Amateur Radio

Earmuff headset reverse engineering

So, previously I’ve tried looking for a suitable earmuff headset, and drew blanks: they wanted $400+ for them and I wasn’t willing to spend that much. That said, there are times when such a headset is useful: if it’s raining heavily on the roof of the annex, hearing the radio is bloody difficult!

Now, my tactical headset should fulfil that, but really it was intended for less noisy environments. What if that’s not enough? Years ago, Brisbane WICEN used to help out with the car rallies, and there you really do need something that will muffle outside noise. I had tried to make my own, with limited success, but one wondered how the commercial options compared.

The other day, I spotted this earmuff headset. One thing I note, the seller seems unaware of how these things are worn — that’s a neck band fellas, not a head band. (Or maybe their ears are wider than they are tall? Mine are taller than they are wide.)

This is up the upper limit of what I was willing to spend, but what the hell… we’ll try it. They arrived today (about 6 days ahead of schedule). They’re comfortable enough — sound dampening is reasonable. I like the fact the microphone is on the right side. There’s a PTT button on the left ear-cup and a volume control on the right.

Being a behind-the-head design, it plays nice with my hard hat too. The head strap is a little tricky in my case, since my hard hat has a chin strap — I figured out I had to undo the head strap, thread the headset through the chin strap, then put hard hat and headset on together. I should be able to wear it with the coolie hat as well.

A downside is basically when I do this, I can’t take the headset off without taking the hard hat off too, but the intent of this was something that I was going to leave on anyway, and the same criticism is true of the tactical headset too.

The headset, with its packaging and cables.

One wrinkle is that this headset you can see, uses a Kenwood-style pin-out — my Kenwood TH-D72A died recently, so great timing there. Luckily for us though, it’s just a small pigtail: we can make our own up to suit this pin-out. The pig-tail actually is a 6-pin Mini-DIN: Jaycar part number PP0366. I was thinking of chopping cables, but this is even simpler, we’ll just make our own pigtail.

At the other end, it appears to be a 5-pin mini-XLR, but I haven’t tried buzzing that out at this stage. As is typical with comms headsets, this one is mono. There’s a 3.5mm jack (left earcup) for plugging in a comms receiver or media player, and it works — in mono. The microphone appears to be an electret.

For now, I’ve decided to have a look at reverse-engineering the pin-out to use the headset as-is. I rummaged around and found the aforementioned connector in my junk box, still sealed in its packet, so I opened that up, and used the little insert inside to plug into the socket, put the headset on, and went buzzing with the multimeter. Using the Kenwood pigtail for clues (since I know the Kenwood pin-out), I located the PTT, speaker and microphone connections on the headset cable.

One pin appears to be a no-connect; the PTT and microphone are commoned.

Reverse-engineered Mini-DIN 6 pin-out

Yaesu FTM-350AR audio interface: part two

Today I rummaged through my junk box and pulled out:

  • a screw-terminal type RJ-45 jack
  • a 3.5mm stereo panel-mount socket

Sadly, the socket is too big to fit inside the RJ-45 jack housing, but I was able to cobble together a test using the jack as a break-out.

As it happens, there’s some repeater traffic that I’m hearing through the tablet beautifully. I set up Mumble to just transmit on VOX activity — this seems good enough. The signal out of the radio is quiet, so VOX works well enough for detecting the incoming signal with no false detection.

There’s a fraction-second delay, which is to be expected for a cobbled together Radio-over-IP solution such as this. It’ll be annoying if you happen to be next to the radio, but probably fine if you’re away from the radio (or you use a headset so you hear the delayed signal through the headset louder than the real-time signal out of the radio).

Things I need to look into from here:

  • Computer transmit audio interface
  • Computer PTT interface
  • Mumble integration into the above

Yaesu FTM-350AR audio interface: part one

I do a lot of support for horse endurance rides up at Imbil, and that means running a base for about 3 or 4 check-points. My go-to radio for this has been the Yaesu FTM-350AR, which is a good rig, but the head unit has woefully pathetic audio output.

The mono speaker is better, and you can get pretty good results plugging an un-amplified pair of speakers into the back — I use some old “SoundBLASTER” speakers from a SoundBLASTER 16 sound card. Works great if you’re in earshot of the radio, and much better than the built-in speaker in the radio body or the pathetic excuse for speakers in the head unit.

The radio can do cross-band, and this works pretty well, assuming you can find a pair of frequencies that don’t have interference. However, cross-band means you can’t use the radio directly as a standard radio, you must use a second radio to communicate on the cross-band link. In addition, it also means you can’t monitor more than one frequency at a time in base, or run packet from the same radio.

I’ve considered whether I make an audio interface that would link the radio to Mumble. Mumble is a VoIP solution for online gaming, and amongst other things, behaves much like a PTT-style radio in operation. The thinking was to interface the audio and PTT signals between the radio and the Mumble client, so that any transmit audio on the Mumble channel is fed to the radio, and vice versa.

