IC-502 + DigiVFO

 The Icom IC-502 from the mid 1970's is a standalone 3 watt, 6 meter band SSB / CW transceiver.  I've made contacts with this radio during e-skip openings.  Its a tough little radio to tune because the knob requires the steady hand of a safe cracker to operate.  It also drifted with the original analog VFO during a conversation.  The original VFO is a completely analog device, with less accuracy that we're used to the 21st century.

QRP Labs came out with their Digi VFO product late in 2025 based on the popular Prog Rock 2 product.  This tiny board now boasts a display and rotary encoder, as well as CAT control capability for a modest price.

Based upon the suggestions of others in the amateur radio community, it seems rather easy to remove / or simply disconnect the original VFO and use the Digi VFO in its place (after providing a good low pass filter), The attenuated signal came out to be just less than about 1 volt peak to peak.

The original VFO was easily removed with only 4 electrical connections.  The gear reduction drive and VFO unit separated with just two set screws.

The plan was to make a mounting plate for the Digi VFO and mount it back in the original location and use the original knob.  This required a shaft extension, but that's a simple mechanical adapter that I made on the 3D printer out of PLA with carbon fiber for added strength.

I mounted the Digi VFO board directly to the rotary encoder assembly simply because it was convenient to do so.  The low pass filter design ended up being a modification of the QRP Labs LPF kit to turn the square wave output into a smooth fundamental 36Mhz to 38Mhz signal out of CLK0 pin.  The BFO setting is at 13.99600 Mhz and Low setting for a heterodyne radio Local Oscillator injection. In the Digi VFO setup menu and starts displaying at 50.100 Mhz for convenience of the operator to produce at 36Mhz output at a display reading of 50.000 Mhz

(The Digi VFO could use an option for 10Khz per knob rotation to move quickly through the band with the single click of the knob, but I won't knock the product. It is very good.)

Packaging is key.  At least when the new product is displacing a much larger component, it makes it easier.  I managed to solder everything to mount to the rotary encoder with shorter jumpers than in the previous photo.  It fits nicely in place of the original with a carefully manufactured adapter plate.  The output of the low pass filter is clean and sinusoidal.  The spectrum analyzer shows a clean output from the transmitter.

The result was so encouraging, I decided to modify the original radio cover to accommodate the frequency readout.  The display sits directly above the VFO tuning knob.  The tuning knob uses a shaft extension to employ the original tuning knob without the reduction gearbox.

This project was a complete success bringing life back to an excellent product.

APRSTASTIC: Automated Packet Reporting System with LoRa Mesh Networking at W3HZU

The W3HZU Keystone VHF Radio Club is embracing innovation with the APRSTASTIC project, utilizing MESHTASTIC firmware over LoRa to transform Amateur Radio Positioning System (APRS) communication. Traditional APRS relies on a network of fixed stations.  Traditional APRS on the 2-meter band typically involves devices sending packets with location data and other info to an APRS digipeater (digital repeater) or an Internet-connected gateway (IGate). These packets are usually transmitted at 1200 baud using AFSK (Audio Frequency Shift Keying) modulation.  The APRSTASTIC software project takes it further by leveraging a mesh network on the 900 MHz frequency.  https://github.com/afourney/aprstastic 

So, how does it work? APRSTASTIC, created by Adam Fourney KK7CMT, is a project that integrates MESHTASTIC firmware with APRS functionality. It allows devices to join a mesh network, broadcasting APRS packets that include location data, messages, and more. These packets are transmitted over LoRa modulation, which offers long-range, low-power communication ideal for this setup.  Only amateur users are permitted to use the APRS network, so the software requires users to register with the service.  This attaches the eligible user's callsign to messages and allows access to the gateway functionality.  The basic function of GPS tracking is supporting reporting mobile node location to the APRS map.  As part of the mesh, devices can relay signals, extending the network's range and coverage. This makes APRSTASTIC particularly useful for tracking, emergency communications, and community networking – all without needing extensive infrastructure.

