The RM Italy KL-145 Linear Amplifier in Digital Mode

140-152 MHz Linear Amplifier Performance in WSPR Mode

by Dr. Carol F. Milazzo, KP4MD (posted 16 October 2012)
E-mail: kp4md@arrl.net

RM Italy has replaced the KL-145 amplifier listing with a LA-145 model that appears externally identical except for color and is rated at 85 watts output for 4 watts input.


RM KL-145 Linear Amplifier

1.  An RM Italy KL-145 Linear Amplifier purchased from DNJ Radio.   The manufacturer's specifications rated this unit at 110 watts output for 25 watts input.  5 watts from my Elecraft XV144 transverter drove its SD1477 transistor to 50 watts output. The SD1477 transistor in these KL-145 amplifiers had a frequent failure rate with higher applied RF drive as there is no overdrive protection. RM Italy has replaced the KL-145 listing with a LA-145 model that appears externally identical except for color and is rated at 85 watts output for 4 watts input.

On 18 June 2012 I put this unit into service
                      on WSPR, a digital mode running 20% duty cycle, 2
                      minutes on, 8 minutes off.  On 30 June, the
                      amplifier failed and developed a zero ohm short
                      circuit as measured across its power cord.

2.  On 18 June 2012 I put this unit into service at 50 watts output power on WSPR, a digital mode running 20% duty cycle, 2 minutes on, 8 minutes off.  On 30 June, the amplifier failed and developed a zero ohm short circuit as measured across its power cord.  The RM Italy technical support staff promptly responded to my inquiry, advising that the failure may have been caused by excessive temperature as the fixed idling current decreases amplifier efficiency at lower output power levels.

Here is a replacement RM Italy KL-145 Linear
                      Amplifier under test with a SilenX Effizio
                      EFX-10-12 fan on the heat sink. The amplifier is
                      being driven to to 50 watts into a 50 ohm
                      non-reactive load and the DC voltage and current
                      are being monitored with a Turnigy 130A watt
                      meter. A temperature probe was placed on the
                      warmest part of the heat sink to monitor heating
                      during operation.

3.  Here is a replacement RM Italy KL-145 Linear Amplifier under test with a SilenX Effizio EFX-10-12 fan on the heat sink. The amplifier is being driven to to 55 watts into a 50 ohm non-reactive load and the DC voltage and current are being monitored with a Turnigy 130A watt meter.  DC power consumption is 108 watts and the efficiency is approximately 50%, normal for a linear amplifier.  A temperature probe was placed on the warmest part of the heat sink to monitor heating during operation.

32. The
                      RM Italy KL-145 amplifier temperature during WSPR
                      operation. Without fan cooling, successive
                      transmission cycles at this duty cycle caused
                      cumulative temperature rise eventually causing
                      amplifier failure. With a SilenX EFX-10-12 fan on
                      the heat sink, the amplifier's temperature never
                      exceeded 39C.

4.  The RM Italy KL-145 amplifier temperature test during WSPR operation. Without fan cooling, successive transmission cycles at this duty cycle had caused cumulative temperature rise eventually causing amplifier failure. With the SilenX EFX-10-12 fan on the heat sink, the amplifier's temperature never exceeded 39C and has been in constant operation since July 2012.

The WaveNode WN-2 LCD display unit, a
                      precision calibrated digital SWR/Power Meter,
                      interfaces with a computer through a USB serial
                      cable. The WaveNode software displays all
                      parameters, oscilloscope and modulation frequency
                      analyses on the computer monitor.
                      http://www.wavenode.com/wn-2.htm

5.  The WaveNode WN-2 LCD display unit, a precision calibrated digital SWR/Power Meter, interfaces with a computer through a USB serial cable. The WaveNode software displays all parameters, oscilloscope and modulation frequency analyses on the computer monitor. http://www.wavenode.com/wn-2.htm

Here are two WaveNode UHF-1 RF sensor units,
                      one attached to the input and the other attached
                      to the output of the RM Italy KL-145 linear
                      amplifier. The top cover of the Elecraft XV144
                      transverter is seen in the foreground. A Waters
                      model 336 coaxial transfer switch is behind the
                      sensor units.