Computer to radio is easy enough. Some years ago when I was doing the Brisbane to Gold Coast bicycle ride (net controller, in the back seat of the control vehicle), I had made an adaptor that let me plug in my DIN-5 headsets into the microphone port. I basically ignored most of the contacts, just paying attention to 0V (GND), EXTMIC and PTT.

Microphone pin-out for the FTM-350AR

An annoyance at the time is there was nowhere to plug headphones except the external speaker port, which is a little over-powered for headphones, so still had to rely on the radio’s speaker with my headset.

For a two-way radio interface, I’ll need to tap into that speaker audio. Now, an attenuator pad for the external speaker connector is a viable option, however it has the downside that it disables the internal speakers, meaning you need either a double-adaptor break-out, or you rely on the computer forwarding the audio somehow.

I contemplated opening up the head unit and adding a headphone jack, but then came to the conclusion that the audio is unlikely to be a digital signal being sent to the head unit — it must exist in analogue form on the 8-wire link between the head-unit and main-unit. Sure enough, I found some schematics, and there it is:

FTM-350AR head unit connector, showing left and right speaker connections

This goes off to a (rather anaemic) audio amplifier, so likely are line-level signals. Looks like I should be able to make a cable that taps off pins 2, 3 and 4 bringing those out to a 3.5mm jack which I can plug into an audio interface of my choosing. I have a Behringer U202 USB audio interface, seems like a good candidate for this experiment.

I lack the PTT signal on this connector, it is likely multiplexed in the TXD line, so unless I feel like reverse-engineering Yaesu’s protocols, the easiest bet is that I only tap received audio from here, and use the microphone socket for transmit audio (which I already know how to drive).

As for the software side, talKKonnect is one such option I could employ here.

Time to rummage through the junk box and see what I have on hand.

A stereo/binaural tactical headset: part three

So, last time I 90% finished the headset I’m likely to use at horse endurance ride and other “quiet” emergency comms events in the near future. The audio quality (at least on receive) sounds great. From what I can tell between hand-helds, the transmit audio sounds good. It’s quite comfortable to wear for extended periods, and while my modifications do muffle sound slightly, it’s perfectly workable.

There are just a couple of niggles:

  1. the headset uses a dynamic microphone, thus is not compatible (microphone-wise) with the other radio interfaces I have
  2. I used solid-core CAT5 which is sure to develop a fault at some inconvenient moment
  3. the cable to the connector is way too short

CAT5 was fine for a proof-of-concept, but really, I want a stranded cable for this. Being a dynamic microphone, it’s not necessary for it to be screened, and in fact, we should not be using unbalanced coaxial-type cable like we’d use on an electret microphone. That brings up another problem: interfaces designed for an electret will not work with this microphone — the impedance is too low and they’ll supply a bias current which needs to be blocked for dynamic microphones.

Right now I use a DIN-5 connector, but this is misleading — it implies it’ll connect to any radio interface with a DIN-5, and that my electret headsets will plug into its interfaces. At most I can listen with such a set-up, but not talk. The real answer is to use a completely different connector to avoid getting them mixed up. I decided whatever I used, it should be relatively common: exotic connectors are a pain to replace when they break. My criteria is as follows:

  • As discussed, common, readily available.
  • Cheap
  • Able to carry both speaker and microphone audio in a single connector so we don’t get speaker and microphone mixed up
  • Polarised, so we can’t get a connector around the wrong way
  • Ruggedised
  • Panel and cable mount versions available

Contenders I was considering were the 240° DIN-5 (I bought some by mistake once), 5-pin XLR and mini-XLRs, and the humble “CB microphone” connector. Other options I’ve used in the past include the DIN-7/DIN-8 and DE15HD (aka “VGA” connectors). DIN-7/DIN-8s can be fiddly to solder, and are overkill for the number of contacts. Same with DE15HDs — and the DE15HDs do not like moisture!

In the end, I decided the CB microphone connector seemed like my best bet. Altronics and Jaycar both sell these. I don’t know what the official name of these things is. They were common on radio equipment made between the mid-70s through to the late 80s — my Yaesu FT-290R-II uses an 8-pin connector, my Kenwood TS-120S uses a 4-pin. They’re pretty rugged, feature a screwing locking ring, and have beefy contacts for passing current. Usually the socket is available as a panel-mount only, but I found Altronics sell a cable-mount version (and today I notice Jaycar do too). If someone knows a RS/Mouser/Element14/Digikey link for these, I’ll put it here.

The big decision was to also consider how to wire the connector up. As this is “my own” standard, I can use whatever I like, but for the sake of future-me, I’ll document what I decided as I’ve forgotten how I wired up DIN-5’s before. I did have it written down, but misplaced that scrap of paper. I ended up quickly opening up a connector and taking this photo to refresh my memory.

A photo of an actual headset connector, showing the connections.

To wit, I therefore shall commit to public record, exactly how I wired this thing, and propose a standard for dynamic microphone headsets.

