Sep 22, 2020


Oh, how things have changed over the years, it's hard to believe.

On the bottom is a Sony 16 megabyte memory card I used in my first digital camera. At the time, we thought it was such a great thing, but now we realize how little we really knew and understood about the world of technological possibilities.

On the top left, is a current model SanDisk 128 gigabyte SD card. It's about one quarter the size, half as thick, and has 8,000 times the capacity of the old Sony. Consider the per megabyte cost to produce the two memory cards in their respective days, and that difference alone is astounding. Buying 8,000 Sony memory cards in that day would have cost you around $70,000. The 128 gigabyte SanDisk today, a mere $10. Wow!

On the top right is a penny. Imprinted on it's face is the likeness of one of our nation's greatest presidents, Abraham Lincoln. And so too, the words, "In God We Trust" and "Liberty". Remember when these words were words thought of and heard on an almost daily basis? Even every day, in public school, when we recited the Pledge of Allegiance at the beginning of the day? Remember when these words actually meant something?

"No", you say? Well, let that be loud and compelling evidence of something very distressing. For the people of our nation, as a whole, we have not advanced, but devolved, into a world of selfishness and godlessness, demanding tolerance from others while expressing contempt and hate for those who are "intolerant" of our ideas. This intolerant tolerance has been clearly displayed in places like Ferguson, Minneapolis, Seattle, Kenosha, New York, Chicago, and many other places.

Is hate and destruction the new "advancement" in social development? What ever happened to statesmanship, peaceful protests, public discord, the thoughtful exchange of ideas? What happened to following the law, and following the Constitution? What ever happened to critical thinking, listening considerately to contrary ideas, and thoughtful discussion? 

More importantly, what ever happened to, "In God We Trust" and, "Liberty"? Therein lies the answer, if we are willing to be honest with ourselves, and with each other. 

For those who do remember; it's one matter for those who never learned these things, but it's an entirely different matter for those of us who have learned these things. We, the "Yes, I remember" people are accountable for what we know, and also for what we teach, and fail to teach. 

May we hear God calling us, and return to Him with a repentant heart. May we forsake ourselves and draw near to God, seeing what God has already provided for us through his risen son, Christ Jesus. May we act, rather than continue in omission, and accept His forgiveness, His mercy, and His healing for us, personally, and as a nation. Then, and only then, will we again be united as one nation, under God. 

Oh, how things have changed over the years, it's hard to believe.

Raspberry Pi APRS with SDR

For complete information on this project, see the APRS page.

While experimenting with the Raspberry Pi 3B+ APRS receiver, the Pi is temporarily running Gqrx SDR software with an AFSK1200 decoder. No internet gateway has been established as of yet, so all data remains on the device.

How does the RPi 3B+ handle the demand of processing SDR data? The CPU is averaging a pretty busy 55% load. The Argon programmable fan is doing a good job keeping everything cool as it cycles on at 42C with 10% fan speed, and off at 38C. The fan cycle time is about 1:3 minutes on/off in a 69F degree environment. 

In comparison, monitoring the CPU load on the K9KMS MMDVM repeater while it's in use (not idle), I found it to be less than a 2% load. This MMDVM repeater runs on a Raspberry Pi 4B, so it's not exactly an apples-to-apples comparison, but processing SDR data is obviously much more demanding. This will likely result in a shorter life expectancy for the RPi while using the SDR.

On Sep 21, 2020 at 17:39 UTC, the decoder ran until 00:30 (6+ hours) and logged 1,029 hits, an average of 171.5 hits per hour. Not too bad considering the surrounding forest and lowland lakefront area.

Sep 12, 2020

DMR Round 2

 I listened all day to TAC310 and all I heard were mic clicks and almost no talking. Two new-to-DMR hams started talking, but their radios were so over-driven and had so much packet loss, they were hardly intelligible. Lower the mic gain, fellas. The couple of others I heard were "Testing 1, 2, 3...". I really am trying to give DMR a fair shake, but I need some air-time experience before I can develop any sort of opinion about the mode itself, not just the programming. That's just not happening. 

