So, for close to a decade now, I’ve had a bicycle-mobile station. Originally just restricted to 2m/70cm FM, it expanded to 2m SSB with the FT-290RII, then later all-band using a FT-857D.
It’s remained largely unchanged all this time. The station is able to receive MW/SW stations as well, and with some limitations, FM broadcast as well. My recent radio purchases will expand this a bit, freeing up the FT-857D’s general-coverage receiver to just focus on amateur bands. It’s been a long-term project though to move to SDR for reception.
What I have now
Already acquired is a Raspberry Pi 4 (8GB model) and a NWDR DRAWS interface board. I actually started out with a Raspberry Pi 3 + DRAWS and was waiting for the case for it to fit into. At that stage was the idea that the FT-897D would do much as it does now, no SDR involved, and I’d put a small hand-held with its own antenna as an APRS rig being driven by the second port on the DRAWS.
Since then; I bought the HackRF One for work (I needed something that could give me a view of the 2.4GHz ISM band for development of the WideSky Hub), the SDR bug firmly bit. Initially it was just DAB+ reception, I decided to get a RTL-SDR to do that so my radio listening wouldn’t be interrupted when a colleague needed to borrow the HackRF. That RTL-SDR saw some use receiving UHF CB traffic at horse endurance ride events at Imbil — I stated to consider whether maybe this might be a better option as a receiver for more than just commercial radio broadcasts.
Hence I purchased the Pi4: I figured that’d have enough CPU grunt that it’d still be able to decode a reasonable amount even if the CPU throttled itself for thermal management purposes. A pair of SDR interfaces would allow me to monitor a couple of bands simultaneously, such as 2m and 70cm together, or 2m/70cm and one of the HF bands.
Even the RTL-SDR v3 dongles are wide enough to watch the entire 2m band. With CAT control of the FT-857D, it’d be possible for the Pi4 to switch the FT-857D to the same frequency and possibly manage some antenna switching relays as well.
A rough design
This morning I came up with this:
A rough design of the SDR set-up
A critical design feature is that this must have a “pass-through” option so that in the event the computer crashes/fails, I can bypass all the fancy stuff and still use the FT-857D safely as I do now without all the fancy SDR stuff.
So while in SDR mode: the station pushbuttons on the handlebar go to a small sequencing MCU that can report events to the Pi4, on transmit the Pi4 can then instruct that MCU to connect the antennas into bypass mode, short-out the SDR inputs to protect them, then engage the PTT on the FT-857D, and transmit audio can either be delivered direct via the analogue inputs as they are now, or over USB/WiFi/Bluetooth through the MiniDIN6 DATA port.
The thinking is to have two SDRs, one of which is “agile” between HF/6m and 2m/70cm modes.
The front-end will be handled via the tablet: a Samsung Galaxy Active3 which can connect over WiFi or USB CDC-Ethernet.
I’ve shown gain-blocks between the antennas and the receivers, this is largely for impedance matching as well as to account for the losses involved in antenna sharing. Not sure what these will technically look like.
The two on the HF side should be ideally 0-60MHz devices. If I use the AirSpy HF+ as pictured, the VHF/UHF LNA connected to it only has to concentrate on the VHF band below 260MHz (really 144-148MHz, but let’s widen that to 87-230MHz for FM broadcast, air-band and DAB+) since that’s where the AirSpy stops.
The other, for now I’m looking at a RTL-SDR since I have one spare, but that could be any VHF/UHF capable SDR including the AirSpy Mini — the LNA on it, as well as the one feeding the FT-857D in receive mode will both need to handle 144-450MHz at a minimum.
It may be these frequency bands are “too wide” for a single device, and so I need to consider band-pass filters + separate band-specific LNAs and additional switching circuitry.
SDR selection
There are a couple of options I’ve considered:
KerberosSDR: a 4-channel RTL-SDR intended for direction-finding applications, these days replaced by the KrakenSDR which is 5-channel.
RTL-SDR or clone in direct sampling mode with an active filter + LNA
The thing I don’t like about the SDRPlay Duo is the non-free nature of its libraries which seem to be only available for i386 or AMD64. Otherwise on paper it looks like a nice option.