The current (left) DIN-5 pin-out, and my proposed “CB microphone” pin-out — both looking into socket

Some will point out that yes, I’m creating yet another standard. In my defence, mine is aimed at stereo headsets, which traditionally have been two separate 3.5mm phone jacks. Very easy to mix up. Some might argue that there exists a new standard in the form of the 4-pole TRRS connector, however not all interfaces are compatible — at the time when I devised the DIN-5 connector, I was using a Nokia 3310 which did not like having the microphone and speaker connected to a common pin.

Keeping them separate also allows me to do balanced audio tricks for interfacing electret microphones with radios like the Yaesu FT-857D which expect a dynamic microphone. For this; I need 5 contacts — left/right speaker, speaker common, and two for the microphone. There are 5-pole TRRRS connectors, the TP-105 is one such example — but they’re not common outside of the aviation industry where they are used.

For the cabling, I’ve cut the CAT5 cabling shorter, and spliced onto the end some 4-wire telephone ribbon onto each side. That makes the headset cable a comfortable length. I began by first soldering the “CB microphone” connector, choosing colours for the speaker and microphone connections and wiring it up in a “loop”, before cutting the far end of the loop, stripping back insulation and tinning the wires. I used a multimeter to decide which was the “left” and “right” connections — then these were spliced with some heat shrink.

After a quick test on the radio, I sealed it up using some hot-melt glue. This should prevent the solder joints from flexing and thus prolong the life of the connection.

I might look at a small J-FET or BJT adaptor cable that will allow me to use this headset in place of an electret microphone headset — as it’d be nice to be able to just plug this into the tablet to listen to music or use with VoIP. I’ve got extra line-mounted sockets for that. Not sure if it’s viable to go the other direction — I’d need a small battery to power the electret I think, that or a bypass switch on the PTT cable to allow me to power an electret microphone.

That though, is a project for another day.

A stereo/binaural tactical headset: part two

So a few weeks back, a couple of tactical headsets turned up ordered from Amazon. When I tested them out, the first thing I found was the speaker audio, whilst okay for speech, was very tinny. I wanted a headset that I could tolerate wearing for horse endurance ride events where I often need to juggle a notepad, radio and maybe a tablet or keyboard. A headset works well for this. Also, if there’s a rain event and you’re under a canvas roof, hearing the radio can be a real challenge!

At the same time I wanted to be able to hear ambient noises, so I needed something that didn’t completely enclose me off. If IRoQ ever starts up again, I might be re-thinking this but for now, this is what I’m doing.

The two I bought are “bowman”-style headsets, which are normally mono. I wanted a stereo headset, so bought two, figuring they’re modular enough that I should be able to cobble them into one. I didn’t expect to have to do surgery on them, but there you go. I dug through my junk box, and found an old computer headset that was minus its microphone with 30mm drivers in it and foam ear pads. Pretty cheap set that you can probably buy at a corner-store computer shop for no more than about $15.

As a test, I grabbed the dissected headset from the previous post, and heated up the soldering iron. I de-soldered the original speaker, grabbed a speaker from this computer headset, de-soldered it from its original cabling and tacked the two wires from the bowman headset to it. I then grabbed my Alinco set and tried a little listening. BIG improvement! No, not audiophile-grade, but not crappy telephone grade either!

The speaker out of the computer headset was glued to a piece of plastic that clipped to the earcup and provided a surface for the foam padding to stretch over. As such, it didn’t quite “fit” in the space of the old one — so I trimmed the plastic back a bit and found I could jam it in there quite snugly. I then just needed something to “hold” it there. Anyway, proof of concept done, time to attack the second victim.

I tore open the second bowman headset I had, and fired up the soldering iron to liberate its speaker. It’s a similar (but not identical) one to the other headset. Also, the foam spacer is a different shape — I guess they just grab whatever is laying around the workshop. (sounds familiar!)

The one on the left was pulled out of the second headset this morning. The one on the right is from the previous teardown.

I grabbed the other speaker from the computer headset, tacked it onto the wires and tested — it too sounded a lot better. A little trimming, and it was ready for permanent installation.

Now, if I just wanted mono headsets, I could have left it there, but I wanted one stereo one. The U94 connector does have enough conductors to support this if I common the microphone and speakers, but there’s already civilian and military “standards” for these things, I don’t need to muddy the waters further with a custom one! For now I thought I’ll use my DIN-5 connector standard for this. So rummaged through the junk box, found a DIN-5 plug and socket. I also grabbed a length of CAT5 cable (solid-core, although stranded would have been better).

I de-soldered the U94 cables from both headsets, stripped the jacket off the CAT5, and separated two pairs for each side. To each headset, I soldered two of the four pairs: left side – blue/white blue to speaker, brown/white brown to microphone; right side – orange/white orange to speaker, green/white green to microphone. I then soldered the other ends to my DIN-5 plug — paralleling the two microphone connections so that I could choose which side I used the microphone on. (Or even put one microphone on each side — this does work although it looks damn silly!)

I wired up the DIN-5 socket to one of the U94 cables, bridging left/right channels. My standard actually uses electret microphones, and I suspect these headsets use dynamic microphones. When I plugged in the headset into my tablet — the microphone was not detected, so I’d say the tablet was expecting a 2kOhm electret not a 900ohm dynamic. But, plugging everything into the PTT cable for the Alinco, it all works — and sounds a lot better.

