Ideas for cheap and effective loop antennas


prog
 

This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?


Siegfried Jackstien
 

you "unbalance" it with connecting your coax direct to the loop

dg9bfc sigi


Am 04.08.2017 um 19:33 schrieb prog:

This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?



prog
 

The loop itself is unbalanced. See the top.


doug
 


On 08/04/2017 02:33 PM, prog wrote:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?

30 cM =11.8 inches. What kind of transformer is envisioned here? What frequency is it supposed to work at, and what is the turns ratio?



Tom Frobase
 

I build a kit for an HF active loop, here are the docs on it.  http://www.kitparts.com/loop


prog
 

The loop itself is high impedance and the impedance gets higher with lower frequencies. So the transformer will define the usable frequency range.
I have a bunch of BN-73-202's and will be experimenting this idea. Probably also try a diff input high impedance amp.


prog
 

I was thinking about something similar with jfets.


Ivan Boring
 

But you said it was balanced in your original post. I don't think such a small loop with is efficient on the low frequency bands. What is the frequency range and data for the transformer?

prog <info@...> skrev: (4 augusti 2017 22:39:02 CEST)

The loop itself is unbalanced. See the top.

--
Skickat från min Android-telefon med K-9 E-post. Ursäkta min fåordighet.


jdow
 

It is inherently unbalanced.

{o.o}

On 2017-08-04 13:31, Siegfried Jackstien wrote:
you "unbalance" it with connecting your coax direct to the loop
dg9bfc sigi
Am 04.08.2017 um 19:33 schrieb prog:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?


jdow
 

Probably very low impedance to a higher impedance such as 50 ohms. A really low input impedance LNA can materially boost a small loop's performance.

{^_^}

On 2017-08-04 15:13, doug wrote:
On 08/04/2017 02:33 PM, prog wrote:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?
30 cM =11.8 inches. What kind of transformer is envisioned here? What frequency is it supposed to work at, and what is the turns ratio?


Leif Asbrink
 

Hi Doug,

I can not understand the drawing. Two black turns and one yellow.
With two turns of a coax I expect four conductors....

To me thi figure looks like a (very ineffective) whip antenna
and not a loop.

The impedance is high, but the coupling to E-fields is weak
because of the high capacitive load. I do not think this
antenna would have any sensitivity to H-fields, but maybe
I misunderstand the diagram. The meaning of black vs yellow
is unclear to me.

73

Leif


On 08/04/2017 02:33 PM, prog wrote:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?
30 cM =11.8 inches. What kind of transformer is envisioned here? What
frequency is it supposed to work at, and what is the turns ratio?


doug
 

On 08/04/2017 07:57 PM, Leif Asbrink wrote:
Hi Doug,

I can not understand the drawing. Two black turns and one yellow.
With two turns of a coax I expect four conductors....

To me thi figure looks like a (very ineffective) whip antenna
and not a loop.

The impedance is high, but the coupling to E-fields is weak
because of the high capacitive load. I do not think this
antenna would have any sensitivity to H-fields, but maybe
I misunderstand the diagram. The meaning of black vs yellow
is unclear to me.

73

Leif

I didn't attempt to analyze the antenna. I know that small loops are effective receiving antennas at low and medium frequencies. My input was simply to translate the
metric measurement into US standard notation, and define the transformer. You will have to go back to the original posting person to determine what the desired impedance
may be and other questions. I will hesitate a guess that the impedance is quite low, based on the smallness of the antenna and the frequencies that I assume it is
supposed to operate at.

--doug



04/2017 02:33 PM, prog wrote:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?
30 cM =11.8 inches. What kind of transformer is envisioned here? What
frequency is it supposed to work at, and what is the turns ratio?


jdow
 

On a closer look at the diagram it's not a traditional small loop such as this ( http://topband.blog.cz/0612/receiving-loops-part-i-by-merv-k9fd ) or this ( http://f5rds.free.fr/F5RDS_magnetic_loops.html ). The drawing appears to generate a pair of loops in parallel in an attempt to balance the configuration. It, as with all small loops, would have a very low impedance on most or all HF frequencies. So a nice common base LNA should do nicely.

{^_^}

On 2017-08-04 17:57, Leif Asbrink wrote:
Hi Doug,
I can not understand the drawing. Two black turns and one yellow.
With two turns of a coax I expect four conductors....
To me thi figure looks like a (very ineffective) whip antenna
and not a loop.
The impedance is high, but the coupling to E-fields is weak
because of the high capacitive load. I do not think this
antenna would have any sensitivity to H-fields, but maybe
I misunderstand the diagram. The meaning of black vs yellow
is unclear to me.
73
Leif


On 08/04/2017 02:33 PM, prog wrote:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?
30 cM =11.8 inches. What kind of transformer is envisioned here? What
frequency is it supposed to work at, and what is the turns ratio?


prog
 
Edited

Look again. The loop has two turns in series with a center tap. The loops swap between the inner and outer conductors of the coax.
I simplified the diagram a bit:


prog
 
Edited

If it can help, at the top of the loops, we should have something similar to this:



PS: Who remembers ADSB collinear antennas?


Roberto Zinelli
 

Ok, now more clear!

Inviato da OldPhone

Il giorno 05 ago 2017, alle ore 08:26, prog <info@...> ha scritto:

Look again. The loop has two turns in series with a center tap. The loops swap between the inner and outer condictors of the coax.
I simplified the diagram a bit:

<dummyfile.0.part>


prog
 

Hi Leif, glad to see you here. The impedance is high, and the coupling to E-Field is intentionally made weak to avoid local electric noise in urban environment like mine.
Black is the outer (shield) conductor of the coax, and orange/yellow is the inner conductor.
Check my other reply here: https://groups.io/g/airspy/message/23174


Leif Asbrink
 

The new drawing is quite different. It shows a simple
two turn loop with its midpoint grounded.

The old image was NOT a loop, try follow the yellow line
from one side of the transformer to the other side.
Impossible. Some connection is missing.

The way the transformer is drawn is misleading. The primary
winding should have few turns and the secondary winding
many turns if you connect to a 50 ohm system.

Look again. The loop has two turns in series with a center tap.
The loops swap between the inner and outer condictors of the coax.
I simplified the diagram a bit:
It is clear now:-)

73

Leif


prog
 

I only removed the other side of the shielding from the same diagram.
Now this build technique ensures the currents induced by the E-fields will be canceled at the grounding point, which is a desirable property.


joe@polcari.com <Joe@...>
 

Isn¹t the original also out of phase, input to output? Or is that part of
the design?

On 8/5/17, 1:06 PM, "Leif Asbrink" <airspy@groups.io on behalf of
leif@sm5bsz.com> wrote:

The new drawing is quite different. It shows a simple
two turn loop with its midpoint grounded.

The old image was NOT a loop, try follow the yellow line
from one side of the transformer to the other side.
Impossible. Some connection is missing.

The way the transformer is drawn is misleading. The primary
winding should have few turns and the secondary winding
many turns if you connect to a 50 ohm system.

Look again. The loop has two turns in series with a center tap.
The loops swap between the inner and outer condictors of the coax.
I simplified the diagram a bit:
It is clear now:-)

73

Leif