KerberosSDR/KrakenSDR seems like overkill. It’s basically four (or five) RTL-SDRs sharing a common oscillator which is essential for direction-finding, but let’s face it, I’ll never have enough antennas to make such an application feasible on the bicycle. It looks like an echidna now!
BladeRF looks nice, but is pricey and stops short of the HF band so would need an up-converter like the RTL-SDR — not a show-stopper. That said, it’s dual-channel and can transmit as well as receive, so cross-band repeater would be doable.
I should try this with the HackRF One some day, see if I can combine a conventional transceiver + RPi + DRAWS/UDRC + HackRF One to make a cross-band repeater.
The Airspy HF+ is available domestically, and isn’t too badly priced. It doesn’t transmit like the HackRF does, but then again I could stuff one of my Wouxun KG-UVD1Ps in there wired up to the second DRAWS port if I wanted a traditional cross-band set-up.
Next steps
It would seem the LNA / antenna sharing side of things needs consideration next. RF relays will need to be procured that can handle seeing 100W of RF. Where I’ve drawn a single switch, that’ll likely be multiple in reality — when the transmitter is connected to the antenna, the receivers should all be shorted to ground so they don’t get blown up by stray RF.
Maybe the LNAs feeding the FT-857D will need to be connected to a dummy-load to protect them, not sure. Perhaps LNAs aren’t strictly necessary, and I can “cheat” by just connecting receivers in parallel, but I’m not comfortable with this idea right now. So this is the area of research I’m focusing on right now.
So, I’ve been wanting to do this for the better part of a decade… but lately, the cost of more capable embedded devices has come right down to make this actually feasible.
It’s taken a number of incarnations, the earliest being the idea of DIYing it myself with a UHF-band analogue transceiver. Then the thought was to pair a I²S audio CODEC with a ESP8266 or ESP32.
I don’t want to rely on technology that might disappear from the market should relations with China suddenly get narky, and of course, time marches on… I learn about protocols like ROC. Bluetooth also isn’t what it was back when I first started down this path — back then A2DP was one-way and sounded terrible, HSP was limited to 8kHz mono audio.
Today, Bluetooth headsets are actually pretty good. I’ve been quite happy with the Logitech Zone Wireless for the most part — the first one I bought had a microphone that failed, but Logitech themselves were good about replacing it under warranty. It does have a limitation though: it will talk to no more than two Bluetooth devices. The USB dongle it’s supplied with, whilst a USB Audio class device, also occupies one of those two slots.
The other day I spent up on a DAB+ radio and a shortwave radio — it’d be nice to listen to these via the same Bluetooth headset I use for calls and the tablet. There are Bluetooth audio devices that I could plug into either of these, then pair with my headset, but I’d have to disconnect either the phone or the tablet to use it.
So, bugger it… the wireless headset interface will get an upgrade. The plan is a small pocket audio swiss-army-knife that can connect to…
an analogue device such as a wired headset or radio receiver/transceiver
my phone via Bluetooth
my tablet via Bluetooth
the aforementioned Bluetooth headset
a desktop PC or laptop over WiFi
…and route audio between them as needs require.
The device will have a small LCD display for control with a directional joystick button for control, and will be able to connect to a USB host for management.
Proposed parts list
The chip crisis is actually a big limitation, some of the bits aren’t as easily available as I’d like. But, I’ve managed to pull together the following:
A LCD module pulled from an Ericsson A1018S mobile phone – believed to be PCF8563 based
Directional joystick button
The only bit that’s old stock is the LCD, it’s been sitting on my shelf gathering dust for over a decade. Somewhere in one of my junk boxes I’ve got some joystick buttons also bought many years ago.
Proposed software
For the sake of others looking to duplicate my efforts, I’ll stick with Raspberry Pi OS. As my device is an ARMv6 device, I’ll have to stick with the 32-bit release. Not that big a deal, and long-term I’ll probably look at using OpenEmbedded or Gentoo Embedded long-term to make a minimalist image that just does what I need it to do.
