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K3 and Expert 1.3K-FA amplifier power

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Bill Frantz

K3 and Expert 1.3K-FA amplifier power

I have just set up an Expert 1.3K-FA amplifier with my K3 (with
most of the upgrades to become a K3S). My question is, when I
drive it with 10W set on the K3 output power, it shows a drive
level of about 30W and and output level of 950W. What is going on?

Details: The two boxes are connected with about 6' of RG-58 for
the RF and a custom cable made by KC5PCB, Dan Tassell for the
rest of the signals. The output is into a dummy load, although
very similar measurements occur with my trapped vertical
antenna. Tests were in the CW portion of the 20M band.

The Amp is powered from a dedicated 120V circuit which shows a 7
volt drop at 12.7A during CW key down transmission. (Voltage is
measured by a Fluke 87 DVM and current by a Kill-A-Watt PA4400.)
An external YS-60 power meter shows 800W, which seems reasonable
agreement given the accuracy of RF power measurements.

Why does the K3 show 10W and the amp show 30W? Is there
something screwy here, or is it normal?

73 Bill AE6JV

-------------------------------------------------------------------------
Bill Frantz | The first thing you need when | Periwinkle
(408)356-8506 | using a perimeter defense is a | 16345
Englewood Ave
www.pwpconsult.com | perimeter. | Los Gatos,
CA 95032

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AB2E Darrell

Re: K3 and Expert 1.3K-FA amplifier power

Hi Bill,
The non-US model, or the modified US model only needs 10w to drive the 1.3 to full output.
I also Ave a k3/1.3 combo and 9W gives me legal out on at least a couple bands, 1200-1400w out all other bands..
I also have an ic7800 for rig 2 and that drives the 1.3 to fiI'll output with 9W as well.
73 Darrell AB2E

Sent via the Samsung GALAXY S® 5, an AT&T 4G LTE smartphone

-------- Original message --------
From: Bill Frantz <[hidden email]>
Date: 9/10/17 5:10 PM (GMT-04:00)
To: [hidden email]
Subject: [Elecraft] K3 and Expert 1.3K-FA amplifier power

I have just set up an Expert 1.3K-FA amplifier with my K3 (with
most of the upgrades to become a K3S). My question is, when I
drive it with 10W set on the K3 output power, it shows a drive
level of about 30W and and output level of 950W. What is going on?

Details: The two boxes are connected with about 6' of RG-58 for
the RF and a custom cable made by KC5PCB, Dan Tassell for the
rest of the signals. The output is into a dummy load, although
very similar measurements occur with my trapped vertical
antenna. Tests were in the CW portion of the 20M band.

The Amp is powered from a dedicated 120V circuit which shows a 7
volt drop at 12.7A during CW key down transmission. (Voltage is
measured by a Fluke 87 DVM and current by a Kill-A-Watt PA4400.)
An external YS-60 power meter shows 800W, which seems reasonable
agreement given the accuracy of RF power measurements.

Why does the K3 show 10W and the amp show 30W? Is there
something screwy here, or is it normal?

73 Bill AE6JV

-------------------------------------------------------------------------
Bill Frantz | The first thing you need when | Periwinkle
(408)356-8506 | using a perimeter defense is a | 16345
Englewood Ave
www.pwpconsult.com<http://www.pwpconsult.com> | perimeter. | Los Gatos,
CA 95032

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Don Wilhelm

Re: K3 and Expert 1.3K-FA amplifier power

In reply to this post by Bill Frantz

Bill,

I would say something is not calibrated correctly - either the K3
wattmeter or the power determining device in the amp. It is difficult
to say which one without doing some measurements.

I would connect the K3 to a dummy load for the 1st test. Get a 'scope
out with a 10x probe. The 'scope and probe should have a frequency
rating of at least 3 times the operating frequency.

A coax TEE adapter inserted in-line will give you access to the coax
center conductor so you can read the RF voltage peak to peak value.
That RF voltage should be used to compute the actual power developed by
the K3. Compare that to the power reading shown on the K3 - you can use
the formula {V(p-p) squared} divided by 400 to obtain the power in watts
to a 50 ohm load. Derivation of that formula is "left to the student",
but if you don't believe it, you can always convert to RMS voltage and
calculate from there. Formula reduction is required before plugging in
values.

Once you know the actual power when the K3 reads 10 watts, remove the
dummy load and connect the amp (leaving the TEE adapter in-line). Now
send what the K3 indicates as 10 watts, and again measure the RF
voltage. That will tell you whether the K3 power indication is correct
or the amplifier indication is correct.

