Hardware recommendations for RPi / Small Linux PC SBC system

[NR9V]

After having a ClearNode for a few months, and having been a EE and Audio Engineer for decades, I have decided to build my own node, that will use high-quality radios, support full-duplex and use a professional-grade audio interface, rather than continue with the poor audio and RF performance of the ‘Nice RF’ modules used in most nodes such as the SHARI, etc., which all have very noticeable and distinctive buzz/whine/EFI/RFI and frequent ‘clunk’ type of noises on both their Rx and Tx audio.

For the audio interface I ordered a Masters Communications DRA-100 which sounds like it should have super low noise and be very easy to adjust the audio levels with the front panel knobs.(They’re a bit pricey and maybe a Kits for Hams DINAH would work nearly as well for 1/3 the price, but initially I’d rather not have any potential weak links in the system.)

For radios I plan to use a couple of HTs such as Yaesu FT-65s as they should work very well and are cheap but should last a lot longer than Chinese brands. For the COS input line I’m going to stick a photodiode on the receive HT’s RX LED and run that into a comparator circuit. I may alternatively at some point switch to a mobile radio such as a Yaesu FT-8800R or Kenwood TM-V71A, which do cross-band full-duplex and have the 6-pin Mini DIN connector, but using a couple HTs should be cheaper and more self-contained.

My first question is what is the best, lowest-cost computer device to use. I could just get an RPi 3B/4 with a metal case and fan as that seems like the most standard and simple option, however it seems those are all sold out at conventional suppliers and are all being scalped for higher prices, ie. at least twice what they are supposed to cost, $150+ by the time you add the case, fan, heatsinks, power supply, micro-port-adapters, SD Card, etc. Are there better options? It doesn’t need to be super-compact, it will just sit in a closet in my house, so I’d probably be fine with any old micro-PC or any other platform similar to RPi.

Questions:

1. It seems there are only 2 image downloads for ASL, one for RPi and one for Intel-AMD. There does not seem to be a lot of documentation on hardware requirements / OS details. Is ASL only available as a complete monolithic image that includes the OS and all drivers, or can it be separately installed on any Debian system?

2. If I were to get a micro/mini-PC that had a small SSD and I installed the latest Debian on it could I then just install the ASL files to a folder and run it that way? Or is better to just get a small Intel/AMD SBC and put in a bootable SD Card with the ASL image?

3. Does anyone have any recommendations for a good SBC that is in the < $200 range and should work as well or better than a RPi 3B/4? I’d think I’d want 4GB RAM, high-quality metal case with low-noise fan, ethernet jack, (no built-in wifi needed), HDMI jack, a few USB ports, and power supply.

If RPi is in fact the most cost-effective approach, what’s the best place to get one? Amazon seems to be way overpriced but I do see some bare RPi 4’s on ebay for a little over $100

Thanks,
David NR9V

[Jim_Aspinwall_No1PC]

“professional-grade audio interface”

What’s wrong with the typical node ASL interface? Realizing we have only 300-3000 Hz to work with, and only so much dynamic modulation bandwidth at the radios, +/- limited CODEC options on the A-D and D-A bits to/from other nodes, over whatever Internet bandwidth may be available?

• AllStar link builds are open-source - which is what you may need to work with to provide channel drivers for other than the CM-108/-109 chips and their USB interfaces. HamVoIP, not so much.

• A Pi has much lower power requirements and more than adequate performance for the task at hand, but going to x86/x64 based platforms at least you’ll normally be working off probably an SSD vs fragile SD card.

[Andy_Schrack]

I have two Allstar nodes built.

First node is a RPI4 with 4gig RAM, HAMVOIP, RIM-ALINCO interface, Alinco DR-135T MKIII radio. Works very well and has very good audio. I bought my RPI4 as a kit from canakit in 2020.

Second node is an HP T620 Thin Client, I got off ebay from a PC refurbishing company for less than $50. Installed ASL 2.0 beta 6 (and other Linux software I choose to add on). Has an AMD GX-415 quad core processor, 4 gig RAM, 128GB SSD. Uses the RIM-Alinco interface and the Alinco DR-135T MKIII radio. This also works very well with good audio. This was cheaper to build than the RPI4 node since I got the thin client complete and cheap.

I bought the DR-135T MKIII radios when they were on sale. They work very well for Allstarlink nodes.

