Building an HF Portable Station

I’ve spent much of the summer building an HF portable ham radio station. I chose the µBITX kit from India, with a case from Amateur Radio Kits (also based in India). This was mainly done on the basis of:

  1. Low current draw (particularly on receive), and
  2. Low cost, because money is scarce right now.

The µBITX seemed to satisfy both requirements and still had fairly good reviews. Its biggest annoyance is that the receiver doesn’t have an AGC (so volume varies greatly depending on signal strength) or an AM mode (which limits its usefulness for shortwave listening). All in all, though, it was still a good deal and I am not disappointed with it. For under $200 and some assembly work, I got a decent HF portable rig.

That leaves the antenna. I’ve fought the portable antenna struggle a bit before. My first such purchase, several years ago, was the Buddistick. I was not impressed, mainly because the loading coils are extremely awkward and fiddly to adjust. You must hook one of these special banana sockets onto the coil at exactly the right point, and the tiny hooks that engage with the coil are a pain to both engage and disengage. Worse, you virtually never get the right spot to tap on first try, so you have to fiddle with the darned things multiple times to get the antenna tuned up. So scratch that idea.

I came up with the idea of using a doublet fed by window line and tuned with a balanced-line tuner (the latter item purchased used for about $30 at a hamfest). That idea ended up being dumped (after building and using the antenna a couple times) for a variety of reasons:

  1. Window line is a pain to deal with. It’s stiff, plus its conductors are brittle and fracture easily, plus there’s no good ready-made connectors for them that screw together and resist spontaneous disconnection (a must if the height and distance of the antenna varies due to portable use).
  2. Putting an antenna into a tree is a pain. Antenna launchers are prone to tangle line and get stuck in the tree. Do this twice, and odds are you’ll have at least one headache. Spending hours putting a doublet or a dipole into the trees is a justifiable time expense if the antenna is permanent and going to be used for years. Not so for a portable one that will be used for days or hours.
  3. A doublet cut for the 60 meter band is just under 100 feet (30 meters) long. That’s more demanding of real estate than your typical campsite can offer. And you still can’t use it on the 75 meter band, which is a big minus during a sunspot minimum (and if you’re interested in regional communications).

So enter the random wire. I did end up with an MFJ-971 tuner as a result of my doublet fiasco. Turns out it does an excellent job of matching most random wires as well. And I had the wire from the doublet I could salvage and use for the random wire.

But “random wire” is a misnomer: you won’t always get acceptable results from tuning up any old random length of wire. If your tuner is at the feed point, and your random wire is not even ¼ wavelength long, you will get no current peaks on the wire. This will seriously compromise its ability to radiate. If the random wire ends up being ½ wavelength or a multiple thereof, you will have a voltage peak at the feed point, which will frustrate your ability to feed energy into the antenna, which in turn compromise your ability to make the antenna radiate. One must choose a length which avoids these pitfalls at any frequency of interest. If one also wants to maximize portability, that means you must choose the shortest such length. The exact answer varies, but comes out to somewhere in the neighborhood of 72 feet, depending on who does the calculating, if you want to use all the ham HF bands from 80 to 10 meters.

That leaves the issue of feeding the antenna. The simplest thing is to just use a single lead-in wire. No coax (and no associated losses due to a very poor match between coax and random wire), no awkward, stiff, breakage-prone ladder line, just a nice, simple, inexpensive, easy-to-use wire. But “lead-in” and “antenna” are big misnomers. There is no difference between the two in this case; the “lead-in” will radiate just like the “antenna” does! Connect a lead-in wire to an antenna at a carefully-chosen length, and the length is no longer carefully chosen, and you might be at a multiple of ½ wavelength again.

There’s a simple, elegant solution to that problem: cut a piece of 72′ wire, design an insulator that can hold the near end of it using friction alone, use that for the near-side anchor, and connect the tuner directly to the single piece of 72′ wire. Place the near-end insulator wherever is needed to get the required bit of slack wire to serve as a lead-in. But that begs the issue of designing such an insulator.

This is what I came up with:

I used shock cord because I hadn’t brought enough rope to the test site.

