USB Push-to-Talk Interface

12 Feb

Part of most every digital interface box is a switch for the Push To Talk button on the radio. Some radios can do this via CAT control, some hams do it with VOX. In my situation the Icom 718 doesn’t do PTT via CAT, and the radio can hear its own output via the mixer so VOX just doesn’t work. I was sick of holding down the footswitch during digital QSOs, so I needed to go old-school and build a serial interface.

The basic premise of the project is to take a serial line and use it to turn on an optoisolator that will pull a pin to ground. That’s all a PTT switch is, a small voltage from the radio that is shorted to ground and the radio switches into transmit. As an added feature, the morse key line is basically the same.

My computer, like most modern systems, doesn’t have an actual serial port. All of the software I wanted to use has provisions for serial keying and not much else. So I was forced to use a USB to Serial adapter. I chose the FTDI-based RS232 breakout board from Sparkfun (not a sponsor) because it has plated through holes that provide easy access to the proper outputs.

The software gives me two options, RTS and DTR. These lines are supposed to go high when the PTT is activated. So I pushed an LED with a current limiting resistor into the RTS hole and the hole marked GND. This provided me with a nice steady green light that went out when I keyed the PTT in FLDIGI. I was OK with this, figuring I would just have to check a box for “reverse” or something. There’s a box in FLDIGI for “RTS +V”, and that did exactly what I wanted it to do.

I temporarily soldered on one of the optoisolators and connected its output in parallel to my footswitch that is wired into the 718’s PTT line. Everything seemed to work the way it was supposed to until I tested it with DM780. The “RTS +V” option didn’t exist in that program.

So I started thinking that maybe something was backwards. I desoldered the opto, got out my LED and flipped it around, put it in other ports. I tried a lot of stuff with no results.


Sometimes you have to take a break and come back with fresh eyes to see what you need to see. I came back the next evening and started measuring with the trusty multimeter. There was 5v between RTS and ground, DTR and ground, TX-0 and ground, RX-1 and ground, the list goes on. I started to think “What if ground isn’t ground?”  and tried something different. I probed between RTS and DTR, TX-0 and RX-1, and a few others all while changing states with the software. I hit upon something interesting. There was no potential between RTS and TX-0 when PTT was inactive. There was also no potential between DTR and TX-0 when PTT was inactive. When PTT WAS active there was -5v between each of those signal lines and TX-0. I had just found my ground, sorta.

So the whole thing was a little backwards because the LED in the optoisolator is a diode and requires me to think in conventional current flow instead of electron flow.  That just means that I had to think like the TX-0 line was the current source and the DTR and RTS lines were just pushing back with equal force when the PTT wasn’t active.

I had used the demo schematic for the optoisolator in my testing, but I found that the 5v and associated current supplied by the USB to serial adapter was well within spec for the input of the opto. The output side was a very minimal current being pulled to ground, resistors might actually hamper the operation. So I tried it without any of those parts. When it worked as expected I started building. If it fails in a year because those parts are missing, I guess I’ll have to repair it.

I was going to drill off some of the copper to make islands for the opto pins, but I couldn’t find the hole saw bit I purchased for exactly that purpose. So I made some of the ugliest manhattan pads ever. If you score PCB with a utility knife and secure it in a vice, it will break on the line with a nice ragged edge. I made four for each optoisolator and glued them to another piece of PCB with some super glue. While the CA was drying I decided to use RCA jacks for the output so I could move the box to other computers and other radios by building a cable instead of rewiring.

I soldered a piece of shielded audio cable with an RCA end in parallel with my footswitch and made up a RCA to 3.5mm plug. I used a stereo plug but only put the signal on the tip. The IC-718 doesn’t like mono plugs in its CW key jack.

When the glue was dry I soldered down the Optoisolators, ran the wires to the serial adapter, and tested the assembled product with a voltmeter. Everything was working as expected. When I plugged it into the PTT line parallel with the footswitch it didn’t work. 

Yep, just my luck. After thinking for a second I realized that I had just guessed which wire was signal and ground on the PTT switch interface. I flipped those two lines and everything was happy. I even plugged in my DTR line to the CW key jack and it works like a champ.

During setup I made a nice short QSO on 40m PSK. I’ve tested my setup with DM780, FLDIGI, and N1MM and they all worked as expected. I’ve used it with N1MM in a couple CW contests and so far it’s working great.