APRSTASTIC presently supports features like SMS messaging and Winlink integration, making it a versatile tool for emergency communications, and remote messaging.  The hardware consists of a Heltec V3 LoRa node running Meshtastic firmware.  The short name is assigned "APRS" and the long name is "W3HZU-12".  The Heltec V3 board is attached to a Raspberry Pi computer with a simple USB-C cable.  The Raspberry Pi runs the APRSTASTIC python software package on a fresh install of the standard Raspbian OS.  Very little customization needs to be done to get this running.  It is low-cost and low power.  The club member Ron K3HIL developed a few linux cron job scripts to keep APRSTASTIC running reliably, and restarted if there is a problem.  The W3HZU-12 node communicates easily to the repeater node on the club's 100 foot tower, which supplies APRS network access for many miles in York County, into parts of nearby Lancaster and Lebanon Counties, and lower Dauphin County.  Infrequently the APRS node announces its presence and invites amateur users to register by replying with a Meshstastic message containing a "?"

At W3HZU, this technology is opening new doors for radio enthusiasts.  It is a stepping stone to gain interest in licensed amateur radio, as we have a large Meshtastic user community in the tri-county area.  The project's open-source nature, hosted on GitHub, invites collaboration and customization, making it a promising development for the amateur radio community advancing the art of radio.  Club members Eric N3FIX and Ron K3HIL have been working to encourage the maker community to join forces with the Amateur Radio community in this project.  The support received from both the Keystone VHF Club and the Susquehanna Valley Mesh community has been mutually beneficial.

https://www.w3hzu.com/aprs-gateway/

FT-817 FT-818 Bluetooth Digital Mode Adapter

 Discovery of the BG6LH Bluetooth Digital Adapter board for the Yaesu FT-81x radios lead me to build one of my own.  The boards were sourced from JLCPCB company based on the provided Gerber files in the github repository.

I modified the population of the board slightly, since my FT-817 was already modified to only power the ACC Pin 1 (+13.8v) when the radio is ON.  This was greatly preferred to eliminate the transistors Q1 and Q2, and freed up the PTT pin.

I also brought out ACC Pin 2 (TX GND) to a flying lead so the radio could key my external amplifier.

The final product is excellent, however the driver can be a bit twitchy.  Make sure to connect to the Bluetooth module first, before trying to access it with Android software, or the Android device will just use its internal speaker.AT-NAMAFT-187-AUDIO

I also renamed the Bluetooth SSID to FT-817-Audio per this Instructable.

AT+NAMAFT-817-Audio

Parallel Dipole for the 6 meter band

 My 3 element gamma-fed yagi crashed about a year ago.  I hadn't done anything with it, and its mangled carcass has been lurking behind the shed.  Recently my club built a cage dipole for 40m, which got me thinking.  Why couldn't I just make a cage or parallel dipole for 6 meters?  It should work.

So over lunch I took the old antenna apart, and tossed the broken pieces.  There were enough good parts to make my experimental parallel dipole.

The pieces I had left over were just a tad short, so it does cover the whole band at 1.5:1 at top of the band, with the ideal resonance somewhere around 51Mhz.

Mobilinkd TNC4 and Alinco DJ-F1

 Yes, the Mobilinkd TNC4 will work with the Alinco DJ-F1 handheld transceiver.  The PTT needs to be set to Multiplex.

The required cable is not shown on the website, since this Alinco radio is fairly old.  It does work well, however.

AEA Iso Loop 10-30Mhz antenna

We were given this AEA Iso Loop which covers 10 to 30 Mhz.  The date codes go back to 1982, and for the age its pretty good.  It was really quite difficult to keep in tune.  The mechanism was sloppy and needed some tender care and improvement.

There are a couple things to look for when restoring one of these.  The axial play must be eliminated to keep the capacitor in a precise location.  Also any gear lash must be eliminated.  Watch the video to see what was done to repair this antenna.

Here's the detail of where the additional screw was placed for the motor bracket.

Beam Me Up! Star Trek TOS Communicator for 70cm

 I've been a life long Star Trek original series fan.  Yes, it is pretty nerdy I know.  I was talking with my friend Ed KA3LJL about what it might take to create a working communicator.  We tossed around a few ideas and I settled on the Chip Carter toy that came with a nice illustrated book.  For the price I couldn't go wrong, or could I?  When it finally arrived just before Christmas, I discovered that this toy is actually 2/3 the size of the original series prop from the show.  Ok, so now I have a real challenge in miniaturization.

