Digital only POTA Activation using FT8 on the sBitx V3

So today was a good day for radio. I had a block of time and wanted to see how hard it would be to get the activation only on FT8. I know it is possible to do this, but I also wanted to do it on 15 meters too and that is where the problems come in. You see the last couple of weeks have been tough for 15 meters operations what with the solar flares and CMEs and all. So to secure the activation on the higher bands will be… interesting…

I get to the park and in the spirit of time savings I chose to go to Sitton’s Gulch which is significantly closer and saved me almost and hour of driving (well, 40 minutes as it is 20 minutes on to the operating position at the top of the mountain and another 20 back to the point at the bottom). I also was happy to see the parking lot was almost empty too. This gave me to opportunity to setup in the corner next to the changing sheds which is a good corner for my antenna radials. This gets them out of the way so that people dont trip over them going to and fro…

I set up in short order for the 15 meter band and get started calling CQ. I call for several minutes and then switch over to answering CQ calls that I see in the waterfall for a few more minutes with zilch to show for it. Literally nothing. I am starting to wonder if there was some sort of flare that I was not aware of or some such as that as I was getting stations into the radio but no one could hear me. I chalked it up to that they must have been running a kilowatt and my paltry little 12 watts into a compromise antenna just wasnt getting it done today.

One of the things that I like most about this radio is the clean layout of the FT8 mode. It is not cluttered with an endless array of different information and on screen settings. The other programs, while very versatile and powerful, are rife with buttons and information that really is not needed for simple QSO contacts. The sBitx could be a little easier though so it is not perfect either. One thing that has come up a couple of times is that it needs the ability to be able to sort the information display to just stations calling CQ so you can pick one easier. I agree with this as it can be tough to grab a calling station in that 2.5 second window of time. So being able to sort by CQ would be a big help there. One other thing that is mildly frustrating is that there is no way to scroll the display so if there is a lot of stations on the band then you will not be able to see them all. It pushes them off the top of the screen and then they are just gone.

Today though, there was plenty of room to see both even and odd stations so it was not a problem. I was glad to see there was a good amount of activity on the 17 meter band.

The truck cab sure it a convenient operation center for POTA!!! I find it almost perfect to be honest. It is so close that I have used it all winter without modifications but at some point I do think I want to modify it. I have been considering the Kenwood TS480 as a permanent installation in the truck just for POTA, but then I would still need either a computer or the sBitx to operate FT8 in thr fireld. This just circles back to using this radio like you see in the photo below till something better comes along.

Here is the antenna setup for today along with the nanoVNA I used to measure it while I “tuned” the system. Tuning literally involves just moving the radials around till the SWR reads as low as possible. Sometimes it involves adding another radial to the system to get the SWR below 2:1 (which is my personal high limit) and I have even done odd things like run one REALLY long radial way out to give the lower bands a chance at working. This has worked really well too when I want to use 40 meters with a hamstick.

To answer some obvious questions that will show up, yes, there are two nanoVNAs in the box…long story but I have two now. Haha. The case came from GigaParts as they had a bunch of them at the Huntsville hamfest one year for super good prices and I got a couple of them. This one houses the nanoVNA and multimeter and the other holds all my POTA radials. You can see it above on the truck bed cover. I plan to get more of these at some point as they are super useful containers for small equipment like you see here. That is why I wrote on the lid of the yellow one, plus it identifies it as mine as that is my handwriting too.

As you can see though, I had a pretty good run on 17 meters FT8, securing the successful activation just in this mode alone. I never like to stop at just ten so once I had worked everyone I could hear I moved down to 20 meters and worked two more there before calling QRT and packing up. 20 meters is the campground of POTA these day and if you want to simply claim a quick activation then go there, it should not take long to get your ten if you are pressed for time. I know some people do activations on their lunch break and 20 meters is great for that. If you want a bigger challenge though, move up to the higher bands. Seems here lately that when 15 meters is open I will work a ton of dx stations and the lower I go in the bands to closer to home the stations. So if you have not ventured higher in the bands, I recommend you give it a shot sometime, you will most likely be pleasantly surprised

WK4DS

Broken antennas and a quick activation at K-2169 is what ham radio is all about!