"Stop listening and start talking!", you say? Yeah, no DMR repeaters near here, so it's all by hotspot. I tried talking the other day, but HughesNet satellite internet has so much latency (seconds, not milliseconds) and speed fluctuation (from 3Mb/s to 4,000 bits/s - really, no joke), that I can't do anything requiring a live, continuous connection, like a VPN or, say... radio transmissions on WIRES-X or hotspots. I'm serious! The other day it took 55 minutes to download a 73 MB file, and that's not uncommon! What's up with that? Sure makes me very thankful for real RF! Star Link! Where are you?!

UPDATE: This evening, Lon and Tom, both 2-land stations, were on TAC310 just t-t-t-t-t-t-talking away! Boy, it was g-g-g-grea-t-t-t-t-t-t-t to hear hams on DMR like I hear on America-a-a-aLink. Finally, there is hope. Maybe I can see some li-i-i-i-i-i-i-ght in this dark tunnel...   ...rescued me from the thought of b-b-b-b-b-b-eing single-mode'd-d-d-d-d-d-d. Diversity, I say. Div-v-v-v-v-versity of digital modes l-l-l-l-l-leads to new front-t-t-t-tiers in the world of amateur radio. And that, m-m-m-m-m-my friends is....

...just havin' fun!

Sep 8, 2020

Wire Antenna Suspension System

Back in October, 2019 I started planning a way to get the Barker & Williamson BWD-90 folded dipole up and running. Well, now it's up and here's how I did it.


350 feet of good 3/16" cord

Three (3) stainless steel pulleys (only 2 if your tower standoff arm already has pulleys)

Three (3) weights of the same weight (I cut solid metal bars to 5 pounds each)


A good throw line with launcher

A cutter for the cord

A lighter to melt the cord ends

How To

With a throw line, pull the two pulley cords (the red lines in the drawing) up and over the two support branches. Temporarily, leave the end with the pulley within reach from the ground.

Attach a cord to each end of the dipole antenna. 

Pass the antenna cords through the pulleys, leaving a generous length of cord on each end to accommodate for it's final horizontal length and vertical height. 

Temporarily attach a weight to each of these antenna cord ends.

If you are using a center support cord, attach a cord to an insulated center part of the antenna. Take the other end and run it through the center pulley. Tie a knot so it can't fall out of the pulley.

Pull the pulley cords, lifting the pulleys to full height. Leave about 18 inches of cord between the pulley and the support branch. While lifting the pulleys, the antenna cords should be moving through the pulleys and start raising the antenna.

When the pulleys are up in final position, cut the pulley cords just above ground height. Tie a loop and attach the loop to the base of the tree with a screw eye.

Pull the center antenna cord up to bring the antenna center into final position. Just above ground level, cut the cord and attach a weight. Temporarily secure this line to the tower to maintain the center positioning.

Pull the end cords to bring the antenna ends into final position. Just above ground level, cut the cords and attach the weights. The weights must be free to move, unrestricted, up to the pulleys.

Remove the device temporarily securing the center cord and weight. All three weights should now be just above ground level and free to move up as needed.

From time to time you may need to lower the antenna, so keep a length of cord to attach on the pulley lines for lowering. 

With this system, there is no extra cord laying on the ground to get caught in the lawn mower!

Enjoy your free-floating, suspended wire antenna without worry every time a storm blows!

Sep 3, 2020

FT-7900R ZUM Repeater Build - Part 3

Over the last two weeks, I have been experimenting with various settings on the FT-7900R ZUM Radio Pi-Star repeater. After going through frequency calibrations, TX delay and TX/RX offset settings, I'm still having an issue with one particular thing.

The Problem

I have been unable to mitigate what seems to be a delay in the digital processing. This occurs after releasing the PTT of a transmitting radio. A short <1 second clip of the last transmission is heard coming back over the transmitting radio from the repeater. If you have ever heard a short-path long-path echo, you know what I'm trying to describe. It's more annoying than anything else, but something I'd rather not have happening, if at all possible.

Having gone through everything I could think of with the Pi-Star software settings (a short list for me), I began looking at hardware. Everything appeared to be working as it should, but then I had a light-bulb moment: "Maybe it really is a signal processing-induced delay."


The repeater is built around a Raspberry Pi 3 B+ that I once used as a desktop computer, even though it was pretty slow. When the Raspberry Pi 4 came out, I made the 3B to 4B change, and Wow! What a difference in performance! So if it made such a huge difference in a desktop environment, I wonder what it will do in a repeater controller environment. There's one way to find out.

