"Owen Duffy" wrote in message
...
Michael Coslo wrote in news:gvhhkj$do4m$1
@tr22n12.aset.psu.edu:

I'm starting up an old project that I never quite finished - my loop
antenna.

When I first put it together, I tried a simple loop of coax to couple
the radio to the loop. Was never really satisfied with that though.

I'm wanting to try a gamma match, possibly something a little like what
Owen Duffy posted a nice version of.

The Gamma match is fairly understandable to me, and I expect it to work
well.

What I am wondering about is in the coax loop coupling system, how is
the best match obtained? Loop size? orientation? Luck?

Mike, you haven't given much information about the loop (size,
frequency). Is loop balance / symmetry important?

If it was a small loop, I would not be thinking about a gamma match
because of the impedance ratios for just one reason.

Owen


Owen -

I've had this nagging idea for a couple of years: What if the (single-turn?)
loop passes through a toroid which already has, say, 10 or so turns on it?
That should give an impedance step-up of 100 or so. Would that not be a good
way to at least get the matching closer? In fact, the tuning capacitor could
be connected to the high impedance side to reduce the capacitor's value.

Your comments will be appreciated.

John

John KD5YI wrote:

"Owen Duffy" wrote in message
...
Michael Coslo wrote in news:gvhhkj$do4m$1
@tr22n12.aset.psu.edu:

I'm starting up an old project that I never quite finished - my loop
antenna.

When I first put it together, I tried a simple loop of coax to couple
the radio to the loop. Was never really satisfied with that though.

I'm wanting to try a gamma match, possibly something a little like what
Owen Duffy posted a nice version of.

The Gamma match is fairly understandable to me, and I expect it to work
well.

What I am wondering about is in the coax loop coupling system, how is
the best match obtained? Loop size? orientation? Luck?

Mike, you haven't given much information about the loop (size,
frequency). Is loop balance / symmetry important?

If it was a small loop, I would not be thinking about a gamma match
because of the impedance ratios for just one reason.

Owen


Owen -

I've had this nagging idea for a couple of years: What if the
(single-turn?) loop passes through a toroid which already has, say, 10
or so turns on it? That should give an impedance step-up of 100 or so.
Would that not be a good way to at least get the matching closer? In
fact, the tuning capacitor could be connected to the high impedance side
to reduce the capacitor's value.


This has been done in a variety of ways (notably some papers from 20
years ago where they used this scheme to couple to the windshield window
frame on a jeep.

For Rx only, there's no real issues

For Tx, though, a small loop will tend to have high currents. There's a
LOT of energy stored in the magnetic field (and in the E field of the
capacitor that tunes the system). All that reactive energy will be
flowing back and forth through the transformer, so it will need a high
VA rating.

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.

Jim Lux wrote:

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.

Works on zero point energy?

- 73 de Mike N3LI -

Ian Jackson wrote:
The question is, "Do you use a quarterwave of 75 ohm cable to get
something like a 50 ohm impedance at the TX end - even if this means
using more coax than you really need or, to minimise losses, do you
simply use the shortest length of coax - either 50 or 75 ohm?"

Usually not a problem since 1/4WL of RG-11
at 4 MHz is only ~40 feet - hopefully less
than the height of the antenna. 1/4WL at any
higher HF frequency would be shorter than that.
Excess coax can usually be coiled into a choke.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

"Jim Lux" wrote in message
...
John KD5YI wrote:

"Owen Duffy" wrote in message
...
Michael Coslo wrote in news:gvhhkj$do4m$1
@tr22n12.aset.psu.edu:

I'm starting up an old project that I never quite finished - my loop
antenna.

When I first put it together, I tried a simple loop of coax to couple
the radio to the loop. Was never really satisfied with that though.

I'm wanting to try a gamma match, possibly something a little like what
Owen Duffy posted a nice version of.

The Gamma match is fairly understandable to me, and I expect it to work
well.

What I am wondering about is in the coax loop coupling system, how is
the best match obtained? Loop size? orientation? Luck?

Mike, you haven't given much information about the loop (size,
frequency). Is loop balance / symmetry important?

If it was a small loop, I would not be thinking about a gamma match
because of the impedance ratios for just one reason.