Every rig is different and every computer is different, but if you take a second to think differently you might find your solution. Remember, the amateur radio license is really just a lifetime learners permit.

Don’t hesitate to leave questions in the comments or on facebook or twitter.



Join the Resistance.


Center Insulators 101

12 Feb

The feedpoint or center insulator of a direct-feed antenna is where the coax meets the driven elements. We’ll focus on verticals and dipoles today for simplicity.

There are a few things a feedpoint insulator needs to do for each kind of antenna. For a center fed wire dipole it has to provide mechanical stability for the wire elements as well as for the center support. It provides RF insulation between the positive and negative side of the antenna, and the feedline attachment point. For verticals it can also support aluminum elements. The center insulator is also a convenient place to put a balun if needed.

Any feedpoint insulator needs a few things to meet these requirements, but some things can be ignored for more portable or temporary installations. It needs to provide RF insulation at the frequency of use and mechanical support for the wires and itself. The ability to handle weather and UV exposure are less important for portable antennas, but very important for permanent installations.

Several materials are available that work well and are popular for feedpoint and end insulators. I’ll go through the pros and cons of each:

PVC is probably the most popular material for homemade insulators. It’s easy to work with common woodworking tools, it comes in all shapes and sizes, and it’s available at pretty much any hardware store. The only real downside of PVC is that it’s not especially good at UV resistance unless it’s coated.

Polycarbonate, or plexiglass, is another material that is available at almost any hardware store. It’s lightweight and resists UV exposure very well. The downsides are that it’s brittle and cracks easily as well as only being available in flat sheets.

Delrin is the most popular material for commercial RF insulators. It is a great RF insulator that really has no downside except that it’s not available at your local hardware store.

Glass and Ceramics are also used for some commercial RF insulators. They are a little more available in the form of insulators meant for electric livestock fence, but you have to work with designs that may not be exactly what you’re looking for.

Many other materials have been used for insulators by hams. Soda bottles or any other type of scrap plastic will work for a portable antenna using thin wire and light feedline. Just remember the things that every insulator needs to do.

Wood was a common material used by hams in the past. It is easy to work, easy to find, and is a pretty good RF insulator. That RF insulation breaks down significantly when the wood gets wet and it tends to rot when not painted. Well before my time hams used to make ladder line with wood spacers that had been boiled in paraffin wax to protect them from the weather and keep them insulating when wet.

The two most common feed lines that hams use are coaxial cable and balanced lines. These lines have different demands for their feed point insulator.

Balanced lines can use a flat piece of material with holes drilled for strain relief and a lift point. PVC boards and polycarbonate can be used for these very easily.

A Coax fed antenna can use a connector secured to the insulator. Be aware that this connector and the connector on the coax have to bear the weight of the coax. I don’t suggest hanging 50′ of RG-8 from an SO-239. Just support the coax on the support structure or loop it over, as long as you mind the bend radius of any co-ax cable. You don’t have to use a connector though, for permanent installations you can solder the coax directly to the antenna elements.

For wire connections you have to make sure you secure them both mechanically and electrically. Mechanical connections are what keeps your wire from pulling at the solder joint. This usually involves a strain relief of some kind. For stranded wire I always tie a knot. It does reduce the working strength of the wire, but it also makes it less likely for the wire to pull out of the strain relief. At HF this shouldn’t make much difference to the RF. For permanent center insulators we like to use eye bolts but for portable antennas a hole in the material works just fine. The mechanical connection has to ensure that the solder never becomes the support for your antenna.

As for the electrical connection, I’ve been working on the lineman’s splice but until then I use the wire nut style twist and solder method. Weatherproof with your favorite electrical sealer and secure from as much movement as possible.

Our favorite center insulator is made by connecting two PVC caps together with a short piece of pipe. We put an eye bolt on top for the hoist rope and two more on the sides to support the elements. The connector is attached to the bottom PVC cap and wires are fed through small holes to attach to the elements. We usually just knot the wires around the support eyes and solder them to the feed wires. If you need a balun, just use bigger pipe and put it inside the center insulator.