6.  Here are two WaveNode UHF-1 RF sensor units, one attached to the input and the other attached to the output of the RM Italy KL-145 linear amplifier. The top cover of the Elecraft XV144 transverter is seen in the foreground. A Waters model 336 coaxial transfer switch is behind the sensor units.

PowerSDR
                      running on a FLEX-3000 and a FLEX-1500 with 2
                      meter transverter, with instances of WSPR for HF
                      and VHF. WaveNode monitors the input power to the
                      RM Italy KL-145 linear amplifier and power output
                      of both transmitters.

7.  PowerSDR running on a FLEX-3000 and a FLEX-1500 with 2 meter transverter, with instances of WSPR for HF and VHF. The WaveNode WN-2 monitors the input power to the RM Italy KL-145 linear amplifier and power output of both transmitters.

The WaveNode
                      WN-2 produced this power vs. gain performance
                      graph for the RM Italy KL-145 amplifier, showing
                      nearly constant gain measured at 11-12 dB from 25
                      to 100 watts output.  Above this level the
                      gain decreases to 8 dB at 150 watts output. This
                      behavior is normal for solid state linear
                      amplifiers.

8.  The WaveNode WN-2 produced this power vs. gain performance graph for the RM Italy KL-145 amplifier, showing nearly constant gain measured at 11-12 dB from 25 to 100 watts output.  Above this level the gain decreases to 8 dB at 150 watts output. This behavior is normal for solid state linear amplifiers.

For comparison,
                      here is a power vs. gain performance graph for the
                      Mirage B-2518-G linear amplifier, also showing
                      nearly constant gain measured at 11-12 dB from 25
                      to 100 watts output. Above this level the gain
                      decreases to 10 dB at 120 watts output.

9.  For comparison, here is a power vs. gain performance graph for the $369 Mirage B-2518-G linear amplifier, also showing similar gain measured at 11-12 dB from 25 to 100 watts output. Above this level the gain decreases to 10 dB at 120 watts output.

Here the
                      WaveNode displays simultaneous input and output
                      measurements of the RM Italy KL-145 amplifier.

10.  Here the WaveNode displays simultaneous input and output measurements of the RM Italy KL-145 linear amplifier.

The internal
                      view of the RM Italy KL-145 linear amplifier
                      showing clean, solid construction and excellent
                      workmanship.

11.  The internal view of the RM Italy KL-145 linear amplifier showing clean, solid construction and excellent workmanship.

A close-up view
                      showing the SD1477 transistor in the RM Italy
                      KL-145 linear amplifier.

12.  A close-up view showing the SD1477 transistor in the RM Italy KL-145 linear amplifier.

The measured
                      performance of the RM Italy KL-145 amplifier
                      approximates the manufacturer's specifications for
                      its SD1477 transistor.

13.  The measured performance of the RM Italy KL-145 amplifier approximates the manufacturer's specifications for its SD1477 transistor.

The RM Italy
                      KL-145 linear amplifier's circuit is a
                      straightforward design, similar to the PA10-80BL
                      amplifier formerly made by KLM Electronics. The
                      user must take precautions to avoid excess drive
                      power, SWR and operating temperature.

14.  As the RM Italy KL-145 linear amplifier's circuit is a basic, straightforward design, similar to the PA10-80BL amplifier formerly made by KLM Electronics, the user must take precautions to avoid excess drive power, SWR and operating temperature.

The RM Italy
                      KL-145 amplifier performed dependably at 50 watts
                      output on WSPR mode since July 2012. With the
                      supplemental cooling fan there was little
                      perceptible heating of the amplifier during
                      digital mode transmissions. For typical use, the
                      KL-145 at $130 is an economical alternative to
                      similar VHF amplifiers in this power range.

15.  The RM Italy KL-145 amplifier performed dependably at 50 watts output on WSPR mode since July 2012.  With the supplemental cooling fan there was little perceptible heating of the amplifier during digital mode transmissions.  For typical use, the KL-145 from DNJ Radio at $130 is an economical alternative to similar VHF amplifiers in this power range.

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