My opinion: The HAMVOIP RPI4 node is the way to go but prices are high and availability is low.
If cost is an issue, buy a cheap thin client PC off ebay or PC re-seller and install ASL 2.0beta. Use a mobile radio and run it on low or med power and use a cheap PC fan to provide cooling for the radio. My nodes run 24/7 and never overheat. No problems so far.

N8ZTA

[NR9V]

The Masters Comms. DRA-100 uses a CM119A chipset, which is stated as having the best quality among the CM 108, 109, 119 series. Does Allstar support the CM119A? I’m trying the DRA-100 for the audio interface initially because it’s specifically designed for very low noise and particularly for full-duplex. The wide frequency response indeed is not important but the dynamic range and low noise are, as is having easily adjustable wide gain ranges to support various HTs and mobile radios.

A cheaper audio interface would probably be fine also and deliver way higher quality than the SA118 RF module (which barely manages ~20 dB SNR on any ClearNode or SHARI I’ve heard) but when building my first node I didn’t want to cut corners or need to add extra buffer circuitry and figured the DRA-100 should work very well, plus also support other modes such as APRS & WinLink.

Sounds right about a micro-PC having higher power usage, I was just looking at a $99 Intel “NUC Micro PC i3 4GB” on ebay and its power supply puts out 19V at 3.4A (65W). That’s no comparison to an RPi 3B which is ~12.5W. 50W of difference if run 12 hrs per day could easily add up to $5+/month in electric use. So looks I should scratch Micro-PC systems off my list, but there are lots of other low-power optimized SBC’s out there, for example there’s the ‘Rock Pi X’ which has an Intel Atom processor and looks very similar to a RPi, and some other similar SBCs. Would it be unrealistic to try and save a few $ with one of these less popular SBCs and expect everything to work well with Allstar?

Thanks

[NR9V]

Sounds good re. a HP thin client, looked them up on ebay and there’s many available starting around $40 with power supply. Can’t beat that for the upfront cost, only issue is the first one I looked at takes 19V at 3+ Amps which could be ~$100/year in electric costs if run 12+ hours/day. So I think I’ll need to go with the RPi type SBC form factor. Hopefully someone knows a Pi alternative low-power SBC that will work fine with AllStar but off hand my guess is that anything less common probably won’t work or will take a lot of hacking to get it to work? Thanks, David

[Jim_Aspinwall_No1PC]

I suspect Kevin chose the CM119 as the 108 and 109 have probably been deprecated or short supply, +/- low noise factors. All support full duplex, as you’ll find in many computer implementations ala Skype, Zoom, etc.

Kevin’s also literally a master at clean audio RF systems. He knows how to handle the audio in and out interfaces within the scope of the task - our world of 300-3000 Hz at the very least, I suspect broadcast as well. That said, what we feed such interfaces with or take from them (be they IRLP boards, DMK’s Pi-hat interface, etc.) for radios - be they hacked Baofengs, Yaesu, Kenwood, Icom, or commercial gear from Motorola, GE, Kenwood, etc. have probably much worse audio noise performance coming and going.

The AllStar interfaces, CM108, 109 or 119, etc. are probably the cleanest stages of the overall resulting systems - and since we don’t have much control over the intervening CODECs that convey the resulting audio product digitally - meh. “Better audio” almost seems like trying to make a fine Scotch whiskey out of Bubba’s moonshine. I guess that presents a different key question - what is the “noise performance” of one versus the other CODEC? ~20dB S/N in one stage could easily disappear in worse digital conditions.

The SA118 RF module is originally designed as a remote control fob/receiver tool. Not exactly a ‘hi-fi’ application for sending and receiving ‘AFSK’ digit codes, and if this is in the same family as most pre-fab hotspots the RF stages aren’t anywhere near 50 ohms, and have little or no bandpass filtering. Poor folks who are trying to make base stations/extend the range of some of these products with a 50 ohm antenna… sigh.

I own/operate about 1/4-1/3 of a mostly AllStar-linked UHF system throughout California. The majority of the system is analog/RF linked otherwise with absolutely superb audio end-to-any-other-end and no one can tell if they are listening to an operator through 2-3 AllStar hops or analog hops. I learned how to do this first from some fantastic broadcast and commercial two-way folks in Texas when I was a b/c engineer there. (No trophy or bonus, but of then 9 Group W stations, ours exceeded the others in studio gear to transmitter performance - and I’d only been on the job 6 months.) They and the systems I am now part of think and implement essentially the same… make it all much better than most/any other wanna-be systems. We can and do do that no matter what the RF package is. Time on the bench beats time on the hill everytime.

