Salvage for salvation: budget FM radios in a post apocalyptic world

Historical records suggest that this electronics shoot out was conducted during a chilly, overcast winter morning. It was as bleak and lifeless as a post nuclear apocalyptic scene akin to the Terminator. It was speculated that a small gang of elitists running the incumbent government had somehow vaporized the masses of decent folk with their relentless, soul-destroying dogma and double talk.

Apocalypse © 2008 Michael Lehenbauer

All was not lost. The ‘suits’ had left some populist toys to play with. The few broken souls that remained in the city post apocalypse grabbed their toy radios. These were amongst their only remaining electronic devices. Could these rescue them from sheer desperation?

Graffiti: Greed is deadly © 2007 Bart Everson

It was rumoured that the internet – the old world hub of information transfer had been sold by the self-interested elite to the highest bidder. Restricted to the highest echelons, few mortals possessed the social connections to enable access to the electronic network that once had the capacity to empower the disenfranchised and wealthy alike. Now, social mobility was virtually impossible.

No weather indicators to were available. Accordingly, tropospheric enhancement to FM signals could be tracked on-line. Synoptic charts were not available. The FM band that did exist was as boring as hell, filled only with those routine permanent FM signals. DX enthusiasts (those that monitored distant radio signals) were a forgotten breed. In this new world order, survival was the only concern. Hobbies became solely the domain of the wealthy.

Wise words, In Greed We Trust © 2014 Ed Suominen

But the nightmare was only beginning. It is clear that the poor mortals (those determined few that were left) struggled on with their souls intact. As pointless as it seemed to be in that environment, their capacity to test and experiment would endure.

It is now known that amongst the ruins of their old municipalities they conducted many seemingly fruitless tests. What follows is one such test; a shoot-out. Where possible, the original source material is quoted from…

Populist’s dream radio shoot out

The simpletons focused on two cheap ‘bastards’ with a ‘fearsome’ reputation to uphold. When the economy still functioned, these radios were purchased at retailers like Junk World. It was said that the two machines the simpletons had chosen empowered them, coupled with their tenacity to ‘fight it out until the death’!

Junkworld © 2010 Danny Choo

A populist’s dream, the contenders consisted of the ADS Tech RDX-155 Instant Radio USB device versus discounter Aldi’s entry level Bauhn ADS-215 dual band portable radio…

Testers’ performance data

Table 1: Sensitivity equivalence illustrating selected moderate-weak stations

FREQUENCY	DISTANCE	POWER	INSTANT RADIO	BAUHN
88.5	53mi	26 kW	YES	YES
89.3	48mi	25 kW	YES	YES
90.5	43mi	200 watts	YES	YES
91.1	35mi	10 kW	YES, RDS	YES,  RDS
91.7	53mi	26 kW	YES	YES
92.1	43mi	5 kW	YES	YES
92.5	48mi	25 kW	YES	YES
94.1	48mi	25 kW	YES	YES
94.5	88mi	100 kW	YES	YES
94.9	26mi	50 kW	YES	YES
95.3	88mi	100 kW	YES	YES
95.7	53mi	26 kW	YES	YES
96.9	88mi	100 kW	YES	YES
97.7	53mi	26 kW	YES	YES
98.5	88mi	100 kW	YES	YES
102.9	25mi	48 kW	YES	YES
104.1	65mi	1 kW	YES	YES
105.7	48mi	10 kW	YES	YES
107.3	48mi	10 kW	YES	YES

 

Table 2: Marginal signals illustrating reception differences between the two budget receivers

FREQUENCY	DISTANCE	POWER	INSTANT RADIO	BAUHN
90.9	25 mi	48 kW	2 / 2	0 / 2 – ACI
95.9	40 mi	1.6 kW	0 / 2 – RFI	2 / 2
96.1	88 mi	100 kW	0 / 2 – RFI	1 / 2
99.4	48 mi	2 kW	2 / 2	1 / 2
100.6	48 mi	2 kW	2 / 2	1 / 2

Salvaging suitable antenna connections

The Bauhn ADS-215 radio was also connected to the rooftop antenna via a 1 m / 3.28 ft high grade RG59 cable. To connect the antenna internally would void the warranty. Moreover, it is difficult to achieve this as the plastic case must be plied open, since there are no screws!

