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--- rs928ampreview [2026/02/08 12:03] – created g7bcs
+++ rs928ampreview [2026/02/08 13:13] (current) – [Inside the box] g7bcs
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 About a year ago I wanted an SDR transceiver and didn't really take to the user interfaces on any of the "black box" SDRs, so started to think about PC-based SDRs. The performance of a Flex or Anan would have been wasted for the odd rag chew on my backyard antenna system, I needed something Linux based and wanted something with a bit of potential for tinkering-with so I settled on a Hermes Lite 2.
-Having played with it for a while, both barefoot on HF and driving a transverter on 2M, I longed for a bit more power than its' 5W on the HF bands so started looking around for an amplifier to get me up to 100W or so. I thought about utilising a PA stage from an old HF rig and writing some code for the HL2 IO board to do the band switching but there was a danger that this would join the back of my never ending project queue and a coversation on the HF bands brought a recommendation for this amplifier so I thought I'd give it a go.
+Having played with it for a while, both barefoot on HF and driving a transverter on 2M, I longed for a bit more power than its' 5W on the HF bands so started looking around for an amplifier to get me up to 100W or so. I thought about utilising a PA stage from an old HF rig and writing some code for the HL2 IO board to do the band switching but there was a danger that this would join the back of my never ending project queue and a conversation on the HF bands brought a recommendation for this amplifier so I thought I'd give it a go.
 The amplifier is touted as an "RS-928" on Alibaba, Ebay and AliExpress. I found a UK based Ebayer called electro.tek and purchased mine from him. It arrived well packged within a day or two so I was delighted with the service from him.
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 Up against the rear heatsink panel is the RF deck which consists of a pair of Mitsubishi 2SC2904s in a conventional push pull class AB setup, along with bias stabilisation circuitry and impedance matching magnetics.
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 A board on the bottom of the case contains 6 low pass output filter networks along with switching relays for the filters, TX and RX signal path switching and two input attenuators. This also contains a directional coupler for forward and reverse power sensing, some relay drivers and a current sensing chip to detect the final current drain.
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 Against the front panel is a control board containing the LCD display, front panel buttons, a dsPIC30F6014 processor, an RS-232 level converter, some fan speed control circuitry and power supply regulators.
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 There is one further board which houses the three rear panel jack sockets for the control signals and some signal conditioning for the input transmit frequency detection.
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 Few 100W HF amplifiers on the market represent as good value for money as the RS-928, and the sample I received performs well.
 The RS-928 is a Chinese clone of Juma's work and this may put off some buyers. The performance of the RS-928 would give me confidence in purchasing the Juma PA-100D from Rowaves too, however. It's likely that the latter will have had better attention to component quality and matching, and calibration during production, possibly giving even better performance, albeit at a higher price.
 Out-of the box, in my opinion, the RS-928 would be a great companion to the Hermes Lite, FT-817/817, IC-705 and other QRP rigs when used attended in the shack or in a vehicle. Its size and weight probably don't lend it to portable use a significant distance from a vehicle.
 The firmware supplied with the RS-928 is clearly based on an old or stripped-back version of the PA-100D code, doesn't have usable remote control facilities that would allow easy unattended remote operation, and suffers from an irritating issue with the SWR alarm when tuning-up. It is, apparently, possible to flash it with later Juma firmware.
 Overall, I am very happy with this amplifier, and would recommend it and the Juma PA-100D to anyone wanting a few more watts out of a QRP HF rig.