I started today’s activation at the Sitton’s Gulch parking area. This is a quick access location for me as it is only about 15 minutes from my house to this spot.

First thing I had to do before the activation though was make a new center conductor for my hamstick mount. Since I made the truck mount out of thicker flat bar stainless steel in the machine shop, it didn’t occur to me that the antenna adapter is going to be too short. Well, it was and I ended up stripping out the last 2 threads on the stud because that was all that was holding it together. Problem here was that I couldn’t reuse it like it was, enter the machine shop at this point.

Below shows the arbor press pushing out the center conductor from the mount itself. This turned out to be a fairly straight forward affair as well, which was nice.

Once out of the arbor press, I was able to examine it more closely. It is a simple part so I decided to make a new one out of bar stock. I dug around in a couple of bins and came up with some brass bar stock and set it up in the lathe and proceeded to cut out a new center stud that was the right size for my needs…

Here we have the new part coming out of the bar and all the unneeded parts (chips) flying off at high speed! Lol. I love machining brass, it is such a joy to work with compared to stainless steel or titanium… Since the stud is press fitted into the body I really had to watch a couple of the dimensions to make sure they would fit properly, but several were pretty loose and were really not critical so I was able to get this part cut out in about an hour total, which for me isn’t too bad.

The solution was to make a new stud that is .200” longer thus allowing for the thickness of my mount. I simply replicated the same measurements, other than the length of the threads, and pressed it back into the housing and now I have an antenna mount with the correct amount of threads for my particular application. I also did one other thing too, I hand fitted the threads to the coupler that screws onto it, this gives me the best possible thread fit between these two part as well as the strongest fit as well. Since I know this is the only place these two devices will ever be together I don’t think it will turn out to be a problem later should there be some need to use it with another setup.

With it repaired and installed on the riser frame, I can now get back on the air and stay warm in the truck too!

Something of note in the below photo is that I use the nanoVNA to check my antenna every time I setup now (or as often as possible as long as I have it with me and it is charged up). I have found some odd stuff a couple of times too because of it. This is how I found the broken coax center conductor a while back as well as some band Sta-kon connectors on my radials a couple of times.

I will even use it between band changes just to see what the SWR is going to be like in a certain band location now. It is a really handy little tool. I highly recommend you picking one of these up and learning a little about it at some point, they are fairly inexpensive compared to the antenna analyzers and will give you the same information plus some. It just takes a little time with YouTube and some patience…

Once the antenna was deployed, I got back in the truck and powered up the radio to see if there was anything going on and boy was there! In this photo I am working FT8 on 15meters and as you can see the band was not very active with FT8 operators (you can see it on the waterfall). No one answered me, probably because they couldn’t hear me very well compared to other ops, and after a while I decided to see if there was any CW contacts on 15. After several minutes of calling CQ, I had netted just two contacts. These two showed how good 15 meters is for distance though with both of them being a great distance away from my park. So sometimes the band just isnt there for you to make contacts even if the RBN says it is.

All that aside, I started on 20 meters as it is my goto band if I dont have a lot of time. If you have been reading my blog posts for a while, you will know this, so here I am on 20 meters and I decide to start on CW this time and see what I can find. I get my spot on the POTA site and off we go, it didnt take long to secure the activation and then some and once I had cleared the little pile up I had going I decided to hop on FT8 to see what I could do. FT8 went really well there to with me netting 14 QSOs there as well before I decided to move up to 15 meters. What I really like about FT8 is that it is pretty hands off, this allowed me to fill out me log on HAMRS and get it caught up to the most recent QSO before I finished out this mode and changed bands. That is really cool in my book.

