Here we take a look at the RS-918 HF SDR Transceiver, a typical clone of the mcHF.
Specification:
– HF QRP Transceiver,put battery 12v and ANT can qso.
– DC IN:9-13V Max:3A
– Output POWER:<=10W
– Transmit: 160,80,60,40,30,20,17,15,12 and 10 meter amateur bands.
– Receive: 3.5-30 MHz nominal including general coverage,0.8-32 MHz at reduced specifications.
– MODE:CW,LSB,USB,AM,FM(N,W),SAM,FreeDV
– Bandwidth:300Hz-10Khz Adj
– SWR:Display 1-5
– Better than -108 dBm (0.89uV) in a 2.3 kHz bandwidth
– Better than -120 dBm (0.22uV) in a 300 Hz bandwidth
– Enclosure Design: Removable
– stm32f407VGT6 1M memory
Technical Specifications:
Because this is a software-defined radio and due to ongoing modifications/improvements of the software and hardware,the specifications continue to improve.
– Receiver sensitivity for 10dB S/N,CCITT filtering,taken at 28.3 MHz:
– Frequency Translation enabled:
Better than -111 dBm (0.6uV) in a 2.3 kHz bandwidth
Better than -126 dBm (0.11uV) in a 300 Hz bandwidth
Frequency Translation Disabled:
Better than -108 dBm (0.89uV) in a 2.3 kHz bandwidth
Better than -120 dBm (0.22uV) in a 300 Hz bandwidth
The above specifications are for a receiver on which the published sensitivity modifications are performed.
Frequency coverage:
– Transmit: 160,80,60,40,30,20,17,15,12 and 10 meter amateur bands.
– Receive: 3.5-30 MHz nominal including general coverage,0.8-32 MHz at reduced specifications.
Note: The ability of the Si570 to tune the radio below 2.5 MHz is not guaranteed in its specifications,but most units have enough range to tune just below 1.8 Mhz.Maybe there are some small gaps where LO does not work-if it orks,it works fine.Indicator is the color of
The frequency digits:
– White: fully working
– Yellow: mostly working, maybe there are some small gaps
– Red: not working
Spectral Display Modes:
– Spectrum Scope: This is a spectrum analyzer with the vertical divisions representing userdefinable amplitude variations of 5,7.5,10, 15,20,1 S-Unit (6dB),2 S-Units (12dB) or 3 S-Units).The baseline (“reference level”) of the analyzer is automatically adjusted so that the signals within the displayed passband best fit the dynamic range selected by the userselected dB/division.A graticule along the bottom of the display indicates the approximate frequency of the signal being displayed over a width of +/- 24 kHz.((48 kHz total)
– Waterfall Display: As with the spectrum scope,the frequency is displayed along the “x” axis but the signal strength is implied by the displayed color.The newest signals are displayed along the bottom of the screen,but as new readings arrive,the representations of the older signals are shifted upwards giving an ephemeral time record of recent activity on nearby frequencies.There are several options for color “palettes” that range from simple grayscale to “cold-hot” to “rainbow” to represent weak to strong signals.
There is also a “Magnify” mode for both the Spectrum Scope and Waterfall Display mode that provides 2x magnification, reducing the visible spectral width to just +/- 12 kHz (24 kHz total.) Both the Spectrum Scope and Waterfall Display are very highly configurable. It is possible to disable one or both spectral display modes if desired.
Large-signal handling capability: Continuous “Clip Warning” occurs above approximately -28 dBm and actual A/D clipping and distortion occurs at and above approximately -18 dBm for signals +/- the local oscillator frequency and higher for signals outside this range.
Transmitter power output: <=10 Watts,typical,linear.Modifications may be made to increase this: Follow the discussions in the Yahoo group.
Frequency stability: +/- 30 Hz at 14 MHz over the range of 10 to 35 C,ambient with the transceiver in the case or better with the TCXO active. (It can be much better than this.
Available TX/RX modes:
– CW,USB,LSB,AM (full-carrier,double-sideband),SAM (double side band reception) and FM.AM transmit and FM transmit/receive capabilities are available ONLY if the “frequency translate” is activated (highly recommended!)