External antenna connection on Bauhn ADS-215 © 2014 FM DXing

On the unit, cable was connected to the DC adapter ground [not pictured] and the collapsed telescopic antenna. The radio was powered using the supplied 5 volt DC adapter.

Optionally, if cutting coaxial cables is unpleasant, connection can be easily made via a 30 cm / 1 ft twin-lead wire then a 4:1 matching transformer. To be perfectly honest, transformers do pose some insertion loss as part of any antenna system. Surprisingly, no difference in signal strength of weak stations was detected between connection methods.

RDX-155 Instant Radio was connected to the rooftop antenna via a 1 m / 3.28 ft high grade RG59 cable. This cable also may cause some loss of signal and be susceptible to interference from the USB device. Sure, RG6 quad shield cable is better, but in practice the centre conductor is too thick to reliably connect to a pint- sized USB PCB. The laptop was powered using a battery.

It is speculated that access to laptop computers was not a trivial matter. Computers were  rare and prized possessions in post apocalyptic life. Because access to the internet was predominantly impossible, these computers were useful for processing needs only and recording data.

Fortunately, Instant Radio posed few Central Processing Unit (CPU) demands and looks to have functioned remarkably well on these old machines. How the simpletons ever charged that battery without a reliable mains power grid (they could not afford the onerous electricity bills) remains a mystery…

Post apocalyptic broadcasting

Records show that only an FM test was possible. But it was noted (amongst the word processing files found) that with the Bauhn dual band radio, full strength DAB+ reception (174 – 240 MHz) was available with the rooftop antenna. Photos were found of the graphical bars of the signal meter. Its Gyro Signal 1128 chip permitted satisfactory dual band reception at this time. (We don’t know the manufacturer’s objective sensitivity measurements for this module, but an Adobe Reader document with the FM performance of their 2005 module can be found via the end links). Retailing at $30, the Bauhn ADS-215 radio was likely to be an affordable choice for those with limited fiscal capabilities.

No contemporary music was being released or recorded. The broadcasts on the DAB+ multiplexes in these times included songs performed by old school cover bands such as Il Divo & Celtic Thunder. Music that was deemed to be fodder for the oppressed was reportedly banned for broadcast. For example, ‘aggressive’ releases by Neil Young, Metallica, the Dixie Chicks & John Butler Trio were illegal to broadcast, even if the recordings had been retained by some members of the elite. It has been suggested that the themes in these artists’ works may have been incompatible with the extremist ideology of the ruling elite…

Bauhn ADS-215 post Apocalypse © 2014 FM DXing

Luxurious RDS performance suggested

Seven signals in the [above] table are known to provide digital Radio Data System (RDS) data. Six of these signals were too weak to decode. Only one quieting-level signal was included in the test, a broadcast on 91.1 MHz. On this channel, RDS data decoded easily on both units. RDX-155 Instant Radio offers faster decoding than the Bauhn ADS-215 radio. The Programme Type data (alone) decoded reasonably quickly on the Bauhn radio, but Instant Radio has a clear edge.

PI code mode on Bauhn ADS-215 © 2014 FM DXing

Close up, PI code mode on Bauhn ADS-215 © 2014 FM DXing

The Bauhn ADS-215 radio will display unique station identification codes called PI codes as part of the RDS digital data. This feature may offer potential value for DXing.

Post war, it is known that the elite took control of electronics and computing power. Whilst the elite played real life games on the stock market, the mortals continued their desperate simple tests. Trivial? Indeed. But it is all they had. They continue…

Riding out the Apocalypse © 2011 David Blackwell

Differences testers observed

Where differences were noted between receivers on any particular frequency, the test was conducted twice. Between 95.9 – 96.1 MHz, no signal was heard due to heavy interference obstructing potential reception on RDX-155 Instant Radio. The interference was caused by a spurious signal.

