Switcher,

AM/MW Loop Antenna - Inductive Coupling -vice- Resistor Spoiler
http://groups.yahoo.com/group/Shortw...a/message/9407

To some degree all Circuits are L+C+R
- - - Although anyone of the three may not be significant
enough to factor into the Circuit Design parameters.
- - - Hence an AM/MW Loop Antenna is simply presented
as an L+C Circuit.

"IF" you were to use a Resistor in the Circuit of an
AM/MW Loop Antenna it would be 'because' the Radio
that you were using it with was being OverLoaded by
the Signal from the Loop Antenna.

You could simply achieve the same thing by varying the
AM/MW Loop Antenna 'coupling' with the Radio -by- Moving
the Loop Antenna nearer-to -or- farther-away from the Radio.

AM/MW LOOP ANTENNA COUPLING :
* The Coil of the external AM/MW Loop Antenna
is an Inductor {RF Transformer Coil}
* The Coil of the Radio's internal AM/MW Antenna
is an Inductor {RF Transformer Coil}
* Together the Two Coils form an RF Transformer
Moving the Two Coils and changing their relationship
to each other varies the "Coupling" between them.


THINGS TO READ :

READ - AM/MW DXing = Your Radio + Lazy Susan + Loop Antenna
for better AM/MW Band Reception and DXing with an AM Radio.
http://groups.yahoo.com/group/Shortw...a/message/1787
http://groups.yahoo.com/group/Shortw...a/message/1811

READ - Using the Built-in WHIP Antenna for better AM/MW Band
Reception and DXing with an AM Radio.
http://groups.yahoo.com/group/Shortw...na/message/875

READ - AM/MW Radio Reception : Whip Antenna Up? -or- Down?
for better AM/MW Band Reception and DXing with an AM Radio.
http://groups.yahoo.com/group/Shortw...a/message/1105

READ - AM/MW Random Wire Antenna Tuner using a AM/MW Loop
Antenna for better AM/MW Band Reception and DXing with an AM Radio.
http://groups.yahoo.com/group/Shortw...a/message/1150

READ - "HOW TO USE" a AM/MW Loop Antenna with a 'portable'
AM/FM Shortwave for better AM/MW Band Reception and DXing
with an AM Radio.
http://groups.yahoo.com/group/Shortw...a/message/1865

READ - For Improved AM/MW DXing
- Think Loop Antenna as a Coupler Tuner for better
AM/MW Band Reception and DXing with an AM Radio.
http://groups.yahoo.com/group/Shortw...a/message/2240
http://groups.yahoo.com/group/Shortw...a/message/2272
http://groups.yahoo.com/group/Shortw...a/message/2769

READ - Two 'basic' optional In-Door Antennas for better
AM/MW Band and FM Band using a 'portable' AM/FM Radio.
http://groups.yahoo.com/group/Shortw...a/message/2936

READ - Long "LoopStick" Antenna for AM/MW/BCB DXing
-by- Bill Bowden
http://groups.yahoo.com/group/Shortw...a/message/3075
http://groups.yahoo.com/group/Shortw...a/message/3100
The "L O N G" -Liner- {Skinny} Loop Antenna for better
AM/MW Band Reception and DXing with an AM Radio.


READ - Every Grundig Satellit 800 M Owner's Dream...
a 21" Lazy Susan for better AM/MW Band Reception and
AM/MW DXing )
http://groups.yahoo.com/group/Shortw...a/message/4406

READ - Setting-Up the Sony ICF-SW7600GR with a Loop Antenna
on a Lazy Susan for better AM/MW Band Reception and DXing.
http://groups.yahoo.com/group/Shortw...a/message/5886


RESISTOR AS A SPOILER IN AN AM/MW LOOP ANTENNA CIRCUIT :
-However- If you must use a Resistor in the Circuit of the
AM/MW Loop Antenna - Consider using a Series 1000 Ohm (1K)
Potentiometer (Pot) - So that you could adjust and fine-tune
the Circuit to achieve the Maximum Signal without OverLoading
the Radio. Hook the "Pot" up with the two ends connected
together and the Center Wiper as teh other end of the
Resistance Element of the Circuit. With the Wipper at either
end the Pot is out of the Circuit. As the Wiper is moved
from one of the ends to the Center of the Pot the amount
of Resistance in the Circuit 'increases' and the RF Signal
{EMF Field} of the Loop Antenna is Decreased. Wiring-Up
the Pot this way makes the Resistance Curve non-liner from
"0" to 500 Ohms sort of more like an Audio Taper Pot.


and now you know - iane ~ RHF

Telamon,

The objective is the impedance transformation.
-R- True

The voltage transformation is a result of the
impedance transformation.
-R- True - However for most situations the Voltage
Transformation is a good thing and another
benefit in using the Matching Transformer.

I've wondered about whether the input radio is responding
as a voltage or power sensing device. The answer is power
because the receiver input is low impedance so the
transformer is not changing the dynamic range of the
antenna/transformer/radio as power in equals power out
of the transformer.
-R- Yes - WRT the Matching Transformer Power "In"
and Power "Out" are the same. - It is MHO the the
'relative' Voltage Dynamic Range between the
Antenna-Side and Radio-Side of the Matching
Transformer does change. The Receivers Input is
Low Impedance - However IMHO it is the Voltage that
is being 'sensed' and processed within the Receiver
from RF to IF and then AF Power Ampified into an
Audio Signal.

A problem with the way some questions above are
posed is that there are not enough specifics defined
so I'll define them.
-R- True.

Let's say this is in regards to a long or a random wire
antenna. As a single element in the air it will function
as a voltage common mode antenna. This one element
is really half an antenna. For it to do useful work you
need an RF ground. You also have the problem of getting
the power it develops to be absorbed by the radio input.
-R- OK.

The voltage type transformer provides the impedance
transformation from the high impedance of the wire to
low impedance of the receiver input or coax of the same
value so the energy is transfered efficiently.
-R- The Key-Objective in using the Matching Transformer
is to 'match' the Impedance of the Radio-Side to the
Antenna Input {Impedance} of the Radio.

Now the transformer (UNUN) can be wired in more than
one way. One way is to use the radio ground, which is
in part the mains system ground as the RF return. This
is just fine to do as long as your local mains ground is
quiet in the frequency range you intend to use it. However,
this is not likely so you create a ground with the explicit
purpose of being the RF ground. This can be a ground
rod or radial wire on or under the ground routed under
the wire antenna.
-R- Yes - The selection and use of a Ground {Grounding
Point} can contribute significantly to the performance of
an Antenna + Matching Transformer + Feed-in-Line + Radio
System.

Another benefit is a static charge on the wire is shunted
to ground instead of through the radio input.
-R- True

To Re-State My Two Points :
* To my way of thinking Matching the Impedance
of the Radio-Side of the Matching Transformer to
the Radio's Input Impedance 'optimizes' Signal
Transfer from the Antenna {Ground} to the Radio.
* Plus reducing the Voltage Dynamic Range of
the Signals coming out of the Radio-Side of the
Matching Transformer 'feeds' the Receiver with
Signals that the Radio can more easily process.

it's just the way that i envision things - iane ~ RHF