Quite a bit has changed over the years with respect to scanner radios. Scanners are used for many purposes, by hobbyists, amateur radio operators, the media and press, and for more than I can list here.

One of the more recent scanner models is the Uniden SDS100, which was released back in 2018. This scanner, as of the writing of this post, is already 7 years old.

This post is not intended to be a comprehensive review of the SDS100, as I am certain this scanner has had its fair share of reviews over the years. Instead, I will give some context for how I arrived at purchasing this scanner and what my experiences were from the very beginning of the scanning hobby until now.

The Beginning

Back many decades ago, when I was in middle school, a friend of mine had a Radio Shack scanner and it was interesting listening in to local police, EMS, and fire. This was in the late 80s into the very early 90s, way before internet was available in everyone’s pocket via a smart phone.

News broadcasts in the evenings would be the first time you would be able to hear events of the day, and very rarely would anything local (in my town) be on the news (from a small suburb outside a small city). The scanner was a window into what was happening locally, in real time. Of course, in that small suburb, at the time, the majority of the police activity was traffic stops.

Not only could we listen to police, fire, EMS, we could also listen to weather forecasts via NOAA, and we could hear many other services within receiving range.

I bought my first scanner shortly afterwards, and it was a portable model. It was the Realistic PRO-41, a 10 channel “programmable” scanner. Programmable refers to the ability to enter frequencies directly into the scanner as opposed to having to purchase and install crystals.

Programmable scanners (with a VFO) were a major advancement at the time, since crystals were expensive and limiting in many ways. If you wanted to listen to something new, a crystal for that frequency was needed. You would not be able to simply enter the frequency directly into the VFO or a channel memory.

Incidentally, the very first portable 3-channel CB walkie-talkies I had used crystals, one for transmit and one for receive. The units came with crystals for only one channel, channel 14. If you wanted channel 9, 19, or any other channel, Radio Shack would sell them as add-ons. Most of the time these needed to be special ordered.

For the older scanners, having to have a crystal cut for a specific frequency meant that you could not simply explore the band(s) for activity in your area and discover new frequencies in use. Crystal controlled scanners were used with known frequencies you selected, and were not useful for exploring around the bands for new activity.

Frequency Databases

Having a scanner by itself is not very useful unless you know the frequencies of the services you want to listen to. At the time, before internet was widely available and popularized, there were reference guides or books published with various agencies, services, and associated frequencies for scanner hobbyists.

At the time I purchased my first scanner, Radio Shack sold a reference guide titled “Police Call”. This was the only reference I was aware of, at the time, for many frequencies related to scanning hobbyist interests.

The contents for the guide, I presume, were acquired from FCC licensing data. Frequencies did not usually change very often, and even though these were released every year, you did not really need to purchase a new updated version often.

In order to listen into something of interest, I would need to look up the service or agency in the Police Call reference book and then enter the corresponding frequency into one of the 10 channel memories in the scanner.

The book had several different volumes, where each volume covered a specific area of the country. This was because a book which covered all of the United States would be much larger and more costly. Usually each volume would cover not only your local listening area, but several neighboring states as well.

Of course, 10 channels did not provide for an easy way to listen to everything I was interested in, so I would keep a list of interesting frequencies handy. Further, the PRO-41 did not have a way to “search”. Many scanners I would use years later had the ability to start at a given frequency and search either up or down and stop when it heard something.

The search feature was a good way to discover new frequencies that were used nearby, but you did not necessarily find in the reference book. Incidentally, this is how I stumbled across cordless phone and baby monitor frequencies in the 46 – 50 MHz range.

The PRO-41 could receive only FM transmissions. Air band or any other service using AM was not receivable on this model. Back then, the majority of the coverage range of this scanner was being utilized with FM modulation anyhow.

More Channels and Features

A few years later, I bought a new scanner, another portable model, the PRO-46.

This model was a major upgrade to my previous model (with a much higher price tag). It had 100 channels and it had a search feature. With this model, I never used all of the channels, as 100 channels was more than enough (for my area at the time).

The scanning speed was much faster, it had a backlight for the display, and built-in NOAA weather frequencies. In addition, it would receive AM on the air band frequency allocation. This model even had 800-900 MHz capability that my previous model did not have.