This annoying side effect is a widely reported issue with the device that cannot be readily remedied by ferrite suppression chokes. It will be offset by a masthead amplifier, of course. Conversely, no spurious signals were observed on the Bauhn ADS-215.

Bauhn ADS-215 post Apocalypse © 2014 FM DXing

On 99.4 MHz & 100.6 MHz, only weak signals were detected. Nonetheless,  RDX-155 Instant Radio appeared to outperform its rival in terms of sensitivity. On 90.9 MHz, no signal was detectable due to adjacent channel interference obstructing potential reception of the broadcast on the Bauhn radio. Again, this suggests selectivity out-performance by the Silicon Laboratories’ (Silabs) integrated circuit inside in the Instant Radio.

It is thought that back in the ‘olden days’, Silabs produced radio electronics that every man, woman or android could afford. Although Silabs mainly produced chips for portable standalone radios at this time, the RDX-155 Instant Radio represented somewhat of an oddity; a discontinued $17 computer-based tuner in a tiny USB enclosure.

Intermodulation dynamic range was tested on empty or very weak channels. Strong signal immunity is extremely important for FM reception applications and arguably a more important characteristic for any FM tuner than any simplistic sensitivity measurement or test. It is pleasing to report that no ‘ghost signals’ were detected on either receiver, despite the congested band. Accordingly, a high quality signal amplifier (ideally a masthead amplifier, positioned at the antenna) may increase sensitivity without compromising performance.

Instant FM Radio post Apocalypse © 2011 Synx 508

Simpletons’ summarized observations

The test (as collated in the table) suggests that potential differences in sensitivity, (if any exist) are likely to be negligible between ADS Technologies’ RDX-155 Instant Radio & Aldi’s Bauhn ADS-215. Weaker signals, such as the 90.5 MHz translator are not readily detected in flat winter conditions. The performance of Instant Radio was superior on three stations (probably due to better sensitivity and selectivity) but internally generated interference tended to offset any gains.

These findings suggest that the simpletons were confident both units would provide satisfactory FM reception for the modest outlay they originally paid at retailers like Junk World.

The broken souls understood a masthead amplifier could be used with these inexpensive receivers to improve performance when coupled with an external antenna.

Junk electronics © 2007 Marco Bernardini

It was beyond the means of most, but they found some antenna pre-amplifiers on the streets; regrettably their beloved streets had become so littered with redundant electronics their suburbs resembled a rubbish dump. These cheap radios gave the broken souls hope for the future. Finally their story of hope can now be shared for the benefit of future generations.

Society’s future is unwritten. Government policy or individual action that promotes greed, entrenches class divisions & exacerbates poverty is the real ‘junk’ of the world!

Non-fiction reference material!

Extensive test of Instant Radio RDX-155

Boxing kangaroo test of Bauhn ADS-215

Gyrosignal 1122 FM/DAB receiver module specifications

Masthead amplifiers potentially benefit weak FM signals

Role of RDS data in long distance FM reception

FM USB Tuner Shootout: PC Ear vs Instant Radio (ADS Tech RDX-155)

Welcome to another radio shootout, Boxing Kangaroo edition! These shootouts feature ‘dirt cheap’ radios and are intended to appeal to a variety of different potential audiences, including terrestrial FM radio listeners and hobbyists interested in elementary electronics or FM reception capabilities.

Digital Signal Processing on the cheap?

At the time of writing, the cheapest Chinese portable FM radio currently available incorporating Silicon Labs’ (Silabs) Digital Signal Processing (DSP) costs about $49 including delivery. This model is the Tecsun PL-606. For those with a laptop and access to a directional antenna, USB computer devices with the SI4700/01 integrated circuit (IC) are considerably more inexpensive, representing a cheap entry to Silabs DSP.

The contenders: Two popular Silabs USB FM tuner

Instant FM Radio (Instant Radio) costs about $17 including delivery.

