Re: [Repeater-Builder] Z-Matcher adjustment

[Eric Lemmon]

An excellent summation, Jeff!  I have found that some PA designs are
unstable by nature, as if the maker took out expensive coils and
capacitors one by one, until the amp either ran away or blew up, and
then put that one part back in and started selling the product.  I am
sad to note that many aftermarket VHF and UHF power amplifier brands are
"popular" only because they are cheap, not because they are
well-designed and well-made.

I ran across a one-page paper of Z-Matcher Tuning Instructions from
Decibel Products here:



73, Eric Lemmon WB6FLY


Jeff DePolo WN3A wrote:

... The original premise was that a Z-matcher was needed on the output
of some
> PA's because the PA itself was *not* properly matched when terminated in a
> 50 ohm load.  Wasn't that the original discussion?  The goal wasn't to
> minimize VSWR looking into the cavities.  With that in mind, the "best
> match" isn't necessarily that which produces the least reflected power.  The
> "best match" is the load Z that the amplifier is most happy transferring
> power to, and the only way to know that is by looking at PA efficiency...
> 
... Now, if you have a PA that runs away when presented with a
known-good load,
> then you've got a problem that needs to be fixed IN THE PA.  Using a
> Z-matcher, or the crude equivalent of feedline pruning, to help tame an
> unstable PA isn't a fix, it's a band-aid that will eventually come off...



 

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RE: [Repeater-Builder] Z-Matcher adjustment

[Jeff DePolo WN3A]

> 
> > Because the meter and its cable's electrical length will change the
> tuning.
> > You can read it at the antenna port of the duplexer if 
> youre using one.
> This
> > has already been covered in previous posts.  73,Lee
> 
> I must be dense .  From what I understand you have the transmitter (no
> tuning in the amplifier stages) , then the swr meter ,the 
> Z-matcher , and
> then the duplexer.  It will not change the tuning of anything 
> if you tune
> fhr z-matcher for minimum reflected power and then remove the 
> swr meter.
> It will only change what the transmitter sees and it is not 
> tunable anyway.
> That is all that the matching section does in the duplex 
> transmitter.  It
> does not tune for maximum efficiency if you follow the GE tuning
> instructions.

This discussion has gone full-circle and is now to the point of confusion.

The original premise was that a Z-matcher was needed on the output of some
PA's because the PA itself was *not* properly matched when terminated in a
50 ohm load.  Wasn't that the original discussion?  The goal wasn't to
minimize VSWR looking into the cavities.  With that in mind, the "best
match" isn't necessarily that which produces the least reflected power.  The
"best match" is the load Z that the amplifier is most happy transferring
power to, and the only way to know that is by looking at PA efficiency.

GE's procedure which is based on the least-reflected-power method is only
correct IF we assume that the output stage of the Mastr II PA is "best
matched" when looking into a perfect 50+j0 load.  But that's not what we're
trying to accomplish here.  The original premise was that many PA's,
especially when operated outside their design range or at reduced power,
were NOT best-matched when terminated in a purely-resistive 50 ohm load.
So, if you tune your GE Mastr II matching network for least reflected power
as indicated by the test pin on the onboard directional coupler, you're not
accomplishing what you set out to do.

Contrary to popular belief, and over-simplification by manufacturers, least
insertion loss and maximum power output aren't always the right answers when
tuning amplifiers, filter cavities, and other devices in the transmission
system.  Maximum return loss in filter cavities and antenna systems, and
maximum efficiency in PA tuning, are steps in the right direction if the
goal is to have a transmission system that is stable and the least immune to
external influences including temperature.

Now, if you have a PA that runs away when presented with a known-good load,
then you've got a problem that needs to be fixed IN THE PA.  Using a
Z-matcher, or the crude equivalent of feedline pruning, to help tame an
unstable PA isn't a fix, it's a band-aid that will eventually come off...

--- Jeff


Jeff DePolo WN3A - [EMAIL PROTECTED]
Broadcast and Communications Consultant 





 

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Re: [Repeater-Builder] Z-Matcher adjustment

[NØATH]

I would certainly be interested to know where you obtained the digital
meters - that looks really
nice. I wonder if they are illuminated? Dave / NØATH

- Original Message - 
From: "Tony King - W4ZT" <[EMAIL PROTECTED]>
To: 
Sent: Monday, January 26, 2004 8:58 PM
Subject: [Repeater-Builder] Z-Matcher adjustment


Couldn't agree with you more.  The important point is that you can't
insert
an SWR meter or wattmeter in the line to make adjustments and then
take it
out.  The GE Z-match gives you the directional coupler which gives you
a
leg up on the adjustment process.  Otherwise you are stuck with the
max
output for min current.  Of course that should be our objective anyhow
but
many don't have an ammeter or voltmeter on the power source (I just
replaced stuck plastic meters on one of my Astrons with digital panel
meters: ).




 

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Re: [Repeater-Builder] Z-Matcher adjustment

[Neil McKie]

  And unbending the pins too? 

  Neil - WA6KLA 

Don wrote:
> 
> At 09:58 PM 1/26/04 -0500, you wrote:
> >I just
> >replaced stuck plastic meters on one of my Astrons with digital 
> >panel meters: ).
> 
> And Tony that is One Nice Great job too .
> 
> Back to warming up old Solder Joints On a Micor Backplane
> 
> Don KA9QJG
> 
> 
> 
> Yahoo! Groups Links
> 
> To visit your group on the web, go to:
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Re: [Repeater-Builder] Z-Matcher adjustment

[Don]

At 09:58 PM 1/26/04 -0500, you wrote:
>I just
>replaced stuck plastic meters on one of my Astrons with digital panel
>meters: ).


