POTA Monster

 So, I've gotten more interested in POTA activations, recently.  I had a lot of fun with my first activation in the Spring.  I bought myself a Xiegu G90 for my birthday, and put together a go bag and EFHW antenna.  It works OK, but honestly, at 20 watts, kind of lacks the "punching power" I wanted.  There is an "Erie Canal Bicentennial Celebration" POTA event coming up this week.  It runs for 8 days, and I'd love to be able to run out to a local park and activate a few times.  That said, my last two attempted activations were flops, as no one was hearing me.  Also, the portable setup with EFHW is nice, but it involves throwing a wire into a tree in a State Park.  Many parks don't care for that.  I've tried the Xiegu with a Hamstick and, frankly, it sucked.

Considering the problem, I recalled I have some hamsticks, and a Kenwood TS-480HX (200 watt) in a box.  I removed them from our previous truck when we got rid of it, and haven't used it since.  I decided to resurrect it.  Slapping a hamstick on the car roof, and using a powerful radio from a go-box should allow for quick activations and more satisfying results.  As a result, I decided to make a GO box for my TS-480.

 

 First, I busted out my hamsticks and checked them over.  Unfortunately, the 20m stick (the one I'd use the most) has some kind of failure and won't tune.  I ordered a replacement.

Looking at my TS-480 and taking some measurements of it, along with the tuner, I decided I needed a somewhat large box.  I decided I could make it work in an Apache 4800 case from Harbor Freight.  Note, that I always use separate battery boxes.  I prefer to be able to grab a box with a radio, and a box with battery in an a-la-carte fashion.  That seems more versatile, and frankly, a lot easier to move around, than the huge 19" rack-in-a-box kind that many people assemble.

I'd really >like< to be able to operate the radio without having the case open, so I purchased some bulkhead RJ45 adapters.  I learned, upon assembly, that I had forgotten that the radio head actually uses RJ12.  Fortunately, you can use RJ12 in an RJ45 jack, but I've since ordered the correct bulkhead adapter.

I had an SO-239 and Powerpole bulkhead adapter kicking around my parts boxes, so I threw it together over the weekend.  Pictured here is the complete go box with all the cabling necessary to plug it into a separate, powerpole, supply.

 

I stacked my 200W tuner on top of the radio.  I left a channel underneath everything for air to flow from a hole in the right side of the case through the radio, the fans, and out holes on the left side.  Ultimately, I'll 3D print some "mesh" to cover these holes, and perhaps even print up some "channels" so that nothing can block the flow if the foam gets compressed.

 

  It has Panel and Mic jacks on the front.

 

 The right side has an air hole, and jacks for the antenna and power.  You can see why I need some "channels" to keep wires and foam inside the box from blocking airflow.  The power wires are right in that area, and they keep migrating to right in front of the hole.

 

 

 

I cut and crimped some short patch cables to go from the radio to the internal ports on the bulkhead adapters, and a shorter patch cable for the radio head.   The cable that comes with the TS-480 is really long.  I also slapped some ferrites along the control cabling, since the stock cable came with one.  I put one near the radio head, and another inside the box, just before the internal cable plugs into the radio.

 

 
Testing completed, the last thing to do was to give it a name.  I give you the "POTA Monster".  200 watts of cloud-burning fury.

 

I'm looking forward to trying it out when my new 20m hamstick arrives. 

Hojo and the Case of the Silent DR-1200T

We seem to have a fleet of Alinco DR-1200T's kicking around.  The local APRS expert uses them, along with a TNC, for APRS nodes in the area.  I've repaired, recapped, and aligned several of them over the years.  A new one (to me) hit the bench today.

 

 

 

I popped on the service monitor and ran a few tests.  It generates no audio either to speaker or headphone jack.  However, I do see the S-meter doing sane things as I adjust my service monitor up and down, so it's receiving, but not generating audio.  TX tests seemed good.  I fed a tone into the Mic in and threw the PTT.  It generates a signal of the appropriate strength - about 20 watts or so.

So, something's amiss with the audio out.  My first guess is that there might be something wrong with the final audio amplifier.  That seemed like a reasonable place to begin.  I could check the AF-in and AF-out to see what I might see.

Consulting the block diagram:

 

It appears I'm looking for IC4.  I see an "AF Mute" signal there too, which might be suspicious.  I'll look into that.