The starter kit came with a SD card loaded with NOOBS… I ignored this and just flashed the SD card with a bare minimum Debian Bullseye image. The plan is I’ll get PipeWire up and running on this for its Bluetooth audio interface. Then we’ll try and get the hardware bits going.
Right now, I have the zero booting up, connecting to my local WiFi network, and making itself available via SSH. A good start.
Data sheet for the LCD
The LCD will possibly be one of the more challenging bits. This is from a phone that was new last century! As it happens though, Bergthaller Iulian-Alexandru was kind enough to publish some details on a number of LCD screens. Someone’s since bought and squatted the domain, but The Wayback Machine has an archive of the site.
I’ve mirrored his notes on various Ericsson LCDs here:
The diagrams on that page appear to show the connections as viewed from the front of the LCD panel. I guess if I let magic smoke out, too bad! The alternative is I do have two Nokia 3310s floating around, so harvest the LCDs out of them — in short, I have a fallback plan!
PipeWire on the Pi Zero
This will be the interesting bit. Not sure how well it’ll work, but we’ll give it a shot. The trickiest bit is getting binaries for the device, no one builds for armhf yet. There are these binaries for Ubuntu AMD64, and luckily there are source packages available.
I guess worst case scenario is I put the Pi Zero W aside and get a Pi Zero 2 W instead. Key will be to test PipeWire first before I warm up the soldering iron, let’s at least prove the software side of things, maybe using USB audio devices in place of the AudioInjector board.
I’m going through and building the .debs for armhf myself now, taking notes as I go. I’ll post these when I’m done.
Lately, I’ve been stuck at home with not much bicycle mobile operation happening, and it’s given me time to review where I’m going with the station and the onboard communications systems.
At home, I’ve been listening to a lot of commercial radio, whereas on the bicycle, in pre-COVID times I was basically restricted to recorded music unless I wanted to use the FT-897D for broadcast radio reception.
Now, the Yaesu rig actually isn’t a bad receiver for broadcast radio… but a few downsides:
Wideband FM sounds good, but is only received in mono
Medium wave and shortwave broadcast requires a rather bulky HF antenna to be deployed
The FT-897D is thirsty for power: about 1A on receive
When receiving broadcast radio, I obviously cannot monitor amateur frequencies
Some of the stations I like listening to are on DAB+, which the FT-897D will never receive
Long-term plan
Long term, the plan is to use SDR to augment the FT-897D, basically I rig up a Raspberry Pi 4 (already procured) with a SDR, and through some antenna switching, basically use the FT-897D as the transmitter with the Raspberry Pi 4 implementing an all-band scanning receiver. That would give me dual-watch (actually, I could watch entire bands) capability which I miss on the FT-897D.
Likely, the SDR chosen will either be a multi-channel one so I can watch a couple of bands: 2m + 70cm; or maybe I monitor 2m whilst listening to a radio broadcast on the other. SDR would also open up DAB+ to me.
This is a long-way off though. And also is rather fixed to the bike, I can’t take any of this stuff on a walk, which lately in COVID times has been my more likely form of exercise.
Current MW rig
For medium wave reception, I do have a small portable transistor radio, a Sanyo BC-088 which I was given years ago in non-working condition. The fault at first was broken PCB traces from the unit being thrown against a wall by its previous owner, which was fixed and allowed the radio to give many years of entertainment for over a decade until another incident on the bike smacked it against Waterworks Road, breaking a few connections to the internal loop-stick antenna.
I’ve repaired that, and the unit now works, but found it does not get along with any microprocessor-based device; picking up all manner of hash when placed near my handheld GPS (Garmin Rino 650) and squealing like a banshee next to my desktop PC. It also seems to be a tad deaf.
SDR is one possible option, but the SDRs I have in my possession: a couple of RTL-SDR v3 dongles and a HackRF One, none of them will tune down to 693kHz where I normally have the BC-088 tuned. The HackRF One gets close at 1MHz, but anything below 10MHz sounds terrible with noise and birdies galore. Even for shortwave, the HackRF One seems to suffer; trying it out on the HF antenna at home, I find myself picking up 4BH at 18883kHz — they normally broadcast at 882kHz.