It’s a 1/2″ PVC tee connector. One of the straight ends has been drilled with a 5/16″ hole for passing an anchoring rope through. The wire passes in through the 90° end and out the end opposite the drilled one. Where it enters, it is secured by a No. 4 rubber stopper; as the tension of the wire pulls on the stopper, it will merely tend to pull the stopper in tighter, thus the stopper holds the wire securely.

A random wire requires a counterpoise, of course: there is in reality no such thing as a “monopole” antenna; all antennas are two-terminal devices. What I am doing is trailing a 60-foot wire along the ground, plus using an alligator-clip lead to ground the tuner to my truck chassis.

How does it work? Quite well, based on my initial results. It seems to get out much better on 75 meters than my previous random wire (which was too short to have a current peak). It’s twice as easy to set up as the doublet (only one end must be launched into a tree, not two). It’s shorter than than the doublet, and installs at an angle, further reducing its real-estate demands. It can fit in a standard campsite. Yet despite the smaller size, unlike the doublet it allows me to operate on 75 meters. I noticed no slippage at the near-end insulator, which behaved exactly as intended.

There is a drawback to this design, and it is RF exposure. Because it doesn’t use transmission line to feed the antenna, this design will radiate in the immediate vicinity of the operator and radio equipment. That’s not so big a deal at QRP power levels, but I wouldn’t want to use this design at higher power. Overall, I consider the freedom to use a simpler antenna design to be yet another advantage of QRP for portable use.

More uBITX Errata

The instructions are unclear on how to connect the rotary encoder. If you look at the encoder from the rear (shaft facing away from you), with two terminals on the left and three on the right, the correct way to wire it is with the black wire on the top terminal and the brown wire on the bottom. The diagram and the written instructions show those two wires reversed, but the photograph in the instructions shows them connected correctly.

Correct wiring for the uBITX encoder.

This is the correct wiring.

I guessed (incorrectly) that the way in which two pieces of information indicated was the correct way was the way to wire them. I also guessed (correctly) that since the two wires on the other side were for a normally open pushbutton switch, and the middle contact on the encoder side was grounded, the controller was simply detecting which of the brown and black wires were getting grounded in which order to determine the direction of the shaft rotation, so there wouldn’t be any drastic consequences to wiring those two wrong, just reversed tuning.

Naturally I opened it up again, warmed up my soldering iron again, and switched the two wires around. Every normal radio in the known universe has a tuning knob where turning it clockwise makes the frequency go up, and it was very annoying to have a radio that acted in the opposite way.

Warning: Bad Instructions for uBITX

The official instructions for the uBITX transceiver kit recommend wiring the hot side of the audio out to both the tip and ring connectors. I consider this to be a faulty design and thus an error.

If you plug a stereo device into the jack wired per those instructions, it will work. If you plug a monaural device into the jack, it will cause a short circuit between ring and sleeve, because the sleeve on a mono plug is longer than the sleeve on a stereo one (the tips being the same size, and there being no ring). This short circuit can cause the receiver’s audio section (specifically its output transistor) to self-destruct!

Contrast that with wiring it with the hot side of the audio to tip only, as I recommend. That way you have something that works completely with a monaural device and works somewhat (left channel only) on a stereo device. Works (to at least some degree) with both versus works on one and self-destructs on another. It’s pretty darn obvious which is the better engineering choice.

This is mentioned on uBITX.net, but it isn’t mentioned as prominently as some other errata are (or even labeled as an error), so I figured I’d mention it here. In my opinion, it definitely is incorrect, because it qualifies as faulty design.

It’s particularly nasty because the uBITX receiver is of course a monaural device, making it only logical to assume it has a standard monaural output. Murphy’s Law means that uBITX wired per the standard instructions will sooner or later have an unwitting user (a guest, someone at Field Day, etc.) fall into this pitfall that was laid for them.

What they were trying to do is use a stereo jack in a manner that causes both stereo and monaural devices to fully and properly work. There is a way to do that: use a stereo jack whose sleeve is isolated from ground, and wire ground to ring and hot to tip. This will cause a mono plug to get signal presented at tip and sleeve, and a stereo one to get signal presented at tip and ring. The latter will result in both speakers being connected in series, if the sleeve is isolated from ground.