I finished up by fabricating new pieces of plastic to hold the speakers in — an old 2L milk bottle gave up some PET plastic for the job. I cut an oval-shaped piece with a hole in the centre for the speaker’s sound, and glued that over the speaker. I note the plastic now covers the openings that I was supposed to hear through, but the impact is minimal.

I still need to do something better for cable retention, but I’ll think of something. Maybe hot glue…

The two new speakers installed.

For the headband, I ditched the top-band and just used the two elastic straps — one across the front, one around the back. I find this works well — although the headsets are designed to use a single elastic strap, I suspect the strap was designed with smaller heads in mind (often the way with Made-in-China stuff) — I found it got a tad uncomfortable after a couple of hours.

Mostly Finished headset.

With the two straps on this “stereo” set, it’s a lot more balanced and comfortable. Plus, the speakers being of higher quality, listening comfort is improved — a big plus given horse ride events can go 24 hours, and I’ll likely be there operating for that entire period.

I’ll have to source an alternate 5-pin connector for these — being dynamic microphones, compatibility with devices that expect electret microphones is not a given. Maybe I need to use 120° 5-pin DINs or something. Something other than a U94 or a standard DIN-5, because this is stereo (unlike normal U94 headsets) and uses a dynamic microphone (unlike my other headsets).

FT5DR repeater database for Australia

I’ve just finished inserting all of the country’s repeaters into my FT5DR and have taken a dump of the memory to save others the trouble should they need it. This is based on the WIA’s Repeater Directory, dated 2022-08-07, and includes all 2m and 70cm FM and C4FM repeaters.

How was this organised

The WIA publish their repeater directory on a regular basis from their website in both CSV and PDF formats. Using this information, I coded up a Python script that re-organised the CSV version of the repeater directory into a linear string of repeaters to be loaded into the radio.

You can find the script on Github. In this case, I tweaked the script settings to exclude all repeaters other than 2m/70cm repeaters using FM or C4FM, as these are the only repeaters useful to FT5DR users. The script uses the GPS co-ordinates (or failing that, the nearest town) to group the repeaters into “sectors”. The sectors are divided by the heading from Alice Springs, and the distance.

The script then orders these “sectors”: iterating first by distance, then heading. The result is a list of repeaters where the repeaters are roughly “grouped” by their geographical position.

Here’s hoping this will work out. It’s an experiment on my part, in the past I’ve ordered repeaters by frequency (mostly on channel-constrained radios like the Wouxun KG-UVD1P), and by call-sign. This is the first time I’ve tried using positional information to group repeaters. I suspect it’ll need fine-tuning long-term, but let’s see how this goes.

How was the file created

By hand, through the radio keypad. I then told it to save the memory to the MicroSDHC card. Yes, Yaesu make a piece of software to let you edit this on your computer, if your computer runs Microsoft Windows. I don’t, so I did it the hard and slow way.

I am working on getting CHIRP to support the FT5DR, to save ourselves some trouble in the future.

Errata from the repeater database

There are some notes about this repeater database which are potential gotchas:

  • VK3RNB “CBD Melbourne” repeater at 438 550kHz is shown with a repeater input of 431 555 kHz which equates to an offset of -6995kHz, this is recorded as -7000kHz since the FT5DR does not support -6995kHz offsets.
  • VK5RSC “Mt. Terrible” repeater on input frequency 147 675kHz actually outputs on the 10m band at 29 620 kHz — as the FT5DR cannot receive 10m FM, this is recorded as a simplex frequency.

How to load

NOTICE: You do this at your own risk. I accept no responsibility for any damage that may occur to the radio loading files from this site, nor any legal action that may arise as a result of using the repeater data supplied from this site.

  1. Download and unpack the ZIP file.
  2. Insert a FAT32-formatted MicroSDHC card, 32GiB or smaller into your computer’s SD card slot and mount it.
  3. Create a directory named FT5D_MEMORY-CH in the root of the SD card
  4. Copy MEMORY.dat to this newly created directory
  5. Unmount the MicroSDHC card
  6. Power your radio off if it’s turned on, then insert the MicroSDHC card into the radio’s MicroSDHC slot (right-hand side — contacts face the front)
  7. Power on the radio
  8. Hold F Menu for 3 seconds
  9. Tap SD Card on the touchscreen
  10. Use the channel knob up the top of the radio to highlight 2 MEMORY CH
  11. Press F Menu
  12. Use the channel knob up the top of the radio to highlight 2 Read from SD
  13. Press F-Menu
  14. The radio will ask “READ?“, tap OK on the screen twice.
  15. The radio should read the file, then do a reset. When it boots back up, you should find the repeater database is loaded.

A stereo/binaural tactical headset

One thing I hate doing when I’m taking down notes at a radio comms event is juggling a hand-microphone and pen/paper/tablet/computer simultaneously. So I tend to prefer a headset for my radios rather than a hand-microphone. Some models (especially Kenwood) have lots of selections available, but some are very much restricted. In particular, I prefer a binaural headset as I find it more difficult to hear a voice on one side than via both sides — particularly in noisy conditions. The only options I could find for Yaesu/Alinco sets were big chunky earmuff headsets — great in those noisy situations, but not so great if you need situational awareness.

