On Sat, 11 Dec 2010 16:21:29 -0800, Richard Clark wrote:

On 11 Dec 2010 23:28:18 GMT, Sébastien MEDARD wrote:

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

Hi Sebastien,

This is a good lesson.

Thanks. I think I will try long wire again... I don't like to give up
without fighting a little bit. But perhaps I will try it outdoor putting
my receiver in the car outside any city or in a place where I get some
place. So everything about antenna tuners need more investigation.

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.

This is an excellent antenna for BCB and Tropical Bands.

The problem seems to be related to wave propagation... I need to test
that a little bit more but... It is easier to receive radio broadcast
during the night. I need to know what are the differences between night/
day for wave propagation. What should I listen during the night and what
I should better listen during daylight...

I need to know a little bit more about digital transmission modes... To
be able to recognize digital patterns (on the waterfall display) to be
able apply the good settings for decoding... Easy for CW... Easy for RTTY
used by HAM... But what is the pattern for Meteo Faxes for example...?

By the way... I searched for good free software to decode meteo faxes...
But it seems not easy to find something free and easy to use... Do you
know shere I could find something interesting?

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.

This is a great solution.

This is something I found on a website.... When you don't know anything
about electronics... Your learning curve is quite flat ))

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 ))

One point to consider, this large loop will not perform the same when
its diameter is large when compared to the wavelength you are tuning to.
Your longwire with tuner will probably be better in the 50M band and
higher.

I need to make a tuner first... Then I will tell you about it.

However, experimentation may prove different, especially if you
can tip the loop over (or change its angle to earth).

Well.... not so easy for now... My "experimentation board" is a big wood
shelf with a lot of books on it... Not so easy to flip, rotate or.... But
it is well oriented (east-west)

My next tries will be on a multiple turns loops. With or without matching
loop inside. I will try with simple wire but connection ribbon cables
could be a good alternative... (like old hard drive ribbon cable)

I was wondering... It seems loop antennas are a never ending story. As
far as I know, it seems there is no book that makes a good overview of
the different loop designs, with accessible schematics for preamp or
tuning stuff, how to avoid QRMs... There could be a very interesting area
both for SWL and HAM...

Perhaps the "Joe Carr's Loop Antenna Handbook" may be interesting, but it
is quite expensive and an Amazon reviewer says it is not so
interesting... What about the "Joe Carr's Receiving Antenna Handbook" ?

Sebastien.

On 12 Dec 2010 13:59:06 GMT, Sébastien MEDARD wrote:

The problem seems to be related to wave propagation... I need to test
that a little bit more but... It is easier to receive radio broadcast
during the night. I need to know what are the differences between night/
day for wave propagation. What should I listen during the night and what
I should better listen during daylight...

Hi Sébastien,

What you are talking about is common to DXing. Get yourself a globe
of the world. Light it up with an artificial "sun." The edge of the
dark/light should be half way between you and the transmitter you want
to hear. So, during the late day, your best signals are probably from
Eastern Europe, Turkey, and Asia. During the early-to-late night,
your best signals are probably from the Americas. During the late
afternoon to early evening you best signals are from the south or the
north.

I need to know a little bit more about digital transmission modes... To
be able to recognize digital patterns (on the waterfall display) to be
able apply the good settings for decoding... Easy for CW... Easy for RTTY
used by HAM... But what is the pattern for Meteo Faxes for example...?

When I used to teach RTTY there were only two tones. If modem
technology is any indication, that number has been raised and phase is
important.

By the way... I searched for good free software to decode meteo faxes...
But it seems not easy to find something free and easy to use... Do you
know shere I could find something interesting?

Nope.

My next tries will be on a multiple turns loops. With or without matching
loop inside. I will try with simple wire but connection ribbon cables
could be a good alternative... (like old hard drive ribbon cable)

This will reveal the "Law of Diminishing Returns" (the more you add,
the less you get back).

I was wondering... It seems loop antennas are a never ending story. As
far as I know, it seems there is no book that makes a good overview of
the different loop designs, with accessible schematics for preamp or
tuning stuff, how to avoid QRMs... There could be a very interesting area
both for SWL and HAM...

Oh, I am sure there are many such books gathering dust on shelves.
Loops have been around for more than a century, and if they were such
a good idea, then everyone would be using them.

Well, at one time they were a good idea, and EVERYONE used them - when
we had transistor pocket radios with analog tuning. The ferrite
antenna was the king of antennas for the vast majority of radio
owners. Before the transistor radio and ferrites, every table radio
had a flat pancake loop antenna in the back of the radio behind all
the glowing tubes.

Oddly enough, no radios in this age have either of these antennas
anymore, and they still seem to pick up stations.

So, there you have a century of technical perspective on the topic.

Perhaps the "Joe Carr's Loop Antenna Handbook" may be interesting, but it
is quite expensive and an Amazon reviewer says it is not so
interesting... What about the "Joe Carr's Receiving Antenna Handbook" ?

He is a respected author. I always look at the bad Amazon reviews to
see if something is terribly wrong with the product or terribly wrong
with the customer. Quite often the customer is disappointed because
that customer is stupid. If I encounter a smart customer that is
disappointed, I can well imagine all the good comments are not very
reliable.

The thing about all these -um- books is that many of them serve up old
wives' tales about low noise and other magical characteristics.
Remember the lessons of a century worth of experience with loop
antennas within an inch of the guts of any radio. That worked fine
for a billion radios and radios were not bought if they were "noisy."

The real science of low noise is found in the distance to the source.
Quite often it is your neighbor's aquarium heater that is noisy (the
most often complained of source of noise reported here). Your loop
sits in your shack and that aquarium is 10 Meters away. You switch to
your longwire that runs to the fence and the aquarium is 1 meter away.
Do I have to work out the math on that? Is the loop quieter because
of its magic design - or simply because it is 10 times further away
(20dB) from the noise?

We get writers here who pound the table because their magic loop in
the shack is noisy and their long wire 10M away in the back yard is
quiet. They have to be told to turn off the flourescent light in the
shack if they want their magic loop to work.
(Their magic loop low score on Amazon) = (stupid.)

73's
Richard Clark, KB7QHC

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