If the latter is not the case (and it cannot be with a metal case and the stock jacks furnished with the uBITX), ring and sleeve will end up being shorted and you’re back to seeing a signal in the left channel only. Not drastic, but not the full universal performance desired, either.

Instead of using a nonstandard technique that paves the path to a future mishap, it’s far better to just wire it as a mono device and use an easily-obtainable external mono-to-stereo adaptor if you want to feed audio to a stereo device.

220 MHz Adventures

35 years old and still working fine!

There’s a ham band at 220 MHz, but in most places its uses are limited to obscure control links, even though the band has frequencies allocated for repeater and simplex use. It was actually used where I lived as a teen and young adult in northern New Mexico (there was a very nice wide-area-coverage repeater with autopatch on that band). That was long enough ago that autopatch was still quite the thing (cell phones existed, but were very expensive, and most of New Mexico was outside of cell coverage). So I naturally grabbed a used 220 rig when I saw one for sale at a hamfest.

Sadly, I then proceeded to destroy said rig by hooking it up incorrectly to a power supply within a year of purchasing it. Then I left New Mexico to move out on my own and didn’t much think of getting anything to replace it for a while; I was living in a dorm room and it was tricky enough to put just one VHF antenna up for the 2 meter band.

I assumed when I moved to Seattle that given how as sparsely-populated a place as rural New Mexico had a useful (and used) 220 repeater, there would definitely be activity on that band in Seattle as well. So when I upgraded my mobile rig, I got a 2m/220 dual-bander, and also proceeded to snag an inexpensive older 220 HT at a hamfest when I saw one in good shape being offered for a good price.

Incorrect assumption; while there were repeaters on the 220 band up this way, they were virtually never used. All the local activity was on 2 meters and 70 centimeters. The old HT couldn’t do CTCSS tones, either, which at that time were increasingly needed to access repeaters, so it quickly found itself relegated to my spare parts box. The mobile rig just got used on 2 meters.

When I moved to Bainbridge Island, I learned that there were no 2m repeaters on the island, because by the time the island’s ham radio club had thought to erect a repeater of its own, all the local 2m frequency pairs had been allocated. So they put a repeater up on 70cm instead. That prompted me to sell the old mobile rig and upgrade to a new 2m/70cm dual-bander.

Last month, I started hearing about there being increasing activity (actual QSOs, not just control links) on 220 locally. There was even a weekly net that some people started talking about. For a moment I cursed my decision to sell the mobile rig then I remembered that old (by now about 35 years old) HT which by then had been sitting completely unused for well over 20 years. Would it even still work? It took some rummaging through my collection of old spare parts to assemble it: the battery packs were in one box, the antenna was in another, and the body of the radio was in a third.

I sprang for 6 new alkaline AA cells at the hardware store (not worth throwing money at expensive rechargeables for a radio that’s probably dead), plopped them in the battery holder, and put the holder on the radio. It sprang to life as a working receiver! But I couldn’t use it on any repeaters, because the radio can’t generate CTCSS tones and all repeaters are on tone squelch these days.

I arrange a simplex test with one of my ham radio friends in Seattle one weekend. Darned if I didn’t get an excellent signal report; it transmits just fine, too! So I purchase a third-party CTCSS board and install it. The latter required adjusting signal levels on a service monitor at another ham’s house, which also showed that the overall signal coming out of the radio was nice and clean.

From battery to battery eliminator.

Next came a base station setup: a simple ground-plane antenna built around a coax connector, followed by my taking apart one of the long-dead NiCd rechargeable battery packs for the thing and turning it into a battery eliminator by installing a simple voltage regulator (an LM7810 and two capacitors) inside its case.

It’s a low-powered base station; the HT comes from the days when the “high power” setting was only 1.5 to 2 Watts. Not that it matters; when doing some tests on the repeater of greatest interest, I dropped my power to the 0.5 Watt low setting and continued getting the same full-quieting signal reports. So on low it will tend to stay.

