On 12 dic, 00:28, Sébastien MEDARD wrote:
Hello,

On Fri, 10 Dec 2010 06:15:51 -0800, Wimpie wrote:

it may result in worse
reception because of overloading electronic circuits in your receiver.

OK for that.

If your balcony has a metal fence (that may be connected to rebar also),
you can use this as a ground provision for a wire antenna of about 5…
10m.

I didn't test that until now. I will.

Adding a 9:1 transformer (outside, directly below the antenna) will
increase antenna output at the lower bands. This does not automatically
mean that your S/N ratio increases also.

Portable receivers may experience overload. A preselector may help.
http://www.tetech.nl/divers/SimplePr...tor2.jpg*shows an (old) example.

I better see what could be a home made tuner. Seems quite easy to
build )

This one tunes from 3.3 to 26 MHz. By changing the crocodile clips, you
can perform some matching to get more output from the antenna, and
change the bandwidth of the preselection.

The crocodile clips can be replaced by a selector. Am I OK on that?

Correct, you can use two selectors instead of the clips.


For the lower bands (AM broadcast) a loop may have advantage.
Figure 2(a) in
http://www.compliance-club.com/archi...30718.htmshows the
construction of a loop out of coaxial cable. These types of loops have
built-in balanced to coaxial transition. *A square or circle of about 1m
(diameter) is a good start for the AM BC band.

It is called a shielded loop. Am I wrong?

Correct. To have the balun function, the cut in the shield must be
opposite to the position where the feeder leaves the loop.


Be careful with (expensive) loop antennas. If you can't get reception
with a simple well-constructed (tuned) loop because of local
interference (noise), the most expensive loop will not change that.

For now, I tried a lot of different things... The best result were on
loops.

A big loop (1.6mx4 = *6.4 meters), one turn, with an air variable
capacitor + an inside loop connected to the coaxial cable seems to give
better ways to give something to eat to my receiver. Sometimes my air
capacitor was not powerful enough, in the lower bands if I remember
well... To improve that I will have to add a fixed capacitor (lets say
300pF) in parallel (to be bypassed) or more depending on the band I am
listening to. For now I am just experimenting (with some simple wire),
but I think I will build a more solid one...

A big loop (1.6mx4 = *6.4 meters), one turn, with the the universal balun
from Wellbrook. Don't know why, but, it gives very good results, far
better than a long wire in my flat, or a short wire on my balcony... At
this time it seems there is a Ham Contest in Italia... I can get them
fully on 80m LSB/CW/RTTY... Well I live in South of France, so it is
easier for me ))

My experience is that at the lower bands (AM BC up to 3.6 MHz), loops
show better S/N ratio. However for the higher bands, performance
becomes similar to dipoles or monopoles. For reception I like the
small loops, as you can rotate them easily. They give less output,
but here tuning (even tuning inside close to the receiver) will
improve output (and noise….).

Regarding the large resonant loop with inside coupling loop, yes that
works well. I have a small one (0.6*0.4m) that tunes on the ham bands
from 3.6 to 30 MHz, it uses additional fixed capacitance for the lower
bands.
Unless you live in a very quiet environment, you can reduce the size
without sacrificing S/N ratio.



But the first solution seems more efficient. Need to do further
investigations....

Sebastien.

Best regards,


Wim
PA3DJS
www.tetech.nl