Here’s the gist of my understanding about baluns: On a balanced feed antenna you don’t need a balun as the voltage is referenced to the opposite side of the antenna. The matching device should be of a balanced type to prevent common mode current from causing issues. Most T-match tuners have a 4:1 balun built in, this may work depending on the impedance of the system at the desired frequency. On a coax fed antenna the driven side is referenced to ground. As I understand it, your opposite antenna wire is just presenting a resonant ground wire in the proper position to provide the right pattern and to minimize return loss. If you are having problems with RF on the shield of a coax fed antenna it is a good idea to try to choke that off. Several turns on a coil form, some ferrites, or a transformer type balun are all acceptable ways to do this. The feedpoint insulator is a convenient place to put a balun for a coax fed antenna.

I hope this clears up some questions anyone might have about feed point insulators. If you have more questions you can ask them in the comments or on facebook or twitter.

73, Join the resistance.

YouTube Channel

19 Oct

This is awkward.
I just left you here all alone without pointing you toward the other videos. I had planned to write a blog post to coincide with each video. I even write a script and everything. But I forgot.
I’m really sorry for leaving you. It must be lonely without any new posts in such a long time.
Here’s a link to the YouTube Channel, Facebook Group, and Twitter account for the new project:

It’s called “The Resistance” and it’s based on the idea that there’s a lot of misleading information and silly traditions in ham radio. We don’t assume, we test. Just because that’s the way it’s always been done, doesn’t mean it’s right.
Join The Resistance!


The Jumpered Monopole Failure/Success

17 Apr


When you’re a new ham there’s all kinds of things you’d like to have for your station. My friend Alex, KD0YNH, made a wire vertical for 20m and mounted it to the side of his house. The location caused high noise and he didn’t seem too enthusiastic about burying the radials. So he came up with the idea of mounting a vertical on his shed. The shed is made of steel and would make a fairly good ground plane on the high bands. His idea rekindled an idea I had after building my 20m monoband vertical, the jumpered monopole.

The idea was to use EMT conduit due to its price and availability at any local lumber yard. It’s not the best material, but I’ve read about other hams using it successfully. The ½” size nests into ¾” with a bit of a gap and the ¾” nests into the 1” with about the same gap.

I had found many plans over the years for jumpered dipoles. It’s a wire tuned for a higher band, with another wire or wires attached in series to make it longer for lower bands. I thought it might work to insulate the EMT sections from each other and place a jumper between them with some kind of connector.

To make band changes easier we decided to hinge the antenna so a single person could tip it over and connect or disconnect the jumpers.

This drawing was my original plan:


The bottom section would be cut for 10m at 8.27’, the middle section would make the total length 11’ for 15m operation, and the final 5.51’ would bring us down to the 20m band with a total length of 16.47’.

I had thought of the intersections acting as a capacitor since I had once read an article about using a “trombone capacitor” for a small transmitting loop antenna. The possibility that this idea could fail was always in my head, but Alex said he would be happy with a 20m monoband antenna if it didn’t work.

We built the base and first section and mounted it to the shed. When Dan, AB0RE, hooked up his analyzer to the antenna it showed a resonant dip somewhere in the 500 Mhz range. I had forgotten to check for continuity between the driven element and ground. Our mounting bolts through the shed’s steel were shorting out. Matthew, W0ZZY, quickly remedied the situation with a tin shears.

After re-mounting the antenna we found the first section was a bit long on 10m, so we trimmed that up and moved its resonant point to the middle of the band. Final VSWR for a 1” conduit monopole on 10m was 1.5:1 across the band, about what you would expect from an antenna with a characteristic impedance of 37 ohms.

The trouble started when we installed the 15m element. We hoisted it and tested it with the analyzer. The reading was way off. There was a VSWR dip at 36 Mhz, but the whole HF spectrum was 10:1 with a few dips to 5:1. Looking back on it now there might have been something we shorted or missed, but we were in a hurry. With the darkness and some light rain upon us, we decided to forego the experiment and just directly connect the elements.

So we removed the tape from the top two elements and tested and tuned them one at a time, marking the point where they had lowest SWR in the desired band. Band switching would now involve loosening a hose clamp and removing a piece of tube, not a bad solution.

This project taught us a few things beyond the failure of my antenna plan. We were reminded that we need to slow down. Rushing through things can be dangerous with power tools and you may miss some important details.