Two of my repeaters are Kenwood TK-820s with Kevin’s AllStar interfaces to nodes only. Two others are conventional controllers with AllStar interfaces to link them. (I think I still have my hearing, and other good test equipment.) Amid that I just completed a cross-country RV trip and kept in touch with a HotSpotRadios portable node via cellular. No one could tell I was hanging out on Long Island via cellular vs any of the analog linked sites.

As to the challenge of RaspberryPi 3xx being available vs. more expensive 4s… I’m seeing a handful of pi-sized alternative products that I hope the ASL and/or HamVoip folks start developing images for. That’s mainly OS-level work, perhaps some I/O and “channel driver” work. We’ll see. I hope it won’t be too long before we see at least Beta-level OS+AllStar builds coming along. Meanwhile I’m also going to look into using small cheap SSDs for the OS, etc. vs potential SD card rot.

If I have to suffer a Pi failure or two I’ll have to re-work nodes with laptops or go back to putting analog radios/RF links in place - which cost even more power and complexity. It’s hard to battery backup a 3-4 link radio site + 440 that draws 35+ amps key-down vs 10-15A.

[NR9V]

Sounds good about CalNet which I have heard on 448.4 and if I recall a YSF room also. I just sent a request for info on the calnet org site. BTW I had tried a ZumSpot MMDVM for a bit hoping to find some C4FM-VW or P25 activity but all the YSF rooms seem to default to the half-rate DN mode and P25 seems to be a ghost town so I’m planning to sell the ZumSpot since they don’t seem to have any way to do AllStar. I don’t like low-bitrate digital modes but thought I might be OK with the higher-rate modes, but after trying them out for a couple months they just don’t sound good, still a bit too robotic and muffled sounding for me to want to have a real QSO.

AllStar is much better and can indeed sound like analog FM, with significant flexibility and VOIP codec options, but the node builders then opted to go with cheapo SA818 RF modules which have a characteristic whine which seems to be comprised of 1KHz and harmonics plus other random noise, occasional 60Hz harmonics, thunks, etc.

BTW I also notice ‘thunk’ noises on some repeaters (probably more often on RF-linked systems), and wonder what causes that, my guess would be it’s multipath / phase noise causing discontinuities in the demodulator output, but if any repeater/RF experts have a better explanation I’d be interested to know. I never hear that if I transmit from one good quality radio to another, but do hear it on the ClearNode Rx audio if transmitting from an HT and moving around. It happens less if the node has a good antenna, but then with a larger antenna on these nodes more hum/buzz is picked up.

The Tx audio (coming from ASL) from the cheap nodes is actually not that bad, just has a slight whine noise, making it easy enough to not notice, but their Rx audio (going into ASL) is significantly worse, and most users rarely if ever check that.

I happened to see a Yaesu FT-530 on QRZ today in good condition with new batteries for $160 with shipping which on eham is very highly rated and considered one of the best full-duplex HTs, so I just bought that and hopefully it will work great as a cross-band full-duplex node radio at an even lower cost than 2 FT-65s and smaller footprint.

Once I’m done with this if all works well I plan to put together a page with the parts list, etc. and maybe even offer kits with the necessary cables to go to an HT speaker-mic jacks and get the COS output ie. with a photodiode on the HT Rx signal LED, or a comparator on the Rx line itself looking for > ~1mV of signal.

I would imagine this could be a popular kit because the only other alternative now seems to be to use a mobile radio, which use way more power, can’t be adjusted below 5W output, need a 5+ Amp 12V supply, take up more space and need a larger antenna, putting you at twice the cost of a SHARI-type node and 5-10 times the size. Whereas with my current plan you’d have a full-duplex node using only a small HT, a small audio interface, RPi and small power supply. Most people wouldn’t care about full-duplex and could use any old HT but the full-duplex is a nice option if you have local repeaters that have extra receivers or if you like to be able to monitor yourself with a headset and avoid doubles, which are very nice capabilities that can really improve FM and AllStar communications, and which can be done for less than the cost of a basic HT. (Hopefully users would stay away from Chinese radios and their poor Tx spectral quality and Rx intermod susceptibility.) Anyhow a generic AllStar kit that supported various HT speaker-mic jack wiring, 1 or 2 HTs, full-duplex, seems like it would be a great option for people wanting full analog FM quality at only a very small price difference over a SHARI type node.