A few minutes later, I had the Rpi 3 B+ disconnected from the ZUM Radio controller and replaced with a Raspberry Pi 4 B 2GB fitted with a full heat sink case and Argon programmable fan. I swapped out the Raspberry Pi OS card with a back-up copy of the Pi-Star repeater image and in under five minutes, the repeater was up and running.


Almost any reasonable thing is worth trying when you are experimenting. For this repeater project, it has been a little of this. a little of that, old parts, spare parts, and a lot of fun. As for the Raspberry Pi 3 B+ to 4 B computer swap, I hear no perceptible difference with the original delay echo problem.

Hey, if nothing else, it looks like the blinking LED on the USB/Serial converter for the Nextion display is blinking a little faster, but that could just be me. So for now, I'll leave it with the Rpi 4 B and monitor the CPU temperature and Argon fan activation cycle frequency for a while.

New Hypothesis

Maybe the delay echo is caused by the collinear antenna setup feeding back, even running at very low power. I guess I'll find out when I get my frequency allocations from the Wisconsin Association of Repeaters and get a duplexer ordered, tuned, and installed.

Aug 25, 2020

DMR Trials and Tribulations

First off I have to say, if I had started in amateur radio with DMR, I might be typing a blog right now for some other interesting hobby. From that, you can probably guess the last several days have been, oh, less than fun, more than troublesome, and filled with frustration over DMR.

It all started when I was downstairs looking through some boxes for coax ends. Buried in the bottom of a box, I found my virgin, never-QSO'ed, plastic bagged and ready to sell, new Tytera MD-390 DMR handheld radio. The castaway. And yet again, a reminder that gut feelings can be very meaningful and should not be ignored.

Forgetting the past, and ever-hopeful for a better today, I pulled the radio and it's paraphernalia from the box and brought it all upstairs to my desk. In hindsight, this was the first of several follies that day.

Carelessly ignoring the admonishments offered by my better conscience, I opened the plastic bags. Immediately, it seemed the radio was cooler looking, brighter, more awesome than the last time I remembered. It felt so good in my hands. Was I mistaken before? I thought I came to hate this radio. But now it seems so good, so right, so tech-savvy cool. 

Yes, with all the enthusiasm that purportedly follows the DMR mode, I recklessly dove headlong into re-researching codeplugs and DMR repeaters in Wisconsin. 


Day 1

Maybe I just didn't give DMR a fair shake the first time.

Oops, I forgot I deleted the Tytera CPS software from my Windows 10 laptop because it caused problems and crashes. Ah, but I'm sure there's been updates... 

Google search.  Hey, there's a firmware update for my radio. I should probably do the update so I have the very latest technology for this awesome radio. 

Download firmware update. Downloading... still downloading... the CPS software. 

Man, HughesNet is slow! Fifty five minutes to download a 73 megabyte file! ... Finally! 

Install. Okay. Hmm. 

Reinstall. Click, click, press and hold, power on. Update. Finished, I think (in Chinese). Cool(?). 

Power on. What?! White screen?! $#@%!

Google search: white screen md-390. No. No. Ah, okay. 

YouTube. Ten minutes later, the radio is in pieces.  Hmm. On the inside, this radio doesn't look exactly like the one in the video. Ah, bad advice. 


Google search.  No... No... No... Yes. Download and revert to the old firmware.  Success, if you can call it that.

Three hours later. I'm right back where I started, but now I'm hangry. Time for a late lunch. 

What a crappy day so far. You know, I think I've had enough DMR for today. I'm sure when I pick it up again tomorrow, everything will work out just fine. I mean, people on the internet are so excited about DMR, like it's the biggest thing in amateur radio since, since Al Gore invented the internet. Right?

There it is, sitting on my desk, staring at me, begging me to build codeplugs and get on the air! 

Alright already! There's still time left in the day. 

Google search: wisconsin dmr codeplugs.  No, wait. I can only use the TG's that are on the repeaters. 

Google search: wisconsin dmr repeaters.  Hmm. Okay, that's not very many repeaters, and why are most of them around southern interstate roads? And why aren't the TG's listed? Oh well. I'll just pick one...

Google search: chicagoland dmr.  Okay. Here's a big list of the TG's and repeaters under ChicagoLand CC. 

What, no downloads for the popular MD-380/390? 