Reviewing the (blurry) schematic:

 

It appears that IC4 is a "uPC 1241H".   With a few googles to double-check my assumptions and reading of the schematic, it would appear that 

• Pin: AF In
• Pin 2: Bypass cap?
• Pin 3: Unknown
• Pin 4: GND
• Pin 5: GND
• Pin 6: AF Out
• Pin 7: Unknown
• Pin 8: Vin

Looking at the board layout, I located the chip:

 

 

Busting open the case, I found it against the rear heat sink: 

 

 

Starting with the multimeter, I read 11.6 volts on VIN.  That's down a bit from the 13.6 I'm feeding it.  The current draw showing on my bench multimeter doesn't seem unusually high compared to another unit I had, nor is the chip particularly warm.

So, I grabbed an amplified speaker, and touched it to Pins 1 and 4 (AF In and Ground).  Sure enough, I hear static.  Turning the volume knob on the radio, static volume changed.  Turning squelch, static went away.  Seems reasonable.

I hooked my service monitor back to the antenna port and sure 'nuff, I'm hearing tone on AF In.  Volume and squelch continue to work as expected.  Switching my probes to AF Out, I get nada.

I looked at the remainder of the output chain, wondering of something might be pulling the AF Out down to ground or something.  I don't see much.  C90 seems to connect AF Out back to Pin 7.  Probably some kind of feedback thing.  C91 is along the way to the remainder of the output chain.

I pulled out my ESR meter and checked all of the caps in the neighborhood.  Though not highly scientific about it, all showed an ESR of about 1.5 ohms or less.  Nothing stuck out as a dead short or anything.  

I'm reasonably content that the amp chip is the problem.  If I replace the chip and all is well, I'll probably recap the entire radio, just on principles, but I'd rather not change too many variables at once.

 The chip is, of course, long out of manufacture.  There seem to be plenty of options on eBay for $20, shipped, or less.  I'm contacting the radio owner for next steps.  I'll update this post if I proceed.

 

 

Hojo and the case of the "bouncy" D710

I own a few Kenwood TM-D710 radios (one 710, and one 710G).  Both have been fairly sturdy workhorses, but recently, the D710 in my car started manifesting a BUNCH of problems.

 

 

Last year, I started having intermittent problems where the radio would reboot when I keyed up.  At the time, I tracked it to a weak battery in my battery box (I don't run the radio off the car battery, but rather a separate battery box which I charge from the cigarette lighter socket).  The battery box had a pair of 9AH UPS batteries, and they just wore out.  I replaced them a few times, and then managed to blow the fuse in the cigarette lighter.  

That was just before winter, so I left it for the season, since this is our "backup" vehicle anyway.  Getting back to it this year, I picked up a 100aH LiFEPO4 battery.   I put that in the car and it seemed to work OK, until suddenly, the radio started rebooting on key-up again.  Mainly when I used high power.  Switching to medium or low power seemed to resolve the issue.

I took the radio into my shack and ran extensive tests.  I couldn't make it fail.  I put it back in the car, and it failed within a day or so.

Thinking it might be a dirty wiring connection, I cleaned all of the CAT5 connectors, and cables, and even the GPS connectors.  That seemed to work for a short time, and then it failed AGAIN.

So, I began slowly testing by swapping one wire at a time, still sure it was a wiring issue.  Again, it might work for a day or a week, and then it would fail again.

I was nearing my wit's end when a buddy mentioned that his new radio was causing his LiFEPO4 battery's BMS to crash every time he keyed up.  He resolved it by putting some chokes on the power wires to the battery.

With a forehead-smack, I went out to my car and began by moving my battery farther from the radio.  The problem cleared immediately.  In fact, I used it all day for a public safety event with no difficulties.... until...  a fellow ham drove up behind my car.  He keyed up his radio to check in with net-control, and MY radio crashed!  Yep, it's RF getting into the battery BMS.  Thinking back, I did reposition my antenna at some point along the way.  I think that was probably the root cause all along.

So, I've put a few chokes on the battery wire now.  I moved it closer to the radio and it still seems fine.    

Moral of the story: LiFEPO4 batteries have BMS's.... they are sensitive to RF.  Be advised.

Now, to add insult to injury, during this time I also discovered that my radio had stopped beaconing.  I couldn't even force it manually.  After a bunch of debugging, I found that the radio would actually key up and send a brief silent burst before stopping.   A google search popped out a result that it could be a bad cable between the radio body and panel.  I swapped in a different CAT5 cable and voila, it started beaconing just fine.  So, I took the old cable out and cut off the ends to avoid temptation to use it again.  I'll crimp on some new ones someday and see if it works, but I'm out of patience with fighting with that radio for the moment.