With any experiment, documentation is key. I had taken some notes about the original design, but did not write down any of the changes, measurements, or analyzer data. So today, I sit here second guessing the reading we used to decide that the overlap idea didn’t work. Taking notes will also force you to focus on checking everything instead of “just winging it”.

The last and most important lesson here is: Don’t be afraid to fail. Matthew was adamant that my idea wouldn’t work. He continued to rib me about the elements coupling to each other as we were building. Others may have changed their mind from the beginning, but I wanted to test it. As they say on Mythbusters “Failure is always an option”.

So the experiment failed, we have one data point. If you have a reason to build a multi-band monopole on the cheap, try it again and let me know if it works for you. Maybe some other material would be a better dielectric than vinyl tape. Maybe you could skip the overlap entirely with some kind of PVC sleve. Or maybe you’re fine with the idea of removing sections of your antenna to change bands, like Alex is.



Thoughts on Learning Morse Code

21 Mar

I haven’t blogged in a while. I’ve even changed the URL of my blog since the last post because I’m now N0ECK. The vanity call was my gift to myself for passing my Extra Class license exam.

While deciding what I should get for a vanity call I had decided that I wanted to make sure it included my initials. Thanks to my geographic location in “0 Land” this became problematic when I asked the most important person in my life what she thought. I’ll just quote her “nothing that looks like ‘cock’ on your license plate, we live across the street from a school”. So, there went the AC0CK that I was hoping for.

I searched around on and found some available calls. I really wanted a 1×2 or 2×1 call for contest purposes. It seems to me that short calls make faster contacts, I could be wrong.

The list was made and I started filling out my FCC application for KA0S (spoilers, I didn’t get it). The backup list was also compiled and was ordered by CW weight. The next one on the list was N0ECK.

Some people say it looks like “no neck” or just “neck”. Nope, it says “No ‘e’ Cory Klumper”. People have been putting an ‘e’ in my first name since childhood. That guy is a distant cousin and he’s way older than I am.

So back to the topic at hand. I chose N0ECK because it has a low “CW weight”. That means it has fewer dits and dahs than the other calls I had on my list. I did this because I’ve always wanted to learn morse, but it’s been a long journey. They say morse is supposed to be easy for someone with a musical background. Well, I have never been good at reading rhythm from sheet music either.

Why would someone bother to learn a skill as archaic as morse code? The telegraph went out of service before my grandfather was born and the last commercial morse station went SK in 1999. For me it was about building my own gear, cheaply.

There are CW transceiver kits floating around the internet for as low as $10. Ok, that’s a “rockbound” rig with no sidetone and an oscillator that leaks to the antenna almost as much as when the plastic final is keyed, but it exists. On a more realistic note, there’s a whole website full of small and inexpensive CW gear over at among other places. I built myself a PigRig, a 40m rockbound CW transceiver with a full 5w of output for less than $50 including shipping and an enclosure.

The great thing about these little QRP rigs is that they can run on a small battery. I grabbed an 8xAA battery holder at Radio Shack and filled it with batteries to test the PigRig, it was perfectly happy and put out all 5w. The little milliwatt rigs will run on a 9V battery for a whole weekend. The small radio and the small battery is great to throw in the backpack with a small antenna. I thought I would bring a minimalist rig along while camping to make a few contacts here and there.

If you haven’t figured this out yet, I love building things. So the idea of building my own rig was a big draw to radio. The simple circuits required to produce a sine wave carrier aren’t very complicated and most anyone who can read a schematic should be able to construct a simple CW transceiver. I’m working my way toward some phone/data rigs but, you know, baby steps.

Another really cool thing about morse is that it’s very efficient. Since the transceiver only has to focus on a small bandwidth the receiver can be more sensitive and selective. The transmitter can focus all of your 5w into a tiny little sine wave instead of spreading voice out over 3kc. This means that a CW radio that puts out 5w is a lot like operating a full 100w on SSB. Which also means that running a full 100w is like running a full KW on voice. Learning morse code is a LOT cheaper than an amplifier.

Everyone in the US speaks english, albeit some better than others, but those scary parts of the world that are not America have some really cool people. I’d like to talk to them. They may not be super interested in learning how to speak english, but learning a few things so you can carry on a basic QSO in morse is less difficult. When I watch my new favorite DX cluster, , I see a lot more DX working CW.