Back then, and even today, scanners had the cellular telephone frequencies “blocked” from being tuned into. Even though the scanner covered the spectrum where the cellular telephones operated, there were gaps in coverage within those areas of the spectrum. Searching modes would skip over those areas, and direct VFO entry was not possible in those areas.

Many scanners could be easily modified to restore the ability to tune in to these frequencies, and back then, cellular telephones were analog. This meant they could be listened into quite easily. I heard that in most cases, scanner modification was as easy as removing some zero ohm surface mount resistors, such as the case on the PRO-46.

These days cell phones are digital and encrypted, as are many other services, rendering the ability to listen into many types of transmissions difficult to impossible, even if unlocking the VFO is possible.

Leap Forward

For a few decades, I had not been interested in the hobby all that much, until a friend of mine sent me a link to a software defined radio (SDR) device available on Amazon that (at the time) was less than $40. It was the RTL-SDR which plugs into a USB port on a PC or Mac (or a Raspberry Pi) and can tune in from 500 kHz to 1.7 GHz.

Of course, these devices require a computer and software which is really what provides the features needed to decode various modulation types. For example, the SDR software would be able to receive not only FM and AM, but narrow, wide, and sideband modes. Software replaced much of the hardware for receiving.

This was possible without hardware demodulating circuits because the software has a wide window into direct sampling of the RF signal (in most cases).

Not only can an SDR decode various modulation types, it can also decode digital transmissions such as DMR for example, ADSB, pagers, weather fax and other satellite imagery, and much more. Usually this added decoding functionality is provided by “plugins” or modules which are able to be fed the data stream directly from the SDR and/or the demodulated audio stream and perform the specialized decoding. In theory, an SDR is upgradeable via a software update to cover new modes of modulation or encoding.

Further, SDRs provide a “waterfall” and panadapter type view, which is a timeline of realtime signal reception over a fairly wide bandwidth.

The waterfall and panadapter feature allows the user to visually see where signals are in real-time. The user can then click on a signal to instantly move the VFO to the desired signal to listen to.

Further, as you become experienced in viewing the waterfall, you can visually distinguish between various modulation types, such as differences between an AM signal, sideband signal, FM signal, or CW (continuous wave, or morse code). With even more experience, you can also see other modulation types such as data transmissions and other obscure formats.

This is quite a bit easier to help discover new frequencies in use nearby compared to the search feature on older scanners which were far slower and required a transmission to occur right at the moment the scanner was on that frequency.

Unless your timing was lucky, you would often need to sweep a range of frequency quite a few times or over a long duration to be able to discover new frequency usage. With the waterfall, you can see up to 10 MHz or more all at once, depending on the SDR hardware and resolution chosen.

Many SDR software packages can also store frequencies in lists and perform basic scanning features. Many can record as well, which is useful for monitoring. Many of the SDR software packages can record the IQ data directly, as opposed to simple audio recording. This allows not only audio output for playback later, but it can cover a large portion of bandwidth, and, all of the original data. For example, this means you can capture all of the activity which occurred within a 10 MHz slice of bandwidth, without needing to specify the modulation used (AM, FM, sideband).

The RTL-SDR along with the RSPdx were quite a leap forward over the previous scanners I had owned and used. Of course the SDR is not designed specifically to “scan” but it certainly can do so, on a basic level.

Of course many newer amateur radios provide similar features for waterfall, panadapter, and scanning. Many have general coverage receiving capability built-in.

The Uniden SDS100

I read an article in the January 2025 issue of QST about the Uniden SDS100. Up until that point, I had not kept up with the evolving technology incorporated into scanners. Although the article in QST was more a review than a general article on the technology of today’s scanners, after reading it, I began to look at scanner reviews and videos on youtube.

I ultimately ended up purchasing an SDS100, not so much for this specific model or brand loyalty, but for what it can do (I am sure there are or will be other comparable models) that my previous scanners could not.

The features that most appeal to me for primary use of this scanner is that it can follow trunked systems, and decode P25, DMR, and other formats which are commonly used in public service agencies these days.

