Radio Projects

Didn't want to tart-up the Amateur Radio FAQ thread, so I'm moving my "build" post over here. Please feel free to contribute radio-related things you've built or done (there are plenty of other threads for "operation.")

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I've been toying with some emergency comms ideas for a while now. I've been planning to hack up my Baofeng BF-888s radios when an appropriate project tickled my fancy. Well, my fancy has been tickled.

(yeah, that sounds nasty ...)

The BF-888 radio is an el-cheapo 70cm (440MHz) UHF radio that is available for about $10 each. No frills - no keyboard, no display, minimal controls. You can program 16 channels using remote-control software from a PC. It also appears to be discontinued due to the recent FCC kerfuffle with being not-type-accepted for transmitting on certain bands like FRS and GMRS. Regardless, it's still pretty available on eBay and Amazon.

I found a nifty project on Github for a Raspberry Pi simplex repeater. It's targeted at the Pi 2+, but I happen to have a handful of Pi Zero Ws in my project box. The Zero W doesn't have an audio interface, but I also have a Sabrent USB audio dongle that I'm not using. Seems like a good match. I'm thinking that I can remove the speaker and mic from the 888 and stuff the Pi Zero W and Sabrent dongle in the available space.

First up, I cloned the Git repo and confirmed that the software runs on the Pi Zero W without issue.
https://github.com/allebb/pirrot
It works fine, in spite of complaining that it can't initialize the speaker (something left over from ALSA configuration on the Pi 2?) I confirmed that I can play back the beacon ID audio over the Sabrent interface, and I can manually trigger the Radio COR input ("carrier operated relay" aka "squelch has broken") and make the simplex repeater function properly - receive the inbound voice, record it, and replay it back immediately.

Next up, I want to run the whole sheabang off the Baofeng's internal battery. That's a single LiPo cell, so I'm looking at 3.7-4.2V rather than the 5V the Raspberry Pi wants (and who knows what the Sabrent soundcard requires.) I put the system on a bench supply, and it's happily trundling along at 3.7V drawing about 180mA. I re-tested the system at 3.7V, and everything seems to be working fine.

That's where I am so far. I'm going to pull apart the 888 soon and see how much room I have with the speaker and mic cleared out. Docs are available online showing where to pick-off the COR, PTT (push to talk) and other signals from the 888.

Pulled the 888s apart, and noticed that there just wasn't enough room inside the factory enclosure to install what I wanted. I would have to either a) chop the enclosure and graft something on, or b) reverse-engineer the relevant bits of the enclosure and move forward with a 3D printed box. I opted for "b".

Here's what I'm starting with:

Here's the general concept for where I want to go (sound module will go underneath the Pi W in that space near the aluminum heatsink):

(one of the objectives is that I still want to be able to use the stock, unmodified charging cradle.)

Built me a bunch of enclosure test-articles. Reverse engineering was difficult, to say the least. Baofeng got all artsy with the swooshy curves on the enclosure, and there are few flat spots from which to take dimensional references. Took six or seven iterations of print to get an enclosure body that fit well enough (it ain't perfect, but it's good enough.) I dumped a lot of the cosmetic features to simplify the print. There are a couple of places where Baofeng is running some very thin sections in the mold, and I suffered some punch-through in places - one is visible inside the volume knob hole setback. Shouldn't cause issues, and I'm smacking my OCD on the back of the head because I don't want to spend another 2h fixing the hole (maybe) and re-printing.

Printed up a cover, and mounted the Pi W and sound module. (The Pi Zero and Zero W don't have onboard sound hardware like the bigger brothers do, and I had a cheapie Sabrent sound dongle that needed an application.)

First step - make the Sabrent module nekkid. They solvent-welded the enclosure halves together, but the #11 X-Acto blade made quick work of that (and I didn't bleed, which is nice.) I de-soldered the chunky USB and 3.5mm jacks, and secured it to the Pi W with some double-sticky tape. Not my favorite method, but it's effective. I also removed the onboard mic so I wouldn't get ambient audio mixed in with repeater retransmissions.

Wired it all up using location info from other HAM-hacking-types. It actually looks pretty intentional, yes?

Crud - a note about power availability: The previous photo shows the location of "DC" and that's a direct battery connection. Baofeng routes unswitched battery into the final power-amp section, and relies on the output power FET's high "off" resistance to not drain the battery. The final amp is energized if the battery is installed. I don't want to run the Raspberry Pi continuously.

The power switch does turn off some of the circuitry, so I identified that node and tapped power from the switch output to operate the Raspberry Pi.