Oh well. I'll just build my own codeplugs from this giant spreadsheet they provide. 

What, only in PDF format? Where's the CSV file? 

Okay, I'm just going to make codeplugs for the closest four repeaters. 

Okay, I'm just going to make codeplugs for the best sixteen TG's for the four closest repeaters. 

Okay, I'm going to pick this up in the morning.

Day 2

Ah, fresh coffee in the morning, and there's that awesome DMR radio just waiting to get on the air! 

Man, what's up with the CPS programming software? I can't read Chinese. Oh, that's better. Now go to import... 

Where's the "import" button? No import button. You've got to be kidding me. 

Wait, there's import... Import .txt file? But what text format? 

Export useless file I saved from last year to see it in the .txt format. You have to be kidding me! 

Two hours later. There, I finally have a Contacts list to import. What crappy software. 

How do you sort it alphabetically? Great, no way to sort Contacts, or anything! 

Finishing up the codeplugs. Oh wait, that's just one repeater... Ugh!

There must be a better way to do this! The internet said everyone and his brother has the TYT MD-380. The MD-390 is just an upgraded MD-380, so that's good, right? 

Google search: rt systems md-380/390.  What, no software?! 

Google search: chirp md-380/390.  Oh, of course, nothing. I guess I'm stuck with this Tytera CPS software that crashes more often than the test dummies at NHTSA!

End of day two, and I think I'm done. 

I now have four (4) ChicagoLand repeaters, each programmed alike with the same sixteen (16) TG's. Let's see, that would be sixty four (64) codeplugs to get sixteen (16) TG's on four (4) of the many (lots of them) ChicagoLand repeaters. 

Somehow I feel sort of disappointed after considering the cost/benefit analyses here. 

Finally, it's time to make this awesome radio fly the airwaves! 

Click, click, twist. Power on.  I'm on the big X300 antenna on my 55 foot tower with 5 power-packed watts of pure DMR! 

Click the PTT and... ... ... burp!  What, no Milwaukee tower connection? I'll try Allenton. 

Click... ... ... burp!  This is a bummer, for sure.

Okay, how about simplex? Yeah, that will work! Oh wait, do I need codeplugs for simplex?

Day 3

I'm heading to HRO with Stu for stuff. 

Hey, I'll bring the DMR and see if I can connect to Milwaukee when I'm down there. Cool! 

Power on, beep, on Milwaukee 'Wisconsin TG". Push PTT... dit, dit, dit. Hey, I'm on! Way cool! 

Listening... nothing. "This is K9KMS, first time on DMR, on the Wisconsin TG, Milwaukee repeater."

Nothing. Hmm. "This is K9KMS, first time on DMR, on the Wisconsin TG, Milwaukee repeater." 

Nothing. Now it somehow doesn't feel right to say, "first time on DMR" again. 

Still nothing heard. I know, I'll try TAC310... 

Still nothing heard. Okay, I'll go back to the Wisconsin TG.

Hey Stu, maybe I don't have this programmed right. It seems right. I mean, it beeps like the tower recognizes me, right? A fast dit, dit, dit? I'm on, right?  

What's that, Stu?... DMR means Digital Mobile Radio. It's like... Oh, never mind. 

Lets try Wisconsin TG again. "This is K9KMS, first time on DMR (not really any more), on the Wisconsin TG, Milwaukee repeater." 

Waiting, waiting... then, "Blah, blah, blah". Cool!

"Station ending in blah, blah, blah, this is K9KMS, my first time on DMR and I'm checking to see if I programmed my radio correctly. How is my audio?"

Answer: "Well I'm talking to you, aren't I". Okay, I can see this is going to go really well. 

Blah, blah, blah... blah, blah... (for five minutes...). Does this repeater not time-out or something? 

"Okay, well I'm destinated, so I have to go. Thanks for the QSO. K9KMS, 73". "Blah, blah, blah, bye." 

Well, that was interesting, eh? Somewhat disappointing, but interesting, eh Stu? 

What's that, Stu? ... It's like C4FM but different, you know, with time slots, two of them, and these color codes, and talk groups, which are sort of like rooms, and you have to build lots of these things called codeplugs, one for each... Oh, never mind. 

Where do you want to go for lunch? ... How about the Jewish deli? Sounds good. 

