Handheld SDR radio based on LIME

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This project was completed by a Senior Design team. It is now obsolete due to the unavailability of the original Lime Mini and high cost of its replacements.

Sponsor
Amateur Radio Club
Majors
CS, EE, Club? (Amateur Radio license required for testing)
Difficulty
medium
Target cost for final product
$300-$500 (prototyping may cost more), additional accessories (such as GPS) would be budgeted separately

Problem: Design a handheld radio using an off the shelf SDR radio as the core RF component, with an added final TX amplifiers, user interface, SDR modulation and demodulation, and power budget.

External links for support hardware:

This project has gone through one team already, but additional work needs to be done. Phase one documentation will be added here eventually. Phase one mostly worked on hardware design.

Required features[edit]

All of these features should be fully supported in the final result.

  • FM RX/TX, AM RX
  • Include required filters and amplifiers to transmit 5W on specific bands; suggested bands: 2m, 70cm, maybe 1.25m; power level should be adjustable 0.1W-5W.
  • T/R hardware so a single antenna can be used by both.
  • display and controls for field use, probably will required an external embedded cpu
  • minimum 6 hour stand by time (power budget)
  • open source software design
  • should include memory presets for FM use and interface to field program frequencies (minimum 100, typical 1000)
  • Repeater interaction features: CTCSS standard subaudible tones (88-200hz) and tone squelch (RX/TX); duplex operation (TX/RX offset, offset polarity (+ 0 -) ), touchtone generation
  • fully programmable from a laptop or desktop

Optional features[edit]

Ideally, the design should support eventually adding these features. If the final product does not include them, they should be supportable either as software expansion or added plugin hardware modules.

  • GPS support for APRS and time sync (should be an optional module as this adds cost)
  • full touchscreen control for field use
  • transmit support for 900MHz (1W-5W maybe)
  • multiple mode encode and decode, including AM FM DFM APRS DSTAR Fusion DMR DRM codec2 SSB
  • scanning and waterfall display (spectrum scope)
  • automatic signal recognition
  • Data storage ability; record to microSD either demodulated voice or direct I/Q samples
  • satellite communication features, especially automatic doppler frequency adjust (possibly with external preprogramming and/or active FM tracking)
  • internal battery charging circuit and battery level indicator
  • Possible extensions of UI through phone interface via bluetooth or USB
  • NOAA weather radio RX with stand by monitoring and alerting with SAME support
  • some attempt at waterproofing (rain / sweat at least)

Block diagram[edit]

(future block diagram goes here) Components:

  • SDR core (lime or cariboulite or ???)
  • embedded control cpu (raspberry pi or ???)
  • TX amplifier and maybe T/R switch
  • external antenna port (sma? bnc? must have good mechanical support!!)
  • Touchscreen display
  • speaker
  • microphone
  • external mic / speaker connections?
  • tuning and volume knobs?
  • PTT switch
  • battery and battery charge controller
  • external power supply port (for charging and desktop operation)

Individual feature details[edit]

This section is for ideas for details of individual features.

Waterfall / panadapter[edit]

Here is a sample of my existing panadapter for HF, for those who have never seen a waterfall. Note that the vertical axis on waterfalls is time, and is frequently unlabled. Some programs have options to control speed that samples are added, and some have controls to change scrolling direction. The point of the waterfall is to get a quick visualization of activity on the band or within a small section of the spectrum over time. Things it shows are noise floor, activity, possibly mode of the activity (which sometimes is visually distinguishable). This is more interesting on HF which is not channelized, and less interesting on VHF where it is frequently channelized (unless doing SSB on vhf) and maybe less detail would be OK.

This shows a large slice of the 40m band. Each vertical stripe could be one station. Modes visible include (roughly left to right with some mixing) morse code, ft8, jt65, SSB, and a lot of noise.


Here is a smaller slice of bandwidth, screenshot from the waterfall portion of the FLdigi program, showing a few psk31 stations.

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