Even though it is possible to use software such as SDRTrunk (and others) to follow trunked systems, it could require several SDR units depending on the spacing of the voice channels from the control channels, and how many channels there are in total for the trunked system you wish to listen to. The SDS100 and many other scanners will do this work for you. Trunk tracking scanners have been around for quite awhile now, and this is not a recent feature.

PC Programming

The programming of the SDS100 can be done either directly on the unit itself or via the “Sentinel” software package provided by Uniden. The software is not all that modern looking, runs only on windows, and is very basic.

The Sentinel software does not have a search function (not that I could find), and therefore can require a bit of clicking around to find what you are looking for.

It does however organize the services by country (United States and Canada), then state, then county. However, some systems are county-wide or state-wide and finding your local police department might take some digging around at various levels, as it did in my case.

Programming via a PC, like trunk tracking, is not a recent technology upgrade for scanners, as these features have existed for quite awhile now. However, this is new to me, for scanners. Of course, amateur radio transceivers have also been programmable via PC as well.

SD Card Storage

The programming for the scanner is stored on an SD card which is located under the removable battery pack. The scanner came with an 8 GB SD card and was less than 1% utilized when first initialized and the database updated.

The SD card for storage is new to me for a scanner, but I have seen this feature in several amateur radio transceivers over the years. For example, the Yaesu FT5D HT and the FTM-500DR mobile radio also have SD card slots, as do many other transceivers.

This is useful for both storing not only the programming but it also holds the voice recordings. The SD card is located under the battery pack and is removable.

When you plug the SDS100 into a PC, it detects the PC being connected and prompts you on the screen if you wish to enable either USB mass storage or serial port on the USB interface. If you select mass storage, the SD card will appear as a drive on the PC. Note that the scanner is not operational otherwise when in the mass storage mode.

With the direct exposure to the SD card as a drive on the PC, you can then use the Sentinel software to read from the scanner or write to the scanner to update the programming.

Built-In Frequency Database

The SDS100 has a built-in frequency database, pulled directly from radioreference.com. You can either enter a zip code into the unit and it will automatically scan frequencies for selected services within that zip code, or, you can connect a GPS and the unit will track your location and update what it scans based on what is nearby as you travel.

Of course, you can look up frequencies on your own using radioreference.com or other sources, but having the database in your hand and off-grid is useful.

This database being included removes any need to directly program in a trunked system for example. In some cases, a paid subscription to a reference source might be needed in order to get some of the technical details of a trunked system without this database being provided for you by Uniden.

This is a great feature because it eliminates the guess work and detective work of finding frequencies, especially compared to decades ago when “Police Call” was the go-to reference for me and many others.

Uniden claims this database is updated weekly. The updates can be downloaded via the Sentinel software and is stored on the SD card within the scanner.

Favorites Lists

The on-board database in the SDS100 is searchable and you can build “favorites” lists, adding services to the lists as needed. You can have more than one favorite list (up to 256), and you can enable and disable them independently.

For example, if you had a favorite list for each nearby area, you can turn them on or off independently, allowing you to build a range of services and locations on-demand. This would be similar functionality to “banks” on older scanners, where you can use a bank for each local area nearby (or by service) and turn on and off banks as needed, when you wish to listen to each area (or service). This can be useful for travel as well, such as a home location and away location.

There is no longer a concept of “channels” with the SDS100 where there is a limit of 10, 100, 1000, or more channels for example.

Recording

The SDS100 can record all audio received during scanning. The audio recording has the gaps removed, which allows you to record several hours or even days of received audio directly onto the SD card. As I described in a previous section, you can attach the SDS100 to a PC via a USB cable and enable mass storage mode on the scanner, and the SD card is then visible as a drive on the PC.

You can then browse to the audio folder, then the user_rec folder. There will then be one or more folders (depending on duration of recording). Each folder contains the WAV files of the audio recordings – each WAV file is one continuous opening of the squelch or a scan “hit”:

I continue to be impressed with the SDS100 with respect to thoughtfulness of the features. Not only is each scan hit recorded to a separate WAV file, each WAV file has some headers, or metadata added which indicate the channel (or talk group) the recording is for and also the site name. In the example above, I can see the date and time of the recording (the file name itself contains this information) and the exact channel information in order to know what the recording is from.

