On 13 dic, 22:01, Sébastien MEDARD wrote:
On Sun, 12 Dec 2010 12:25:59 -0800, Richard Clark wrote:
On 12 Dec 2010 13:59:06 GMT, Sébastien MEDARD wrote:

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 understand better what is the purpose of this kind of map (on SDR-
Radio.com software for example). Where you can see an OM, you are pretty
sure to see this kind of map.

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.

The reason why they call you OM ? )

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.

OK. I will try that later... For now I get some problems to use Linrad
with the SDR-IQ... Painful to boot on windows every time I want to listen
to shortwaves... And using a virtual system is not very efficient on my
old computer...

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).

Interesting. What would be the best ratio?

I was wondering... It seems loop antennas are a never ending story.

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.

I will try to find one when they are cheaper.

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."

OK. But today we probably ask more to radios than yesterday, no?

The real science of low noise is found in the distance to the source.

Lapalisse would have said exactly the same thing. He would have said that
the real science of good reception is found in the distance to the source
too )

Is the loop quieter because of its
magic design - or simply because it is 10 times further away (20dB) from
the noise?

OK for that.

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.)

Lesson one = learned.

Thanks.

Sebastien.

Hello Sébastien,

Regarding tuning, loops and (long) wires.

You probably locate your antenna far away from noise sources. Mostly
this is not where your receiver is.

In case of tuned loops, you have to go outside for each significant
frequency change. This is one of the reasons that I want my
preselection / tuning adjacent to the receiver.

Loops aren't magic things. A wire from your balcony to a tree or other
tie point may give better S/N ratio then the best (expensive) loop on
your balcony.

Best matching isn't required for reception at HF, just sufficient
signal. In case of a PI tuning / preselector device, you need to
adjust two capacitors in case of major frequency change. In my
opinion a single capacitor device is more pleasant to use.

(deep) Nulls in the radiation pattern at low frequency (AM BC and
below) are the main benefit of the loop if you are willing to change
the orientation frequently when tuning across the bands. At increasing
frequency, the nulls are less pronounced because of propagation
issues. Off course a small horizontally oriented dipole has also
figure-of-eight radiation pattern, but polarization isn't good for AM
BC and lower.

For experimentation / comparison, I used a 1m diameter non-tuned loop
in the attic with preselection / tuning adjacent to the receiver. In
most cases a 5 m outdoor wire with same preselector and receiver gives
similar or better S/N ratio. This may be because of the attic has
mains wiring and I didn't want to go to the attic for reorientation
of the loop.

If you want to experiment with some long wire (unbalanced) antennas,
make sure to have a ground (counterpoise) provision outside; otherwise
your coaxial cable will be part of the antenna. This may result in
more interference from indoor sources.

Whether or not you have sufficient signal from your antenna is easy to
check. Listen to a known station. Tune your preselector to maximum
signal. Now tune to a free frequency close to your station's frequency
so that you hear noise. Remove the antenna, the audio noise should be
less now.

If you use a tapped coil preselector (like the one in my link), and
have sufficient noise from the antenna, you may even change the taps.
The preselector will give more insertion loss, but it will be more
selective also. This can be of use when you have strong signals in
your neighborhood. Because of portability, I frequently use an AOR
AR8200. Without preselection, such a wide band receiver is useless
with an external antenna.

Best regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me very likely

On Tue, 14 Dec 2010 09:17:40 -0800, Wimpie wrote:

Regarding tuning, loops and (long) wires.

You probably locate your antenna far away from noise sources. Mostly
this is not where your receiver is.

That's a problem, indeed.

In case of tuned loops, you have to go outside for each significant
frequency change. This is one of the reasons that I want my
preselection / tuning adjacent to the receiver.

It seems there is another solution. The varactor diodes seem to act as a
variable capacitor driven by their voltage (the capacitance of this kind
of diode decreases as the potential is increased).

It seems there are some loop designs with varactor diodes as tuners.

But I don't know what could be the price of a such solution.

Loops aren't magic things. A wire from your balcony to a tree or other
tie point may give better S/N ratio then the best (expensive) loop on
your balcony.

I think so, but there is nothing I can change for that today.

Best matching isn't required for reception at HF, just sufficient
signal. In case of a PI tuning / preselector device, you need to adjust
two capacitors in case of major frequency change. In my opinion a
single capacitor device is more pleasant to use.

I will try different configurations when I get them.

If you want to experiment with some long wire (unbalanced) antennas,
make sure to have a ground (counterpoise) provision outside; otherwise
your coaxial cable will be part of the antenna. This may result in more
interference from indoor sources.