Now that I have the wiring in the doors repaired I am able to route the antenna coax though the window the easy way as long as it isn’t raining… This is really fast and doesn’t pinch the coax like running it through the door jamb does when I operate in the rain. You really don’t know how convenient this is till you don’t have access to a feature like windows that roll down… It is almost comical how long I put off repairing the wiring in the two back doors and to be honest, it really wasnt that hard either…live and learn.

In the above screenshot you can see that there was plenty of signal but there just wasn’t many CW ops on the band. I did get one Canadian and Paul up in Idaho before going QRT though. I was happy to get at least a couple of contacts once I setup on the band. It is always interesting to see what the range of a band is when the higher bands are open. I have gotten some pretty long distance stuff with some really bad antennas on 10, 12 and 15 meters in the past. It just takes going up to those bands and looking around and the right time of day for it to work…the band has to be open too, but we all know that at this point…lol.

Today’s key was the Gemini Ham Radio travel key, This little key is great for me as it is the perfect size for my hand and I really like how it collapses into the housing for travel. When you take it apart, you see how simple the design is and that you don’t have to have this super complex device to send good code. This thing really is pretty simple and it works great.

Below shows the radial field I laid out today and this was just to give it something to work with as they are all on the same side of the truck! I used one of my tuned 20 meter radials and the set of 17 meter radials and this gave me great SWR on 15 and 20 meters. I like it when this works out… Of course, since I am using a ham stick, the truck body is part of the ground plane and the radials interact with it so the SWR will depend on where I put the radials. This is why I always attempt to put them at right angles to the mount if at all possible as this is how I tuned them initially and also allows me to adjust SWR somewhat by simply moving them around behind the truck.

This is also a first for me as my log shows almost as many FT8 contacts as CW contacts. (14) FT8 contacts and (19) CW contacts is a good day when you only have an hour and a half or so to operate. I have never been one to try to get hundreds of contacts in one outing, even though it has happened a couple of times, I am more about just getting on the air and having some fun. So at some point I hope to work you on one of my POTA trips!

73

WK4DS

Activated Cold Mtn K-6895 TWICE

Here is the AAR for two separate activations over a two day period at the same park. This is Cold Mountain State Gameland near Waynesville NC. K-6895. It is a great place to do some vehicle mounted POTA and I recommend it.

In this photo above you can see the entrance to the parking lot and how small this area is. I also ran out a single radial on the first trip as I was only going to be on 20 meters as this park doesn’t have cell coverage. I also didn’t know how well I would be able to do with this park as I did literally zero scouting before hand. I scheduled the activation as I wasn’t sure about cell service and this turned out to be a good thing.

I have learned to search out parking lots that are fully within the park boundaries. I do this by pulling the park up on a couple of map applications and then zooming in on the roads around them and scouring these areas for parking lots. Just like in these two screen shots I found the park boundaries pass over Lake Logan road a few times and upon closer inspection, I found what I was searching for… A parking lot within the park boundaries that I can operate out of the truck with is a luxury that I love to land on if at all possible. I didn’t take a man portable rig this time as I wasn’t thinking about POTA being the main reason for this trip but rather something to do if the weather got bad or I just got a hankering for some radio time (which is what happened)…

The radio for today was the sBitx v2 and I am learning more and more about it as I use it. The message memory is really nice with this machine. I really like the whole process of operating CW with this radio and FT8 as well. It is almost effortless. The dev that wrote the code for this radio is working on a v3 release… I guess is the version. I am not sure what version we are on at this point to be honest, but it does have a couple of issues that make it less fun to use at times, but to be honest about it I have had a blast with this radio.

Day 1 was nice because there wasnt anyone except a fly fisherman who was down in the river. Here you can see the radial ran out to the side.

Since I had come to this park and didnt know much about it other than it was a game reserve, it was nice to see that amateur radio wasn’t on the prohibited list of activities. Lol. Keep those activations low key and it probably won’t get added too.

