OT: Problems with Icom 756 Pro III internal tuner

[K2QI]

Greetings fellow Elecrafters,

I'm sorry for emailing this question to the group, but the folks on this
reflector are a smart bunch.  Maybe someone could give me some advice or
suggestions.  I posted this question to the Icom 756 Pro III group and QRZ,
but no one seems to have an answer.

I'm diagnosing a problem with an Icom 756 Pro III.  It's tuner's "insertion
loss" is quite high.  For example, when the tuner is off, sending an
unmodulated FSK carrier shows the transceiver putting out 100W.  As soon as
the tuner is activated, power drops by 10-15%.  That's a lot of power being
dissipated somewhere, and I don't think it's good especially for 100% duty
cycle modes.  It doesn't matter whether the Icom is connected to a dummy
load or resonant antenna.  The results are always the same on every band.

In comparison, the K3's tuner seems to be incredibly efficient.  If there is
a loss of output power on the K3 whenever its tuner is inline, it's not
noticeable.  More often than not, power increases when the K3 finds a good
impedence match.

I've gone as far as recalibrating the Icom's tuner.  This was done by
terminating the remote jack on the rear panel, and entering the tuner
service mode.  The tuner calibration process completed with no errors
reported by the Pro3.

Any suggestions?  I'm going to call Icom support tomorrow to see what they
say.

-
73 de James K2QI
President UNARC/4U1UN
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[K2QI]

Hello group!

I'd like to close this thread now; many thanks to everyone who replied
off-list with suggestions and assistance.  In summary, I was referred to an
Icom technician who I was able to speak too over the phone and describe the
situation.

The tech told me that he sees this behavior on many Pro II's and Pro III's.
He also stated that a 10% insertion loss seems to be the norm with these
radios, although he didn't have any documentation officially stating so.
Finally, he confirmed that the Icom uses a T network for its ATU versus the
modified Pi/L C-in/C-out network the K3 uses.  That obviously explains the
huge difference in efficiency.

With that said, I'll leave well enough alone.  He believes from my
description that the Pro 3 is working within manufacturer permitted
tolerances.

This experience also reconfirmed my belief that our K3's are superbly
engineered products, and I'm glad to be a part of this family.

Mni tnx,
James K2QI

On Mon, Nov 15, 2010 at 10:18 PM, James Sarte <[hidden email]> wrote:

> Greetings fellow Elecrafters,
>
> I'm sorry for emailing this question to the group, but the folks on this
> reflector are a smart bunch.  Maybe someone could give me some advice or
> suggestions.  I posted this question to the Icom 756 Pro III group and QRZ,
> but no one seems to have an answer.
>
> I'm diagnosing a problem with an Icom 756 Pro III.  It's tuner's "insertion
> loss" is quite high.  For example, when the tuner is off, sending an
> unmodulated FSK carrier shows the transceiver putting out 100W.  As soon as
> the tuner is activated, power drops by 10-15%.  That's a lot of power being
> dissipated somewhere, and I don't think it's good especially for 100% duty
> cycle modes.  It doesn't matter whether the Icom is connected to a dummy
> load or resonant antenna.  The results are always the same on every band.
>
> In comparison, the K3's tuner seems to be incredibly efficient.  If there
> is a loss of output power on the K3 whenever its tuner is inline, it's not
> noticeable.  More often than not, power increases when the K3 finds a good
> impedence match.
>
> I've gone as far as recalibrating the Icom's tuner.  This was done by
> terminating the remote jack on the rear panel, and entering the tuner
> service mode.  The tuner calibration process completed with no errors
> reported by the Pro3.
>
> Any suggestions?  I'm going to call Icom support tomorrow to see what they
> say.
>
> -
> 73 de James K2QI
> President UNARC/4U1UN
>
>

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