PC Ear costs about $17 wholesale but is no longer readily available new.

Gunning for the best: PC Ear versus Instant Radio

A rudimentary inspection of the datasheets suggest the FM sensitivity measurements are equivalent for the Silabs ICs inside PC Ear and Instant Radio. To test this, a modest directional antenna was connected to the devices. Both devices were housed in a metal enclosure with two suppression chokes and operated with a Radio Frequency (RF) quiet laptop running from battery power.

Reception conditions were well below average with heavy, unrelenting rain. 15 stations were chosen for the test. Of these, 13 stations were detected with the minimum signal strength of 0, where signals are just audible above the noise floor. Because of the heavy rain, two of the usual weak signals were not audible during the test and accordingly, do not appear in the performance table.

Software

PC Ear does NOT support firmware upgrades using the Windows-based Silabs configuration software utility. Firmware updates to PC Ear can be done under Ubuntu/Linux, but the process may be complicated. The Silabs Radio DLL software appears to function, but audio issues were evident when tested briefly with PC Ear. According to the developers, it is supported.

The upgraded firmware was used with Instant Radio. The upgrade was performed per the ADS Configuration user guide instructions for Silabs Radio DLL, developed by Beezer, Guino and Pete.

Characteristic	PC EAR	INSTANT RADIO
Tunable frequency range	76 – 90 MHz, 87.5 – 108 MHz	76 – 90 MHz, 87.5 – 108 MHz
Circuit board approximate size	1.3 x 0.6 inches	2.4 x 1.1 inches
Tuning steps	50 kHz	50 kHz
Radio Data System support	No	Yes
Software support	USB Radio 2.0-3.0 (supplied), FM Signal Strength Analyzer 1.0.0.19, Silabs Radio DLL, Silabs configuration software utility.	Instant Radio 1.0.0.11 (supplied), Silabs Radio DLL, FM Signal Strength Analyzer 1.0.0.19, Silabs configuration software utility.
Hardware version	PC Ear 1.77	Silabs 1.7.15
Firmware upgradable	No, Please refer to body of article	Yes, ADS NoiseMod Primary.dec

The software support listed in the characteristics table (above) is NOT exhaustive. Please understand that the priority was to test reception performance.

Any frequency (or broadcast) can be easily recorded for hours ‘on schedule’ using third party Windows audio recording schedule software such as Fox Magic Audio Recorder (free) and High Criteria Total Recorder Professional ($36). The software supplied with the devices also offers recording ‘on demand’. ADS Tech Instant Radio software is especially recommended for this purpose, since it offers high resolution 96 kHz uncompressed recording capabilities.

Comparative performance

PC Ear is constructed on a double sided printed circuit board, whilst the Instant Radio device uses a much larger single sided board (above). Unsurprisingly, both designs feature surface mount components.

RADIO STATION FREQUENCY (MHz)	PC EAR MAXIMUM SIGNAL STRENGTH (BARS)	INSTANT RADIO MAXIMUM SIGNAL STRENGTH (NUMBER)	INSTANT RADIO RDS DECODING	DISTANCE (MILES)
90.5	0	3	No	43mi (200 W)
91.1	2 – Quieting Mono	19 – Quieting Mono	Instant	35mi
92.1	0	6	N/A	43mi
93.7	0	0	N/A	62mi
94.9	0	6	No	27mi
95.3	1	6	N/A	88mi
98.5	1 – Quieting Mono	9 – Quieting Mono	N/A	88mi
99.4	0	0	No	48mi (2 kW)
99.5	No signal, Slight high adjacent channel interference (99.7)	0	N/A	208mi
102.9	0	6	N/A	48mi
104.5	4 – Quieting Stereo	50 – Quieting Stereo	Instant	11mi
105.7	0	5	No	48mi
107.7	5 – Quieting Stereo	57 – Quieting Stereo	N/A	11mi

Instant Radio consistently offered a slight edge with superior adjacent channel suppression on one station and the advantage of RDS. PC Ear did ‘stutter’ occasionally on one RDS-enabled station. A change to the device settings (below) and immediately unplugging the device solved the problem. This trivial audio issue could not be replicated again after 15 minutes of listening to the station, nor the next day.