Powering down...

Aug 15, 2020

FT-7900R ZUM Repeater Build - Part 2

October of last year I set out to make a MMDVM repeater with my Yaesu FT-7800 and FT-7900 transceivers. At the time, the setup was in simplex mode as I researched duplexers for the two frequency, one antenna system. And there the project sat in the shack just taking up space and collecting dust. With my invested time accumulating and the research folder growing thicker, I found several characteristics about my repeater build that I decided to change.

Enclosures and Heat

In the former computer case with all the components situated side by side, the homebrew repeater occupied a large footprint in the shack. Taking a second look at this, with the transceivers being the same size and short in height, stacking them greatly reduces the required footprint.

Since my components already have protective cases on them, placing everything into yet another case is unnecessary and only inhibits heat dissipation. In the stacked configuration with the receive radio on top, mounting them on a single Yaesu SMB-201 cooling fan will allow better open-air circulation as well as direct fan cooling to the bottom of the transmitting radio's heat sink.


For now, I am keeping the repeater in the shack, so a second power supply is not needed. My Yaesu FP-1030A has more than enough capacity to run the repeater while also running my FT-991A, FTM-7250, and a few other accessories. If and when the time comes to move it out, I have a 23 amp power supply with an attached RIGrunner 4004U ready to go. This will not only power the two radios, but the RPi controller as well with it's two USB 5 volt ports. Handy dandy cotton candy!
Raspberry Pi Cooling

The Raspberry Pi 3B+ and ZUM Radio GPIO hat setup I originally made was satisfactory, but a passive cooling setup would be better. To fix this, I put the RPi in an aluminum heat sink case, added a programmable Argon One Artik fan hat on an extended GPIO, and placed the ZUM Radio board on top of that. I placed the Pi setup on it's side (GPIO edge down) to allow better natural airflow up the warm faces.

My three other Raspberry Pi 4B's require cooling so each have an Argon One fan, but in this 3B+ application it really isn't necessary, though it's a nice feature to have if things do get too warm. I programmed the fan to turn on at 42 degrees C at 10% speed. With this, the fan rarely activates, and then only briefly. The higher quality fan, reduced run time, and modified speed should greatly extend the life if this setup. After watching this setup for some time, I found the Pi temperature stays around 39 C with only passive cooling.

Here, the MMDVM repeater RPi is on the left of my shack's four-Pi setup. All computers are on a LAN switch to help reduce RF exposure in the shack.

Wiring Harness

One thing I don't like is having a harness that's too long or too short for whatever the project is, especially in the shack where extra wires can turn into interference-producing antennas. For this reason, I modified the harness and made two ends using two standard RJ45 jacks. The DIN cables were shortened to 16 inches and combined into a single RJ45. The repeater board connection was also joined to a single RJ45 jack. The two components now connect together with a standard computer network cable of whatever length is needed for the components' location. Perfect!


The biggest change of plans may forgo the use of a duplexer and single antenna setup. Instead, I may go with a less expensive collinear setup using two Diamond X50 antennas mounted on separate tower standoff arms. I've been running a similar setup at 5 watts for a short time and found it works quite well. So far, I have one LMR400-fed antenna up and working on the tower arm.

Considering my location in a tall forested lakefront area widely known as a difficult corridor for RF, and having a tower only 55 feet tall, there is no point in spending a lot of money on any setup here. Besides, this is for experimentation and just having fun with RF. That's a big part of what this is all about, right?

Nextion Screen

Having all this figured out left me with a little unused creativity, so I redesigned my Nextion screen appearance and layout. Thanks to WA6HXG for the original Nextion 3.2 HMI file, I just moved a few things around, changed the fonts and background images, and called it a day. The colors in this photo are off, but you get the idea. Still on the to-do list are: (1) purchase and install the X50 antennas, and (2) receive frequency allocation from Wisconsin Association of Repeaters.

Jul 7, 2020

Updated Shack - Episode II

I thought I was done making changes and additions to the shack, but I guess not. Just as summer arrives, so too, some new things have arrived at the shack.

The first addition to the shack is a Heil PR781 mic mounted on a PL2T boom, with a Pro 7 PTT hand button. The CC-1-YM wire harness connects everything to my Yaesu FT-991A. Using the equalizer settings suggested by Bob Heil, the audio reports are very favorable to this setup. Thanks Bob!

