Tech Flashback: Radio Scanning (feat. Uniden UBC93XLT, DSE DTS-96, Icom IC-R20)

Towards my later high-school years, in the mid-2000s, armed with a small amount of money, I picked up the hobby of radio scanning. As a person who was curious by nature and had built a number of FM radio microphone “bug” kits, I always wondered exactly what was going on “behind the scenes” – what were those employees on their handheld radios talking about? For a modest outlay of about AU$300, a radio scanner promised to let you into this “secret” world, kind of like “gossip for nerds”. While it was already late in the days of the scanning hobby, there were still many transmissions worth listening to.

What is “Scanning”?

The hobby of scanning is pretty much named after the “scanner radio”, aptly named due to its scanning mode of operation. Unlike a regular broadcast receiver, or a handheld radio transceiver (sometimes known as a walkie talkie) that would be set to a channel and stays on that channel, a scanner radio is configured in such a way that it has a number of channels (e.g. by having a crystal bank or programmable PLL/VCO synthesizer) which it scans across, only stopping when it receives a signal strong enough to break the squelch.

As most professional radios are only used in case of an immediate need to pass messages, the channels (simplex or repeater output) often remain quiet for a lot of the time. A radio that only listened to one channel wouldn’t be much fun because it’d be silent most of the time. As a result, the scanner allows you to monitor multiple systems (e.g. police, fire, ambulance, delivery drivers, taxis etc) by tuning rapidly between their frequencies and stopping only when it receives a transmission. When multiple simultaneous transmissions are occurring, you will miss one (or the other) transmission, but this was an “acceptable” trade-off compared to sitting in silence or having an (expensive) radio for each frequency!

The transmission frequencies used for these professional radios are outside those normally used for broadcast and use much narrower modulation modes, lower transmission powers and can also convey low-speed data using various modulations (e.g. paging). This is why a specialist radio is needed, however, due to the state of radio technology in the early 2000’s, most transmissions were still analog narrowband FM in commercial bands, so all you needed to get started was the frequencies that a given organisation uses!

Back in those days, wide bandwidth SDR receivers were not a reality – even the computing power needed to realise the DSP computations needed to handle multiple channels simultaneously were too taxing for many home computers. It was not until 2010 that I obtained my first 2Mhz-bandwidth SDR which was enough to stress out even a decently specced dual-core Intel Centrino Duo T2300E-based laptop on a single channel decode!

Uniden Bearcat UBC93XLT Scanner

My first scanner was actually the prior model – a UBC92XLT, however, I ended up selling that off as surplus to needs while keeping the UBC93XLT which I purchased second hand at a good price. To my knowledge, the two units shared identical specifications, with the exception of an updated included radio frequency database CD-ROM. While a big deal is made about their inclusion, those CD-ROMs were woefully out of date – it was just more useful to look up ACMA’s Radiocommunications Register directly for the frequencies we needed! Otherwise, you could just do a blind sweep of the frequencies hoping to catch a transmission …

The UBC92XLT and UBC93XLT was sold as a whole retail bundle including a frequency database CD-ROM, “rubber ducky” antenna, earphones, rechargeable batteries, a car cigarette lighter adapter and a power adapter for about AU$300 in Dick Smith Electronics. This model was the “upgraded” UBC72XLT which featured support for the UHF band, making it a little more expensive but was something I felt was good to have. It had a 200-channel memory separated into 10 separate banks, support for 25-88, 108-174, 400-512, 806-956Mhz frequency ranges and “close call” capture of high-powered nearby transmissions allowing for detection of unknown frequencies. There were also pre-programmed service search banks for police, railroad, air, marine, UHF CB and AM CB, although these weren’t exactly that useful.

The front of the unit had a keypad, with most buttons having more than one feature that can be accessed by using the Func+ key combinations. This was already considered slightly complicated by some due to the segment-LCD display being slightly unintuitive to operate. The speaker in the unit is also in the front, although often when out and about, you’d rather use the headphone output.

On the rear, there is a belt clip that allows for you to conveniently wear the unit when out and about. I have also modified the unit to provide the “discriminator output”, basically an unfiltered output from the demodulator for use with data signal decoding over the sound card. The battery compartment door can be completely detached, with the scanner running on 2xAA batteries. An internal switch controlled whether the unit would attempt to charge the cells or not.

The side of the unit has the DC barrel jack input for a 6v 500mA power supply that can charge the batteries and run the unit at the same time.