Things got dark in a hurry since it was overcast as well. I ended up finishing the activation by flashlight. Here is a photography trick for you. Dont point the light directly at the thing you are using (here it is the logbook) but point it at the ceiling and the light will bounce back and fill the area making it easier to see and work.

Day 2…

The next day showed more fishermen than the previous day but still there was plenty of room to put out some wire radials. Today I wanted to get on 30 meters and see what I could do as the band was open… or so I thought. So I put out the radials for 30 meters and since they would reach the trees, I ran then horizontal from the antenna mount to see how they would perform as elevated radials. Turns out that was a terrible idea, the SWR was horrendous so I started playing with them a little. I next just laid them in the grass to do it the lazy way and the SWR still wasnt great, better but still fairly high. Lastly, I put down a stake and pulled just one wire taught and BAM 1:1 SWR! Seriously, that was all I had to do???

So I also scheduled this activation as well, but unbeknownst to me, I failed to convert local time to UTC time so the schedule was way off. So I was running dark mode. I called CQ on 30 meters and in ten minutes or so had made a whopping 2 contacts. At one poi t someone tunes up on top of me and starts calling cq as well! Lol. So I figured I would switch over to FT8 and see if the time was still synced well enough for it to work. Ten minutes into this I had successfully made two more QSOs for the log.

At this point I switch antennas and get on 20 meters CW and start calling CQ. I actually think at this point that the spot was working and there just wasnt anyone on 30 meters as I started getting QSOs in the log like normal but then it just fell off again and I decided to try 20meters FT8 and see what would happen and again I only made a couple of QSOs. Not sure why but it is what it is. I am happy at this point as I have the activation in the bag but still have a ton of time so I go back to 30 meters and the waterfall is covered up in activity. I am stoked! I setup and strt calling CQ… and I call…and I call and FINALLY I get an answer.

Over the next 12 minutes or so I work 3 contacts withthe band covered in activity. So I simply ask W4ELP if he would spot me and he said he would. Thank you Ed for the spot because you can see what one simple little thing loke a spot on the POTA website can do for an activation. QSO #19 is Ed and in about 35 minutes had made 19 contacts. This is awesome considering the lack of a spot on the network. As you can see, having the spot though got the word out and I quickly added another 36 QSOs to the log with a couple coming with nice little pile ups.

I learned a valuable lesson today in the I need to check the time on my scheduled activation carefully so it happens at the time I am there. Lol. The next one did happen right. Just like the Smokey Mtn National Park one. The RBN works great and scheduled activations making not having internet access a moot point. This is a fairly new practice for me so I plan to use it more in the future.

All in all I had a great trip to Cold Mountain and will probably go back the next time I go to Maggie Valley to photograph the elk heard since it is so close to the motel. Thanks for coming along and I hope to work you soon!

WK4DS

73

Something special finally happened to me at a POTA park...

Today had been a pretty busy one at work, so afterwards I wanted to go over to K-2169 (Cloudland Canyon State Park) and just work some contacts to take my mind off things and to just relax for a while since it was 77 degrees on November 7th!

I get my sBitx V2 and head over there with the plan to run my hamsticks since I only have about 2 hours, maybe less, to get my activation in before dark. I roll up to the frisbee golf parking lot and notice another car in the lot with an antenna on the roof…a very large antenna mind you when compared to the ones you usually see on top of smaller cars.

I go ahead and park in my usual location and decide to walk over to see if there is someone in the car and THERE WAS! What do you know, I found another ham already doing POTA! It was none other than KB4QXI (John Law) and he was working SSB with a 20 meter hamstick on the roof of his car none the less. It only took me a year and a half and over 120 activations at this one park to finally run into another ham radio operator doing POTA. John had a pretty sweet system setup in his car with a computer, I assume for logging as I failed to ask him if that is what it was for, but I am pretty sure it is. He was also running a Yaesu radio of some sort on a mount that placed it right in hand’s reach but out of the way of the passenger seat, which happened to be where the computer was residing. I failed to get a photo of any of that so just let your minds run amuck with the verbal description and we will move on.

