http://elecraft.85.s1.nabble.com/K3-and-Expert-1-3K-FA-amplifier-power-tp7634331p7634337.html
-15%) near full power, at low power they typically were way off. I
the scale. The load was probably pure resistive and near 50 ohms.
I wonder if anybody has any hard data on this. If it is true, why?
> 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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