Previously, I had tested that the Pi will work down to 3.7V, even though it's expecting 5V. I didn't check to see how low it would go, but a Li-Po battery will start at 4.2V full charged and be fully discharged at 3.7.

Did some bench testing with the unit butterfly'd (which was surprisingly pleasant.) I programmed a suitable channel selection into the 888s's memories using Chirp, but initially, nothing worked properly. Turns out the problem was my inability to distinguish "GPIO" pin numbers from "physical" pin numbers.

GPIO-18 is the COR (Carrier Operated Relay, or "signal detected") on the receive side. That needs to connect to physical Pin-12 on the header. Similarly, GPIO-23 maps to physical Pin-16. Once I fixed those oopsies, everything worked.

Buttoned it up, and went for a radio-walkabout. The repeater was stashed in MM Jr's tree house, elevated about 6m above the local terrain. Took my UV-5R as the mobile, and was able to get good copy up to about 1.5 miles away LOS. Sometimes the audio would get crunchy when I was wandering through local low-spots.

I made contact (by radio, natch) with a friend who lives "over there." We could communicate 3.5 miles apart LOS, but he never heard the repeater, nor could I hear the re-transmission when he attempted to access the repeater. He was running from a 5W Motorola HT. Total LOS distance from the repeater to his site was about 5 miles per Google Maps.

So I can confidently say this thing has a range of at least 1.5 miles, but not 5 miles. Don't know exactly where the limit will be, simply because I don't have a good way to measure the output power of the 888s (I don't have an inverted-SMA antenna adapter to stuff it into my power meter ... yet.)

Most definitely touched on a lot of my favorite things in one project.

I think the accessibility of DIY electronic projects for non-EE techs reached it’s peak in the 60’s. Then with the shift to more chip based microelectronics through 2000 it be came much harder for novices to simply whip out a soldering iron and make anything cool.

However now the DIY movement is alive and well with Pi and Arduino hardware and software along with more tutorials than can be viewed in a lifetime.

I have yet to start my first Pi or Arduino project but I will do so at some time.

Spent the last 8 hours or so poking a hole in Migraine Manor's weather barrier to run a proper feed line outside for the base station. (I may write a separate post detailing my upcoming nomination for "King of Confined Space Injuries," but for now, I have a sensible routing outside to a lightning arrestor terminated at a grounding spike.)

Looks like I'm about to run out of "dry" outside, so I have my dual band mobile tie-wrapped to a temporary mount so I can run some tests.

Followed the recommendations in John White's assessment of surge protectors. (PDF is attached because the link was being wonky for me.) I haz pointy screws now.

Very Interesting..Thank you for the post..

I am not sure what this is.. but I do like it and thank you for sharing.

A simplex repeater is a method for extending radio range - basically a record and replay system. The advantage is that it only requires one radio. The main disadvantage is that every transmission happens twice (original plus replay) which can make real-time communications lumpy.

There have been a bunch of other projects like this, but they involve external boxes and rats-nest wiring mods. I wanted something cleaner and more compact. Here's a pic of the repeater sitting in the charging cradle next to its unmolested brother.

Well done... another thumbs up, too, for 3D printing.

Theatrical rigging skills were applied today - managed to get the mobile antenna almost 60ft in the air. Stayed solidly on terra-firma, too.

This isn't ideal, nor is it final. Mostly, this is an experiment to see how much a little altitude helps with range. Listening to packetses on 144.39, I'm seeing much more traffic than when I had the antenna on the basement stairs handrail. Initial indications are that this is a good thing.

Still trying to hit a friend's 2W HT about 5 miles away. Yesterday, he could hear me, but I couldn't hear him. Will try again this afternoon.

Need to fertilize that tree... get the extra few feet you need in no time.

Success! Got clean copy from a 2W HT over five miles away. Definitely needed to get my antenna off the ground.

Also heard a conversation between two folks in Glen Burnie.

Also also, installed the Direwolf digital packet software on a Raspberry Pi and was able to decode APRS packets received from my base station. Woo hoo!

That is so swift and smart , way above my pay grade . Kudos

What about the use of balloons to suspend those cables at higher altitudes? Tethered balloons?

MigraineMan said:

Theatrical rigging skills were applied today - managed to get the mobile antenna almost 60ft in the air. Stayed solidly on terra-firma, too.

This isn't ideal, nor is it final. Mostly, this is an experiment to see how much a little altitude helps with range. Listening to packetses on 144.39, I'm seeing much more traffic than when I had the antenna on the basement stairs handrail. Initial indications are that this is a good thing.

Still trying to hit a friend's 2W HT about 5 miles away. Yesterday, he could hear me, but I couldn't hear him. Will try again this afternoon.

Click to expand...

What'd ya put up? Ham stick?