Thus, I figured I’d try a couple of off-the-shelf options for the short-term and see how they go. Ideally I wanted a single radio that could do MW, FM and DAB+ bands… bonus points if it could do shortwave too.
New DAB+ rig: Digitech AR-1690
I bought this at a time when I noticed all the Australian Radio Network stations (4KQ, 97.3) suddenly go mute on the Brisbane channel 9A multiplex. I wasn’t sure if it was my end or the station, as other DAB+ stations seemed to be fine, and thought this little rig would both be a useful observer, and scratch that itch of portable listening.
The Digitech AR-1690
This is a basic entry-level DAB+/FM set. It’s a smallish unit, roughly 125mm×73mm×30mm. There’s no real special features of this unit. It has 40 station presets; 20 each for FM and DAB+, and there’s two alarm functions that can be set. The clock is set by the radio transmitter time broadcast. The front panel features the volume and channel buttons, along with a SELECT button. The rest of the controls are on the top.
Top controls
Info/Menu button:
Long-press → enters a configuration menu where you can configure the system time, set the two alarms, see the firmware version or do a factory reset
Short press → scrolls through different pieces of information on the LCD display:
Frequency
Current time
Current date
(DAB+): Signal strength?
(DAB+): Genre
(DAB+): DAB+ Multiplex name
(DAB+): Frequency and channel
(DAB+): Signal error rate
(DAB+): Bit rate and standard (DAB or DAB+)
(FM RDS): Station name
(FM RDS): Genre
Mode: Switches between FM and DAB+ mode
Scan: Initiates a scan on the currently selected mode (so, all FM broadcast, or all DAB+ channels)
Alarm: A shortcut button for setting the alarms (same as holding Info/Menu, then navigating to Alarms)
Preset: Used for accessing memory presets, short press recalls a preset, long press to store a station preset
Power: Switches the radio on, stand-by (short press) or off (long press)
For power, it can either run on 3 AAA cells, or you can buy separately a Nokia BL-5C Lithium battery.
The back of the radio, nothing much to see here.The battery compartment, with Nokia BL-5C installed
As for ports, there’s just the two on the right-hand side:
Connectors
The power jack is a small ~3mm barrel jack, the radio is supplied with a USB cable that interfaces to this connector. Looks like a dead ringer for the old Nokia phone connectors, I might dig up one of my old chargers and see if it works. (Update 2022-03-11: Found one, it doesn’t… the barrel is the same size but the tip in the radio is too big to fit in the bore of the connector.)
In operation
The set seems to do a reasonable job. I’m close to Mt. Coot-tha, so receiving DAB+ really isn’t that difficult. The sound is quite reasonable for the size, I thought the speaker would be a bit on the tinny side, but it’s perfectly listen-able. Certainly it’s a big improvement on the BC-088!
One gripe I do have with this set is that the volume steps are very coarse, and there’s no real “quiet” setting. Minimum volume is mute, one step up is comfortable listening level in a small room. I would have liked maybe 3 or four steps in between.
In both DAB+ mode, it can report the station dynamic labels.
DAB+ dynamic labels
It also can pull a similar stunt with RDS data on FM:
FM RDS reception
New Short wave rig: Tecsun PL-398MP
Now, when I bought the above DAB+ receiver, I ideally wanted something that would do MW broadcast as well, as one of the stations pictured on the DAB set is in fact, a MW station as well.
There is such a beast, Sangean make the DPR-45 which can do MW/FM and DAB+, but it’s enormous. Too big for my needs. Plus I found it after purchasing the little AR-1690 (not that it mattered, as size pretty much rules the DPR-45 out). I figured the next best thing was to get a portable set that had a line-in feature so it could provide the stereo speakers that the AR-1690 lacks.
Enter the Tecsun PL-398MP.