Owen


Owen -

I've had this nagging idea for a couple of years: What if the
(single-turn?) loop passes through a toroid which already has, say, 10 or
so turns on it? That should give an impedance step-up of 100 or so. Would
that not be a good way to at least get the matching closer? In fact, the
tuning capacitor could be connected to the high impedance side to reduce
the capacitor's value.


This has been done in a variety of ways (notably some papers from 20 years
ago where they used this scheme to couple to the windshield window frame
on a jeep.

For Rx only, there's no real issues

For Tx, though, a small loop will tend to have high currents. There's a
LOT of energy stored in the magnetic field (and in the E field of the
capacitor that tunes the system). All that reactive energy will be
flowing back and forth through the transformer, so it will need a high VA
rating.

Consider this.. if the loop has an electrical Q of, say, 1000 (which isn't
unusual), and you're radiating 100W, then there's 100kW of circulating
power in the system.


Adding the transformer changes the circulating energy in the system how?
(Excluding losses)

Michael Coslo wrote:
Jim Lux wrote:

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.

Works on zero point energy?

Nope, the 100k joules/sec was stored in the system
during the initial transient key-down state and was
not radiated. It won't be radiated until the transient
key-up state. This is a characteristic of standing-
wave antennas. In a 1/2WL dipole, only about 20% of
the energy stored in the antenna is radiated. In the
small loop above with its astronomically high SWR,
only about 0.1% of the energy stored in the antenna
is radiated during steady-state.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Michael Coslo wrote:
Jim Lux wrote:

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.

Works on zero point energy?

- 73 de Mike N3LI -

not at all.. that's the definition of Q.. it's the ratio of stored
energy: energy lost in 1 cycle.

John KD5YI wrote:
"Jim Lux" wrote in message
...
John KD5YI wrote:

"Owen Duffy" wrote in message
...
Michael Coslo wrote in news:gvhhkj$do4m$1
@tr22n12.aset.psu.edu:

I'm starting up an old project that I never quite finished - my loop
antenna.

When I first put it together, I tried a simple loop of coax to couple
the radio to the loop. Was never really satisfied with that though.

I'm wanting to try a gamma match, possibly something a little like
what
Owen Duffy posted a nice version of.

The Gamma match is fairly understandable to me, and I expect it to
work
well.

What I am wondering about is in the coax loop coupling system, how is
the best match obtained? Loop size? orientation? Luck?

Mike, you haven't given much information about the loop (size,
frequency). Is loop balance / symmetry important?

If it was a small loop, I would not be thinking about a gamma match
because of the impedance ratios for just one reason.

Owen


Owen -

I've had this nagging idea for a couple of years: What if the
(single-turn?) loop passes through a toroid which already has, say,
10 or so turns on it? That should give an impedance step-up of 100 or
so. Would that not be a good way to at least get the matching closer?
In fact, the tuning capacitor could be connected to the high
impedance side to reduce the capacitor's value.


This has been done in a variety of ways (notably some papers from 20
years ago where they used this scheme to couple to the windshield
window frame on a jeep.

For Rx only, there's no real issues

For Tx, though, a small loop will tend to have high currents. There's
a LOT of energy stored in the magnetic field (and in the E field of
the capacitor that tunes the system). All that reactive energy will
be flowing back and forth through the transformer, so it will need a
high VA rating.

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.


Adding the transformer changes the circulating energy in the system how?
(Excluding losses)



It doesn't.. it's that the circulating energy in a high Q system is
quite large, so you need to size the transformer (core) appropriately.

The transformer size needed to handle a 100W Tx in a resonant dipole is
MUCH smaller than the transformer needed to handle a 100W Tx in a
compact loop with a Q of 1000. The transformer has to handle not only
the input(and radiated) power, but also the circulating power.

Actually, ALL the components have to deal with the circulating power,
but most builders of compact loops are aware of the need for low
resistance in the loop and high voltage ratings in the capacitor.

On May 29, 10:49*am, Jim Lux wrote:
John KD5YI wrote:

"Owen Duffy" wrote in message
...
Michael Coslo wrote in news:gvhhkj$do4m$1
@tr22n12.aset.psu.edu:

I'm starting up an old project that I never quite finished - my loop
antenna.

When I first put it together, I tried a simple loop of coax to couple
the radio to the loop. Was never really satisfied with that though.

I'm wanting to try a gamma match, possibly something a little like what
Owen Duffy posted a nice version of.