The heart of the working amateur radio 70cm band communicator is the SA818 module.  This little wonder costs less than the communicator toy did and will put out 1 watt on high power and 1/2 watt on low power.  To maximize battery life, low power is really all that is needed.  The purpose of this build is to create a small HT that I can use with my AllStarLink node around the house.  And I could also use it at hamfests to impress my fellow nerdy friends.

So the first thing to do was take the toy apart and see how much room was in there.

The SA818 runs easily from a single Lithium Ion battery.  I had a very small battery from an old GPS that still held a nice charge.  This fit PERFECTLY into the toy.  The sound board and internal speaker would have to go.  There just wasn't enough room to maintain the original sounds.  (Maybe I can program AllStarLink to make the sounds?)

There were a lot of supports in the plastic case that had to go as well.  I made a hot wire plastic cutter and went to town slicing up the internals of the case.  The original coin cell battery door would be used to hold a pin header for frequency and tone programming.

The swirly "speaker" would also have to go and be replaced with a real speaker.  The module doesn't produce enough audio for a loudspeaker by itself.  I had to get a little amplifier board to get sufficient audio output.  Despite the SA818 application datasheet showing that a mic could drive the input without a pre-amplifier, this was also not the case.  I had to create a preamp board for an electret mic element.  It was probably the toughest part of the build.  I made it out of surface mount components except for the low gain transistor.  the circuit works a little too well, and the gain had to be dialed back with a few resistor modifications.  In the final version I removed the mic gain adjustment and just left it at a fixed value.  The element was then soldered directly to the board.

The whole system was mocked up on a breadboard just to test the functionality and audio quality.  I didn't want to start building and packaging the final product without a good understanding of how the whole device performed.  The next part of the build took weeks of planning with only a few components added at a time.

One big design challenge was to come up with a functional antenna.  I was just going to use a dummy load resistor to keep the module happy, but that just wasn't practical.  I may want to take this down through the neighborhood on a walk, so I wanted a real antenna.  I tried a magnetic loop for 70cm.  It worked, it was very narrow and it was efficient.  The problem was that it would not fit in the case.  Ed and I kicked around antenna ideas for a couple weeks.  The flip-up grill was supposed to be the antenna, so we decided to make it the antenna.  Some strips of adhesive-backed copper tape zig-zagged back and forth across the grill made a perfect antenna.  I was able to use my NanoVNA to get everything trimmed just right.  The antenna would eventually be fed by a small low pass filter board that I bought on eBay.  It is actually pretty large, so I'm glad that it fit alright after I took off the SMA connectors.  It was impractical to feed the antenna grill with a piece of wire or coax.  It had to be able to move and twist as the grill was opened.  I created a sliding joint using the copper tape that mated to the case and was fed by a small chunk of RG-174 coax.  This design is frankly brilliant if I do say so myself.  It functions perfectly and affords a wide enough bandwidth and is probably better SWR than most rubber ducky antennas.

With the antenna design proven, I moved back to the main construction.  A main perf board would hold the components.  The battery sits underneath everything else.  The RF board and filter were joined together using pieces of copper strip material to provide a mechanical stiffness.  The RF board was then secured to the perf board by just soldering the tabs.

The preamp and audio output boards would just mount to the main perf board.  The mic would use the grill in the front part of the case.  I glued the original rubber grommet to the case.  This was salvaged from the old cordless phone that I stole the mic from.

One requirement was to have it charge from USB.  I had a USB mini jack from the GPS unit that worked perfectly.  The case was notched out to allow access to the USB port.  The battery has an on-board charging circuit, so I just put a single diode to drop things down from 5 volts to be nice to the charging circuit.

Here we see how the board fits in with the USB charging jack mounted.

The programming port is tucked into the old battery compartment.

The header allows the communicator to connect to a 5vdc FTDI TTL adapter.  Top pin is TX then RX and finally ground.

As things got closer parts were fitting exactly where they needed to be.  A potentiometer with a tiny shaft would stick through one button hole to allow the audio to be adjusted.  A Push On / Push Off switch would serve as the power switch.

Things are very tight in the case.  All the interconnecting wires had to be in just the right spots for the case to close.