The Tecsun PL-398MP
As the text above the screen suggests, this is quad-band radio; supporting LW/MW/SW and FM bands, as well as a (primitive!) MP3 player. Unlike the Sanyo BC-088 it’s replacing, which boasted 8 transistors (wow!), this unit is a DSP-based receiver using the common Silicon Labs Si4734 radio receiver IC.
Most of the controls are on the front. The labels marked in red are activated when the radio is turned off; so holding 1 down allows you to switch the FM radio band from the default 88-108MHz to 64-108MHz or 76-108MHz. Holding 2 down switches the clock between 12-hour and 24-hour time, 3 will switch the MW band between using 9kHz steps and 10kHz steps, 0 turns keypad beep on/off and the ST button toggles the “intelligent backlight”.
Unlike the AR-1690, this thing runs on either standard disposable dry-cells, or you can install Ni-MH cells and by holding the M button whilst the radio is turned off, you can enable a built-in charger. Dry cells are not exactly my favourite way of powering a device, for no other reason than the reduced energy density and their nasty habit of leaking electrolyte.
Maybe a future project will be to hack a LiPo cell into this thing.
On the back, are the controls for the MP3 player.
Back of the PL-398MP
I’ll get to the MP3 player part in a moment, but in short, don’t bother!
For tuning and volume, there are two thumbwheels on the right-hand side. These are both rotary encoders driving a small microcontroller inside.
Volume and tuning controls
The “digital” volume control steps aren’t too bad for resolution, certainly nowhere near as coarse as the AR-1690! The tuning knob works well enough for small adjustments, and for moving between presets. Thankfully for moving between stations, there’s the keypad for entering frequencies directly.
On the left are all the ports:
FM/SW antenna, line-in, earphone output, and a 5V mini-USB input
The line-in feature is what set this apart from other MW and SW-capable sets. Being able to connect an external shortwave antenna is a welcome feature, and with this radio, I purchased a Sangean ANT-60 antenna for this purpose.
On top, there’s just the Light/Snooze button; pressing it momentarily turns the lighting on. I presume it’ll also silence the wake-up alarm if you have one set, but I haven’t tried this.
Light / Snooze button on top
In operation
FM Stereo reception
I’m close to the Mt Coot-tha transmitter site, so this isn’t much of a strain for the receiver, I guess I’ll know more when I take it out of town with me, but it seems to receive the local stations well, without getting overloaded from the strong ones (looking at you ABC Classic FM).
Being a dual-speaker device, this can provide stereo without additional hardware. Audio quality is actually decent for a radio this size. The speaker drivers are about 50mm in diameter, appear to be a low-profile mylar construction; not going to win audiophile magazine awards and are outperformed by many Bluetooth speakers, but are decent enough.
Short wave reception
The shortwave feature of this set seems good so far. There’s not as much to listen to on the shortwave bands as there used to be, but I’ve been able to receive China Radio International and Radio New Zealand both quite clearly, and one evening managed to pick up the BBC World service.
It performs decently with its built-in antenna, even without me telescoping it out. I haven’t had a chance to fully try the set with the ANT-60 — I did try it indoors in my room, but I suspect I haven’t really got enough wire “in the air” to make much difference. I’ll have to try it at a camp site some evening.
Medium wave reception
This blew me away actually. Okay, so maybe a late 60’s era transistor radio with leaky vintage germanium transistors that’s had a hard life and more than one ham-fisted repair attempt is not much of a contest, but it left the old Sanyo in the dust.
4KQ on 693kHz was a bit of a fiddle to get tuned on the Sanyo, and even then, I found I had to have the radio oriented right to receive it. 4QR on 612kHz of course, was loud and strong. Both stations are very clear on the PL-398MP. Ohh, and while this set’s no rich console radio, it’s nowhere near as tinny as what I was expecting to hear. For a portable rig, quite acceptable.
Out of the box, my unit used 9kHz frequency steps, which will also suit Europe. For those in the USA, you’ll want to hold that “3” button with the power off to switch the radio to a 10kHz spacing. This will also switch the temperature display to show °F instead of °C.
