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

Hello,

On Fri, 17 Dec 2010 09:20:48 -0800, Richard Clark wrote:

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.

Tonight and yesterday night I played with my experimentation board
(loop...s on my shelves).

I have a 4 loops (square) web :
1 - 8 turns - 1.5 m /side
2 - 3 turns - 1.0m /side
3 - 1 turn - 0.8m /side
4 - 1 turn- 0.65m /side

Each one is inside the other one.

I used the second to be the matching one from the previous, the firts.
The third, to be the mathcing one of the second, etc.

The resonant one gets a variable air capacitor (I change it every time I
need to go higher....).

Very interesting, indeed.

If I understand well, the loop gets the role of inductance and the
capacitor the role of the capacitance... (Lapalisse...). Matching both
gets the best result for a given frequency. I succeed in making apparent
signals that I was not aware of... With this antenna I can tune in the
frequency from 300 KHz to near 7300 KHz... Completely amazing. That's the
first time I can exactly see (thanks to the waterfall information
display) how it does increase, not only the signal, but what's more
important, the signal/noise ratio. I understand now how this is very
important...

What I can see, is that depending on the size of the loop and the
frequency I am monitoring, the variable capacitor may or may not be very
difficult to use, and the bandwidth lack of noise, narrow or wide...
Interesting to see that it is possible to increase the signal without
increasing a lot the signal/noise ratio (better than nothing . But you
can't play when the signal is too weak....

I am quite happy. It does not tell anything about the antenna efficiency,
but it helps me understand how it works. I get somebody in my family who
is a physics teacher... I need to ask her information about "RLC
oscillators for newbies" to be able to put some rational things upon my
experimentations

To do next :
- Try to carry out the tiny preselector from Wim (need to find some coper
wire... And need to try to recover some old radio parts to play with....
(get some ferrite rods, low value variable capacitors, etc.)
- Try to get some time, and some place, to play with long wires, dipoles
and their related matching systems...

Sebastien.

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

Hello,

On Sat, 18 Dec 2010 08:09:52 -0800, Wimpie wrote:

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

I should.... But I was better in chemistry I should have studied RLC
circuits but at this time it was boring... If I had some interest in
shortwave listening, I would have been a better student in physics

But I should be able to understand I think I am going to see if there
is any radio club near the place I live. Because I have a lot of
questions and English is, as you understood it, not my main spoken
language

Seb.

On 19 dic, 23:10, Sébastien MEDARD wrote:
Hello,

On Sat, 18 Dec 2010 08:09:52 -0800, Wimpie wrote:
Do you have some background in electronics and/or AC circuits (concept
of reactance, impedance, resonance, etc)?

I should.... But I was better in chemistry I should have studied RLC
circuits but at this time it was boring... If I had some interest in
shortwave listening, I would have been a better student in physics

But I should be able to understand I think I am going to see if there
is any radio club near the place I live. Because I have a lot of
questions and English is, as you understood it, not my main spoken
language

Seb.

Hello Sébastien,

I think it is a good thing to contact some people locally.

Besides support with the calculation for the inductors and capacitors,
small "construction errors" can degrade performance of a basically
good design significantly.

Be prepared to get many different answers to the same question!

Yesterday evening I experienced strong increase in mains supply
synchronized interference. After some elimination tests, the
"offender" was a new tiny switching plug-in adapter.

I had to use several ferrite cores to reduce the interference from
3.3 MHz to 15 MHz to an acceptable level. The volume and weight of
the ferrite cores I used exceeds that of the adapter.

Best regards,


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