After talking with John for a while we agreed that it would be best if I setup in the next parking area down the hill which is right at 2/10s of a mile away. I personally figured that was far enough that we shouldn’t have problems with cross talk if I went to 30 meters since I was going to be operating with CW anyway since he was already on 20 meters when I arrived. I figured that if 30 meters was really bad that I could just drop down to 40 instead and work all the locals. Lol. Something else I had not noticed was that this lot had powerlines running right over it (as you can see in the above photo). I figured at this point I might as well give it a shot anyway and see if I could get the activation at the minimum. I did only have about 2 hours till the end of the UTC day at this point.

I setup three counter poise wires, you can see one of them in the photo I took above just barely because I forgot to get a closer photo prior to it getting dark… soooo. Suffice it to say, I ran out the two 30 meter tuned radials and even had the opportunity to run them elevated about 5 or 6 feet above grade, which is probably why my radio worked so well on 30 tonight to the point I didn’t move off that band. Tuned radials seem to work SO much better than radials that are just close. The key when I operate from the truck seat can vary between the Gemini and the N3ZN paddle, it just depends on the mood I am in as well as how fast I want to setup as the Gemini is in the carry tote and the paddle is in the hard case with the Argonaut 5… I normally choose my paddle based solely on things like this as I really like using them all.

After talking to some of the more code savvy hams in the email reflector on the bitx group and them helping me solve the code problem (actually they solved it and told me how to implement it), I was able to get the FT8 mode operational. It actually worked when you called CQ already and it had an issue operating when you would answer someone else calling CQ. It is a stop gap fix that does allow it to work but it doesnt work as efficiently as it should. Still it got FT8 working for me so I am stoked!

To be fair, this is Ashhar’s first iteration of this mode in his hand coded software he wrote and it does work so I got no complaints as it allows me to work the mode WITHOUT the need of an additional computer. He is currently testing a revision that works even better so I am excited to see what happens with that. In the photo above you can see the exchanges and the log entry for my QSO with K4SQL. This is all in the radio too!

On the way out, it was pitch black as it now gets dark at 5:30…uggg. Have I mentioned how much I dislike Daylight “Savings” Time? Well, I dont like it… This is a prime reason too. Even without DST being implemented, it would be dark at 8PM in November. Regardless, I had to use a flash light to break down my antenna tonight.

I powered down and quit before the UTC day flipped over as that would have forced me to stay two more hours to get a second activation in…lol. I do need one more activation at this park to get me over 4000 QSOs. I never planned on getting that many QSOs at one park to be honest, my only goal to start off with was to get 20 activations so I could get the repeat offender award, now I am well north of 120 activations and almost 4000 QSOs! By the time this blog post goes live, I should be past that mark.

Something else of note is that I am currently still logging my FT8 QSOs on my paper log and typing them into HAMRS as there isnt that many of them at this point and I can easily keep up with this quantity manually instead of learning how to export them from the radio and then add them to my HAMRS log electronically or even a new logging program of some sort instead. There will be a point when I will have to do that, but for now I can still get them in the log like this really easily. So till next time warm up the air waves with your radio and hopefully I will work you from a park!

73

WK4DS

sBitx V2 Amateur Transceiver Mods for POTA Use

My newest radio, the HF Signals sBitx v2, is an HF radio with so many features that you just need to follow this link over to their website to see what it is capable of. Once you have finished going down that rabbit hole, come back over here to see what mods I have done to mine already for my POTA stuff. I want to say this right away, this radio is kind of in Beta, so if you don’t like to open up the radio and tinker with it in both the software as well as the hardware, this probably isn’t the radio for you. With that out of the way, let’s get started!

