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 Duffy wrote:
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?

It's Octagonal, .75 inch copper tubing, around 8 feet in diameter. It's
designed to just reach into the 80 meter voice segment with it's
capacitor setup. Upper end is either 17 or 15 meters. It's been a few
years since I worked on this, which is the reason for the "around" remarks.

Capacitor is a 4 tube trombone capacitor, each tube roughly a foot in
length. External tube is .75 inch, and internal tube is .5 inch.
Insulation is wrapped Kevlar sheet around internal tube.

Adjustment is via a power screwdriver and a threaded rod setup to move
the trombones in and out.

- 73 de Mike N3LI -

Owen Duffy wrote:

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


Oops, I didn't mention anything about symmetry in that post.

Probably because I'm not sure how important it might be. So if it is an
issue, I'm all ears!

- 73 de Mike N3LI -

Michael Coslo wrote in news:gvju7l$n034$4
@tr22n12.aset.psu.edu:

Owen Duffy wrote:

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


Oops, I didn't mention anything about symmetry in that post.

Probably because I'm not sure how important it might be. So if it is an
issue, I'm all ears!

- 73 de Mike N3LI -

Mike, the symmetry issue is about whether you want the deepest nulls. A
gamma match is not likely to give you the best symmetry and hence the
deepest nulls.

You are talking about a smallish loop, and without modelling it, I wonder
if the gamma feed is as efficient say, as a inner feed loop.

You have gone to a lot of trouble to keep losses in the loop down, it
would be a pity to compromise it too much with the feed system.

Owen

Owen Duffy wrote:
Michael Coslo wrote in news:gvju7l$n034$4

Oops, I didn't mention anything about symmetry in that post.

Probably because I'm not sure how important it might be. So if it is an
issue, I'm all ears!


Mike, the symmetry issue is about whether you want the deepest nulls. A
gamma match is not likely to give you the best symmetry and hence the
deepest nulls.

You are talking about a smallish loop, and without modelling it, I wonder
if the gamma feed is as efficient say, as a inner feed loop.

You have gone to a lot of trouble to keep losses in the loop down, it
would be a pity to compromise it too much with the feed system.


I'm following you here, Owen. I'll put together an inner feed loop and
give that a shot. I was looking at the magloop thread you were in on
eHam from a little over a year ago. Some good info there.

I was thinking about using copper tubing for the loop, but with the area
being a variable, I'm considering using something more flexible. Or
maybe finding out the area by experimentation, then going with a final
loop area in a neater form.


Thanks much!

- 73 de Mike N3LI -

"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 -

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.