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.

 

Icom R75 Tuner Repair

It’s apparently a common failure mode for the rotary encoder which processes the tuning knob input to fail in the Icom R75 (and many other Icom receivers and transceivers). Mind did recently.

A bit of background: most radios these days are completely computer-controlled. There is no variable capacitor connected to the tuner; the radio synthesizes its intermediate frequency under computer control, and if there is a tuning knob, it merely is a device for sending input to the computer. It may appear to be more traditional than a set of up/down buttons or a keypad, but it’s merely a show. A useful “show,” as tuning with a knob is often more convenient than using buttons.

The symptom of a dead rotary encoder is pretty much what logic would tell you it is: the radio still operates, and you can change frequencies by entering them with the keypad, but the knob simply does nothing.

There’s several fixes detailed in the initial link above. Initially, I was debating what to do and procrastinating the job, because none of them are cheap (replacing the chip in the controller requires de-soldering and re-soldering a surface-mount device, since I don’t have any equipment to do that, I’d have to buy it, since I couldn’t locate anyone who had it to lend, and there goes the clear price advantage of that option).

Then my (un)employment situation resolved itself, so I did the easy out and simply ordered a replacement from Icom, which costs just under $90 (not the $130 it is rumored). From the repair manual (which you should definitely download, as it shows how to take the set apart so you can get at the encoder), the part number is 6910012480. That part number may differ for products other than the R75, so please obtain a service manual and check it to be sure in that case.

OK, I suppose the real “easy out” would have been to send the thing in for repair. That would have doubtless cost at least twice as much as fixing it myself did, I was reasonably sure what the culprit was (the symptoms made that pretty obvious), I’ve taken apart reassembled electronic devices many times, I know the precautions to take to avoid damaging things, and this particular repair didn’t even require me to warm up a soldering iron.

So it was pretty much a no-brainer to do it myself. That said, the way the Icom parts person was taken aback at a mere customer troubleshooting his radio then having the audacity to order a part with which to repair it did make me have a little bit of doubt. Which was unfounded: when put back together and powered on, I was rewarded with a fully-working receiver.

Different than I Imagined, but Nice

P9291828wThe main difference between how I imagined the North Fork Skokomish Valley (a.k.a. the Staircase area of Olympic National Park) and how it actually was is that I had imagined it as being much more broad. In fact, there really wasn’t much of a flat valley bottom at all once one got above the campground.

It was, however, full of mile after mile of intact lowland forest, pretty much as I had imagined. It wasn’t all huge old trees (natural calamities do “reset the clock” in forests), but there still were an awful lot of them.

I also did manage to successfully make a couple of PSK31 contacts operating portable, so chalk up another goal for the summer season as accomplished.

The campground was surprisingly well-patronized, given that it was a weekday in late September and the water had been shut off. It’s probably just as well I didn’t even try to get a spot there last summer.

Where is the Null of my HF Loop Antenna?

I’ve been wondering that, since I’ve been using it to null out noise sources, yet I had long forgotten what the pattern of such antennas is.

I couldn’t just use the antenna itself plus noise to find out because I live in town and there’s potential noise sources all around. I couldn’t use the antenna plus signals because the ionosphere compromises the source-directionality of signals that pass through it, and it’s an HF-only antenna. (I suppose I could have spent most of the day delving into the physics of it, and coming up with the answer, but that would have taken most of the day and I just wanted a quick answer.)

Checking on-line wasn’t very helpful. I found articles claiming that both the null and the lobes were “in the plane of the loop”! Part of the issue, I think, is that there are different geometries of loop antennas. What one would tend to think of as the “plane” of a large, flat, air-core loop is perpendicular to what one would tend to think for a compact, multi-turn ferrite loop stick antenna.

A simple experiment with one of my old tube radios (which have a large, flat air-core loop antenna for the medium-wave broadcast band) and KVI’s signal on 570 KHz povided the answer: for “flat” loop antennas with a large diameter and low number of turns, the null is along the plane the loop exists in. It was pretty definitive: when I got the radio aligned so I had difficulty hearing KVI, its back (on which the loop is mounted) was aligned directly on a line running from KVI’s Vashon Island transmitter to me.

So there you have it.

Note that the while the peaks of a loop antenna are very broad, the nulls are by contrast very sharp. I’ve noticed this when nulling out interference; a slight bump on the HF loop antenna (changing its position by mere inches) often makes a significant difference.