I purchased my linear amplifier as a companion to both my Lab599 'Discovery' and Elecraft KX3 transceivers. Whilst QRP operation is certainly rewarding, there are times when just a little more power, especially when band conditions are poor, can make all the difference.
One of the things that makes this amplifier so attractive is the 'plug-and-play' capability straight out of the box. No setting up, no adjustments, no reading the manual, just connect the power lead, a BNC to BNC patch lead from the transceiver to the amplifier's input, and the antenna's RF cable, and you are good to go. RF VOX capability, automatic band detection, and automatic antenna matching all set as the default operating modes.
Naturally those of you who have read any of my other reviews will know that I can't resist putting it on my test bench and checking it out, and so it was with this amplifier.
RF Gain
The amplifier has quite a high power gain, which is both a good and a bad thing. On the positive side it takes very little input power to drive it to maximum O/P, but it also means that it is very easy to saturate the amplifier, so care is needed to ensure that the output from your transceiver is backed off to the 1W or 2W level before keying. In addition, the gain of the amplifier varies significantly from band to band. The highest gain is on 20m, and is about 16dB whereas the lowest gain is about 13dB. This means that to obtain 50W (47dBm) on 20m only takes about 1.25W (31dBm), whereas on the lower gain bands it takes about 2.5W (34dBm). Checking with Oliver, who I have to say was extremely helpful and answered all my technical questions, reveals that this gain variation is unavoidable because there are only 4 low-pass filters for all the bands from 80m to 10m. He did mention that he's working on an 'E' version for expeditions that will have 5 filter groups, and this will give the amplifier a much flatter frequency characteristic.
Efficiency & Power Consumption
The amplifier is quite modest in its power requirements. In my case, when in the standby state it drew around 50mA, in the TX state, with no RF signal it draws about 970mA, and at 50W it draws 6.6A, all with a supply voltage of 13.8V. This gives a DC to RF power conversion efficiency of about 57%, which is quite good for a low-voltage solid-state amplifier.
Note however that even when switched off there is a steady draw of about 10mA, so it is wise to disconnect it from your power source if you are going to leave it for any length of time.
User Interface
The User Interface is by means of 4 push buttons and a series of LEDs. The buttons themselves have a nice positive tactile feel, although because of the small size the layout is somewhat cramped. To switch on you have to simultaneously press both the BYPASS and BAND buttons until the white RF PWR/PTT LED illuminates. The amplifier will initially power up in the BYPASS mode, signified with the blue BYP/10m LED blinking. To enter the OPERATE mode you have to briefly press the BYPASS button. At this point the LEDs will indicate which band is currently selected, 10m, 20m, 40m, or 80m. When the amplifier is actually in the transmit state, these 'BAND' LEDs can indicate either the approximate O/P power, or the approximate SWR, depending upon how you configure them.
In my case the RF O/P power indication was decidedly approximate.
To alter the configuration of the amplifier involves pressing and releasing the BYPASS and BAND buttons in a specific sequence, and because of both the cramped access and critical timing this may take some practice. One thing to be aware of, to save the new configuration it is not sufficient to just switch the amplifier off, you must also disconnect or completely switch off the power supply. Failure to do this will result in some slightly odd LED indications when you next switch on.
At the other end of the amplifier are the RF I/P and O/P sockets, as well as 2 push-buttons and 2 LEDs to indicate ON and READY. Normally the amplifier is in the fully automatic tuning mode, and the green LED is on. In this mode the internal ATU will attempt to match the load as soon as RF O/P is available if the SWR is greater than about 1.5:1. By pressing the AUTO button manual tuning can be selected, and this is 'armed' by pressing the TUNE button, whereupon a tune operation will commence as soon as RF O/P is available.
Output Power & Distortion
The absolute maximum output of 60W is only possible with a supply voltage of 16V. This voltage is only available from a fully charged set of 4 series connected Li-Poly batteries, and even then only for a short time before the voltage falls the plateau of about 15.6V. When using lead-acid gel cells the operating voltage will be about 13.8V initially but again will fairly quickly fall to about 12.6V - 12.8V. At this voltage the 1dB gain compression point is at about 40W. When operating near its maximum O/P the 3rd order IMDs are about -30dBc - about par for the course for an amateur amplifier operating at such low voltages. Be aware however that to avoid significant adjacent channel splatter you should back off the drive as the supply voltage falls during portable operation, and this is where the high power gain can be less than useful. In my case both the Lab599 and the Elecraft transceivers were capable of having their output levels reduced to only the 1W to 2W range to avoid over-driving this amplifier, but this is not always the case. With my JUMA TRX2 transceiver I would have to deliberately reduce the internal drive levels for both CW and SSB to avoid overdriving, and this would be a nuisance to have to reset when I wish to operate barefoot.
So, in summary, a really nice useful linear with the same form-factor as the Lab599 transceiver for which it was designed, but perfectly capable of being used with other rigs such as the Elecraft KX2 and KX3. 'Plug-and-play' capability straight out of the box, with fully automated operation for transmit/receive switching, band selection, and antenna matching.
On the down side, it is an expensive accessory, and because of its high power gain, you need to take care not to over-drive the amplifier, as you risk blowing the internal fuse, although there is a fair amount of protection built in.
Overall I am well pleased which is why I give it 5 stars.
Adrian, 5B4AIY |