So you’re saying “you had me at small and portable”. How do I learn this magical code? I wish I could give you a good answer, because I still suck at it. I recently had my first unassisted QSO and I’m still scared to send the QSL card because I’m not sure I got the guy’s call right.

Here’s what I did, hope it helps. First, I decided I was going to learn morse for all the reasons listed above. I also thought about all that space marked in red on the band plan and what cool stuff might be down there. Digital modes had proven to be a pretty good “lid filter” and maybe CW was the same way. I decided to learn and put my mind to figuring out each character. I listened to some training mp3s I found on spotify and even made some of my own to try to learn while I was driving. This helped me get all the letters and numbers learned, but it wasn’t enough to really get me on the air. I could call CQ and see my spots on but I couldn’t copy strong enough to hold down a QSO.

The morse decoder in FLDIGI worked pretty well, so I gave up the fight of trying to get better at decoding in wetware and looked for a hardware solution. I build a small vox circuit that would key a relay when sent a tone. I hooked it up to the PigRig and it worked pretty well if I set the audio to about 2khz. I tried a few times, but still haven’t made a QSO with this method. I was frustrated to the point of changing my mind and re-dedicating myself to learning to copy by ear.

I found and started using the Morse Machine to practice. I improved quite a bit, but was still itching to hold down a QSO. It’s really hard for me to dedicate myself to daily practice when there are so many other fun radio things to do.

I had a few QSOs from home using HRD’s DM780 digital program to send “MCW” over my Icom 718 in SSB mode. Don’t let anyone tell you this isn’t “real” CW. If the computer is sending a sine wave at 700hz and the radio is transmitting a single sideband, it will be functionally the same and the station on the other end will not hear the difference. From what I gather, there are a lot of high-end transceivers that do nothing more than inject a tone in a very similar way to send CW.

So I’ve settled on “both”. My solution is to use the computer to encode and decode CW so I can make QSOs. I’ve been working the W1AW/* portable stations with this method and I’ve bagged quite a few. Breaking a pileup with 5w is a blast. But I’ve also been working with the MorseMachine more and have actually held down a QSO (I think) with a straight key.

I would really like to get my copy and sending speed up to about 20 wpm for camping and portable operations, but I’m pretty sure I’ll keep using the computer for anything faster than that.

If you have any ideas on what I could do to make this easier, comment below. Also share any ideas that might help other hams who have decided to learn this archaic, but still very useful, method of communication.



sk sk sk

My Wife Will Never Understand Amateur Radio Contesting

28 Dec

Amateur Radio Contesting is in the same category as fishing tournaments, competitive eating, and the World Beard and Moustache Championships when observed from outside the hobby. Inside the hobby there are people who prefer to rag chew and that’s perfectly fine. Today I’m going to tell you why I think contesting is valuable and why I like it so much.

First we start with why I think it’s valuable to the hobby and to an individual ham. The biggest thing for me is that it’s a chance to put a lot of stations in your log. Whether this is for awards or to test the abilities of your station is up to you. I find that each contest has its own way of testing my station.

The next valuable thing about contesting is the skills it builds for the individual ham. When working a contest you have to deal with a spectrum full of signals. Picking one voice from the noise is very challenging. Some contests involve DX or QRP categories that can help you develop an ear for weak signals. I would contend that your ears are more important than anything when it comes to being successful at contesting, that includes big stacked beam antennas.

There are contests for every mode out there. I’ve heard the best way to get faster at CW is to work a few contests, I’m not there yet. The PSK and RTTY modes take the human ear out of the equation and put a waterfall display at your fingertips. With macros you can work stations faster than you ever thought possible. You’ll also find some juicy DX in these contests because the operators don’t have to learn the entire English language to work you.

There are some negative aspects of amateur radio contesting. For one thing, the short exchanges don’t allow you any time to get to know the person on the other end. About the best you will do is learn their name. There are exceptions, and one of my favorite contests below is one of them.

Another down side to contests is that you never get an honest signal report. When using a contest to check your station’s abilities it would be nice if you could get a relative strength reading from the operator on the other end. I know it wouldn’t be that accurate, but it would help.

