FlexRadio PGXL Amplifier

This week I thought I'd do a deep dive into my favourite toy in the shack, the FlexRadio PGXL amplifier. 

I have had owned one of these amplifiers for around 18 months now and is the last of a string of previous amplifiers of other brands starting with an RM Italy 600W amp that lasted less than an hour, to an Andrews Comms 400W solid state amplifier, then an old FL2100 Yaesu amp and an SPE 1K-FA amplifier.

Each amp had its good points. The SPE amp was good value for money and convenient in that it has an internal antenna tuner and a 4 antenna switched O/P, meaning that I could get away with a less than optimal antenna, and I didn’t need to worry about adding a remotely switchable coaxial relay. The amp is externally controllable via a proprietary application and can also follow the radio when connected via a serial port.

Now how about the PGXL? It is a nominally 1.5KW amplifier, however in SSB it will do up to 2KW PEP depending on the band used. With a pair of 1.5KW transistors, and some very robust design, the amp can work comfortably at 1.5Kw all day on any mode (subject of course to local laws limiting power O/P), even on modes running at 100% duty cycle like FT8.

The amp has a few unique features from a performance perspective that are worth mentioning here. Most amplifiers these days have high VSWR protection. The PGXL is no different and will continue to operate up to a VSWR of 3:1, when at that point it alarms out and moves into Standby. Prior to that point, it works just fine with warnings starting at 2:1. Most of my antennas seem to run between 1:1 to 2:1 across most bands except 20m where I seem to only have about 200KHz bandwidth.

On air tests bring out some interesting features. There is an app used to allow monitoring of the important parts of the amp on your PC. A lot of higher end amps have a similar feature, but have created a remote connectivity feature that providing you have a fixed IP address, you can remotely monitor the amp. You do need to create a port forward on the DSL model at the amplifier to allow the comms through to the interwebs.

Other features include 2 inputs/outputs, so you can run two radios independently with two complete data inputs to control the amp and two PTT and ALC I/Ps. Obviously you can’t run two radios in Transmit at the same time but if you use 2 radios and want both to be able to access the amp, this is a neat feature.

On SSB, the amplifier runs in what it calls an AAB mode. This is similar to Class AB but a little bit more linear (and correspondingly a little less efficient). It also runs a mode known as MEffa which is used on non voice modes such as CW and digital modes. This is an algorithm that manages the DC bias on the Drain of the PA final transistors, increasing the efficiency of the amplifier.

Another neat feature is the Harmonics filtering and dummy load. This is a feature that while is common in broadcast transmitter amplifiers, has been used for the first time on an amateur amp. It diplexes the harmonics and feeds the harmonics into a 400W dummy load. Without this facility, the PA continues to amplify any harmonics which are then dissipated by either the final filtering or the PA itself.

To cool the amplifier, there are 3 fans that operate at different speeds or modes depending on the temperature of the amplifier that can also be manually adjusted. When doing the weekly broadcast on 80m, I tend to use the fans in Broadcast mode which keeps the amp very cool even when transmitting constantly at 400W PEP.

If you are using the amp in the shack where you operate from, the amplifier has a front panel that allows complete monitoring of the amplifier locally. Like most 2KW amplifiers, it is a big beasty and heavy but a lot lighter than say an Acom2000A valve amplifier. The amp is mains powered and operates comfortably with a 10A GPO.

Maintenance is often a hot topic with high power solid state amps. These have been sold in Australia for close to 2 years now, and to my knowledge, only one has bounced back on warranty. This fault required the replacement of the 2 PA transistors. The fix was identified quickly by the manufacturer and two new pills were dispatched and received within about 5 days and the amplifier was repaired in Perth with a minimum of fuss.

The amplifier was developed jointly by FlexRadio and so works seamlessly with the Flex 6000 series of transceiver. As long as the amplifier is connected to the same LAN as the radios, all main performance parameters are visible withing SmartSDR – the operator interface used by Flex, and the only hardware connection between the radio and amplifier is the coax cable. All control of the amplifier is via the LAN.

If you are using a non Flex transceiver, there is an RS232 serial port as well as an Icom CI-v port.

The amp will communicate with all main stream radios including Flex, Icom, Yaesu, Kenwood etc. In addition there are separate PTT and ALC I/P for each Input of the amplifier.

A common comment I have heard on this amplifier is that at a healthy price tag of in excess of $10K, it really should have antenna switching and an inbuilt ATU. My take on this is that with the ability to work within 3:1 and less, it really doesn’t need an ATU. If you were operating at 2KW (presumably from overseas where it might be allowed), you really wouldn’t be wanting to be trying to feed 2KW into an antenna with an SWR of more than 2:1 with or without an ATU. If your amplifier alarms out at 1.3:1, then an external or internal ATU would be a complete necessity. A perfectly tuned antenna can easily go up to 1.3:1 with a warmer balun. Having operated the amplifier on a few DX contests, I can tell you this is a robust and trouble free amplifier that I am very happy with and I expect that unless ACMA surprise us with allowing more than 2KW, this will probably be the last brand of amplifier I have in my shack. 

The other comment is on the antenna switching capability. On my site that I share with 2 friends, we currently have 8 antennas and will likely have another 3 or 4 added in the next 12 months, so the 4 antenna ports on my trusty old SPE 1KFA would still fall short, so I opted for a pair of Antenna Genius’ coaxial switches which allow 2 radios to access up to 16 antennas. If I’d bought an amp with 4 antenna ports, I would still only be using one antenna port in addition to the Antenna Genius’.