How to match 190 +j140 to a 50 ohm source?
 

On Sat, 8 Dec 2007 11:22:05 -0800 (PST), wrote:

yep its an end of the semester project. BUT, we never learned anything
about impedance matching, so I feel no shame in asking people like
yourself. Thanks for your help.

The shame is your course approaching the topic to the point of
construction without introducing matching! Only the most trivial
designs escape this necessity.

This, however, may suggest that the particular assigned helix design
was already selected to match, and that your construction, or its
measurement are problematic.

It may be in the measurement given that at this scale (if you in fact
observed scale EXACTLY), it is generally no more complex than
assembling tinker toys.

You may have skipped the step of normalizing your network analyzer
(which I presume you have one, given the resolution of your citation
in the subject line), or you failed to isolate the antenna from the
feed line (aka choking the feedpoint, rather more an archaic term for
students, but well known by those practiced in the art). Both amount
to the same thing.

I'm at home now, and from what I can tell, I can get a good reactive
match by changing the length of the wire from the ground plane to the
connector? (while keeping the wire from the helix to the connector
constant? I think I will try this.

How can you "tell?" The reactive is rarely disassociated from the
real.

The real part I'm not too worried about.

You should, as it is as much a problem as the reactive part.

73's
Richard Clark, KB7QHC

How to match 190 +j140 to a 50 ohm source?
 

I'm worried about the real part, its just that after the reactive part
is nice, I don't think matching the real part will be hard.

I've just been reading on the internet and stuff about gamma matches
and at least one of them has said that gamma matches only match the
reactive part. from what you say I guess this is not true?

Hopefully I can get up to school later and read some real material,
but for right now the internet is all i have.

We weren't given a concrete design. More like make a helical antenna
with 12db forward gain at 450 MHz--that's it.

I'm about 99% sure that we set up the analyzer correctly. We tested
some dummy loads (like opens, shorts, etc) on end of the feedline and
they showed up as expected on the smith chart.

Finally, I kid you not. Nothing about impedance matching in this
class. I know a little about L networks and the like, but I don't
know how to implement these networks at high frequenices.

How to match 190 +j140 to a 50 ohm source?
 

On Sat, 8 Dec 2007 12:01:50 -0800 (PST), wrote:

I'm worried about the real part, its just that after the reactive part
is nice, I don't think matching the real part will be hard.

That is a comforting illusion, but only an illusion. If you are
versed with the Smith Chart (another archaic tool from the student's
perspective, but immensely used by the practitioner), then you would
appreciate this.

If this course is more than a side-bar to your studies (or if you are
progressing into RF or Linear design), then the Smith Chart is your
best friend.

I've just been reading on the internet and stuff about gamma matches
and at least one of them has said that gamma matches only match the
reactive part. from what you say I guess this is not true?

Only partially. You need to read it again to see if that reference
was in fact focusing on removing reactance (it does, as that is one
purpose) while soft pedaling resistance (which for the example may
have been sufficient).

Hopefully I can get up to school later and read some real material,
but for right now the internet is all i have.

It should do quite well.

We weren't given a concrete design. More like make a helical antenna
with 12db forward gain at 450 MHz--that's it.

The Helical antenna was invented by a Ham, who is also one of the most
respected professors of RF and antenna engineering, John Kraus, W8JK.
Google
kraus helix antenna
One of his students, also a professor in RF and antenna engineering,
J.C. "Mac" Mc Laughlin, N8TT, contributes to this group as well. (You
would do well to check your school's teaching directory.)

You are probably close enough, within an hour's drive, to knock on his
door at the University.

I'm about 99% sure that we set up the analyzer correctly. We tested
some dummy loads (like opens, shorts, etc) on end of the feedline and
they showed up as expected on the smith chart.

That should be sufficient.

Finally, I kid you not. Nothing about impedance matching in this
class. I know a little about L networks and the like, but I don't
know how to implement these networks at high frequenices.

It's just at a smaller scale. A stereo microscope can be an useful
aid. The trombone lines are not that problematic either and could
merit extra credit if your scores are a bit shy.

73's
Richard Clark, KB7QHC

How to match 190 +j140 to a 50 ohm source?
 