The Gamma match is fairly understandable to me, and I expect it to work
well.

What I am wondering about is in the coax loop coupling system, how is
the best match obtained? Loop size? orientation? Luck?

Mike, you haven't given much information about the loop (size,
frequency). Is loop balance / symmetry important?

If it was a small loop, I would not be thinking about a gamma match
because of the impedance ratios for just one reason.

Owen

Owen -

I've had this nagging idea for a couple of years: What if the
(single-turn?) loop passes through a toroid which already has, say, 10
or so turns on it? That should give an impedance step-up of 100 or so.
Would that not be a good way to at least get the matching closer? In
fact, the tuning capacitor could be connected to the high impedance side
to reduce the capacitor's value.

This has been done in a variety of ways (notably some papers from 20
years ago where they used this scheme to couple to the windshield window
frame on a jeep.

For Rx only, there's no real issues

For Tx, though, a small loop will tend to have high currents. *There's a
LOT of energy stored in the magnetic field (and in the E field of the
capacitor that tunes the system). *All that reactive energy will be
flowing back and forth through the transformer, so it will need a high
VA rating.

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.

Cecil had something to say like that( different figure) and I find it
quite interesting!
The idea of a loop antenna acting as a battery I find odd. The loop is
a tank circuit
where the power supplied replaces the power lost in the resistance of
the components
Without the resistance it would be continual motion! So where is this
"radiation" ratio coming from as the power supplied is purely a
replacement of resistance losses which includes the energy supplied
for radiation? The voltage is in the kilo volts but with current
extremely low I fail to see where the 100kW comes from which makes it
a
battery
Art

"Jim Lux" wrote in message
...
John KD5YI wrote:
"Jim Lux" wrote in message
...
John KD5YI wrote:

"Owen Duffy" wrote in message
...
Michael Coslo wrote in news:gvhhkj$do4m$1
@tr22n12.aset.psu.edu:

I'm starting up an old project that I never quite finished - my loop
antenna.

When I first put it together, I tried a simple loop of coax to couple
the radio to the loop. Was never really satisfied with that though.

I'm wanting to try a gamma match, possibly something a little like
what
Owen Duffy posted a nice version of.

The Gamma match is fairly understandable to me, and I expect it to
work
well.

What I am wondering about is in the coax loop coupling system, how is
the best match obtained? Loop size? orientation? Luck?

Mike, you haven't given much information about the loop (size,
frequency). Is loop balance / symmetry important?

If it was a small loop, I would not be thinking about a gamma match
because of the impedance ratios for just one reason.

Owen


Owen -

I've had this nagging idea for a couple of years: What if the
(single-turn?) loop passes through a toroid which already has, say, 10
or so turns on it? That should give an impedance step-up of 100 or so.
Would that not be a good way to at least get the matching closer? In
fact, the tuning capacitor could be connected to the high impedance
side to reduce the capacitor's value.


This has been done in a variety of ways (notably some papers from 20
years ago where they used this scheme to couple to the windshield window
frame on a jeep.

For Rx only, there's no real issues

For Tx, though, a small loop will tend to have high currents. There's a
LOT of energy stored in the magnetic field (and in the E field of the
capacitor that tunes the system). All that reactive energy will be
flowing back and forth through the transformer, so it will need a high
VA rating.

Consider this.. if the loop has an electrical Q of, say, 1000 (which
isn't unusual), and you're radiating 100W, then there's 100kW of
circulating power in the system.


Adding the transformer changes the circulating energy in the system how?
(Excluding losses)



It doesn't.. it's that the circulating energy in a high Q system is quite
large, so you need to size the transformer (core) appropriately.

The transformer size needed to handle a 100W Tx in a resonant dipole is
MUCH smaller than the transformer needed to handle a 100W Tx in a compact
loop with a Q of 1000. The transformer has to handle not only the
input(and radiated) power, but also the circulating power.

Actually, ALL the components have to deal with the circulating power, but
most builders of compact loops are aware of the need for low resistance in
the loop and high voltage ratings in the capacitor.


I must have missed something. I did not realize that Michael intended to use
the loop with a 100 watt transmitter. My assumption was that it was
primarily a receiving antenna.

However, it doesn't matter because your comments are equally applicable to a
short wire antenna. Therefore, I would urge readers not to consider the
small loop any worse than a short wire antenna in these regards.