The top of the unit has a BNC connector for antenna input. It also hosts a 3.5mm headphone socket wired for use with analog and stereo plugs – however, this arrangement caused stereo headsets to have two channels “anti-phase” which wasn’t the best. Two knobs are present – the squelch and volume controls.

The unit was a relatively basic model, but it was quite a robust model which served as a good introduction to the hobby. I wore it around from time to time, getting curious looks from some and being mistaken as a “security officer” by others. It was rare, although not impossible, to come across another scanning enthusiast from time to time but this wasn’t a particularly exciting unit.

When it came to scanners, there were a number of metrics used to compare them – the most important includes the frequency bands supported, the sensitivity of the radio receiver (e.g. 12dB SINAD value), the number of memory positions, the scanning step rate and modulation modes supported. As a rather basic unit, it didn’t feature a stellar specification in any regard, but the biggest limitation was that of the sensitivity. I found that even with an aftermarket antenna with higher gain, many signals were noisy/scratchy. For home use, this wasn’t as big of an issue as the location can be tuned carefully, but when mobile, it can get difficult.

The biggest problem was that the radio market was just beginning to change at this time with the introduction of trunking systems using hybrid digital modes such as Motorola Smartnet, transitioning to full APCO P25 in later years, LTR, MPT-1327. Listening to trunked networks with a conventional scanner was difficult, as the base station changes the output frequency on a rotating basis, so following a complete conversation over multiple overs became difficult especially if the “break” between overs was long enough for the trunking controller to relinquish and reallocate a new channel. I was also getting into amateur radio, so the lack of any SSB modes was also not optimal.

Regardless, this model was enough to begin to listen to a lot of signals – the ethnic radio band, aviation band, transmissions from buses, taxis, amateur radio operators and CB radio users. It was also what introduced me to POCSAG pager decoding, ACARS decoding and P25 trunking system control-channel decoding. After I had this taste, I decided to take things further.

Even after it became less useful to me as a scanner radio or a signal source for decoding, there is a “hidden” button combination that enables a frequency counter mode, so it can be used to check an RF device for its output frequency.

Dick Smith Electronics DTS-96 Digital Scanner

With the evolution of radio towards digital technologies, the most important local radio system was the NSW Government Radio Network which hosts all of the fire, ambulance, roads and transport officer staff to name a few. This trunked system began as a Motorola Smartnet 3600bps system, making monitoring using a regular conventional scanner rather frustrating, but began transition to a P25 system with 9600bps C4FM transmission instead. To listen into these required an APCO P25 capable scanner.

I wanted to purchase a Uniden UBCD396XT “Trunktracker” scanner, but I wasn’t able to secure a good price on those, so I ended up buying a DSE DTS-96 second hand instead for about AU$300. This was a GRE/Radioshack Pro-96 rebadged for the local market, with a large boxy appearance and plasticky build quality. It has a 500 channel memory in 10 banks, which can be loaded and stored into 10 slots + 1 working memory, headlining a 5500 channel memory capacity. It supports a rather (disjoint) frequency range of 26.965-27.405, 28-29.7, 50-54, 68-88, 108-174, 406-512, 806-960 and 1240-1300Mhz. It was a very sensitive radio as well, which I modified with a discriminator tap, but it seemed to also be vulnerable to intermodulation and “birdies” – false signals which appear due to self-generated interference and non-linearities.

The unit had rubber strips on the side which have since fallen off due to age, but the paint is also starting to come off. There is a DC jack for power input and charging, as well as a PC interface port which could be connected to a PC to program the unit or to analyse the trunking data with Pro96Com. This worked much better than using Unitrunker with a discriminator tap, as other radios still didn’t provide a “clean enough” signal, whereas this worked purely in the digital domain relying on the radio to demodulate the signal.

It was a bit of a regrettable purchase, as it was physically rather inconveniently chunky (using 4xAA batteries) with rather shoddy build quality and a problematic volume potentiometer results in a situation where you’re not sure whether the radio is quiet because the channel is quiet or because the pot has gone wonky again. The DSP decoder also produces slightly lower-quality audio than some of its rivals, but is also incompatible with later P25 systems using Linear Simulcast Modulation (LSM). Even though my local station still uses C4FM at this stage, this may not be the case into the future. It was, however, my first and only digital audio capable scanner to date.