On Sat, 8 Dec 2007 15:35:55 -0500, "AI4QJ" wrote:


"Richard Clark" wrote in message
.. .
On Sat, 8 Dec 2007 11:22:05 -0800 (PST), wrote:

yep its an end of the semester project. BUT, we never learned anything
about impedance matching, so I feel no shame in asking people like
yourself. Thanks for your help.

The shame is your course approaching the topic to the point of
construction without introducing matching! Only the most trivial
designs escape this necessity.

Richard, this may be the intent of the instructor i.e. to have students
learn this on their own.


Hi Dan,

Having been an RF instructor for a number of years, it is a shabby
intent when it impedes the graded deliverable.

Now, if this was in fact a beginning of the semester assignment; then,
yes it would be a commendable side goal. However, with the statement
of the total absence of matching coverage, it suggests a rather myopic
view of antennas. In a course of 16 weeks, its introduction could
hardly consume more than 5%. More could be discussed, certainly; but
this minimum is hardly prohibitive.

73's
Richard Clark, KB7QHC

How to match 190 +j140 to a 50 ohm source?
 

wrote in message
...
that about sums it up.

stub matching looks attractive, but how do I actually build one of
these suckers? Do I have to carve out a piece of coax and then fit
another one into it, if that makes sense? Won't that be nearly
impossible to solder?

physically, it would be easier to make a stub section with sections of
single wire line, but I don't know how to find Z0 of my 14 gauge wire?

Is stub matching not the answer?

The antenna is designed for about 450 Mhz, if that helps anyone.

Thanks for your help.


Hi

I consider 160+j140 to be an impedance that would be too difficult to
match to 50 ohms. Any small error will produce a major variation from 50
ohms. Would you consider re-designing your Helix?

Dr Cebik has a good article on Helix Antennas at
http://www.cebik.com/ao/ao15.html.
VE3NPC has published alot of information on how to match helix antennas.

I have some AMSAT Journals with some of VE3NPC "blueprints" of 450 MHz
helix antennas. I'd scan the pages for you if you cant get his article
thru the Internet.

Jerry KD6JDJ

How to match 190 +j140 to a 50 ohm source?
 

AI4QJ wrote:

...
Richard, this may be the intent of the instructor i.e. to have students
learn this on their own.



As an instructor, it is none of the instructors "damn business" how a
student learns ... only that he does learn and can prove it--usually the
avenue chosen is a test.

This makes sure the "instructor" is not inclined towards "tipping the
scales", favoring "teachers pets", "assisting" cronies offspring, etc.

However, in the political world of amateur radio where the "good 'ole
buddy" system used to rein--there is not enough moral/ethical fiber to
see the reasons ...

Regards,
JS

How to match 190 +j140 to a 50 ohm source?
 

On Dec 8, 8:58�am, wrote:
that about sums it up.

stub matching looks attractive, but how do I actually build one of
these suckers? �Do I have to carve out a piece of coax and then fit
another one into it, if that makes sense? �Won't that be nearly
impossible to solder?

physically, it would be easier to make a stub section with sections of
single wire line, but I don't know how to find Z0 of my 14 gauge wire?

Is stub matching not the answer?

The antenna is designed for about 450 Mhz, if that helps anyone.

Thanks for your help.

According to the Smith Chart, an L network with a shunt L of 70 nH and
series C of 3.2pF or a shunt C of 3.5pF and a series L of 39 nH will
do it. Physically stubs on a circuit board would make sense. Consult
microwave text books for details.

Gary N4AST

How to match 190 +j140 to a 50 ohm source?
 

Dear Richard and "s.g.hatch"

I am late to this thread. Apparently s.g.hatch is in Michigan, though I did
not catch a hint of his location.

What references about Helix antennas have been studied? Prof. Kraus' book
Antennas (third edition) will be in any technical library and the subject is
dealt with there. Google is also your friend.

If I receive an E-mail with contact information, I will try to help
s.g.hatch. 73, Mac N8TT
--
J. McLaughlin; Michigan, USA
Home:
"Richard Clark" wrote in message
...
On Sat, 8 Dec 2007 12:01:50 -0800 (PST), wrote:

I'm worried about the real part, its just that after the reactive part
is nice, I don't think matching the real part will be hard.