Contest weekends also bring out the guys who are not just disinterested in contesting, but outright opposed to it. On 75m and to a lesser extent 40m there are operators who will pop up on “their” frequency and be very impolite to the contester who has been operating there for hours. I’ve heard many kilowatt carriers tossed out within 3 khz of a net frequency to drive off a contester who has been there all day. It goes the other way as well, contesters will get very close to net frequencies and make the listening experience less pleasant than on a quiet day. To be fair I have also heard a net control station ask a contester very nicely for the frequency and I’ve never heard a contester say no. Neither group is going away, so please try to cooperate.

Now we get to the listy part. I’ll run down my top 5 favorite amateur radio contest events and list why I love them. Comment below if you have any additions, I would love to hear what contests you like and why.

5. ARRL November Sweepstakes

This is the contest that will get you a WAS award in a weekend. The bands fill up with stations around the US and Canada and you can work them with a very modest antenna system. I attach a utility to this contest in that I’m checking my antennas before the harsh Minnesota winter sets in full force.

4. MN QSO Party

The Minnesota QSO Party is held in February, the month when all Minnesotans assume winter will never end. The contest is only one day from 8am to 6pm local time, so you don’t have to skip any sleep to be competitive. My dipole doublet works great for NVIS contacts during this contest. It’s also nice to be wanted as I’ve been the only ham from my county in the contest for the last couple years. I’ve always wanted to work this one mobile, but have yet to put together a mobile station. Maybe this year.


It’s really hard not to say this is my favorite contest, so I’ll say it’s my favorite that I work from home. I’ve deployed a strategy that makes me competitive, I work 20m single band low power. This year I was able to get first place in the US!

As with any DX contest you can work the world. If you work multiple bands you can do DXCC in a weekend (or so I’ve heard).

2. ARRL Field Day

I really enjoy hacking things together with limited resources, so portable operations are great fun for me. Flinging antennas into trees with my trusty catfish pole is a great way to start a day of operating. ARRL Field Day is the most popular operating event in the US and so the spectrum is just packed with stations. You could probably get WAS on a light bulb. I work this contest as part of the Murray County Amateur Radio Club so there’s an element of teamwork. We split up the stations by band and have group meals and chat with each other on breaks from operating. Camping and radio in the same weekend, awesome! We should find a lake to operate from which brings me to:

1. Winter Field Day

The idea of ARRL Field Day is to test your emergency response. That’s great, but the weather doesn’t always cooperate. Disasters can happen in any season, so The Society for the Preservation of Amateur Radio has another Field Day in January. In Minnesota this means that you’re working in below freezing, sometimes sub-zero, temperatures. But with even more teamwork than ARRL Field Day we put up antennas and work stations all around the country. There are fewer participants, so you can work a bit slower and have a little chat instead of a quick contest exchange. It’s probably more like working from a special event station than a contest. Also, the best place to find a lot of open area in Minnesota in January is a frozen lake. This, of course, means we’re also fishing. This year we’re going to expand our efforts from two guys in a car to a whole group with several shelters and antennas for every band. It’s going to be great. Hopefully the fishing is better, last year we only caught one small Walleye.

Contesting isn’t for everyone, but for many hams it can be a fun event that fills the log with new contacts and pushes toward that next award. I love the teamwork of portable contests while finding out what each member of your group is best at. Remember, you don’t even have to submit a log (but you should) and you don’t have to work the whole contest. As always, just get on the air and have fun.

73 de KD0QEA /AE

ARRL Centennial Challenge

27 Dec

In honor of the ARRL Centennial and the ARRL Centennial QSO Party I’ve decided that this year will be a challenge year for myself. Here are my goals for 2014:

1. Make at least one QSO every day for the entire year. I got my inspiration for this one from KD0BIK and the Practical Amateur Radio Podcast. I’ve started before, but fizzled out.

2. Get better at CW and make at least one (hopefully more) contact with my PigRig, Little Joe, and Pixie kit built rigs. I may use software to decode but these rigs force me to send by hand.

3. Build a ‘phone rig. The options are either the BITX 20 as a kit or scratch build or the KD1JV Survivor kit.

Hopefully posting these goals online will nudge me toward meeting them. I’ll do my best to keep you up to date.

73 de KD0QEA /AE

P.S. I’m signing /AE because I’ve passed my Extra Class exam. I’m planning to apply for a vanity call that reflects my new license very soon.