Icom IC-R20 Communications Receiver

In fact, two years prior, I decided to drop about $500 on something that isn’t technically a scanner, but more a communications receiver. Bought brand new, this is a much more sophisticated radio compared to the “scanners” above and it definitely shows. The IC-R20 arguably the best handheld radio receiver I have ever owned – and I don’t regret spending my money on it at all. Built like a tank, with a very sensitive front-end, this thing has almost all the features one could ask for in a handheld.

It has a frequency range of 0.15 – 3304.9999Mhz, support for FM, WFM, AM, USB, LSB and CW receive modes, 1250 memory channels with alphanumeric tags, TV audio reception, a 32MB integrated audio recorder (up to 20 tracks, 4 hours), rechargeable Li-Ion battery and is USB programmable and CI-V remote control compatible.

It also decodes CTCSS and DTCS tones, has a repeater offset monitoring button, adjustable RF gain, S-meter, spectrum scope and dual-watch for simultaneously receiving two channels at once (with limitations in each VFO’s range).

As a result, the unit is somewhat larger, but still relatively compact for what it offers. It was by far my favourite unit with a sensitivity that trounces the others. The interface was somewhat complicated – buttons could activate up to three or four different features depending on the mode, short press or long press.

It didn’t have any discriminator output and modifying it was a risk I wasn’t willing to take – but the dual-watch feature and high sensitivity actually made it possible to monitor multiple ACARS frequencies at once, thus this was my primary ACARS receiver for a number of years.

The unit’s recording feature was also particularly of interest, as this allowed for ADPCM recordings that could be downloaded to the PC (slowly, over USB to serial) but converted back into a .wav file with a special tool.

I carried this radio around a lot and it was the unit that I used to first explore shortwave radio and amateur satellites. Because of its wide frequency range, I even used it to explore the output from satellite LNB IFs, even before I got access to wide-range SDR radios. It led to my purchase of an IC-R75 later for shortwave monitoring – another lovely radio. Unfortunately, the IC-R20’s keypad keys have started to become sticky, along with the port covers making it a little less enjoyable to use. Its receiver performance is, however, still just as good as the day I bought it and I still get some use out of it.

Aside from the three radios I’ve shown in this post, I also owned a Uniden Bearcat UBC355XLT car-mount unit for cheap from eBay, but that one failed after a long time serving as a trunking control channel receiver for Unitrunker monitoring the NSW GRN in the past. I also had a Realistic Pro-2021 I got for “scrap” as it wasn’t working, but I repaired it and used it for a few years but the limited sensitivity, frequency range and large size led it to be retired as well.

A Dying Hobby?

While scanning is still a cool hobby to me, with the idea of getting a behind-the-scenes seat hearing what is happening “at the front line as it happens” being a key part of its allure, it seems like this hobby is dying. For one, with the loss of many local electronics stores, scanner units are rarely ever advertised. I almost never see anyone with a scanner in the streets and it seems that the RadioReference databases for my area aren’t being kept up to date either. It’s a sad thing to see, but there’s a good reason for this.

Because of the limited overcrowded 400Mhz spectrum and a desire to “refarm” some of the former 800Mhz spectrum for use with mobile telephones, a number of changes were made to the bands. Former 800Mhz users were all taken off the air, with 400Mhz band users being given an ultimatum to move to more spectrally efficient technologies. To do this, initially, it would be possible to move to narrower NFM as an interim step, but the writing was on the wall – to get to 6.25khz equivalency, you really needed to go digital. To help them on their way, ACMA rejigged the frequencies in such a way that repeater offsets were chosen such that it would play well with digital technologies and since then, scanning enthusiasts have been living with the consequences – not just here but across the world.

Consequence #1: A Myriad of Incompatibility

The first problem is that the move to digital has splintered many services from a single type (e.g. NFM) into several incompatible digital systems. This includes systems such as APCO P25 (Phase I, Phase II), DMR (MotoTRBO), TETRA, NXDN/IDAS just to name a few that operate nearby me at this time. Each of these systems have different on-the-air characteristics requiring specific decoder implementations to decode the bitstream, but the difficulties do not end here.

Consequence #2: Legality Issues

Once you have the bitstream, the problem is that digital radio depends on different digital voice codecs (e.g. the MBE family). These codecs are optimised to carry voice signals using a very low bitrate (often 2kbit/s to 9.6kbit/s), but are patent encumbered. As a result, to produce scanners that can decode these audio streams, either a non-infringing implementation needs to be used (which normally results in audio quality trade-offs) or licensing fees (sometimes additional to the purchase price of the unit) needs to be paid.