Interestingly, my D710G radio is ALSO failing to beacon right now.  I'm going to grab another CAT5 cable and try the swap on that one, too.  I suspect these (10+ year old radios) are just wearing out those cables.  They live a rough life, under the seat of our cars. 

 

Scrap box APRS iGate / Digipeater

 

So, no shit, there I was. Our Tompkins County Amateur Radio Association is getting ready to support the AIDS Ride for Life event this coming weekend. It occurred to me that it might be handy to have an extra fill-in APRS DigiPeater / iGate running at my house, which could serve some places that have poorer coverage. So, I thought "Self, what would I need?" "Well, self, I'd need a radio, a raspberry Pi running Direwolf, and a magic cable to attach the radio to the Pi." As it happens, I have the perfect radio. Years ago, I picked up an ICOM IC-2000 (VHF Only) radio for $20. It was non-functional. I repaired it fairly easily. If I recall, there was just a blown transistor in the power-on circuit. It's been sitting on the shelf ever since. This is a perfect use for it, so I can get it out of moth balls! 

 

 

 

So next, I considered the magic cable. I figured a decent one would have a CM108 audio card for the Pi, a few audio transformers, and a Optocoupler to isolate the PTT ground (I've run into problems in the past when I tried to do it with a transistor). So, with a rough idea in mind, I started digging through my parts bins. I pulled out my trusty box-o-CM108's, and lo and behold if I didn't find a "KF5INZ Easy Digi" kit board that I had built YEARS ago and completely forgotten. That board has the audio transformers and optocoupler built-in! 99% of my work was done! Though I have no recollection of messing with the Easy-digi, I'm sure my knowledge of what I needed to do was based on playing with it years ago. My brain remembers processes, not details, so that tracks.

 

 

 

So, I desoldered the bodge of wiring that was on it from whatever experiment I must have done (probably an allstar node), and put it all together. I hacked off the end of a CAT5 cable to plug into the Microphone port on the radio. That gives me Mic-IN and PTT controls. To get audio, I just had need to plug into the external audio port on the radio. PTT is driven from the Easy-Digi board. I just have to run a few wires to the Raspberry Pi for it. Direwolf can do the rest with a GPIO port. I did hook up a power supply and a little LED to test the Optocoupler to assure it worked as I expected. It did.

 

So, 2 hours later, I had the magic cable to plug between the Raspberry Pi and the IC-2000. 

 

 

The next day, I configured up a new SD card for a Pi in my parts bin.  I built it on Raspbian Bookwork, which turned out to be a minor hassle.  The version of Direwolf that ships with it (1.6) does not have support for the GPIO changes that were made in Raspbian.  I ended up having to download the Dev branch of 1.8 and build the code from scratch.  

 

Testing went very smoothly.   I had one scare, thinking the radio had failed.  It turned out that it had an Auto Poweroff setting enabled.  Everything else pretty much worked right out of the can.   The audio was pretty sensitive.  I had to turn it WAY down so that direwolf wasn't complaining about it being overdriven.  I also noted that the volume POT on the radio is dirty.  A few times, the volume went from "low" to "off" without touching the knob.  Just wiggling it solved the problem.  I'll spray some cleaner on it.

Since this is really a temporary setup, I just zip-tied the Pi and cabling to the radio to make it somewhat secure.  We ran this over the weekend for the event, and it worked great!

 

Testing RS41 current draw at different TX_POWER settings

 

Introduction

RS41ng on the RS-41 allows you to configure the output power via the  RADIO_SI4032_TX_POWER setting in the config.h file.  It allows values from 0-7.   I set out to determine how that setting impacts the RF output power as well as the current draw from the batteries during transmission.

Testing configuration

 

I configured a RS-41 with RS41ng.  The RS-41 has an SMA connector attached so that it could be wired through 19db of attenuators into a Spectrum Analyzer.  Power was provided by a bench power supply.  I varied the RADIO_SI4032_TX_POWER through various settings and measured both current draw and TX output power.  The basic setup as as follows:

Bench power supply voltage: 3.2 volts
Bench power supply max current: 0.650 amps

 

Frequency: 432.605mhz
Modulation: Horus Binary V2

Testing

For each test, I reprogrammed the RS-41 with a different RADIO_SI4032_TX_POWER setting and measured the output on the Spectrum Analyzer as well as the current draw on the bench power supply.

Example current draw when testing with the TX power set to 30:

Example Spectrum Analyzer result:

Results

 

RADIO_SI4032_TX_POWER	DBM	Current (ma)
Idle Consumption	n/a	133
0	-4.5	172
1	-1.25	174
2	1.0	179
3	4.5	184
4	7.7	190
5	10.9	205
6	13.6	218
7	15.0	225

Conclusions

For airborne use,  14dbm (25mW) has been observed to be sufficient for line of site reception of Horus Binary using other trackers.  By setting RADIO_SI4032_TX_POWER set to 6 or 7, the desired output power is achieved. 