I decided to get in on this idea of a open source architecture radio design. I found this company, HFSignals, and they make several radios with their latest model being the sBitx V2. This is a touch screen radio with a huge screen and it is powered by a Raspberry Pi SBC. Using a legit computer to power the radio unlocks so many things that this radio can do that other radios can not do. For one, it will do FT8 IN THE RADIO! Yeah, no external computer needed at all, that in itself is a gamechanger and don’t be surprised if you see the big names in the industry doing this in the near future because of it. By using a Raspberry Pi SBC for the brains, this little machine is just chocked full of goodies that those other radios cant do.

FT8 is native inside the radio on the sBitx v2.

You heard that right, as I type this blog post it is on the bench next to me finishing a QSO with I1RJP, and when it does it will automatically put the QSO in my log for me. How awesome is that? Did I mention it is open source? Yeah, both the software AND the hardware are open source and it is encouraged to take your radio apart and tinker with it. Shoot, it even shipped to me with a spare set of output transistors in the accessory bag. These are well thought out but they are still rather simple overall designs with features like they are passively cooled radios and use a crystal filter network. Another thing about being passively cooled is that it means there is no fan noise to deal with at all this way, since there are no fans.

Well… I used it on a POTA activation and the little radio got HOT. Really hot to be honest. So I decided that since this radio is designed from the outset to be open source and to be tinkered with by the end user and I wanted to use it for POTA activations, that I would add some fans to cool the little machine on activations.

The first thing I wanted to tackle was the power amplifier heat sink. It is a great heat sink and does a wonderful job as it became really hot during the activation. I first started looking for a suitable fan in my junk box and found the perfect fan in an old computer power supply that I have cut apart for another project. The fan was still mounted in the sheet metal case which also happened to fit perfectly over the outer edges of the heatsink. All I needed to do was trim the sides down so it sat next to the heatsink and add some screw holes to attach it with.

Once I had it mounted with a couple of self threading screws, it was time to get it running. I went inside the radio and started looking for a suitable place to tap power out to it and found the incoming source point was the best, but the fan would run all the time if I used this spot…

Enter a simple electronic circuit that could be used for any temperature of fan control and could even be adjustable with a potentiometer if you were so inclined. This circuit is a simple power transistor rated for 6 amps of max draw (I used this so it could handle the 300mA of draw from the fan and not need a heat sink and they are still really cheap too). You simple have a voltage divider network for the base of the transistor where you have a fixed resistance between the base and ground and you add a thermistor (a temperature reactive resistor) between the voltage source and the base.

I chose a 10K ohm negative coefficient thermistor for my needs as this design has the resistance go down as the temperature goes up. The fan is simply wired in series with the transistor’s collector and the voltage source and the transistor is basically used as a electronic relay in the simplest form. I know the MOSFETS are more efficient, but this works and I had all of these parts (except the thermistor) on hand so I used these instead.

What happens during operation is that when powered up, the thermistor has so much resistance at a lower temperature that the base voltage is less than the .7 VDC required to bias the transistor since the fixed resistance of the base to emitter side of the voltage divider is calculated for the desired temperature. The thermistors have a chart showing the resistance at different temperatures so you can make these calculations fairly easily. Mine worked out to 270 ohms for the fixed resistance between the base and emitter. So you can imagine that with 10,000 ohms (at 77 degrees) on the other half of the voltage divider you only get .363 VDC on the base of the transistor and the transistor stays “OFF”…

I found the above chart online for 10k ohm thermistors and grabbed it for reference only. This may not be the right chart for your thermistor as they have different resistance curves so check with your brand of device and make sure you have the right chart for your device. Back to the story in progress…

Well knowing this, as per the chart above when the temp rises to about 107 degrees then the resistance drops in the thermistor to about 4980 ohms and this now allows about .7 VDC to develop across the base of the transistor, forward biasing it. Notice how I made the contact with the hear sink. I soldered on a pair of wires and put heat shrink tubing on them to insulate the connections then I ran a 1/4-28 tap down into the space between two fins cutting something resembling threads into the fins. Then I took a piece of a zip tie and put it on the thermistor and ran a setscrew down against the ziptie/thermistor stack to hold the thermistor against the heat sink it works really well too. The ziptie is only there to do two things, to prevent me from cracking the outer shell of the thermistor and to insulate the thermistor from the setscrew so the setscrew wont bleed off heat, I am not certain it helps, but it sounded good in my head at the time. LOL. I located it near the transistors so it will pick up the heat faster. I also changed the mica thermal spacers out for aluminum ceramic instead as those are supposed to conduct heat significantly better between the power transistors and the heatsink.