Demodulating ACARS

ACARS is a digital protocol used by aircraft to transmit messages. It’s been around since the late 1970’s and is decodable using nothing but a sound card and the right software. But, after helping a friend (a technologically-sophisticated one; like me, he has a ham license) who has previously had no luck decoding the messages, it’s clear there’s some tricks involved.

  • Don’t use squelch. Squelch will chop off the first tiny fraction of information in a packet, causing decoding errors (typically, messages simply won’t decode). There’s no need to use squelch, anyhow. Squelch exists to prevent humans from being annoyed by listening to the background noise when a frequency is not in use. Computers don’t care about being forced to analyze static, and can easily distinguish between static and an ACARS packet.
  • Use a wide bandwidth. A big part of my friend’s problem was that he was using the default AM bandwidth on his communications receiver, which was apparently too narrow. I have myself tried using both the wide and narrow filters on my receiver; only the wide one works. ACARS is apparently a wide-bandwidth mode, and a narrow filter throws away critical information needed to decode a message.
  • If using ACARSD, configuration is critical. ACARSD is the most popular freeware package for decoding ACARS. Alas, it’s not exactly user-friendly. To install it you must first configure the installer and manually tell it to create the directories it needs. To configure it you must use a separate program that (re)writes the necessary .INI file. Moreover, that program doesn’t always default to reasonable values as advertised. It claims ACARSD will use the default sound card if none is specified. I found it necessary to explicitly specify the sound card for the default one to be used on my friend’s computer.

Some shortwave recordings

Haven’t made any of these in a long time. Since getting a cellular modem to allow Internet use on the ferry, my Internet sessions while commuting have been productive enough to enable me to do some SWLing after work at times.

Saudi Broadcasting Services with Islamic chant on 15170 kHz, starting at 0309 UTC.

A mystery (to me). Some sort of digital mode recorded in upper sideband on 9048.5 kHz at about 0410 UTC.

Radio Rebelde, Cuba, 5025 kHz, broadcasting a news item about the recent earthquake in Ecuador.

Voice of Korea on 15180 kHz, first eight minutes of 0330 UTC Spanish language broadcast, which means nothing but the standard lengthy lead-in of songs praising the country and the Kim dynasty.

All were recorded on 5 May 2016.

 

 

The Kiss of Death for SDR

So, after trying a cheap RTL2832 dongle for a month or two, I’ve decided that throwing more money at software defined radio at the present moment would be a waste of same.

The reason is Microsoft Windows. I still hate using it as much as ever, and if you don’t run Windows, your options for SDR software are extremely limited at the present time.

Given that this is all a hobby for me, “I hate using it” is the kiss of death. So I’ve basically given up on SDR for the time being.

It was of very little loss. The software was free and my hardware investment cost under $10.

SDR: The Executive Summary

One of the RTL2832 dongles I ordered from Ebay finally arrived. The other I have chalked up as a no-show. I’ll try to get my money back, but even if it turns out to be a loss the total cost for both was under $20. That’s very cheap for a software defined radio.

The executive summary: using a general-purpose computer instead of a traditional radio interface generally sucks from a user-interface point of view, but it has its one very intriguing and useful aspect. That latter is how an SDR captures a whole swath of spectrum and typically has a waterfall display to visually plot what it receives.

It’s a most useful feature when searching for non-broadcast signals; one doesn’t have to rely on chance for the particular frequency one is listening to to become active. Instead, you can see activity as it appears on any nearby frequency in the range being displayed, and immediately point and click to tune to it.

I’d suspect the sucky parts of the user interface aren’t nearly so bad with some other SDR programs. Right now I’m using gqrx, because I have only Macs in my house and gqrx is basically the only SDR software that runs on a Mac. I’m going to be getting a dedicated Windows machine soon (there’s enough software I want to run that only runs on Windows that it’s become worthwhile to do so), and once I have that I’ll be giving some other software a try.

Hardware wise, an RTL2832 isn’t exactly the greatest receiver. It’s sensitivity isn’t that great and it’s full of birdies (I suspect a better antenna, further from my computer, would help with some of that). Even my 25-year-old Bearcat scanner runs circles around it. But what can one expect from a consumer-grade device that didn’t even cost $10? It is what I purchased it to be: a low-cost way to experiment with SDR.