Yes, but the place I plan to experiment should be far away from this kind
of trouble... I won't be able to get a good ground there.

If you use a tapped coil preselector (like the one in my link),

Sorry, where is it in your web site?

and have
sufficient noise from the antenna, you may even change the taps. The
preselector will give more insertion loss, but it will be more selective
also.

How is called this design?

This can be of use when you have strong signals in your
neighborhood. Because of portability, I frequently use an AOR AR8200.
Without preselection, such a wide band receiver is useless with an
external antenna.

I don't like these receivers... Or they should be used with
optoelectronics frequency counters to drive the receiver... But more than
that, the screen of these receivers is too small, too few information...
I prefer being at home (or in a car) with a laptop computer displaying a
beautiful waterfall picture )

That's the reason why I owned a SDR-IQ. And on upper frequencies, it will
keep being useful with an appropriate scanner (if I see a cheap one on
the second hand market).

For the moment, I prefer exploring the bands than picking up a frequency
in a database (it may change...)

Sebastien.

On 15 dic, 22:32, Sébastien MEDARD wrote:
On Tue, 14 Dec 2010 09:17:40 -0800, Wimpie wrote:
Regarding tuning, loops and (long) wires.

You probably locate your antenna far away from noise sources. *Mostly
this is not where your receiver is.

That's a problem, indeed.

In case of tuned loops, you have to go outside for each significant
frequency change. *This is one of the reasons that I want my
preselection / tuning adjacent to the receiver.

It seems there is another solution. The varactor diodes seem to act as a
variable capacitor driven by their voltage (the capacitance of this kind
of diode decreases as the potential is increased).

It seems there are some loop designs with varactor diodes as tuners.

But I don't know what could be the price of a such solution.

That is an option, as they are frequently used in VHF/UHF systems. The
varactor is a non-linear device, so you may get intermodulation in a
large signal environment. You may use the varactor as fine tuning in
combination with fixed capacitors.


Loops aren't magic things. A wire from your balcony to a tree or other
tie point may give better S/N ratio then the best (expensive) loop on
your balcony.

I think so, but there is nothing I can change for that today.

Best matching isn't required for reception at HF, just sufficient
signal. *In case of a PI tuning / preselector device, you need to adjust
two capacitors in case of major frequency change. *In my opinion a
single capacitor device is more pleasant to use.

I will try different configurations when I get them.

If you want to experiment with some long wire (unbalanced) antennas,
make sure to have a ground (counterpoise) provision outside; otherwise
your coaxial cable will be part of the antenna. This may result in more
interference from indoor sources.

Yes, but the place I plan to experiment should be far away from this kind
of trouble... I won't be able to get a good ground there.

Did you try the balcony fence or other large metallic structure as
floating ground (counterpoise)?


If you use a tapped coil preselector (like the one in my link),

Sorry, where is it in your web site?

It is the simple thing I referenced earlier
www.tetech.nl/divers/SimplePreselector2.jpg


and have
sufficient noise from the antenna, you may even change the taps. The
preselector will give more insertion loss, but it will be more selective
also.

How is called this design?

I don't know the name for it, it is just a parallel resonant LC
circuit where the input and output goes via an inductive tap. Moving
the tap changes the coupling between the source/load and the resonant
circuit, hance changing the loaded Q-factor.


This can be of use when you have strong signals in your
neighborhood. * Because of portability, I frequently use an AOR AR8200.

On Thu, 16 Dec 2010 03:34:56 -0800, Wimpie wrote:

It seems there are some loop designs with varactor diodes as tuners.

But I don't know what could be the price of a such solution.

That is an option, as they are frequently used in VHF/UHF systems. The
varactor is a non-linear device, so you may get intermodulation in a
large signal environment. You may use the varactor as fine tuning in
combination with fixed capacitors.

OK.

If you want to experiment with some long wire (unbalanced) antennas,
make sure to have a ground (counterpoise) provision outside;
otherwise your coaxial cable will be part of the antenna. This may
result in more interference from indoor sources.

Yes, but the place I plan to experiment should be far away from this
kind of trouble... I won't be able to get a good ground there.

Then I shall use a dipole...

Did you try the balcony fence or other large metallic structure as
floating ground (counterpoise)?

Not at this time. This is planned.

If you use a tapped coil preselector (like the one in my link),

Sorry, where is it in your web site?

It is the simple thing I referenced earlier
www.tetech.nl/divers/SimplePreselector2.jpg

Sorry... Yes, your design seems quite simple. But as a beginer, I think i
get some problems to understand how things are connected to the variable
capacitor, I mean I think the way the variable capacitor works is missing
in my information pool...