The second addition is KF7P combo antenna tower standoff arm which now suspends the center of my trusty old Barker & Williamson BWD-90 folded dipole antenna in a flat-top configuration at 40 feet. The antenna's heading is 140-320 degrees. So far, signal reports have been very good, but no DX attempts as of yet. Field Day, 13 Colonies and other special events, and POTA stations have been my focus for most of June. The 10 meter openings afforded fantastic QSO's all over the USA. A review of my log should help map out what the antenna is doing in it's current configuration and location.

The third addition is an MFJ-4712RC remote antenna switch between the BWD-90 folded dipole and the GAP Titan DX. It is interesting switching back and forth between each antenna and hearing their different characteristics. The folded dipole is far quieter and much better at pulling out even the quietest of signals. Love that Barker and Williamson BWD-90!

The Raspberry Pi computers also got an update. The 8G and 4G RPi's now sport an Argon Artik fan hat on top of a Geekworm heat sink armor case. Talk about nice! The fan hats are programmable for temperature and fan speed settings in custom configurations. I set mine to run 10% at 43 C, 25% at 47 C, 50% at 50, 75% at 53 C, and 100% at 56 C. With the huge Geekworm heat sink, the fan hat runs maybe every five minutes for a short time, even with the RTL-SDR dongle running the CPU with a constant 20-30% load. And with temps never getting above 43 C and the large fan running at only 10% every time it turns on, they are extremely quiet. No more worrying about heat on a Raspberry Pi 4!

The latest addition is the software package Barrier from the Raspberry Pi OS repositories. Super simple to set up and run, this package allows me to run my two (or more) desktop Raspberry Pi computers from one keyboard and mouse setup. Simply slide the mouse cursor to the edge of the screen, and it seamlessly goes to the other computer and screen. My small desk space just got a lot bigger with only one keyboard and mouse on it! Amazing! Open a terminal and run sudo apt install barrier on each computer. Select one as a server and the rest as terminals. Details here.

May 10, 2020

Updated Shack - Episode I

The planet earth has seasons, and that's a good thing because who can take twelve months of winter? I go through seasons too, probably just like you. Sometimes I get kind of bored with things and just need a change. Other times, after using something for a while, I get to a certain level of frustration that I ask myself, "Why do I put up with this?". Then the creative juices begin to flow and my tiny Shack gets an update!

I decided to take my credenza and add a small shelf to the front to hold a keyboard or two. Then I added a small back-angled shelf on top to hold the radios and allow small storage under the radios. Lastly, I added a back panel to mount two monitors, an antenna selector switch (behind the right monitor), and a RigRunner 4007U (below the monitors). The HP VH240a HDMI monitors with built-in speakers are mounted with Mount-It! MI-2829 tilt-swivel brackets. Two large pass-through holes at the base of the back panel put all wiring behind the credenza for a nice, clean install. A small shelf up top is home for the HTs, the ZUMspot and some other small things.

The shack is now run entirely on a Raspberry Pi 4B 4GB with the latest Raspberry Pi OS. The Debian Ham radio bundle which includes CQRLOG, JS8Call, WSJT-X, FreeDV, and a few other helpful programs, drive my USB connected Yaesu FT-991A. A Rowetel SM1000 sits to the right of the FT-991A. Also pictured is a Yaesu FTM-7250DR, and my old FT-7800R which will be trading places with my less-old FT-7900R, now used for local repeaters and simplex in my workshop.

Right now, I am quite content with this setup. But yes, I still have to get the old Barker & Williamson BWD-90 folded dipole up for HF. I like the GAP Titan DX, but verticals are so noisy compared to the folded dipole. And then I should probably do this, and maybe do that, or maybe just... be content!

So now I can enjoy Ham radio again at my tiny new shack. And then the next season will come. Change can be good, and God is always good!

Oct 14, 2019

FT-7900R ZUM Repeater Build - Part 1

Here is a project involving a ZUM Radio duplex MMDVM and a Raspberry Pi 3 B+ combined with my trusty old Yaesu FT-7900 and FT-7800 radios, and a couple of mini-DIN cables. Together, a trial version of small digital all-mode repeater capable of full duplex D*Star, DMR, NXDN, P25, POCSAG, and Yaesu System Fusion should be the result. If this works out as expected, I will likely be seeking out an old GE Master II, or any other robust analog repeater, to handle whatever mode is selected.