Of course, with the popularisation of low-cost SDR technology (through RTL2832U TV-dongles), it is possible to now decode and even listen to these transmissions but either you have to build your own MBE decoder or download software which is of questionable legality.

Consequence #3: A Loss of Access

While the above points make monitoring digital systems somewhat inconvenient, the move to digital also enables easy access to encryption. Many of the systems allow for “basic” encryption which can be easily provisioned at very low cost to prevent anyone else from listening into the transmissions. More sophisticated encryption module based systems with 3DES/AES/etc are available and used by some agencies already. Transmissions on TETRA systems are encrypted by default. All of this serves to limit our access to the information – of course, it was nice to listen in while it lasted but the transition to digital definitely puts the remainder of the transmissions at risk.

More than that, because of the cost of handheld radios compared to the cost of smartphones, some agencies are foregoing the whole radio idea and instead substituting various telephone-based dial-in systems (e.g. Taxis in Hong Kong) or various application-based solutions to emulate a radio over LTE data.

Consequence #4: Reduced Audio Quality

While the use of forward error correction and robust symbologies, digital systems can provide increased coverage and better reliability with no static or hiss. However, in reality, it is not without its limits.

Tied in with the use of codecs, the digital systems frequently have reduced audio quality that makes listening fatiguing and produces intelligibility issues especially in the case of “reverse engineered” decoders. But even without such issues, many dispatch operators seem to request repeats more frequently due to interactions between background noise and the vocoders causing strange “burbles, underwater noises”. While the digital systems can mask a limited amount of errors, it seems some users like to push the limits of coverage while others are suffering from sub-par equipment installation or strong multi-path issues.

Consequence #5: Increased Expense/Complexity

As mentioned earlier, because of the variety of systems and patents involved, as well as the declining popularity of the hobby, the increased cost and complexity seems to make it even more difficult to affordably purchase a useful scanner.

For example, looking for a DMR-capable portable scanner today, the only options seem to be:

  • GRE/Whistler PSR-800 (Paid Upgrade Required)
  • GRE/Whistler Pro-668 (Paid Upgrade Required)
  • GRE/Whistler Pro-18 (Paid Upgrade Required)
  • Whistler WS1080
  • Whistler WS1088
  • Whistler TRX-1
  • Uniden BCD325P2 (Paid Upgrade Required)
  • Uniden BCD436HP (Paid Upgrade Required)
  • Uniden SDS100 (Paid Upgrade Required)

Even then, it’s not clear as to what the total cost is, as a number of these units seem to require paid upgrades to unlock these features. But if you also want NXDN on top, then you’re down to just the TRX-1, BCD436HP or SDS100. A quick search seems to show that all units are relatively hard to obtain locally, the TRX-1 is about AU$760, the BCD436HP is about AU$673 and the SDS100 is around AU$1032. Of note is the latter two will still require a paid upgrade to decode DMR and NXDN, so this is hardly a friendly “introduction” to a hobby which … frankly … you can’t be sure you’re going to hear anything at all. Part of the reason I say this is that digital systems also need some extra work to determine the correct frequency tables, offsets, talkgroups, etc so that you can actually listen to what you’re interested in. This information, while in the past, might have been kept up to date and openly shared is now rare to find.

Conclusion

Radio scanning was a hobby that I picked up relatively late in the game, but still, was something I enjoyed and led to a number of things including getting my amateur radio license, doing some shortwave DXing, following amateur radio satellites etc. It wasn’t cheap back then, but with the move towards digital voice for spectral efficiency, use of proprietary voice codecs and encryption, the days of scanning may well be numbered. To get into it in the same way now would entail a fairly expensive investment and uncertainty whether there is anything to listen to.

As a result, those who might want to try are better off using SDR radios and (sometimes questionable) software to decode the transmissions. It’s much more flexible and the information displayed is much more useful – the only downside is that it’s not very portable, the audio quality may be sub-par, the reception quality is limited by the SDRs as well and it can also be a bit buggy. Maybe I’ll talk more about this in an upcoming post.

Now with the internet, I guess people like to keep themselves entertained by other means (watching cat videos, perhaps) and old fashioned radio might continue to decline in popularity as communications over the internet become so effortless that it’s taken for granted. I’m a bit sad to see scanning in a decline … but I’m not letting it go. Not just yet.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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