To make these kinds of measurements with amateur equipment and accuracy, I
suggest acquiring some directional couplers and/or high power attenuators. A
spare K3 or a decent SDR receiver then makes an excellent "power meter" with
significant dynamic range. Gain measurements are really ratio
The saturation can be due:
- transistor limit -not the case here
- power supply drop - not if well designed switching PS or a commercial
unit
- winding ratio in final transistor module
You can test the last one by measuring max power at saturation. Should be at
least 2 KW.
I have Expert 2k-fa
Yes, the linearity of the two power meters is suspect. However, the
compression of interest is near the high end for that of both the
KPA1500 and the K3, so I wouldn't expect their nonlinearity there to
make much difference. Note that absolute accuracy isn't critical.
73,
Scott K9MA
On
Yes and most power meters are voltage sensing instruments which are
calibrated to a specific value or load. Thus is the load being used may
not be the identical value to which it was calibrated, hence another
error enters the equation.
To wit, I have 3 "allegedly" 50 ohm dummy loads. Only
Most, if not all analog measurement devices are spec'd at % of full
scale which can lead to high absolute variances if the levels being
measured are significantly below full scale. A Bird with a 100W slug
accurate to 10% of full scale [+/- 5W] would be within spec if it
indicated a real 10 W
John,
You are exactly right for bring that factor to attention. Typically
wattmeters use diodes in their detectors, and the response will vary by
frequency and by the power level.
I would trust only something that has been calibrated to NIST traceable
standards. The Telepost LP-100 is one
Hi Scott,
I wonder how the linearity of the two power meters was evaluated?
Some years ago I checked the K3 and KX3 power meter against two other
meters. They were just within 10%
http://www.kn5l.net/Elecraft/Power.html
John KN5L
On 06/19/2018 04:56 PM, K9MA wrote:
> I just repeated the
I just repeated the linearity measurements, on both 40 and 15 meters. I
used the KPA1500 meter to measure output, and the K3 power setting for
input. Results on the two bands were similar, though 15 required much
more drive.
On 40, the maximum gain occurred at about 800 W out, 17.2 dB. At
I'll have to make some more measurements, but Paul's seem to have much less
gain compression than mine. (0.6 vs 1.4 dB from 1 kW to 1.5 kW) That's also
closer to the specs for a pair of BLF88XR's.
73,
Scott K9MA
--
Scott Ellington
--- via iPad
> On Jun 15, 2018, at 11:24 PM, Paul
I received my KPA-1500 yesterday (#244) and did some linearity tests today
14.2MHz, Dummy Load, ATU Bypassed. Using KPA-1500
internal Power Meter. Continuous carrier.
10W drive, Gain = 15.6dB 180W
15W drive, Gain = 15.8dB
20W drive, Gain = 15.9dB
25W drive, Gain = 16.0dB 1.0KW
30W drive, Gain
The gain compression I measured, between 1000 and 1500 W on 40 meters, was 1.4
dB. I used the K3 and KPA1500 power meters. Factory calibration of the
KPA1500.
Scott K9MA
--
Scott Ellington
--- via iPad
> On Jun 14, 2018, at 2:51 PM, Paul Baldock wrote:
>
> What you report of
What you report of compression near the maximum
power is certainly true of the amplifiers like
the SPE-1.5K that use a single device, but I
would have thought this would not be true of the
KPA1500 that uses 2 devices. This is the reason I
returned my SPE and ordered the KPA. Hopefully
the
On 6/9/2018 2:21 PM, K9MA wrote:
While I'm primarily a CW operator, I'd be very reluctant to use the
amplifier on SSB.
CW is 100% Amplitude Modulation of a carrier by a rectangular wave, so
the transitions are rich in harmonics that are heard as clicks, and they
WILL excite IM in a
Thank you for posting this. I have been saying it for years on these forums and
getting told that I didn't know what I was talking about. Now maybe the
naysayers will take note.
Wes N7WS
On 6/9/2018 6:28 PM, Wayne Burdick wrote:
Finally, both the transceiver and amp will vary from band
Thanks, Wayne. I'm glad to hear this isn't typical.
I sent a report to tech support with all the details. I'll call later next
week, as I'll be out of town with the KX2 until Thursday.
73,
Scott K9MA
--
Scott Ellington
--- via iPad
> On Jun 9, 2018, at 8:28 PM, Wayne Burdick
Scott, I don’t know if this helps much but several of the locals have
constructed BLF-188 amps (singles and pairs) in the past two years. The W7,
Israeli and Russian boards were used and they all suffered the same fate in
various degrees. They would cease being very linear at about 75% of
Scott,
I’m not sure how you’re doing the test, but this is definitely not
characteristic.
We test every amp for IMD, and we see an average of about -35 dBc (3rd order,
ARRL method) across all bands. This is state of the art for an LDMOS deign
running class AB. Other SS amps using similar
I did look at the K3 output, and it's much, much better than the KPA1500
output. I also checked that the KPA1500 supply voltage was not dropping much:
53 V in standby, 52 V at 1500 W.
73,
Scott K9MA
--
Scott Ellington
--- via iPad
> On Jun 9, 2018, at 7:26 PM, Wes Stewart wrote:
I don't have a KPA1500 or enough power attenuators to test my KPA500, but I have
spent many dozens of hours looking at TX IMD on my two K3s.
I will simply say, if you haven't already, check the IMD of the bare K3 before
blaming the KPA1500. Garbage in, garbage out. That of course doesn't
I recently ran a two-tone test and measured CW power gain. (SN1078) It
doesn't look good. The two-tone waveform shows distinct "flat-topping",
and the power gain drops 25 percent from 1000 to 1500 Watts. My old
3-500Z amplifier is much better. Has anyone measured IMD or linearity,
or seen
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