One other question, I noticed in another post that the COS line may not be necessary if the Rx line is straight from the discriminator (eg. the ‘9600’ audio pin), but it wasn’t clear why that would be. Does AllStar have some way to determine if there is actually a signal on the line? Since any audio signal is typically going to have at least a few mV of amplitude just from room background noise it seems that should be easy to detect and that a COS line should not really be necessary.

[Jim_Aspinwall_No1PC]

I think you’ll enjoy CalNet, a good mix of folks, polite, friendly, pretty talented mix. There is a DMR and a YSF bridge in the network as well. Given a decent DMR radio that sounds pretty good. I don’t have any YSF gear to evaluate it other than listening to the few/seldom YSF folks.

The ‘thunk’ or clunk you might hear on probably the other big ‘C’ multi-site/-state linked system is an ‘artifact’ of where the audio path is switched in many of their main controllers - it’s not typically at the receiver input interface, but later in the audio chain where it meets the Tx bus - so the controller logic is cause for delay. As well I believe the clunk is related to shunting the audio path the ground - attendant ugly DC glitch imparted. Some systems in the chain don’t present that to the link and/or local 440 Tx because they are using a different controller, or as many of us do, have an audio/squelch interface at the receiver side. Most/all of the carrier detection is done with the old Motorola Micor 7716 squelch chip that controls the Rx audio path gate.

As for the receiver-provided COS signal vs raw detector noise into the AllStar interface, that’s a difference between the USBRadio channel driver and the SimpleUSB channel driver - the ‘magic’ between radio and the ASL VoIP paths. SimpleUSB needs the COS signal and typically squelched at the radio. USBRadio is DSP software that processes raw detector audio, evaluates the noise frequency (somewhere above 4 KHz) and provides the COS logic internally that would otherwise come from a discrete hardware line from the radio or other squelch circuit. The DSP mimics the hysteresis characteristics of the Micor squelch chip - where fluttery noisy signals allow the audio gate to stay open longer, leaving a bit of squelch tail burst, and for full-quieting signals almost immediately closes that audio gate at presence of the white noise = no squelch tail burst of noise. Clever.

USBRadio can/will also decode CTCSS as an additional gating factor for signal present or not.

The USBRadio DSP method MIGHT work on some speaker outputs, just depends on the audio bandpass to that point.

There are also audio bandpass settings, pre-emphasis, de-emphasis and CTCSS encoding with a bit of “reverse burst” type logic that will drop the CTCSS tone a few milliseconds before stopping PTT - so user radios go quiet just a wee bit before the node Tx RF drops.

[NR9V]

Good info there. Re. ‘thunk’ noises I hear those often in the middle of transmits rather than just at the start or end, which would seem to indicate other causes beyond just those in switching or squelch circuits. These happen all the time on the ClearNode, and in a couple of local repeaters also (though I don’t recall which ones off-hand). I attached a short audio test sample that was recorded on my IC-7100: In the first half I transmit from an HT on low power and there are no clunk/thunk noises or really any noise, then in the 2nd half the ClearNode parrots back the Tx – adding the whine, clunks, and occasional buzzing. I was about the same distance from both the ClearNode and 7100 antennas so the ClearNode is clearly just not up to par. There is probably no hope for fixing that in the ClearNode but it would be interesting to know the physics behind the ‘clunks’. Maybe the Rx input signal is too strong and overloads its front-end, but if so you’d think the clunks would occur more consistently or in inverse proportion to distance rather than randomly.

Other notes/updates:

1. I was talking to someone yesterday who makes good quality IRLP nodes and he said there are at least several versions of the SA818 Nice RF chip: He uses a custom version from the mfr with extra filtering and shielding, uses a 4-layer PCB and a metal case, and his nodes definitely are very low noise (though can still pick up 60Hz noise if near large power supplies or other AC devices); the ClearNode however uses the stock version with no shielding and plastic case; and the Kits For Hams SHARI uses another special version with better filtering, and a metal case. I do still hear some noise on some people’s signals who have SHARI nodes, though maybe they have a knockoff or older version. So looks like there can be a wide range of audio quality between nodes that use the NiceRF module, and some of them can sound good, though still probably not nearly as good in a wide range of conditions as a real radio.

2. Got the DRA-100 in the mail today and it looks very nice, very compact and rugged. And ordered an RPi 4 kit on ebay “Vilros Raspberry Pi 4 Basic Starter Kit 2GB” today with aluminum case, fan, and various adapters, was a little under $150 with tax and shipping.