The plan thus is to cobble together my own binaural tactical headset. Stereo using my standard headset connection, so I can re-use it elsewhere.

I did have a Kenwood TH-D72A — a good solid performer… but sadly no longer manufactured (neither is its successor, not that Kenwood ever sold that here), and my particular specimen now refuses to have anything to do with the internal battery. I bought an Alinco DJ-G7T as a back-up hand-held for pure voice comms, and more recently a Yaesu FT5DR. I had made my own Kenwood headset adaptor to use with my headsets, but I had nothing equivalent for the Alinco or Yaesu sets.

As it happens, the headset pin-out of the Alinco is nearly identical to that of the earlier Yaesu VX-6/VX-7: 3.5mm threaded TRRS. Both radios put the speaker on the tip, microphone+PTT (in series) on the sleeve-most ring and 0V on the sleeve. Alinco use the tip-most ring for a 3.3V rail, whereas Yaesu use this same ring for a data/clone connection. Maybe it’s a UART which “idles” at 3.3V on Yaesu rigs, but I wouldn’t bet on all Yaesu accessories working on Alinco and vice-versa — however headsets rarely need a 3.3V rail. (Maybe the VOX ones do… not sure.)

The FT5DR is actually compatible with the earlier VX-6/VX-7, however the connector is on the side of the radio, and while the threaded 3.5mm connectors fit, they stick out the side like a sore thumb: a right-angled 3.5mm TRRS is a better “fit”.

Luckily, Amazon have quite a few options that convert these radios to a U94 “Nexus” military-style connector. I managed to pick up a U94 adaptor that works quite well with the Alinco, and does work with the Yaesu (although is mechanically not optimal due to the “straight” style of the plug and side-mounting of the socket).

Tactical headsets come in a few varieties:

  • ear-tube covert-style headsets
  • D-loop style
  • throat-mic headsets
  • “bowman”-style headband headsets
  • earmuff-style headsets
  • motorcycle headsets

The only ones of this list that are binaural out-of-the-box are the earmuff headsets and the motorcycle headsets. I figured I’d pick up a couple of cheap “bowman”-style ones and see if I can cobble two mono headsets into one stereo set. I looked around, and bought two of these.

The adaptor turned up a week or so ago, and the headsets turned up today. There’s two different varieties of pin-out for the U94 connector — the “NATO” standard interleaves the speaker and microphone pins, whereas the “civilian” standard puts the speaker on the sleeve/sleeve-most ring and microphone on the tip-most ring/tip. Both adaptor and headset turned out to be “civilian” standard, so the first hurdle was cleared.

I tested both headsets and confirmed they both worked. I tried the headsets both with voice comms, then tried tuning to a local FM broadcast station to assess audio quality. They work, but audio quality is not what I’d call wonderful. Very tinny, fine for voice comms, but maybe telephone quality at best. Ookay, so using these as a stereo headset can be done — but if I wanted to use them for anything but straight voice comms, I’d want to swap the speakers out for something decent. Tear-down time!

I picked a “victim” and attempted to disassemble it. These units appear to be glued together, so you wind up partially destroying them to get at the speaker:

The speaker is a conventional 8ohm 500mW jobbie, nothing remarkable… and a frequency response that’s truly awful for anything other than voice comms. Fine for the intended task, but as I say, not really sufficient for what I was after.

I’ll see if I can swap this speaker out with one liberated from some headphones and see about replacing the strip of plastic I had to unceremoniously and destructively rip out — this shouldn’t be a difficult job. The other thing that might help is some sound-damping material behind the speaker, which might account for some tinniness.

If I get this headset working acceptably, I’ll do the same mod to the other, then can look at wiring the two together into a stereo set using a DIN-5 matching my other headsets. I can then re-purpose the U94 plug to make an adaptor to convert my other headsets to use with the U94 adaptors.

Yaesu FT5DR: First thoughts

I had a sad day the other day… the old faithful, my Kenwood TH-D72A finally bit the dust. It had been limping along ever since vibration damaged the barrel jack DC connector… I hacked up my own fix and got it going again, and it seemed mostly reliable and that kept it going for a few years… but in the recent downpours, it seems the battery management circuit died. Wouldn’t charge (just reports “Charge Error”) and wouldn’t run off a charged battery.

So… time for a new one. Kenwood basically no longer exist as a manufacturer of radio equipment now — they refused to sell the successor here in Australia and basically have abandoned us. Thus, it’s time for me to move on.

I had a look at a few options, a big issue is the chip shortage has greatly reduced the options available. I mainly use the Kenwood for APRS, it’s nice that it can function as a full-blown AX.25 TNC too, but by far, the feature I use more is APRS. Icom basically only care about D-Star and its DPRS equivalent. There are some DMR-based radios that do what they call “analog APRS” — whatever that is. The mode that gets used in SE Queensland is 1200 baud AFSK: aka Bell 203 modulation. Not the most reliable, and in many ways a dodgy hack, but that’s what everyone else uses. I wound up buying another Yaesu, the FT5DR. In fact, I bought two, just in case my father’s Kenwood bites the dust.