Re-Thinking Software-Defined Radio

After blowing two evenings trying to get SDR working, I’m beginning to think I was correct in basically writing the technology off as not worth the trouble some years ago. I fight with computers in my day job. I don’t want to do it as a hobby.

First, I use Macs. If you use a Mac, you’re really left out. The vast majority of SDR software supports Windows and Windows only. The few exceptions tend to run on Linux and not Macs.

Sure, I could boot Linux on my Mac, but it’s Linux. That means it was written by hard-core geeks for hard-core geeks, so documentation is incomplete (if available at all). To prove my point, I tried to create a bootable Linux flash drive last night, following all the instructions meticulously. It didn’t work; it failed to even appear as a boot device when the system came up. That means there’s probably some missing step in the by-geeks, for-geeks instructions that was left out because it’s transparently obvious… obvious to a hard-core Linux geek that is. Figuring out the answer to that puzzle could easily involve me blowing my free time on it for the next several weeks. No thanks. I want to geek around with radio, not Linux systems administrivia.

The few exceptions, i.e. SDR programs that run on the Mac natively, tend to involve Mac Ports. Which is (link) currently broken. Sigh.

That leaves running Windows, which probably means buying and setting up a whole new computer. If it comes to that, there goes any cost advantage of SDR; even a sub-$10 dongle like the one working its way to me from Singapore will have a total cost about twice that of the Alinco receiver I just purchased. It actually might come to ruunning Windows… eventually. Right now, there’s higher priorities for spending that sort of cash.

Alinco DJ-X11 First Impressions

Why buy yet another radio? Two reasons:

  1. I’m currently trying to do noise mitigation in the HF bands, and that means walking around the neighborhood with a radio. While I can use one of my existing sets for this purpose, they tend to be very awkward, as they are all desktop models.
  2. I’m also interested in helping friends whose homes might be bugged (seriously; they’re known as activists, and the government has a nasty record of surveillance on such individuals) do some searching for bugs. It’s yet another something for which a small, battery-powered radio is a useful tool.

So I wanted a small, battery-powered wideband receiver that could tune as many frequencies as possible in as many modulation modes as possible. The latter is an important point; most of the wideband receivers out there (such as the Icom R6) can’t receive SSB or CW at all, which is a major limitation on the shortwave bands.

First impressions:

  1. It doesn’t feel super solid and professional, like I’d imagine the Icom R20 (discontinued) or the AOR 8200 (no raw I/Q output) to feel. It doesn’t feel super-fragile either; its plastic case does feel quite rugged and right. But there’s very little metal in the thing; it’s surprisingly lightweight.
  2. It’s very complex, and the manual isn’t the best in explaining the complexity. It can take some searching and experimentation to figure out how to do something.
  3. It won’t put my desktop HF receivers out of work; it’s significantly less sensitive than them, not so easy to use, and tuning SSB signals is somewhat painful.
  4. Notwithstanding the above, it does actually work acceptably on MF (aka AM broadcast) HF, VHF, and UHF signals. Given its small size and wide coverage range, its performance is quite remarkable.
  5. Forget about using the rubber duck antenna it was shipped with for HF; get an SMA-mount whip (thankfully I already have one).
  6. It comes with a rechargable lithium-ion battery and a drop-in charger. The latter was a pleasant surprise; I much prefer drop-in chargers to plug-in ones, and I was expecting the latter, given the price.

This is the USA, so mine is the crippled DX-X11T model with the stupid government-mandated gaps in the 800 MHz band (fuck you very much, Congress). I seriously entertained the idea of taking a trip to Canada and smuggling a non-crippled one across the border, but:

  1. That involves blowing most of a weekend.
  2. There’s always the (slight) risk of my purchase getting confiscated on the way back.
  3. I already have a desktop receiver capable of tuning such frequencies (completely legally; I bought it before the law became effective so it’s grandfathered).
  4. I also have an RTL2832 dongle on order which, together with a free software program, will be a software-defined radio that goes from about 24 to 1700 MHz with no such gaps.
  5. If I do find a bug, I’d rather do so with a 100% legal receiving device, to minimize the very real risk of governmental retribution should I be open to it by possessing contraband.