Long wave reception
Firstly, to even get at LW took a bit of fiddling. The handbook is a little inaccurate, telling you to press a non-existent MW/LW button. The correct procedure to enable LW is to turn the radio off, then long-press the AM button. The display will then show “LW” and “On” to indicate the feature is now enabled.
Turning on LW mode.
The same procedure turns the LW feature off too.
Having done so, when you turn the radio back on, pressing the AM button momentarily will now switch between MW and LW.
Now, ITU region 3 where I am, does not have any official LW stations. Nor does region 2 (Americas), this is a feature that’s more useful to those in Europe.
There used to be a LW weather beacon on 359kHz broadcasting out of Amberley Air base, and my Sony ST-2950F (my very first LW-capable receiver) could pick it up with its loop-stick antenna. Neither it, nor the PL398-MP do today. I guess I could drag out one of my amateur sets out to get a third opinion, but smart money is that the transmitter is now turned off.
Never mind, I’ll just turn LW back off and not worry about it.
Line-in feature
This works pretty simple, the radio is supplied with a 3.5mm male-male stereo cable. Plug one end into the line-in port on the radio, and the other into your audio device. On the LCD screen, a “>>” symbol appears on the right-hand side. Turn the radio on, and get your source playing, you’ll hear it through the radio speakers.
Nice and simple. I’ll be able to use it with the aforementioned AR-1690, my tablet, and the little portable media player I already use on the bike.
MP3 Player
Yes, I did mention it has one. The controls are on the back, and the device takes a SD card via a port hiding under the rear stand.
The SD card port
Plugging in a FAT32-formatted SD card with some MP3s on it (The Goons Show, what else?) and turning the radio on, I then tried getting it to play something. Hitting Pause/Play at first seemed to do nothing, but eventually I must’ve either waited long enough, or managed to coax it to play something, it started playing the first track it found.
I could navigate between the tracks — I have no idea whether it sorts the files by file name or not, the display is too primitive to support showing any track metadata, but it did work. There’s no playlist capability in this device, no random shuffle mode, as I say, it’s primitive.
So I think I’ll just ignore it and pretend it’s not there. A Bluetooth receiver would have had greater utility, but never mind. There is a sister-model to this one, the PL398-BT with exactly this feature… but good luck getting one unless you order direct from China.
Hidden function #1: A lithium charger?
So, fiddling with the radio, I noticed a few hidden features that are undocumented. With the radio off, holding the VM button triggers the display to show “Li On” and the “Ni-MH Battery” indicator starts flashing.
Is this a “Lithium battery” mode?
Exactly what this is doing I’m not sure. There are radios in Tecsun’s line-up that do support and include Lithium batteries, so maybe the project to add this feature isn’t out of the question. I guess a trip into the set with a screw driver will be my next move, but maybe some of that work is done for me.
Hidden feature #2: Self test?
Holding the BW button whilst the radio is turned off seems to perform a self-test of the display.
All segments on the LCD turned on
When the button is released, it switches back to showing the time, plus some 4-digit code (firmware version perhaps?):
“3985”, a code for the gurus to meditate over
Not sure what this is.
Final comments
All in all, both seem to be decent sets. The little DAB+ set is more-or-less a one-trick pony, it’ll be interesting to see if it does any better or worse than the Tecsun. I’m also yet to introduce these to the Garmin GPS that caused my Sanyo so much grief.
It’s nice to know that short wave sets are still being manufactured, and the performance of this set is quite remarkable. Tecsun themselves are based out of Hong Kong, and seem to have a decent reputation from what I’ve seen in reviews online.
While lately it’s been my policy to avoid buying stuff that’s made in China / by Chinese companies — in this case the feature set I wanted was practically a unicorn, no one else makes something like this, and this set seems to perform decently, so we’ll see how it looks after a year or two to see how it is long-term. After all, the little Sanyo has been in my possession since the early 90s, and it was an old radio then… it still goes. Will the Tecsun last as long? We’ll see.
As for the Digitech unit; well, DAB+ has a crazy amount of DSP going on to pick out one station out of a multiplex. I expect being more complicated, it’ll perhaps have a shorter longevity, but hopefully long enough for me to cobble up a replacement. Time will tell.
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