– FM options: Carrier (ultrasonic) squelch,subaudible tone encoding and decoding,tone burst (“whistle up”) generation,”narrow” (+/-2.5 kHz) and “wide” (+/-5 kHz) deviation and the selection of 7.2,10,12 or 15 kHz pre-detection receive bandwidths.
FM sensitivity for 12 dB SINAD,CCITT filtering:
7.2 kHz BW filter: -103.7 dBm (1.46uV) with 1 kHz tone at +/-1.5 kHz
10 kHz BW filter: -102.1 dBm (1.75uV) with 1 kHz tone at +/-1.5 kHz
10 kHz BW filter: -104.0 dBm (1.41uV) with 1 kHz tone at +/- 3kHz
12 kHz BW filter: -102.7 dBm (1.63uV) with 1 kHz tone at +/- 3kHz
15 kHz BW filter: -99dBm dBm (2.50uV) with 1 kHz tone at +/- 3 kHz
CW mode receive/transmit and frequency display details: Nine modes of CW display/shifting are available to emulate the various makes of radios and suit the user’s taste,ranging from no shifting,display-only shifting,display and LO shifting and manual or automatic LSB/USB shifting.
In CW mode “CW-L” or “CW-U”,is displayed depending on whether LSB or USB is being used for reception.
CW Speed range: 5-48 WPM.
Available audio filter bandwidths in this firmware version: 300 Hz, 500 Hz,1.8 kHz,2.3 kHz,3.6 kHz,with a “wide” filter of 5,6,7.5 or 10 kHz being selectable in all modes except FM,where the filtering is done prior to demodulation as described above.All filters are softwaredefined and additional bandwidths could be made available.Filters can be used as BPF or as LPF selectable in main menu.
DSP Filtering Capability: Noise reduction and Automatic Notch Filter with adjustable parameters.Notch filtering is disabled in CW mode for (obvious reasons) or when using a “wide” receive bandwidth.(devel-branch: Because NR activation leads to instability of mcHF it is disabled by default.If you want to use it (and risk instabilities in various scenarios) you can activate NR in config menu “last item”. Setting will NOT BE STORED and must be activated after every powering on. When NR issues are fixed and NR will be improved this function will be obsolete.)
S-Meter calibration: “Industry Standard”(IARU Region 1,Technical recommendation R.1) Smeter calibration where S-9 = -73dBm (50.2uV @ 50 ohms) with each “S” unit representing 6 dB. Units above S-9 are in dB units,as described.
External audio input/output connections:
– “Line In” and “Line Out” audio ports,and a “PTT”(Push-to-Talk) are provided via 3.5mm connectors to allow the connection to an external device.With these connectors it is possible to interface with an external device (a computer or tablet/smart phone) and operate “Sound Card” modes with the mcHF such as SSTV,PSK31,WSPR and other analog/digital modes.
– (devel-branch only): There is CAT function and audio-in and out also as IQ in and out via USB available.Setting of input is in main menu #60 or via long-press of M3.
– Line out signal levels: Nominal 1 volt peak-peak, maximum when AGC is operating.
– Line in signal levels: Nominal 0.1-1.0 volt peak-peak, adjustable using the “Line Input Gain” settings.
– Transmit ALC type: Look-ahead gain compressor with both pre-set and available “custom” settings.
Operating voltage range:
– 16.0 volts maximum (when capacitors C27 and tantalum parallel to C106 both rf board are 25V)
– To 11.0 volts minimum for full transmit power
– To 9.5 volts for reduced transmit power
– As low as 6.5 volts, receive-only: Only very low transmit power may be possible–distortion on peak audio (SSB,AM) may occur.
Current consumption:
1.Receive:
– Unmodified,approx.410mA on 40 meters and below at 13.0 volts,approx.440 mA on 10 meters,minimum volume,maximum display brightness.
– The selection of minimum display brightness can reduce this by 40-60mA.
2.Transmit (At 13.0 volts power supply):at full power around 3A;at 10W around 2.5A
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