The most fiddly part was the PTT button (not pictured).  I was going to cut a hole in the side of the case and just mount it off the main perf board.  This would have been easier, but it wouldn't have been as cool as using the existing holes.  I ended up mounting a tiny tactile switch under the leftmost jewel lamp.  There had to be a lot of precision filing done to make everything sandwich together perfectly.  The other fiddly part was the LED for receive audio.  It put an ultra-blue LED under the rightmost jewel lamp.  It was way too big and had to be filed down to fit as well.  After filing an LED lens it will be cloudy.  Just slather some petroleum jelly over it and it will turn clear again.  (This is just one of those tricks I learned watching MacGyver.)

I'm genuinely please with how this turned out.  It is really slick.  I can stick it in my shirt pocket and flip it open when I get a call on AllStarLink.  I bought enough parts to build two, but I won't do it again with the 2/3 size toy.

Beam Me Up.

73 DE N3FIX

Hi-Par 'Saturn 6' Halo overhaul

 I was fortunate enough to receive this old Saturn 6 Halo antenna from a friend.  It had been stored for the last 25 years.  The aluminum condition was good, but just needed a good polishing.

The fasteners were even in decent shape.  I only replaced the ones at the feed point.

It came without the original matching network.  After reading this eHam article, I learned that the impedance required a 4:1 transformer.  The details of the construction were provided.

I first tried the 25 ohm coax (parallel RG-58) @ 37".  I wasn't quite satisfied with this.  The coax tail was cumbersome and the match wasn't quite as good as it might be.

I then wound the wire transformer.

8 turns of 14 gauge around a 9/16" form spread 2" long.

One end connects to one feed point on the antenna.  Two turns in it connects to the coax ground.  6 turns in it connects to the other feed point of the antenna.  The 8th turn connects to the center of the coax connector.

The whole thing fit in a nice plastic enclosure (formerly from a wall wart).  A little squeeze here and there and the transformer functions well with a much better ideal impedance at resonance.  The ability to massage the transformer made it superior to the coax matching method in my mind.

We are ready for Field Day.

HAMVOIP - email on a Raspberry Pi pin status change

 I wanted to have the clubhouse send me an email if the alarm system went off.  The plan is to have a contact closure bring GPIO 0 (Pin 11) logic low on alarm.

The GPIO example didn't include a way to then detect when the pin went high again, so I had to come up with a slight modification.

The first step is to set up email:

https://www.hamvoip.org/howto/Allstar_email_howto.pdf

Then I wrote some clever scripts to perform an endless round-robbin task of monitoring the GPIO pin in question.

The script /home/email_alarm.sh is started from /etc/rc.local

----------------
home/email_alarm.sh
----------------

#!/bin/bash
# Required button hold down seconds
# set mode to in and pullup pin 0 (Physical pin 11, GPIO17)
PIN="0"
gpio mode $PIN in
gpio mode $PIN up
bash home/alarm_wait_active.sh &
exit

-------------
home/alarm_wait_active.sh
-------------

#!/bin/bash
# Required button hold down seconds
HOLDTIME=5
#define pin to watch
PIN="0"
TIME1=1
while [ 1=1 ]
 # wait in interrupt for pin to go low
 gpio wfi $PIN falling
 do
 # Got the low now poll to see if it stays low for holdtime
 while [ `gpio read $PIN` -eq "0" ];
 do
 sleep 1
 let TIME1+=1
 if [ $TIME1 -gt $HOLDTIME ]; then
 # if greater than holdtime then exit past done
 break 3;
 fi
 done
 TIME1=1
 continue
done
# code to execute when holdtime is exceeded goes here
#echo -e "Subject: Pi alarm active" | sendmail -v email@gmail.com
echo "alarm active"
bash /home/alarm_wait_clear.sh &
exit

---------------
/home/alarm_wait_clear.sh
---------------

#!/bin/bash
# Required button hold down seconds
HOLDTIME=5
#define pin to watch
PIN="0"
TIME1=1
while [ 1=1 ]
 # wait in interrupt for pin to go high
 gpio wfi $PIN rising
 do
 # Got the low now poll to see if it stays high for holdtime
 while [ `gpio read $PIN` -eq "1" ];
 do
 sleep 1
 let TIME1+=1
 if [ $TIME1 -gt $HOLDTIME ]; then
 # if greater than holdtime then exit past done
 break 3;
 fi
 done
 TIME1=1
 continue
done
# code to execute when holdtime is exceeded goes here
#echo -s "Pi alarm cleared" | sendmail -v email@gmail.com
echo "alarm cleared"
bash ./alarm_wait_active.sh
exit