3. There are some very inexpensive and super low-power Intel Atom micro-PCs on ebay that use only a 5V 3A power supply, which is about the same power consumption as an RPi. For about $60 you can get a used one with 8GB SSD and 2GB RAM. What are the chances that ASL or HamVOIP would run on something like this without a huge amount of hacking required?

[Jim_Aspinwall_No1PC]

Audio clips… given the presence of AC hum/buzz, some crackle, sounds like the node Tx may be interfering with itself, or some phase/signal level shifting at/near what that 2nd parroted clip was picking up. I was thinking we were discussing some of the linked repeater systems, so entirely different items at play here.

The SA818 is what HotSpotRadios uses vs what some others use that are the 433 MHz remote fob chips. Their product doesn’t seem to have any noise/hum/clunk artifacts, but the project design/implementation criteria was pretty specific to RF and audio quality all around.

Part of the RF filtering issue is 400-480 and/or 134-174 is pretty broad so the 3rd order RF filtering is not very tight/effective, better than no filtering, but not as good as more specific 144-146 or 430-450 (which is also pretty broad.) Since these node implementations are only valid for amateur spectrum, external filtering beyond the chip can be much tighter.

IRLP has become increasingly more restrictive at some levels. I’ve got two boards, only one I made use of and have since turned off. Single-source of system/node management, not open-source s/w, awkward hardware interface hook-up.

If we need/want restrictive node controls, we can always configure private nodes in AllStar. There is a build of AllStar that has been specifically configured for a non-ham GMRS linking initiative. I helped define a couple of those implementations for a local CERT group interconnecting 3 nodes/GMRS repeaters as private nodes. Works really well for their purposes.

I have yet to build a PC-based node, but for $60 it might be fun to try. If the device can run DOS, Windows, Linux as x86 it should be able to run the x86 builds of AllStar, w/o hacking anything.

[NR9V]

For my next node I just ordered a “DELL WYSE 3040 THIN CLIENT 16GB SSD GB RAM” on ebay, paid only $48. There’s a seller that has 100’s of them available, includes 5V 3A AC Adapter (link). Considering that RPi4B’s with a good quality metal case and microSDCard are going for 3 times that price this definitely seems like a better option, with a similar form factor (slightly larger) and a built-in 16GB SSD which theoretically should be more reliable long-term than an SDCard. And just ordered a Masters Comms. DRA-30 for the audio interface. Will post here soon with an update on how the set up goes.

My current node is using an RPi4B in Vilros metal case which has a good quality super-quiet fan and set up could not have gone any more smoothly. But as a challenge I wanted to do a 2nd node in the most affordable way possible (but with good quality audio, and no CM1xxB no-name mystery FOBs). BTW I made a (long) comment on a QRZ post with a pic and details of the node I just set up, which is full-duplex using a Yaesu FT-530 HT.

[wd6awp]

The price has gone up some since your post. But still it’s less expensive then a RPi these days and a much better option IMHO.

[NR9V]

They’re asking $53 in that listing but accept offers and were fine with $48. From what I hear these Dell 3040’s often go for as low as $30 and seem to be in abundant supply.

I got ASL installed on the 3040 yesterday and it was, an educational experience… The 3040’s have a buggy UEFI-only BIOS that has to have the boot file in a very specific place. So my initial attempts to use a regular bootable USB drive went nowhere and there was a lot of bad advice online about that. Turns out though it’s very easy to make a UEFI USB drive, all you have to do is copy the files over to it, and conveniently the Intel/AMD ASL install image is based on Debian and happens to have the boot file in the specific place the 3040 was looking for.

However once the install finished to the 3040 internal flash drive, it would not boot because the boot .efi file was not in the magic place the BIOS wanted. There was also lots of bad advice online about that and no clear solution. I had to go in with a UEFI clonezilla USB (which has a boot local OS option) and try different boot files in various places and finally got it working by doing a grub-install --target=x86_64-efi --efi-directory=debian --removable and then moving the BOOT folder that created into /boot/EFI/. This link talks about this but in a slightly different use case.