This is quite useful if you wish to leave the scanner on and use it to record all activity it hears for days, weeks, or months. For amateurs, this can be useful to monitor repeater activity and automate the tracking of how often each repeater is used and when.

The recording feature can also be thought of as the RF equivalent to a doorbell camera which can record all motion while you are away, or not actively paying attention to or listening to the scanner.

I will definitely use this feature to try recording weather satellites, amateur satellites, and the ISS as they pass. I had some success doing this with my FT5D recently with SSTV.

Getting Started with the SDS100

Getting started with the SDS100 can be a matter of simply turning it on and entering your zip code. Within seconds, you will have your scanner programmed and you might be hearing broadcasts instantly, depending on your location.

In my case, a few miles outside of NYC, the scanner would output non-stop audio from all the boroughs of NYC, Newark NJ and surrounding areas. From a marketing perspective this is quite a successful demo of the capability not only of the SDS100, but a great example of what can be heard these days with a handheld scanner.

This was not very useful to my preferences for what I wanted to use the scanner for, since I wanted only local traffic to be heard, at least initially. This scanner, like many other modern scanners, would take some getting used to, and relearning a new approach to organizing the programming for my needs.

Manual Selections

Since I wanted to hear only local activity initially, specifically in my town, I ended up selecting a specific site and adding that to a favorite list named “Local”.

In my particular area, many public service agencies, including police, use the NJCIS system. This is a state-wide multi-site trunked system, mostly P25, multicast, and in the 700 MHz area.

I found it was best to have just a few sites (only what is actually needed in order to hear local activity), and delete or remove all other sites and agencies (talk groups) out of the “Local” favorite list.

This was a manual process but simple. The end result is a favorite list that I can enable or disable, which “scans” very quickly. The more sites you add to the scanning program, the longer it will take for the scanner to work its way through the sites and back around again. This could result in missed transmissions if that list has too many sites.

Of course there are ways to mark priorities in the programming but this is not always a perfect solution.

Extra Purchases Might Needed

One of the oddities of this particular model is that it will not decode DMR, ProVoice or NXDN out of the box. In order to decode these formats, an additional license key is needed for each.

I am not familiar with license or intellectual properties of all of these various formats, including P25, but I suspect there are costs associated with these, not only for development, but licensing costs from third parties (if applicable) and maintenance costs (big fixes, protocol changes, etc).

Perhaps Uniden, in an effort to keep costs lower, included P25 decoding out of the box for the U.S. market, since that seems to be more common for public service agencies than the other formats are. Therefore, Uniden made the other formats optional and at an added cost, rather than including everything and having to raise the price of the model.

The process to purchase the extra licenses is simple, and is locked to your radio serial number. I doubt these are easily copied.

Waterfall Feature

One of the extra licenses you can purchase is the waterfall feature. This gives you the ability to visually see a rather large area of the spectrum, up to 20 MHz at a time.

This is really useful for discovery, but not all that useful for the average user, who may simply want to listen to specific sources.

This is quite similar to the waterfall feature on an SDR connected to a computer.

Final Thoughts

After many years of not using a scanner for casual listening of public service agencies, I had not seen the advancements in features and technology until very recently. I had a similar experience with amateur radio a few years ago, when coming back into the hobby, having to catch up on everything new since my last experiences with it.

With the widespread availability of SDR technology, the SDS100 is one of the first consumer level scanners to utilize this technology into a mainstream product. Further, with the simplified programming and massive built-in frequency and system database, an entry level consumer can easily begin listening, right out of the box.

I do believe that eventually all public service agencies will be moved over to encrypted communications, rendering scanners useless for the purpose of listening to fire, police and EMS. However, this could take years, depending on your location. Many areas are already using encryption.

However, there are other good uses for scanners, such as listening in to amateur radio stations, repeaters, satellites and even the international space station.

The SDS100 is a great portable scanner, useful for quite a bit of varied monitoring. It is worth noting that Uniden makes a similar “base” / mobile version of this scanner, the SDS200.

This very well might be the last scanner I buy, with respect to features. As more of the spectrum of public service use gradually becomes encrypted, the scanner use for decoding various digital modes would become less useful.