Pins and Colors

So it's been a little while, and I finally figured it all out. Part of the problem I found was the Yaesu CT-39A mini-DIN wire color was incorrect for the pin location. So lets forget about colors and talk straight up pin number to pin number. Conduct a simple ohms test on your mini-DIN cable pins to determine what color goes to what pin (my Electronics-101 oversight...)

As stated on page 10 of the Yaesu FT-7900R user manual, the pins are identified by both number and function. Using this, combined with the pin information from the ZUM Radio, I found the following connections to work properly using one FT-7900R as a simplex digital mode repeater.

Note: Two wires on the CT-39A mini-DIN are not used: Yellow (RX1200), and second Black (shield ground).

The pins - looking at the back of the FT-7900R - are identified in the following locations. The locator tab will be at the bottom center.


Pin 1: top left - PKD (DATA IN)
Pin 2: top right - GND
Pin 3: middle left - PTT
Pin 4: middle right - RX9600
Pin 5: bottom left - RX1200
Pin 6: bottom right - PKS (SQL)

Keep in mind, this will transmit when anyone keys up on the WIRES-X, YSF, or FSC rooms you are connected to. Be sure to keep the power as low as possible for your needs, and share the air.

Now to get a repeater frequency allocation from the Wisconsin Association of Repeaters and get this working as a duplex repeater!

Pi Cooler

The Raspberry Pi ZUM repeater board gets a new case and a custom fan install to keep things nice and cool. This is a HiFiBerry box, which is tall enough to have a GPIO hat and a fan inside. I cut a 1.125" in the top and mounted a Pi fan inside, blowing directly down on the ZUM Radio hat and Raspberry Pi. Temps stay under 40 degrees C.

Repeater Case

There it was, down in the basement. A lonely old Windows computer that has seen it's better days. Perfect! I gutted all the hardware out, saved everything that was still good, and prepared the case to be converted into my new ZUM repeater box.

I was able to rewire the existing power supply to reduce the number of wires clumped together for the previous occupant of this case. Now I have 17 amps of 12 volts, 18 amps of 5 volts, and 11 amps of 3.3 volts available, all regulated and fan-cooled. This works out perfect for all my needs.

Getting everything positioned in the case is pretty easy, so long as the fans have coordinated air movement over the radios and through the case.

I'll need to fabricate a new front face plate to incorporate the two radio faces, a Nextion touch screen, the voltage and temp monitor, and the power switches. The Raspberry can be controlled via SSH, but a re-program of the Nextion screen can provide the shutdown capabilities I am looking for. It should work well and look pretty nice when it's all done.

Propagation Estimation

I found a tool online to help estimate propagation from the repeater's site at Radio Mobile Online. The parameters I used for the estimate are a 6 db vertical antenna at 55 feet on 146 MHz. This, of course, only gives a general idea of coverage. The actual specs will be used as soon as I get the frequency allocation from the Wisconsin Association of Repeaters.

This map is at 5 watts output. Since the goal is to serve the surrounding communities, I would like to keep the repeater at 5 watts to prolong the life of the FT-7900R driving the repeater, but a real-world test today around the area had the 5 watts barely making 5 miles; at 6 miles there was almost no squelch break on the Yaesu FTM-400XDR in the car. I was always told to expect one mile per watt on the ground, so I'm not really surprised. My Diamond X300 antenna, at 55 feet, is basically on the ground, here in the woods.

For comparison, I can hit the WE9COM repeater in Plymouth from my QTH using my FT-70D and FT-2D on 5 watts. The RFinder app lists this repeater as 14.1 miles from my QTH. This is 2.82 miles per watt. Here is an example of antenna height making all the difference.

Below is a map I made with a 5 mile, 10 mile, and 15 mile radius. If one watt per mile on the ground holds true, this map should be better aligned with real-world expectations and performance.

Dressing Up

I was able to acquire a nice piece of 14ga steel for the front panel of the repeater case from a friend at local metal shop. I mapped out where the various parts will be located and look forward to getting into the shop to get it all cut and finished. Hey, if the repeater looks good and works good, I will me a happy ham. Is this metal floating over my desktop? Well anyway, we're on the road to success here, I think...