The fan control circuit can be seen on the perf board next to it in this photo.

Then once things heat up the fan spools up and blows on the heat sink, in turn cooling it down to the point where the temperature on the thermistor drops enough to raise the resistance back up and shut off the transistor again. This worked like a charm at the last activation I used the sBitx v2 on. The fan doesn’t even come on to drain the battery until the heat sink warms up enough to need it, so if your simply listening around or hunting activators and doing search and pounce, then the fan will not cycle on very often at all… if ever. I do understand that there is some current flowing through the resistor network all the time though as well, but it is low and I am not really worried about 3mAs of current anyway. I have really large batteries in the grand scheme of things and if I am going to hike with a radio it will be the Penntek TR-35 anyway…

The next “upgrade” I did to mine was to add a heat sink and fan module to my Raspberry Pi 4 SBC (single board computer) that is the heart of the sBitx radio. The original configuration has the SBC mounted right on the RF board with very little space between the two for airflow and no room at all for a fan of any kind as you can see above in the photo with the side radio cover removed. I did some experiments with positioning fans above the heat vent opening above the Pi and could feel that the air I was pulling out was quite warm. This led me to the assumption that the SBC would run smoother (and probably last longer) if it had a proper heat sink installed on it. You see as my unit would run, with time, it would start to lag a little from information input, like adjusting the VFO would result in the numbers jumping on the display instead of a smooth change as the knob is turned. I noticed when the fan was pulling air across it that this would be reduced significantly if not eliminated. So the mission became “how do I get a fan on this thing to cool it properly”

So I start looking at adding an external fan but ultimately that didn’t look really feasible as I wanted to pull the heat off of the Pi properly and not with just slight air movement. A case fan would only help a little and I am pretty sure at this point that the SBC needs a little more help than that. Enter a riser kit from amazon and a heat sink assembly with fans from one of those Raspberry Pi bundles that comes with the pi, a small case and a heat sink with fans. I measure every thing and come up with a height to elevate the SBC and check the cabinet and sure enough, there is plenty of room to add it. So I get it all together and when you get the riser kit from amazon, you get the little screw-in standoffs as well as the header socket extender to extend the pins up to the Pi once installed. If you will look closely in the photo below, you can see one of the fans and the heat sink fins for the SBC heat sink that I added to the Raspberry Pi SBC to help cool it.

In the above photo you can see the pin extender i also had to add so the Pi would plug in once elevated for the heat sink module. This worked wonderfully for fitment and I was stoked to have the heat sink on the SBC finally, but I still had to connect the fans to power to get them to run. Instead of putting them on a heat sensor, like the power amp fan, I chose to wire these straight to the main power switch on the sBitx so that when you turn it on, they spool up and run the whole time. My reasoning is that the computer will be working the whole time as the radio is in constant “refresh” mode so to speak as the sBitx software package has to keep everything up to date in real time on the display, then there is the background applications that are also running like the telnet server and dx cluster stuff and the other applications should they be active. Logically the SBC will be running nonstop, so lets just run the fans all the time…

This is where I run into a problem…

Did you notice where I drew power to run the fans? That seems completely reasonable for someone who just successfully wired up a fan on a temperature sensing circuit for the power amplifier. Well, it turns out that the fans for a Raspberry Pi are not 13.8VDC fans but rather 5VDC fans as they are designed to be plugged into the SBC IO header bus and not driven from a 13.8 VDC source. Let me tell you something, when you run a 5 volt fan on nearly 14 volts it sounds like a jet engine preparing for take off! On top of that, I had a pair of them!