Spot Island-style Copper Clad board prototyping

I can't claim to have invented this style of prototype board layout, I'm sure I've seen this somewhere before.  "Dead bug" style prototyping where there is no printed circuit board layout is available is also popular.  The components are glued to a copper clad board in "dead bug" style while the leads are thrust in the air above the board like legs of a dead insect.  This is a messy way to try to attach components.

I prefer this spot island style method, which is similar to Manhattan-style.  Copper clad board is great for prototyping with either through-hole components or even surface mount.  This method isn't appropriate for DIP packages, but for discrete components it works just fine.  A perf board for DIP packages can be used above the level of this method to transition the circuit into IC chips as needed.

We've all got broken drill bits laying around (unless you've thrown them away).  The broken drill bit is still a valuable commodity.  I turned a couple into hole saws for making spot islands on copper clad boards.  First put the bit in your drill or drill press and use a grinding wheel to flatten it back out past the broken point.  Then put it in the vice and cut the center out with a Dremel tool grinding disc leaving only the edges.  This creates two fly cutter blades to act as a hole saw.  Cutting through the thin layer of copper into the circuit board is all that is needed.

Don't try to hold the board in your hand.  The drill press WILL drag it out of your hand the slice up your precious work.  First drill mounting holes in the board and use some screws to hold it to a block of wood.  The wood can be fastened safely into the vice of the drill press allowing for precision machining.  Lower the bit into the board until the copper is machined away leaving an island of copper and a recessed circle of board substrate.  Don't go the whole way through the board.

Once the board is laid out with islands it can be populated using good radio frequency layout practices.  Component leads can be cut short.  In the example below the board is cut with a strip at the top to feed Vcc power to components, where the rest of the board is left for a ground plane.

Here we see the DIP package of an Op Amp floating above the copper clad.  This is done by making "stilts" of components leads.  Once the DIP part of the component is finished, it can be incorporated into the copper-clad board.

When working at VHF frequencies this construction method works very well to keep leads short.  Islands can be drilled and later bridged with short jumps of clipped leads.  I have created two islanding bits.  The larger one can accommodate a hole drilled in the center if needed, while the small bit is good for just a few component leads that must be joined together.

Don't be stifled by a lack of printed circuit boards while experimenting with electronics.  There are many useful circuits that can be manufactured in this way.  If additional RF shielding is required, card stock can be sprayed with contact cement to facilitate the adhesion of ordinary kitchen aluminum foil.  In the photo I sacrificed an old Dilbert comic strip printed on cardstock with Omega advertisements on the opposite side.

The card stock is easily folded up to provide the RF shielding that may be required.  In this project photo below, the entire circuit board is RF shielded leaving only the inductor adjustment slug exposed for alignment tuning.

Chimney Antenna Mount

We had some serious wind gusts with a cold front that moved in.  Usually the winds come in March, but this year they came mid-April. Well, I added one more antenna to the stack.  One more straw that broke the camel's back.  This chimney strap-mount was ok when it was just a 6 meter antenna, but it just couldn't take the wind and all the loading on the mast.

This is how I found it Friday morning.  I had to use a piece of paracord to hold the rotator motor upright and lashed to the edge of the chimney to give myself a warm fuzzy overnight so it wouldn't blow down and wreck all the antennas.

Here we are Saturday morning with the equipment as found.

It took about 3 hours mostly on my own to put everything back together.  The new mount is very stout made out of hardened steel bed frame angle iron.  I stood on it after it was torqued down.  That shouldn't go anywhere.  The antennas were re-arranged in the proper order to minimize the torque moment on the mast.  The 432 is now at the top (center mounted), the 6 is in the middle because it is small.  And the 2/3 rds of the 17B2 Cushcraft is at the bottom because it is so huge and heavy.  I had to put the outriggers on it to support the weight and keep it from sagging.

I can replace the feedline on the 6m antenna later after the roofers have replaced the shingles.  For now we're done.

Happy DX and we're back on the air!