 

Testing DFM17 Current draw at different TX_POWER settings

Introduction

RS41ng on the DFM17 allows you to configure the output power via the  RADIO_SI4063_TX_POWER setting in the config.h file.  It allows values from 0-127.   I set out to determine how that setting impacts the RF output power as well as the current draw from the batteries during transmission.

Testing configuration

 

I configured a DFM-17 with RS41ng.  The DFM-17 has an SMA connector attached so that it could be wired through 19db of attenuators into a Spectrum Analyzer.  Power was provided by a bench power supply.  I varied the RADIO_SI4063_TX_POWER through various settings and measured both current draw and TX output power.  The basic setup as as follows:

Bench power supply voltage: 7.5 volts
Bench power supply max current: 0.650 amps

 

Frequency: 432.605mhz
Modulation: Horus Binary V2

Testing

For each test, I reprogrammed the DFM-17 with a different RADIO_SI4063_TX_POWER setting and measured the output on the Spectrum Analyzer as well as the current draw on the bench power supply.

Example current draw when testing with the TX power set to 30:

Example Spectrum Analyzer result:

Results

 

RADIO_SI4063_TX_POWER	DBM	Current (ma)
Idle Consumption	n/a	65
1	-12.0	76
12	3.0	90
25	9.0	107
30	10.4	112
45	14.0	128
50	14.7	132
75	17.8	151
100	18.8	162
127	19.2	182

Conclusions

For airborne use,  14dbm (25mW) has been observed to be sufficient for line of site reception of Horus Binary using other trackers.  By setting RADIO_SI4063_TX_POWER set to 45, the power consumption is about 70% of transmitting at full power.  The reduced power consuption would lead to longer battery life during flight, or on the ground during a HAB recovery.  

 

A little "science" on the DFM-17 running on 2m vs 70cm

The Experiment

I put on my lab coat, started boiling some test tubes, and made a few bwoo-hahaha noises tonight, as I did some science.  I attached an SMA connector to one of my DFM-17's so that I could run some controlled experiments of RS41ng on both 2m vs 70cm.  The intent was to verify whether the output RF filters on the DFM-17 are appropriate for transmitting beacons on the 2m band.

Modifying the DFM-17

I removed the stock antenna and added an SMA connector on the provided pads.  The board layout was standard, and an SMA connector in my parts bin fit just fine.

 

The test setup

I then cabled the DFM-17 through a pushbutton attenuator and added 40db of attenuation in the path to my Spectrum Analyzer (I didn't want to overdrive the input).  Note, the pushbutton attenuator I was using is built for 75 ohm, not 50 ohm.  This may impact some output power readings, but it should be consistent across frequencies, so while the output measured may not be exact, the relative powers and presence (or lack) of harmonic signals should be close enough for folk music and ham radio.

 

 

70cm Measurement

I then took a look at the spectrum when running at Horus Binary and APRS on 70cm.  I had the Spectrum Analyzer set to full scale (0-1500 mhz).  Note there were no harmonics in evidence at all.  The filters on the board seemed to do an admirable job of keeping it clean.  The SA showed -15 db.  Adding the 40db of attenuation, it's making about 25dbm of output.  Ish.

2m Measurement

I then re-flashed the code to beacon APRS at 144.390, and transmit Horus Binary at 145.600.  Note the harmonics generated.  The filtering on the board appears to be a low pass filter tuned to 70cm  So the harmonics below 400 mhz are coming through loud and clear.  There does seem to be some attenuation, as the signal on 144.390 is showing 10db weaker than the 70cm test).  The first and second harmonics have pretty strong relative output power, since they are presumably going through less attenuation as the frequencies increase.  There could be some variability in the output power of the Si4063 chip at different frequencies as well.  Note that the harmonic up in the 70cm frequency range is even stronger than the base signal at 2m, due to the vagaries of the filtering.

 

Conclusions

Running the DFM-17 below 70cm is going to transmit unwanted harmonics.  Though the overall output power is low, down in the 15dbm range, this would be generated by a balloon aloft, meaning the harmonics will be broadcast for pretty much line of sight across quite a significant radius.  I would advise against doing it unless you modify the filtering on the board.  The DFM-17 seems VERY nicely tuned for signals on 70cm, however.  I was quite pleased to see the results there.

Mike / KD2EAT