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Looking to add LP700 to KPA1500 - ideas?

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Dave wo2x

Looking to add LP700 to KPA1500 - ideas?

Hi All,

I am thinking about adding a Telepost LP700 to my station but I would need
to insert it between the amp and tuner (which are integrated together in the
KPA1500).

Any ideas if it is worth doing something to loop the RF out of the amp to
the coupler and back in again? Probably no easy way to do it.

Just a thought.

Dave wo2x

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Don Wilhelm

Re: Looking to add LP700 to KPA1500 - ideas?

Dave,

The KPA1500 has indicators for both power output and SWR between the amp
ant tuner sections.
If it were mine, I would put the LP700 on the antenna line to monitor
what is going on with the antenna itself.

73,
Don W3FPR

On 5/20/2020 11:24 AM, [hidden email] wrote:

> Hi All,
>
>
>
> I am thinking about adding a Telepost LP700 to my station but I would need
> to insert it between the amp and tuner (which are integrated together in the
> KPA1500).
>
> Any ideas if it is worth doing something to loop the RF out of the amp to
> the coupler and back in again? Probably no easy way to do it.
>

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ANDY DURBIN

Looking to add LP700 to KPA1500 - ideas?

In reply to this post by Dave wo2x

"If it were mine, I would put the LP700 on the antenna line to monitor what is going on with the antenna itself."

My LP-100A is between my KPA500 and my KAT500. I want to know what load is being presented to the KPA500. Neither the KPA500 not the KAT500 can display complex load values. Since the LP-500 and LP-700 are intended to sample amplifier RF input and amplifier RF output I would expect the amplifier output sampling to be performed before the tuner. But no, I don't know how to do that with a KPA1500. It would seem to require an internal modification and two additional rear panel connectors.

73,
Andy, k3wyc
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ANDY DURBIN

Re: Looking to add LP700 to KPA1500 - ideas?

"It would seem to require an internal modification and two additional rear panel connectors."

FCC photos shows LPF RF Out is a BNC and tuner RF In is a BNC. Should be an easy mod if there is room on the rear panel for 2 BNC connectors. Perhaps the LP-700 coupler would fit inside the LP1500 case?

Easy to speculate about mods to someone else's equipment.

73,
Andy, k3wyc

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Dave wo2x

Re: Looking to add LP700 to KPA1500 - ideas?

Thanks Andy.

That is something to think about. Wouldn't be that hard. Have to check my purchase date to make sure it is out of warranty. 😊

Dave wo2x

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Andy Durbin
Sent: Wednesday, May 20, 2020 12:55 PM
To: [hidden email]
Subject: Re: [Elecraft] Looking to add LP700 to KPA1500 - ideas?

"It would seem to require an internal modification and two additional rear panel connectors."

FCC photos shows LPF RF Out is a BNC and tuner RF In is a BNC. Should be an easy mod if there is room on the rear panel for 2 BNC connectors. Perhaps the LP-700 coupler would fit inside the LP1500 case?

Easy to speculate about mods to someone else's equipment.

73,
Andy, k3wyc

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Rick Bates, NK7I

Re: Looking to add LP700 to KPA1500 - ideas?

In reply to this post by ANDY DURBIN

The KAT500 (and utility) can show the values used by the tuner to match
the 50 ohm impedance of the radio. Similar is possible either via the
KPA1500 utility or the front panel of the KPA1500.

While it doesn't show the complex load; it gives enough to begin to
figure out what the antenna is presenting (for use in apps like WinSmith
etc) so one can make intelligent changes in the antenna.

I've used the utility for monitoring (and remote control) of the
KPA500/KAT500 combo for years; now I'm using the KPA1500 utility for the
same reason.

The KPA1500 presents a lot more useful information on the front panel
(click on the menu button then the down triangle to select the menu you
want). Because my antennas are resonant, I park the amp display at
power out, efficiency, volts and amps used and temp. The power out on
the utility also shows the reflected power in watts, nice to know.

