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, donw...@embarqmail.com (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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