I haven’t put it through its full paces yet, but last night charged the units up, and this morning had mine running just beaconing on APRS and monitoring a local repeater.

General comments

The unit is reasonably lightweight… bright clear screen, the audio isn’t too shabby for something its size. I haven’t tried the C4FM mode yet but FM and WFM reception seemed decent. It’ll even begrudgingly receive AM broadcast — including with a 9kHz offset (unlike my Alinco set), although sensitivity is not great.

Text entry quirks

Set-up wasn’t too difficult, it prompts for a call-sign, which you enter from the touchscreen. Text entry is a little inconsistent, and very reminiscent of late 90s mobile phones: there’s no predictive text and the letters are layed out like they would be on a telephone keypad. To type a Z for instance, you’d look for a button labelled wxyz and hit it 8 times if you want capital Z, or 4 for lower-case. Frustrating if you miss and have to cycle around again. Sometimes touching a different button advances the pointer, sometimes not and it just overwrites the current character.

Repeater settings somewhat buried

The handbook does not discuss repeater settings much at all… which is odd since hand-held radios are not known for their DX range unless you’re up high.

To set up CTCSS, one must hit F-Menu, tap SQTYP, then use the channel knob to select TONE and hit PTT, then hit F-Menu again, go to CODE, and use the same knob to select a CTCSS frequency.

To change a repeater offset, one must long-press the F-Menu, tap CONFIG, then use the knob to scroll down to 15. RPT SHIFT, hit F-Menu, then use the channel knob to select between -, SIMPLEX or + and using PTT to confirm.

I’d have made these a simple toggle from the F-Menu options, but sadly, no.

Bluetooth still useless

I tried Bluetooth on a radio back with the VX-8DR. There, I found it was an incompatible mess… might work great if you buy Yaesu’s headset, but the whole point of Bluetooth is to be interoperable with other Bluetooth headsets which may be in a more suitable form-factor for your use case.

I tried the FT5DR with two headsets, a Behringer BB 560M, and a Logitech Zone Wireless. It could see the Behringer, but would not connect. It flatly refused to even recognise the Zone Wireless.

GPS and APRS working quite well

I’m yet to go mobile with this, but it soon found my position and getting the radio beaconing was not difficult. It lacks some niceties of the Kenwood set (e.g. reporting the frequency of the other band), and sadly no digipeating, but it otherwise is a capable APRS implementation.

SD Card support welcome

This radio can take a MicroSD card for various things, including settings back-up and restore, GPS logging, audio recordings, and even storing pictures if you buy the camera microphone option (I didn’t).

I put a few memory channels into the radio then told it to back-up to the SD card… apparently Yaesu’s own desktop software can read/write these files if you have a Windows PC handy (I don’t). That said, the format doesn’t look complex:

RC=0 stuartl@rikishi /media/sdb1/FT5D_MEMORY-CH $ hexdump -C MEMORY.dat 
00000000  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
000012c0  03 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000012d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00001350  00 00 00 00 00 03 00 00  00 00 00 00 00 00 00 00  |................|
00001360  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00001380  00 00 00 00 00 00 00 03  00 00 00 00 00 00 00 00  |................|
00001390  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000013b0  00 00 00 00 00 00 00 00  00 03 00 00 00 00 03 00  |................|
000013c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000016a0  00 00 00 00 00 00 03 00  00 00 00 00 00 00 00 00  |................|
000016b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00001710  00 00 00 00 03 03 03 03  03 03 03 03 03 03 03 03  |................|
00001720  03 03 03 03 03 03 03 03  03 03 03 03 03 03 03 03  |................|
00001800  02 00 14 50 00 d0 00 00  ff ff ff ff ff ff ff ff  |...P............|
00001810  ff ff ff ff ff ff ff ff  00 06 00 0c 00 0d 80 18  |................|
00001820  02 00 14 55 20 00 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001830  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001840  02 00 14 55 20 40 00 00  ff ff ff ff ff ff ff ff  |...U @..........|
00001850  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001860  02 00 14 55 20 80 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001870  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001880  43 07 43 55 00 c0 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
00001890  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
000018a0  43 07 43 55 00 00 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
000018b0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
000018c0  43 07 43 55 00 40 00 00  ff ff ff ff ff ff ff ff  |C.CU.@..........|
000018d0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
000018e0  43 07 43 55 00 80 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
000018f0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001900  02 00 14 55 20 c0 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001910  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001920  02 00 14 55 20 00 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001930  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001940  02 00 14 55 20 40 00 00  ff ff ff ff ff ff ff ff  |...U @..........|
00001950  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001960  02 00 14 55 20 80 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001970  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001980  43 07 43 55 00 c0 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
00001990  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
000019a0  43 07 43 55 00 00 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
000019b0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
000019c0  43 07 43 55 00 40 00 00  ff ff ff ff ff ff ff ff  |C.CU.@..........|
000019d0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
000019e0  43 07 43 55 00 80 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
000019f0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001a00  02 00 14 55 20 c0 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001a10  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001a20  43 07 43 45 00 c0 00 00  ff ff ff ff ff ff ff ff  |C.CE............|
00001a30  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001a40  43 07 43 45 00 c2 00 00  ff ff ff ff ff ff ff ff  |C.CE............|
00001a50  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001a60  43 07 43 45 00 c3 00 00  ff ff ff ff ff ff ff ff  |C.CE............|
00001a70  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001a80  02 00 14 55 20 e0 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001a90  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001aa0  43 07 43 45 00 e0 00 00  ff ff ff ff ff ff ff ff  |C.CE............|
00001ab0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001ac0  02 00 14 48 40 c0 00 00  ff ff ff ff ff ff ff ff  |...H@...........|
00001ad0  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001ae0  43 07 43 55 00 c0 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
00001af0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001b00  07 00 05 25 00 c0 00 00  ff ff ff ff ff ff ff ff  |...%............|
00001b10  ff ff ff ff ff ff ff ff  00 00 00 0c 00 0d 00 18  |................|
00001b20  02 00 14 55 20 c0 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001b30  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001b40  07 06 22 25 00 c0 00 00  ff ff ff ff ff ff ff ff  |.."%............|
00001b50  ff ff ff ff ff ff ff ff  00 00 00 0c 00 0d 00 18  |................|
00001b60  07 04 85 99 00 c0 00 00  ff ff ff ff ff ff ff ff  |................|
00001b70  ff ff ff ff ff ff ff ff  00 00 00 0c 00 0d 00 18  |................|
00001b80  02 00 14 55 20 e0 00 00  ff ff ff ff ff ff ff ff  |...U ...........|
00001b90  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001ba0  43 07 43 55 00 e0 00 00  ff ff ff ff ff ff ff ff  |C.CU............|
00001bb0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001bc0  02 00 14 57 20 c0 00 00  ff ff ff ff ff ff ff ff  |...W ...........|
00001bd0  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001be0  07 00 05 20 20 c0 00 00  ff ff ff ff ff ff ff ff  |...  ...........|
00001bf0  ff ff ff ff ff ff ff ff  00 00 00 0c 00 0d 00 18  |................|
00001c00  02 00 14 50 20 c0 00 00  ff ff ff ff ff ff ff ff  |...P ...........|
00001c10  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001c20  03 00 43 50 20 c0 00 00  ff ff ff ff ff ff ff ff  |..CP ...........|
00001c30  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001c40  07 04 85 99 00 c0 00 00  ff ff ff ff ff ff ff ff  |................|
00001c50  ff ff ff ff ff ff ff ff  00 00 00 0c 00 0d 00 18  |................|
00001c60  02 00 14 50 20 c0 00 00  ff ff ff ff ff ff ff ff  |...P ...........|
00001c70  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001c80  43 07 43 50 20 c0 00 00  ff ff ff ff ff ff ff ff  |C.CP ...........|
00001c90  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001ca0  02 00 14 55 50 60 00 00  ff ff ff ff ff ff ff ff  |...UP`..........|
00001cb0  ff ff ff ff ff ff ff ff  00 06 00 08 00 0d 00 08  |................|
00001cc0  43 07 43 56 00 c0 00 00  ff ff ff ff ff ff ff ff  |C.CV............|
00001cd0  ff ff ff ff ff ff ff ff  00 50 00 08 00 0d 00 08  |.........P......|
00001ce0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
00002aa0  02 10 14 68 75 c1 00 00  34 44 42 20 52 65 64 6c  | Redl|
00002ab0  61 6e 64 73 20 32 6d ff  00 06 00 09 00 0d 00 18  |ands 2m.........|
00002ac0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
000030e0  03 17 43 82 00 c1 00 00  34 5a 42 20 42 72 69 73  |..C.....4ZB Bris|
000030f0  62 61 6e 65 20 37 30 63  00 50 00 09 00 0d 00 18  |bane 70c.P......|
00003100  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
00003720  02 00 14 75 00 c0 00 00  57 49 43 45 4e 20 32 6d  |...u....WICEN 2m|
00003730  ff ff ff ff ff ff ff ff  00 06 00 09 00 0d 00 18  |................|
00003740  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
000037c0  03 07 43 95 00 d0 00 00  55 48 46 20 53 69 6d 70  |..C.....UHF Simp|
000037d0  6c 65 78 ff ff ff ff ff  00 50 00 0c 00 0d 80 18  |lex......P......|
000037e0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
000094c0  02 00 14 51 75 d0 00 00  41 50 52 53 20 32 6d ff  |...Qu...APRS 2m.|
000094d0  ff ff ff ff ff ff ff ff  00 06 00 0c 00 0d 80 18  |................|
000094e0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
0000a180  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
0000a240  00 00 00 00 00 00 00 00  ff ff ff ff ff ff ff ff  |................|
0000a250  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
0000a280  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
0000ab10  00 00 00 00 00 00 00 00  00 99 42 8b 00 00 00 00  |..........B.....|
0000ab20  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

