anarc.org/naswa/badx/ante...e_antenna.html
An RF signal ground needs to be short. Several feet of ground wire is
too much. That's why the grounding method on the website (above) works
so well. The ground wire to the rod is very short. Mine is about
12-inches.
Even if you're not interested in reducing noise with a good RF ground,
it's still a good idea to have some kind of ground for lightning or just
static electricity. I suggest you install a ground rod near the location
where the antenna wire comes inside the house. Connect a lightning
arrestor between the antenna lead wire and the rod. Better yet, build
the antenna design on the website above. This method helps to reduce
noise from domestic appliances such as televisions and computers.
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