Based on your photo let say we get :
On the upper side : two connectors
On the lower side : two other connectors

But the upper side connectors are connected to the lower side
connectors... via the capacitor itself. Am I right?

The tap coil preselectors seem quite easy to carry out. You use different
connectors on the tap to select the band you want to use.

You get a switch on the upper side that seems to avoid using one gang of
the capacitor... But I cannot see of it is connected to the ground or not.

The air capacitor ground is connected to the ground.
On the right side, the tap coil preselectors are connected to the ground
too.
There is a tiny capacitor that connects one gang to the ground again.

The central board should be used to avoid both tapped coil preselectors
to get an inductive action on the other?

Is this correct? Would it be possible to get the schematic so that I
could try to carry it out?

How did you compute the place to put the connectors (number of turns) for
the tapped coil connectors?

and have
sufficient noise from the antenna, you may even change the taps. The
preselector will give more insertion loss, but it will be more
selective also.

How is called this design?

I don't know the name for it, it is just a parallel resonant LC circuit
where the input and output goes via an inductive tap. Moving the tap
changes the coupling between the source/load and the resonant circuit,
hance changing the loaded Q-factor.

How do you use it? Quite a blind test, no?

This can be of use when you have strong signals in your neighborhood.
Â* Because of portability, I frequently use an AOR AR8200. Without
preselection, such a wide band receiver is useless with an external
antenna.

I have a big QRM (well, I don't know what it is) at 1500 MHz and other
smaller ones elsewhere that I cannot switch off )

Sebastien.

Hello Sébastien,

This: http://www.tetech.nl/divers/Simple_HF_Preselector1.png will
help you. It shows the basic idea of a simple single variable
capacitor preselector.

You can use one coil and put two selectors on it, but with two
seperate coils the attenuation for out-of-band signals is much better.
This is because the individual turns of each coil have low mutual
coupling (they don't act as a transformer). As I have sufficient
antenna noise, the selectors (in my case clips) are mostly on the
lowest position (I don't need matching to get more signal and noise).

For AM BC operation you need more turns (w.r.t. the coils on the
photo).


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me in most cases.

Hello,

On Thu, 16 Dec 2010 09:40:15 -0800, Wimpie wrote:

Hello Sébastien,

This: http://www.tetech.nl/divers/Simple_HF_Preselector1.png will help
you. It shows the basic idea of a simple single variable capacitor
preselector.

Many thanks. I will try it as soon as possible.

You can use one coil and put two selectors on it, but with two seperate
coils the attenuation for out-of-band signals is much better. This is
because the individual turns of each coil have low mutual coupling (they
don't act as a transformer). As I have sufficient antenna noise, the
selectors (in my case clips) are mostly on the lowest position (I don't
need matching to get more signal and noise).

OK.

For AM BC operation you need more turns (w.r.t. the coils on the photo).

As I want to use it from 0.5 to 30MHz, what would be size of both coils?
How many turns? What diameter? What would be the value of the C1
capacitor? A lot of questions....

Thanks again.

Sebastien.

On 17 Dec 2010 15:28:08 GMT, Sébastien MEDARD wrote:

As I want to use it from 0.5 to 30MHz, what would be size of both coils?
How many turns? What diameter? What would be the value of the C1
capacitor? A lot of questions....

Hi Sebastien,

Reg Edward's software, that you already have access to, will answer
that far faster than asking here. Reason for that is because of all
the variables that come into play. You can judge for yourself when
you enter them into the program and observe what results are returned.

73's
Richard Clark, KB7QHC

On 17 dic, 16:28, Sébastien MEDARD wrote:
Hello,

On Thu, 16 Dec 2010 09:40:15 -0800, Wimpie wrote:
Hello Sébastien,

This: *http://www.tetech.nl/divers/Simple_H...ctor1.png*will help
you. It shows the basic idea of a simple single variable capacitor
preselector.

Many thanks. I will try it as soon as possible.

You can use one coil and put two selectors on it, but with two seperate
coils the attenuation for out-of-band signals is much better. This is
because the individual turns of each coil have low mutual coupling (they
don't act as a transformer). * As I have sufficient antenna noise, the
selectors (in my case clips) are mostly on the lowest position (I don't
need matching to get more signal and noise).

OK.

For AM BC operation you need more turns (w.r.t. the coils on the photo)..

As I want to use it from 0.5 to 30MHz, what would be size of both coils?
How many turns? What diameter? What would be the value of the C1
capacitor? A lot of questions....

Thanks again.

Sebastien.

Hello,

Do you have some background in electronics and/or AC circuits (concept
of reactance, impedance, resonance, etc)?


Wim
PA3DJS