If you put the LP sensor between the amp and the (not resonant) antenna,
any mismatch will likely give you erroneous readings that would offer no
value. It would compare the antenna value (say 150 ohms of mixed
reactance/resistance) to the tuner value (whatever is required to match
to 50 ohms). The worse the unmatched condition, the more useless the
display becomes. It wants to see 50 ohm in, 50 ohm out to provide
accurate power readings.

So if your antennas demand a matching circuit (tuner), the LP sensor
becomes less valued at the output of the amp.

73,
Rick NK7I

On 5/20/2020 9:41 AM, Andy Durbin wrote:

> "If it were mine, I would put the LP700 on the antenna line to monitor what is going on with the antenna itself."
>
> My LP-100A is between my KPA500 and my KAT500. I want to know what load is being presented to the KPA500. Neither the KPA500 not the KAT500 can display complex load values. Since the LP-500 and LP-700 are intended to sample amplifier RF input and amplifier RF output I would expect the amplifier output sampling to be performed before the tuner. But no, I don't know how to do that with a KPA1500. It would seem to require an internal modification and two additional rear panel connectors.
>
> 73,
> Andy, k3wyc
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
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Jim Brown-10

Re: Looking to add LP700 to KPA1500 - ideas?

In reply to this post by ANDY DURBIN

On 5/20/2020 9:41 AM, Andy Durbin wrote:
> It would seem to require an internal modification and two additional rear panel connectors.

I would STRONGLY urge NO mods to the KPA1500. When showing the amp in
the booth at Visalia, K6XX described how tricky it was to stabilize it
on 6M, and the very small changes that made the difference.

73, Jim K9YC
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Mark Goldberg

Re: Looking to add LP700 to KPA1500 - ideas?

In reply to this post by Rick Bates, NK7I

I tend to agree. With the right calculations, the reported power, SWR and
matching inductors and capacitors from the KPA1500 will tell you more about
the antenna. In addition, the KPA1500 already has a monitoring port that
could be used for an output modulation / spectrum monitor. Of course,
something like that would have to be built that took those inputs. I expect
a K4 will do it!

The KPA500 does get calibrated at the factory for power, SWR, etc, probably
against decent, calibrated test equipment. I'll bet it is designed to hold
some sort of calibration over time. Hams tend to treat uncalibrated test
gear as gospel. An external power meter, just because it reports to the
nearest 0.1W isn't necessarily better. Any commercial operation calibrates
on a regular cycle. Being a slightly less cheap Ham than most, I do get one
scope / spectrum analyzer calibrated every year, so at least I have
something to compare the other stuff to.

Does the KPA500 report the tuner topology (if it is even switchable)? Is it
an L match? Does it report which element is the shunt element?

Does a specific L and C and shunt element match only one unique load? The
other issue is that the Ls and Cs reported are probably 20% or more off, so
the calculation would not be perfect. The C and L ladders are not even
guaranteed monotonic, so a reported LC combination may be off. Tuners often
try the next one higher and lower. I did measurements of an LDG tuner and
the inductance jumped up and down. Step N-1 was not necessarily less
inductance than step N. Two steps generally got in the right direction.

73,

Mark
W7MLG

On Wed, May 20, 2020 at 12:07 PM Rick NK7I <[hidden email]> wrote:

> The KAT500 (and utility) can show the values used by the tuner to match
> the 50 ohm impedance of the radio. Similar is possible either via the
> KPA1500 utility or the front panel of the KPA1500.
>
> While it doesn't show the complex load; it gives enough to begin to
> figure out what the antenna is presenting (for use in apps like WinSmith
> etc) so one can make intelligent changes in the antenna.
>
> I've used the utility for monitoring (and remote control) of the
> KPA500/KAT500 combo for years; now I'm using the KPA1500 utility for the
> same reason.
>
> The KPA1500 presents a lot more useful information on the front panel
> (click on the menu button then the down triangle to select the menu you
> want). Because my antennas are resonant, I park the amp display at
> power out, efficiency, volts and amps used and temp. The power out on
> the utility also shows the reflected power in watts, nice to know.
>
> If you put the LP sensor between the amp and the (not resonant) antenna,
> any mismatch will likely give you erroneous readings that would offer no
> value. It would compare the antenna value (say 150 ohms of mixed
> reactance/resistance) to the tuner value (whatever is required to match
> to 50 ohms). The worse the unmatched condition, the more useless the
> display becomes. It wants to see 50 ohm in, 50 ohm out to provide
> accurate power readings.
>
> So if your antennas demand a matching circuit (tuner), the LP sensor
> becomes less valued at the output of the amp.
>
> 73,
> Rick NK7I
>
> On 5/20/2020 9:41 AM, Andy Durbin wrote:
> > "If it were mine, I would put the LP700 on the antenna line to monitor
> what is going on with the antenna itself."
> >
> > My LP-100A is between my KPA500 and my KAT500. I want to know what load
> is being presented to the KPA500. Neither the KPA500 not the KAT500 can
> display complex load values. Since the LP-500 and LP-700 are intended to
> sample amplifier RF input and amplifier RF output I would expect the
> amplifier output sampling to be performed before the tuner. But no, I
> don't know how to do that with a KPA1500. It would seem to require an
> internal modification and two additional rear panel connectors.
> >
> > 73,
> > Andy, k3wyc
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > Message delivered to [hidden email]
> ______________________________________________________________
> Elecraft mailing list
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>
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Don Wilhelm

Re: Looking to add LP700 to KPA1500 - ideas?

The Telepost LP100 (and I expect the LP700) are calibrated to NIST
traceable standards. I bought an LP100 kit (no longer in kit form) and
did my own calibration after construction - then sent it to Larry for
his real calibration.
Although Larry will not commit to it, I suspect the accuracy to be in
the vicinity of 2% or better.

There are a number of LP100s in the Elecraft working area. I don't know
how often they are sent back to Larry for a calibration check. What I
do know is that they are better than the average Bird used by hams.

73,
Don W3FPR

On 5/20/2020 5:52 PM, Mark Goldberg wrote:
Hams tend to treat uncalibrated test
> gear as gospel. An external power meter, just because it reports to the
> nearest 0.1W isn't necessarily better. Any commercial operation calibrates
> on a regular cycle. Being a slightly less cheap Ham than most, I do get one
> scope / spectrum analyzer calibrated every year, so at least I have
> something to compare the other stuff to.
>
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John Simmons

Re: Looking to add LP700 to KPA1500 - ideas?

There was a recent discussion about this on a forum I belong to,
especially comparing the LP100 to a Bird. The original article
describing the design of the LP100 (not 'A') by Larry said he calibrated
the meter with a Bird 4410. I asked Larry about his calibration
procedure on the LP100 (or LP500- can't remember) email reflector. He no
longer uses a Bird for calibration! So many hams (and CB'ers) think a
Bird is the ultimate in accuracy.... not so! However the Telepost meters
are not field instruments! Check recent posts in the reflector I
mentioned to see Larry's calibration procedure.

BTW, Ameritron/MFJ use an LP100 to calibrate their meters!
--
-de John NIØK

Don Wilhelm wrote on 5/20/2020 5:20 PM:

> The Telepost LP100 (and I expect the LP700) are calibrated to NIST
> traceable standards. I bought an LP100 kit (no longer in kit form)
> and did my own calibration after construction - then sent it to Larry
> for his real calibration.
> Although Larry will not commit to it, I suspect the accuracy to be in
> the vicinity of 2% or better.
>
> There are a number of LP100s in the Elecraft working area. I don't
> know how often they are sent back to Larry for a calibration check.
> What I do know is that they are better than the average Bird used by
> hams.
>
> 73,
> Don W3FPR
>
> On 5/20/2020 5:52 PM, Mark Goldberg wrote:
> Hams tend to treat uncalibrated test
>> gear as gospel. An external power meter, just because it reports to the
>> nearest 0.1W isn't necessarily better. Any commercial operation
>> calibrates
>> on a regular cycle. Being a slightly less cheap Ham than most, I do
>> get one
>> scope / spectrum analyzer calibrated every year, so at least I have
>> something to compare the other stuff to.
>>
> ______________________________________________________________
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