Those thinking of going the Intel/AMD route rather than RPi should also note that the Intel/AMD image is very different from the RPi image. The latter just goes on an SD Card, into the RPi, and the install is done. The former however is an installer image, intended to boot on a removable device and then install Debian and ASL on an internal device or possibly on a separate removable USB/SDCard. And the Debian installer has about 10 different options which are not well documented. I seem to have guessed right on them all but for anyone who is not good with Linux installs an RPi is about 20 times easier and faster to set up.

Below is a pic of the 3040 thin-client PC on left with Masters Comms DRA-30, and my other node on the right, an RPi4 in Vilros metal case w/fan and Masters Comms DRA-100. For use with an HT you don’t need the wide audio gain range of the DRA-100; the DRA-30 are much cheaper and should work fine. Once the DRA-30’s internal gain trim pots are set in the general area they should be it’s easy to make any further adjustments in asl-menu/asterisk.

[NR9V]

Finished the new node a few days ago and it’s working perfectly. The audio quality is outstanding, not the slightest hint of a buzz, hum, clunk, etc.

To make a full-duplex node using high quality FCC-certified radios as cost-effective as possible I’ve also been looking at lower cost HT options, since the FT-530’s go for ~$150 and can be hard to find. I noticed recently that QRZ and gigaparts have a new radio, the QRZ-1, which although Chinese is actually FCC-approved. Turns out it’s a copy of the Retevis RT85, possibly with some changes to the menus. The RT85 are known as “Baofeng-killers” due to their costing only slightly more but having much better RF performance. You can get 2 RT85’s for $50 with free shipping & free returns on amazon. For a simplex node you’d need just one but at only $25 for a 2nd radio that’s quite a low price to add cross-band full-duplex capability. I ordered 2 and will see if they are able to offer a similar level of audio quality and cross-band RF performance as an FT-530.

If so that would mean a high-quality full-duplex node could be built for as little as: $48 (Dell 3040 microPC) + $35 (DRA-30 kit) + $50 (Pair of RT85s) + maybe another $50 at the most for a power supply for the radios and various cables/wires = a grand total of under $200 for a node with far higher audio and RF quality than any commercial node on the market. An optional case, enclosure or maybe a 1U rack shelf could also be provided to hold everything securely and make the whole setup more portable.

FYI the 530 and probably most other HTs do need a well-filtered power supply. I suspect most HTs are intended to primarily run on battery power and thus don’t have much if any filtering or regulation. I have an old Yaesu NC-72B which puts out 12V 500mA which is plenty to run the HT in low-power, but some buzz would come through, which also happens even with an Astron VM-35M. I had an old homebrew variable 5A power supply with a blown transformer so I put the NC-72B in that and its 40mF of capacitance knocked out the ripple, and steps the voltage down to about 6-7V where the HT stays very cool even during 100% duty-cycle TX.

[NR9V]

Got the Retevis RT85 radios today and they work amazingly well considering they’re only $25 each. I wouldn’t want to use one as my main HT, but they’re perfect for node radios. Audio quality seems very good so far, can’t tell any difference from an FT-530. Thus it’s now official: A very good quality, full-duplex AllStar node can be easily built for under $200.

The RT85’s are easy to open up and the Green LED could have a wire soldered on to bring COS out. That does require some precise soldering though. For now the usbradio vox mode works fine for me, though it can require a bit of fine tuning. Also ASL has a hardcoded 2000mS voxhangtime but I put in a pull request to make that configurable, and I set it to 500mS in my usbradio.conf files.

Making a cable to go from a DB9 to 2x 2.5mm plugs and 1x 3.5mm plug can be a bit of a hassle if you want it to look pretty, or, just pick up an old DB9 cable, cut it in half and splice on some aux cables. That’s a lot easier than soldering onto DB9 and mini-phone plugs. With a small terminal block there’d be no need to solder anything and the whole node can be built with off-the-shelf cheap easily obtainable parts.

Wiring - DRA-30 to Kenwood & Retevis, TYT, QRZ, etc. HTs:
DB9 Pin 1 --- TX HT 3.5mm Ring (Tx Audio)
DB9 Pin 3 --- TX HT 3.5mm Sleeve (PTT)
DB9 Pin 6 --- TX HT 2.5mm Sleeve (Ground)
DB9 Pin 5 --- RX HT 2.5mm Tip (Rx Audio)
DB9 Pin 9 --- RX HT 2.5mm Sleeve (Ground)

73, NR9V

[NR9V]

Quick youtube video…

Build a Full-Duplex AllStar Node for Under $150 - AllStarLink DVSwitch Dell Wyse 3040 Retevis RT85s