That’s a complete hex dump of the memory back-up… I can see each memory channel is 32 bytes, and the frequency in kHz is given in BCD format:

000030e0  03 17 43 82 00 c1 00 00  34 5a 42 20 42 72 69 73  |..C.....4ZB Bris|
000030f0  62 61 6e 65 20 37 30 63  00 50 00 09 00 0d 00 18  |bane 70c.P......|

That’s the Mt. Coot-tha WICEN repeater VK4RZB (which I’ve labelled as “4ZB Brisbane 70c“); 438.200MHz, 91.5Hz CTCSS, negative 5MHz offset. I put it at memory location 200. I’m not sure how 12.5kHz offsets are encoded… maybe I might try programming some more in when I get time and see what they look like, but even that might be enough to “generate” a file with the repeaters I want. We’ll see.

New project: a replacement head unit for the Yaesu FT-857(D)

So, for a long while now I’ve been a user of a Yaesu FT-857D. I bought it back in 2011 as shop-soiled stock (someone bought it before me thinking they could make it work on 27MHz!) and have used it on the bicycle pretty much ever since.

The FT-857D is a great rig. Capable of all common amateur bands from 160m through to 70cm, 100W on MF/HF/6m, 50W on 2m, 20W on 70cm, and able to work AM/FM/SSB/CW, in a nice small package. It’s ideal for the bike in that regard. The only thing I could wish for is an actually waterproof head unit, but the stock one has been good, until now.

Last time I rode the bike I had no issues with the head unit display, things were stable and working just fine. That was some months back. Today fired it up to check the battery voltage: it seems I’ve got the dreadded zebra stripe issue. The bike has been in the garage for the past few months, so under cover, not in the sun… anecdotal evidence is that this problem is caused by vibration/heat in vehicle installations, but some reports suggest this can happen for indoor fixed installations too.

The problem

Either way, the zebra has made its home in my radio’s head unit and the display is now pretty much unreadable. Reports suggest I can send it back to Yaesu, pay them $200 (I presume that’s USD, and does not include shipping), and they will replace the defective LCD. However… given they discontinued making these things a few years back, I think I’ve missed the boat on that one!

Time for replacement?

Buying a new replacement isn’t viable right now — Yaesu don’t make anything equivalent: the FT-991A is too big (same size as the FT-897D), the FT-891 doesn’t do 2m/70cm, the FT-818ND is only QRP. Icom’s IC-7100 is the nearest competitor, not out of the question, except it’s a pricey unit for something that will be out in the weather.

Also, a lot of these options are out-of-stock with a big lead time.

Most of the Chinese units only do FM, and are at best quad-banders. Not that I’m interested in buying one: I hear they’re not the longest-lived of transceivers and right now I wish to avoid buying from China anyway.

Kenwood are basically out of the market here in Australia, and they never had an offering like the Icom or Yaesu units; their TS-480SAT was the closest, but does not cover 2m/70cm. The TS-2000 is a monster.

Alinco don’t have anything in a mobile format that competes either. The DX-SR9T does not cover 2m/70cm and is rather big; none of their 2m/70cm sets do HF or SSB.

Keeping the old faithful going

The radio itself works fine. It looks like the wreck of the Hesperus… with paintwork rubbed off the body, screws missing, a DIY fix on the antenna ports, and miscellaneous fixes to other bits. It still works though.

DIY Repair

This could be tricky as I’m not entirely sure what the issue is. It could be just a need for re-flowing everything, or there’s talk of parts needing replacement. The information I have is pretty murky and I could wind up making my partially-working head unit completely non-working.

Replacement used head unit

If someone had a working head unit that they were willing to part with, that might be an option. That said, the used unit could have the same problems my existing unit has, so no guarantee it’ll fix the problem.

CAT port auxiliary display

There are projects that link to the CAT port and present a UI on a separate screen. I was planning on putting a Raspberry Pi 4 there for SDR work, so that’s an option.

Homebrew head unit

Another option is to make a new front head unit. It turns out this has been partially reverse-engineered, so might be a worthy avenue to consider. That would give me a head unit that I can purpose-build for the bike: an attractive option. The hardware interface is 5V TTL UART with a 62kbps baud rate and 8-bits, no parity, two stop bits.

I have a big LCD (128×64) that has been kicking around for a while as well as some TFT resistive touchscreen displays with STM32F103VEs.

The Raspberry Pi 4 scraping the data and presenting it via a remote UI is also an option, in fact may be the direction I wind up going simply because Python on an ARM CPU is much easier to use prototyping something than doing C on a MCU whilst I bed down the finer details of the protocol.

The attraction of this is that I can use what I have on-hand now. Possibly use my tablet as the front-end in the short term. Not good in the rain, but can’t argue with the price!

I’ll go ponder this some more… one thing I am short of though is time to work on this stuff. This week-end is through, and the next one I’ll already be tied up on the Saturday, so I guess I’ll have to squeeze something in.

Thinking about SDR on the bike

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:

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.