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?

- 73 de Mike N3LI -

Last I tried a loop, I used a simple wire loop of about 10 cm diameter
(for a 1 m antenna diameter).

The coax version might save you some noise when receiving, but I never
tried coax myself, I use solid tubes.
For transmitting, coax or not should make no difference.

I do have an antenna tuner for the plain dipol. For the loop, you never
use antenna tuner.

For tuning the loop for transmitting, I find it easy to make the
coupling loop variable in size, and just try smaller/large loops, and
then fix the size when satisfied

Christen
oz1aab

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 -

If I recall, a full wave loop has an impedence of about 100 ohms, so if you
feed it with an electrical half-wave length of 75-ohm coax, you should have
an acceptable match, and a decent vswr.

"Michael Coslo" wrote in message
...
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?

- 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

Hal Rosser wrote:
If I recall, a full wave loop has an impedence of about 100 ohms, so if you
feed it with an electrical half-wave length of 75-ohm coax, you should have
an acceptable match, and a decent vswr.

Methinks you meant *quarter-wave* length of 75-ohm coax.
A half wavelength would merely repeat the feedpoint
impedance.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

In message , Cecil Moore
writes
Hal Rosser wrote:
If I recall, a full wave loop has an impedence of about 100 ohms, so
if you feed it with an electrical half-wave length of 75-ohm coax,
you should have an acceptable match, and a decent vswr.

Methinks you meant *quarter-wave* length of 75-ohm coax.
A half wavelength would merely repeat the feedpoint
impedance.

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?"
--
Ian

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 -