And Tony that is One Nice Great job too .

Back to warming up old Solder Joints On a Micor Backplane

Don KA9QJG





 

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Re: [Repeater-Builder] Z-Matcher adjustment

[Lee Williams]

But when you remove the wattmeter,you change the tuning,it must be after the
duplexer or included within the matcher. Youre not dense,its that
critical...73,Lee
- Original Message -
From: "Ralph Mowery" <[EMAIL PROTECTED]>
To: 
Sent: Monday, January 26, 2004 11:41 PM
Subject: Re: [Repeater-Builder] Z-Matcher adjustment


>
> > Because the meter and its cable's electrical length will change the
> tuning.
> > You can read it at the antenna port of the duplexer if youre using one.
> This
> > has already been covered in previous posts.  73,Lee
>
> I must be dense .  From what I understand you have the transmitter (no
> tuning in the amplifier stages) , then the swr meter ,the Z-matcher , and
> then the duplexer.  It will not change the tuning of anything if you tune
> fhr z-matcher for minimum reflected power and then remove the swr meter.
> It will only change what the transmitter sees and it is not tunable
anyway.
> That is all that the matching section does in the duplex transmitter.  It
> does not tune for maximum efficiency if you follow the GE tuning
> instructions.
>





 

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Re: [Repeater-Builder] Z-Matcher adjustment

[Ralph Mowery]

> Because the meter and its cable's electrical length will change the
tuning.
> You can read it at the antenna port of the duplexer if youre using one.
This
> has already been covered in previous posts.  73,Lee

I must be dense .  From what I understand you have the transmitter (no
tuning in the amplifier stages) , then the swr meter ,the Z-matcher , and
then the duplexer.  It will not change the tuning of anything if you tune
fhr z-matcher for minimum reflected power and then remove the swr meter.
It will only change what the transmitter sees and it is not tunable anyway.
That is all that the matching section does in the duplex transmitter.  It
does not tune for maximum efficiency if you follow the GE tuning
instructions.





 

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Re: [Repeater-Builder] Z-Matcher adjustment

[Virden Clark Beckman]

The zmatcher matches the reactive impedance to the transmitter, not the
resistive load - any cable changes or anything will affect this
reactance.

Ralph Mowery wrote:
> 
> > Couldn't agree with you more.  The important point is that you can't
> insert
> > an SWR meter or wattmeter in the line to make adjustments and then take it
> > out.  The GE Z-match gives you the directional coupler which gives you a
> 
> Why can't you take the swr meter out ?  The Z-matcher is after the place
> where the swr meter is.
> The purpose of the matcher is for minimum swr or reflected power, the same
> as the internal matcher of the GE repeater.
> 
> 
> 
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> 
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> 
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-- 
73...Clark Beckman N8PZD

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Re: [Repeater-Builder] Z-Matcher adjustment

[Tony King - W4ZT]

At 11:10 PM 1/26/2004, you wrote:
>Why can't you take the swr meter out ?  The Z-matcher is after the place
>where the swr meter is.
>The purpose of the matcher is for minimum swr or reflected power, the same
>as the internal matcher of the GE repeater.

That's true, and if you could achieve a perfect match at the impedance of 
the wattmeter, that might work, but remember, we're probably not tuning to 
a 50 ohm match between the PA and the Z-match, rather between the Z-match 
and the duplexer (if it was aligned at the factory etc). So, I would fear 
that a change in length of cables between the PA and the Z-match would 
cause a change in the match and associated problems.

I haven't seen the DB Products Z-match but having the directional coupler 
built in certainly negates the need for placing anything else in line.

This is a very interesting thread and I appreciate all the great ideas 
being shared!

73,
Tony W4ZT




 

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Re: [Repeater-Builder] Z-Matcher adjustment

[Lee Williams]

Because the meter and its cable's electrical length will change the tuning.
You can read it at the antenna port of the duplexer if youre using one. This
has already been covered in previous posts.  73,Lee
- Original Message -
From: "Ralph Mowery" <[EMAIL PROTECTED]>
To: 
Sent: Monday, January 26, 2004 11:10 PM
Subject: Re: [Repeater-Builder] Z-Matcher adjustment


>
>
> > Couldn't agree with you more.  The important point is that you can't
> insert
> > an SWR meter or wattmeter in the line to make adjustments and then take
it
> > out.  The GE Z-match gives you the directional coupler which gives you a
>
> Why can't you take the swr meter out ?  The Z-matcher is after the place
> where the swr meter is.
> The purpose of the matcher is for minimum swr or reflected power, the same
> as the internal matcher of the GE repeater.





 

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Re: [Repeater-Builder] Z-Matcher adjustment

[Ralph Mowery]

> Couldn't agree with you more.  The important point is that you can't
insert
> an SWR meter or wattmeter in the line to make adjustments and then take it
> out.  The GE Z-match gives you the directional coupler which gives you a

Why can't you take the swr meter out ?  The Z-matcher is after the place
where the swr meter is.
The purpose of the matcher is for minimum swr or reflected power, the same
as the internal matcher of the GE repeater.






 

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