I had brought the radio to the house and connected it to power to play with it and hunt some POTA activators and the whole time I am thinking to myself… “Man, these tiny little 25mm fans sure are loud…” but after about 10 minutes (yes, they lasted that long and in fact lasted much longer) I started to smell hot plastic… I shut down the radio and took it apart to find the fans incredibly hot and seriously, “soft” to the touch.

Back to the workshop and I figured out what I had done. So I start working on a way to lower the voltage that would not cause RF hash inside the radio cabinet. Those little buck converters from amazon are notorious for causing RF hash so that was out. This simplest thing to do was to put a big resistor in series with the fans. I had put them on a 5 VDC supply in the shop and measured the current draw so it was a simple matter to do a little ohms law and come up with about 50 ohms of resistance to mitigate the excess voltage from the supply. Also these fans pull very little current and I am running them at 4 VDC instead of the full 5 volts as they are rated to run from 3.3 to 5 VDC. This way they will be a little quieter too or at least that is my thinking and it gives me a little leeway should the voltage go down lower or even a little higher.

Inside this heatshrink is (4) 200 ohm 5 watt resistors soldered in parallel so make a 50 ohm 20 watt resistor.

Well the brute force approach worked and the (4) 200 ohm, 5 watt resistors in parallel dropped the voltage down to a very workable level. The resistors dissipate about 1/2 of a watt of heat total so I put them out of the way from everything else and it works, it just works. Maybe later I will add some sort of active voltage regulator and do it so that I don’t have to just burn off the excess power nonstop to keep the fans at the right speed. Maybe something like a 555 timer biasing a mosfet for pulse width modulation to keep the power draw down and keep fan speed at a constant level. I don’t know, I will look at that later, for now, the brute force resistor idea is working just fine.

Once I got the fans turned back on, I found “I had a rod knocking” in one of the fans… figures that if you run them at almost 3 times the rated voltage that something like a bearing fails in the fan… well I just ordered another set from amazon and swapped them a couple of days later and now we are all set. So it would seem at least as when I went to reassemble the radio I found that my USB and Ethernet ports no longer lined up with the openings in the side plate for the radio.

Turns out that if you have a fully equipped machine shop, this isn’t a real problem though. It could have been solved with a good file and probably a half hour of work, but who wants to do that if you have a CNC milling machine at your disposal? So I put it in the milling machine and manually open up the exiting holes to allow use of the ports and by default I also created air vents for the Pi to get fresh air to it much easier now. This also seems to work really well for the time being. Better air flow, adding a heat sink and FANS!!! The Pi runs cool now.

I also did a couple capacitor mods that I found on YouTube as well. A fellow on the interwebs had done these same capacitor mods and they made sense to me so I went ahead and added them as well. The following video describing these mods and why.

To summarize his video, he added decoupling capacitors to the three jacks on the side of the radio to drain off stray RF. He also adds one across the incoming supply lines to kill transients and possible RF on the power. Please note that in the photo below I have the plus side marked on the capacitor, this is incorrect as the board is marked erroneously and I translated that error to my cap as you can see in the photo. Check the supply on your radio with a meter before installing caps that can not be reverse biased. We all know how that would end…

One last thing I also did was to add some heatsinks (also per the video above) to the power devices inside the radio to help them survive use during digital modes. They worked just fine when I ran them with CW but when operating digital, the duty cycle is a lot higher so I didn’t want to risk thermal failure because of something as simple as adding a heat sink. This also comes from the above video and just made sense to me too, so I added them. The radio operates great and I really like using it for FT8 when calling CQ (more on this later) as well as for CW. I have some other mods planned for the future so another blog post describing these mods will be in order at some point. Till then, thanks for your time and attention and I hope this helps someone out there with their radio.

WK4DS

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