That is a comforting illusion, but only an illusion. If you are
versed with the Smith Chart (another archaic tool from the student's
perspective, but immensely used by the practitioner), then you would
appreciate this.

If this course is more than a side-bar to your studies (or if you are
progressing into RF or Linear design), then the Smith Chart is your
best friend.

I've just been reading on the internet and stuff about gamma matches
and at least one of them has said that gamma matches only match the
reactive part. from what you say I guess this is not true?

Only partially. You need to read it again to see if that reference
was in fact focusing on removing reactance (it does, as that is one
purpose) while soft pedaling resistance (which for the example may
have been sufficient).

Hopefully I can get up to school later and read some real material,
but for right now the internet is all i have.

It should do quite well.

We weren't given a concrete design. More like make a helical antenna
with 12db forward gain at 450 MHz--that's it.

The Helical antenna was invented by a Ham, who is also one of the most
respected professors of RF and antenna engineering, John Kraus, W8JK.
Google
kraus helix antenna
One of his students, also a professor in RF and antenna engineering,
J.C. "Mac" Mc Laughlin, N8TT, contributes to this group as well. (You
would do well to check your school's teaching directory.)

You are probably close enough, within an hour's drive, to knock on his
door at the University.

I'm about 99% sure that we set up the analyzer correctly. We tested
some dummy loads (like opens, shorts, etc) on end of the feedline and
they showed up as expected on the smith chart.

That should be sufficient.

Finally, I kid you not. Nothing about impedance matching in this
class. I know a little about L networks and the like, but I don't
know how to implement these networks at high frequenices.

It's just at a smaller scale. A stereo microscope can be an useful
aid. The trombone lines are not that problematic either and could
merit extra credit if your scores are a bit shy.

73's
Richard Clark, KB7QHC

How to match 190 +j140 to a 50 ohm source?
 

On Sun, 9 Dec 2007 21:27:20 -0500, "J. Mc Laughlin"
wrote:

Dear Richard and "s.g.hatch"

I am late to this thread. Apparently s.g.hatch is in Michigan, though I did
not catch a hint of his location.

What references about Helix antennas have been studied? Prof. Kraus' book
Antennas (third edition) will be in any technical library and the subject is
dealt with there. Google is also your friend.

If I receive an E-mail with contact information, I will try to help
s.g.hatch. 73, Mac N8TT
--
J. McLaughlin; Michigan, USA

Hi Mac,

I read the headers in posts (they are typically hidden to the casual
reader). I can also cross reference the IP address in that header to
a City and State. Our student's location is some 60 miles south of
where you sometimes post. Let's call it a SWAG that he is attending
the University where you are. ;-)

I cannot say that I have been a complete or reliable source, but we've
managed to cover some of the fundamental concerns and it didn't seem
appropriate to finish his semester project for him.

73's
Richard Clark, KB7QHC

How to match 190 +j140 to a 50 ohm source?
 

On Dec 9, 9:43 pm, Richard Clark wrote:
On Sun, 9 Dec 2007 21:27:20 -0500, "J. Mc Laughlin"

wrote:
Dear Richard and "s.g.hatch"

I am late to this thread. Apparently s.g.hatch is in Michigan, though I did
not catch a hint of his location.

What references about Helix antennas have been studied? Prof. Kraus' book
Antennas (third edition) will be in any technical library and the subject is
dealt with there. Google is also your friend.

If I receive an E-mail with contact information, I will try to help
s.g.hatch. 73, Mac N8TT
--
J. McLaughlin; Michigan, USA

Hi Mac,

I read the headers in posts (they are typically hidden to the casual
reader). I can also cross reference the IP address in that header to
a City and State. Our student's location is some 60 miles south of
where you sometimes post. Let's call it a SWAG that he is attending
the University where you are. ;-)

I cannot say that I have been a complete or reliable source, but we've
managed to cover some of the fundamental concerns and it didn't seem
appropriate to finish his semester project for him.

73's
Richard Clark, KB7QHC

you guys are stalkers!

but, I was never expecting a complete answer. I think I have enough
to get somewhere on my own so I thank you all.
I'm going to work on it tomorrow and I'll let you know how it goes.