SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

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.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

On 15 Dec 2010 20:52:22 GMT, Sébastien MEDARD wrote:

There should free software displaying this gray line with UTC time, no?

Hi Sébastien,

I'm sure there is - somewhere. GoogleEarth would be an elaborate tool
to accomplish this.

I found the "Receiving Antenna Handbook" quite cheap, but the "Loop
Antenna Handbook" is still expensive. Between $60 to $257... I will try
the cheapest.

Myself, I would not advise spending more than $20. Professional
antenna books barely give more than one section of the first chapter
to its discussion.

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

No, probably less. Being an OM, (40 years ago) I also taught classes
for repair and maintenance of Collins' famous receiver, the R-390. EVEN
NOW (40 years later), this is probably the best receiver for its price
(and even two to three times its price).

Do you calculate that in constant dollar from the 50's? :)

Today's cost matched with the price of equivalent performance from an
available vendor.

I can imagine the teaching class. Everybody with a Collin's in front of
him/her... A one year project to restore completely one of this legendary
radio. I would like that!

There were two to a radio. 40 to 30 hours learning the schematic
theory of operation; and troubleshooting and tuning procedures and 30
to 40 hours in front of the radio. The class was 2 weeks long.
Complete restore unnessecary, of course, as the last class had fixed
any problem. No, we had a data bank of known problems, known
solutions, and the time to debug them averaged over at least 100
students for each problem.

With a good DSP outside (Audio DSP only), can beat every other ones?

Good for filtering, probably tighter than the mechanical filters
(theoretically), but there are many, many other considerations.

It seems not easy to get one, especially in Europe...

That seems like a very real impediment. And with it weighing in at 85
pounds (40 kilograms), the cost to deliver would add considerably.

So, my comment was a lapalissade? Certainly.

You got the picture :)

In technicolor and 3D.

73's
Richard Clark, KB7QHC

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

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.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

On Dec 15, 2:17*pm, Sébastien MEDARD wrote:


Do you tune it, or not? Is there a small loop inside or not?


Yes for both. The cap is down at the bottom corner, and
I use a separate coupling loop because I'm feeding coax
to the radio. The 42 inch per side loop uses 5 turns on
the main loop. The coupling loop is on the inside, and
maybe 36 or so inches out from center.
Sounds like you are in good shape for caps.
That 500-500 would be good. I'd put a small mini switch
between the two gangs to be able to cut or add the
second gang. That's what I do on mine anyway.
I solder the switches right to the tabs on the cap.
I also have a handful of fixed caps to add if I want to
drop further down into longwave. I don't use them that
often so I just clip them on if needed.
I think my 16 inch round loop has about 12 turns if
I remember right.. It also uses a inner coupling loop.
For me, those loops are mainly for AM-BC, but I do
wander down and listen to the air beacons from time
to time. And the big one covers 160 meters, so I
use it for that sometimes.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

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.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

Hello,

On Wed, 15 Dec 2010 15:40:31 -0800, Richard Clark wrote:

On 15 Dec 2010 20:52:22 GMT, Sébastien MEDARD wrote:

There should free software displaying this gray line with UTC time, no?

I'm sure there is - somewhere. GoogleEarth would be an elaborate tool
to accomplish this.

Well... In French we say that it is like using backhoes to move a bucket
of sand...

I found some software here :
http://www.ac6v.com/software.htm#GEO

Need to be tested...

I found the "Receiving Antenna Handbook" quite cheap, but the "Loop
Antenna Handbook" is still expensive. Between $60 to $257... I will try
the cheapest.

Myself, I would not advise spending more than $20. Professional antenna
books barely give more than one section of the first chapter to its
discussion.

I totally agree, I will see what the seller proposes.

I can imagine the teaching class. Everybody with a Collin's in front of
him/her... A one year project to restore completely one of this
legendary radio. I would like that!

There were two to a radio. 40 to 30 hours learning the schematic theory
of operation; and troubleshooting and tuning procedures and 30 to 40
hours in front of the radio. The class was 2 weeks long. Complete
restore unnecessary, of course, as the last class had fixed any problem.
No, we had a data bank of known problems, known solutions, and the time
to debug them averaged over at least 100 students for each problem.

:)

With a good DSP outside (Audio DSP only), can beat every other ones?

Good for filtering, probably tighter than the mechanical filters
(theoretically), but there are many, many other considerations.

I should try to see if there are any OM near the place I live. Could be
interesting to see those old boxes.

Well, many thanks for the basic information you gave me.

Now, I need to use it.

Sébastien.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

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.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

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.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

Hello,

On Thu, 16 Dec 2010 05:33:58 -0800, nm5k wrote:

Yes for both. The cap is down at the bottom corner, and I use a separate
coupling loop because I'm feeding coax to the radio.

I saw a lot of photos where I saw the cap on the top and the coax feeded
to the coupling loop on the bottom. Is doing the other way OK?

The 42 inch per
side loop uses 5 turns on the main loop. The coupling loop is on the
inside, and maybe 36 or so inches out from center. Sounds like you are
in good shape for caps. That 500-500 would be good.

Great.

I'd put a small mini
switch between the two gangs to be able to cut or add the second gang.

Definitively a good idea.

That's what I do on mine anyway. I solder the switches right to the tabs
on the cap.

Good advice.

I also have a handful of fixed caps to add if I want to drop
further down into longwave. I don't use them that often so I just clip
them on if needed.

Planned.

The thing that can be done is to use the same base board on the different
loops to be used. Tell me your thoughts.... I was planning to put
everything on a wood board...

I think my 16 inch round loop has about 12 turns if I
remember right.. It also uses a inner coupling loop. For me, those loops
are mainly for AM-BC,

It seems the size of the loop (I didn't play with loop software yet) is
not critical, but is it possible to say that the lower band you want to
listen, the taller loop you should use?

but I do wander down and listen to the air beacons
from time to time. And the big one covers 160 meters, so I use it for
that sometimes.

Well... Sorry for the newbie question.... But what do you mean by beacons?

Sebastien.

SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
 

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