73,
Don W3FPR

On 9/10/2017 5:10 PM, Bill Frantz wrote:

> I have just set up an Expert 1.3K-FA amplifier with my K3 (with most of
> the upgrades to become a K3S). My question is, when I drive it with 10W
> set on the K3 output power, it shows a drive level of about 30W and and
> output level of 950W. What is going on?
>
> Details: The two boxes are connected with about 6' of RG-58 for the RF
> and a custom cable made by KC5PCB, Dan Tassell for the rest of the
> signals. The output is into a dummy load, although very similar
> measurements occur with my trapped vertical antenna. Tests were in the
> CW portion of the 20M band.
>
> The Amp is powered from a dedicated 120V circuit which shows a 7 volt
> drop at 12.7A during CW key down transmission. (Voltage is measured by a
> Fluke 87 DVM and current by a Kill-A-Watt PA4400.) An external YS-60
> power meter shows 800W, which seems reasonable agreement given the
> accuracy of RF power measurements.
>
> Why does the K3 show 10W and the amp show 30W? Is there something screwy
> here, or is it normal?
>

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briancom

Re: K3 and Expert 1.3K-FA amplifier power

Brings up an interesting question.

My recollection from numerous amps that they may read OK (within 10
-15%) near full power, at low power they typically were way off. I
suspect whatever calibration was done, if any, was at the high end of
the scale. The load was probably pure resistive and near 50 ohms.

By way off, I mean perhaps 50% not a factor of 3 like being reported.

I wonder if anybody has any hard data on this. If it is true, why?

In the old days with a non-digital meter, nobody could tell....

73 de Brian/K3KO

On 9/10/2017 21:32 PM, Don Wilhelm wrote:

> Bill,
>
> I would say something is not calibrated correctly - either the K3
> wattmeter or the power determining device in the amp. It is difficult
> to say which one without doing some measurements.
>
> I would connect the K3 to a dummy load for the 1st test. Get a 'scope
> out with a 10x probe. The 'scope and probe should have a frequency
> rating of at least 3 times the operating frequency.
>
> A coax TEE adapter inserted in-line will give you access to the coax
> center conductor so you can read the RF voltage peak to peak value.
> That RF voltage should be used to compute the actual power developed by
> the K3. Compare that to the power reading shown on the K3 - you can use
> the formula {V(p-p) squared} divided by 400 to obtain the power in watts
> to a 50 ohm load. Derivation of that formula is "left to the student",
> but if you don't believe it, you can always convert to RMS voltage and
> calculate from there. Formula reduction is required before plugging in
> values.
>
> Once you know the actual power when the K3 reads 10 watts, remove the
> dummy load and connect the amp (leaving the TEE adapter in-line). Now
> send what the K3 indicates as 10 watts, and again measure the RF
> voltage. That will tell you whether the K3 power indication is correct
> or the amplifier indication is correct.
>
> 73,
> Don W3FPR
>
> On 9/10/2017 5:10 PM, Bill Frantz wrote:
>> I have just set up an Expert 1.3K-FA amplifier with my K3 (with most
>> of the upgrades to become a K3S). My question is, when I drive it with
>> 10W set on the K3 output power, it shows a drive level of about 30W
>> and and output level of 950W. What is going on?
>>
>> Details: The two boxes are connected with about 6' of RG-58 for the RF
>> and a custom cable made by KC5PCB, Dan Tassell for the rest of the
>> signals. The output is into a dummy load, although very similar
>> measurements occur with my trapped vertical antenna. Tests were in the
>> CW portion of the 20M band.
>>
>> The Amp is powered from a dedicated 120V circuit which shows a 7 volt
>> drop at 12.7A during CW key down transmission. (Voltage is measured by
>> a Fluke 87 DVM and current by a Kill-A-Watt PA4400.) An external YS-60
>> power meter shows 800W, which seems reasonable agreement given the
>> accuracy of RF power measurements.
>>
>> Why does the K3 show 10W and the amp show 30W? Is there something
>> screwy here, or is it normal?
>>
> ______________________________________________________________
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>
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>
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Bill Frantz

Re: K3 and Expert 1.3K-FA amplifier power

In reply to this post by Don Wilhelm

Thanks Don. I got out my old Phillips 25 MHz scope and looked at
the calibration sticker dated 1983. I decided to check the
readout with a fresh alkaline battery and both the battery,
checked with the DVM, and the scope looked OK.

I did the measurements on both 20M and 40M, since 40M is less
than half the scope bandwidth and got the same result. 6.4v p-p
times 10 for the probe 10.24W, well within the margine of error
for my measuring equipment.

My conclusion is that this is a question for the Expert Amp people.

Thanks for your help.

73 Bill AE6JV

On 9/10/17 at 2:32 PM, [hidden email] (Don Wilhelm) wrote:

>Bill,
>
>I would say something is not calibrated correctly - either the
>K3 wattmeter or the power determining device in the amp. It is
>difficult to say which one without doing some measurements.
>
>I would connect the K3 to a dummy load for the 1st test. Get a
>'scope out with a 10x probe. The 'scope and probe should have
>a frequency rating of at least 3 times the operating frequency.
>
>A coax TEE adapter inserted in-line will give you access to the
>coax center conductor so you can read the RF voltage peak to
>peak value.
>That RF voltage should be used to compute the actual power
>developed by the K3. Compare that to the power reading shown
>on the K3 - you can use the formula {V(p-p) squared} divided by
>400 to obtain the power in watts to a 50 ohm load. Derivation
>of that formula is "left to the student", but if you don't
>believe it, you can always convert to RMS voltage and calculate
>from there. Formula reduction is required before plugging in values.
>
>Once you know the actual power when the K3 reads 10 watts,
>remove the dummy load and connect the amp (leaving the TEE
>adapter in-line). Now send what the K3 indicates as 10 watts,
>and again measure the RF voltage. That will tell you whether
>the K3 power indication is correct or the amplifier indication
>is correct.
>
>73,
>Don W3FPR
>
>On 9/10/2017 5:10 PM, Bill Frantz wrote:
>>I have just set up an Expert 1.3K-FA amplifier with my K3
>>(with most of the upgrades to become a K3S). My question is,
>>when I drive it with 10W set on the K3 output power, it shows
>>a drive level of about 30W and and output level of 950W. What
>>is going on?
>>
>>Details: The two boxes are connected with about 6' of RG-58
>>for the RF and a custom cable made by KC5PCB, Dan Tassell for
>>the rest of the signals. The output is into a dummy load,
>>although very similar measurements occur with my trapped
>>vertical antenna. Tests were in the CW portion of the 20M band.
>>
>>The Amp is powered from a dedicated 120V circuit which shows a
>>7 volt drop at 12.7A during CW key down transmission. (Voltage
>>is measured by a Fluke 87 DVM and current by a Kill-A-Watt
>>PA4400.) An external YS-60 power meter shows 800W, which seems
>>reasonable agreement given the accuracy of RF power measurements.
>>
>>Why does the K3 show 10W and the amp show 30W? Is there
>>something screwy here, or is it normal?
>>
>

-----------------------------------------------------------------------
Bill Frantz | Can't fix stupid, but duct | Periwinkle
(408)356-8506 | tape can muffle the sound... | 16345
Englewood Ave
www.pwpconsult.com | - Bill Liebman | Los Gatos,
CA 95032

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Jim Brown-10

Re: K3 and Expert 1.3K-FA amplifier power

In reply to this post by Bill Frantz

On 9/10/2017 2:10 PM, Bill Frantz wrote:
> I have just set up an Expert 1.3K-FA amplifier with my K3 (with most
> of the upgrades to become a K3S). My question is, when I drive it with
> 10W set on the K3 output power, it shows a drive level of about 30W
> and and output level of 950W. What is going on?

A cynic might suggest that we have the equivalent of VW cheating on
their diesels. Or the K3 might have a power calibration error.

73, Jim

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k6dgw

Re: K3 and Expert 1.3K-FA amplifier power

There is the story, probably apocryphal, of a famous rock star who said
the secret to his success was that the volume knob on his amplifier went
to 11 instead of just 10 like all the others.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 9/10/2017 8:09 PM, Jim Brown wrote:

> On 9/10/2017 2:10 PM, Bill Frantz wrote:
>> I have just set up an Expert 1.3K-FA amplifier with my K3 (with most
>> of the upgrades to become a K3S). My question is, when I drive it
>> with 10W set on the K3 output power, it shows a drive level of about
>> 30W and and output level of 950W. What is going on?
>
> A cynic might suggest that we have the equivalent of VW cheating on
> their diesels. Or the K3 might have a power calibration error.
>
> 73, Jim

Igor Sokolov-2

Re: K3 and Expert 1.3K-FA amplifier power

In reply to this post by Bill Frantz

I have the same setup here and drive the amp with 5-7 W from K3 to 1 Kw
with MEDIUM setting of the amp.

The amp shows input power very close to that set on K3. My amp is EU
version and it would switch overdrive protection ON if input exceeds 20W.

Check if TUNE POWER of your K3 set to NORMAL if you do your measurements
in TUNE mode.

73, Igor UA9CDC

11.09.2017 2:10, Bill Frantz пишет:

> I have just set up an Expert 1.3K-FA amplifier with my K3 (with most
> of the upgrades to become a K3S). My question is, when I drive it with
> 10W set on the K3 output power, it shows a drive level of about 30W
> and and output level of 950W. What is going on?
>
> Details: The two boxes are connected with about 6' of RG-58 for the RF
> and a custom cable made by KC5PCB, Dan Tassell for the rest of the
> signals. The output is into a dummy load, although very similar
> measurements occur with my trapped vertical antenna. Tests were in the
> CW portion of the 20M band.
>
> The Amp is powered from a dedicated 120V circuit which shows a 7 volt
> drop at 12.7A during CW key down transmission. (Voltage is measured by
> a Fluke 87 DVM and current by a Kill-A-Watt PA4400.) An external YS-60
> power meter shows 800W, which seems reasonable agreement given the
> accuracy of RF power measurements.
>
> Why does the K3 show 10W and the amp show 30W? Is there something
> screwy here, or is it normal?
>
> 73 Bill AE6JV
>
> -------------------------------------------------------------------------
> Bill Frantz        | The first thing you need when | Periwinkle
> (408)356-8506      | using a perimeter defense is a | 16345 Englewood Ave
> www.pwpconsult.com | perimeter.                     | Los Gatos, CA 95032
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
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>