There were no consistently observable differences in sensitivity, audio quality or immunity to internally-generated spurious noise (interference) between the devices. This result was somewhat unexpected because PC Ear is rumoured to be an earlier Silabs USB tuner prototype with its share of critics on the world wide web. Perhaps the critics use the supplied wire antenna (in both devices, 29 inches long) and therein lies the problem? But the test suggests PC Ear performs just as well as Instant Radio with a directional antenna. If anything, the test was biased against PC Ear because of expectations the device was of poor design quality relative to its sister models.

Performance improvements

It should be stressed that Instant Radio and other Silabs devices require antenna modifications (below) for connection to a directional antenna such as a rooftop television antenna. Soldering skills are recommended for permanence. The use of other alternatives to ‘mate’ the device with an external antenna, such as passive induction as used in some mobile broadband device antennas might also be feasible, but discussion is beyond the scope of this shootout.

With the additional expense of a metal enclosure, shielded five metre USB cable, pre amplifier and several ferrite suppressors, the total cost equates to approximately $135. Many readers may already own much of this equipment, but it does represent a potential outlay. In this blogger’s opinion it is only worth pursuing such a project for the sheer fun of experimentation!

Notwithstanding the extra Do It Yourself (DIY) effort and cost required to extract the device’s DX potential, Silabs tuners feature satisfactory signal separation and strong signal handling. With the above modifications, Instant Radio is sensitive enough for daily signals from in excess of 265 miles. Momentary meteor pings from distant FM stations are possible to receive. Although untested at the time of writing, it is anticipated that modifications to PC Ear would accomplish the same. The bottom line is that these Silabs devices were designed for learning projects. It is NOT suggested to ‘throw good money after bad’.

Comparative performance with expensive stand alone tuners

As one should realistically expect because of the tiny footprint and price, the devices are outclassed by stand alone tuners with a proper shielded tuner module. Even with a preamplifier used in-line to desperately boost sensitivity, this is apparent. Head-to-head, the following tuners or SDRs (tested without preamplifiers, using the same antenna) all noticeably outperform Instant Radio (FM usable sensitivity* is listed in brackets):

• Blaupunkt Casablanca CD51 (1.68 microvolts),
• Elad FDM-S2,
• Sherwood TX-5090 RDS (1.58 microvolts),
• Yamaha TX-950 (0.8 microvolts).

For example, in a ‘dead-of-winter’ test, the Blaupunkt automotive receiver consistently achieved better performance than Instant Radio. Improved RDS sensitivity meant that the car radio decoded digital RDS data from two extra stations. Like all models in the Sharx range, the car radio more readily discriminated stations spaced 100 kHz apart.

Instant Radio was capable of receiving 2/3 of the 15 weak signals chosen for the test, whilst the car radio nabbed 93% of weak signals! The Silabs devices enable reception of the same stations from in excess of 265 miles as standalone tuners. However, this reception will obviously be more transient and weaker signals are unlikely to be audible. From a DX enthusiast’s perspective, that may be a frustrating prospect.

The number of RDS decodes achieved with Instant Radio was equivalent to the Bauhn ADS-215 dual band portable radio connected to a carefully aligned rabbit ears antenna mounted near a window. Invariably, Instant Radio outperformed the Bauhn portable radio using its inbuilt telescopic antenna.

Summary

The device incorporating the Silicon Labs’ SI4701 IC (marketed as ‘Instant Radio’, above) is one breed of flash-drive sized computer tuner that offers modest potential for weak FM signals. It suits receiving locations with a congested FM band. Its full RDS capabilities can be exploited in locations where broadcasters support the system. PC Ear also offers similar performance, without RDS decoding.

All software tested works successfully on both receivers without noticeable bugs. There is a range of tuning software to choose from. Both Silabs devices are suited to DIY modifications.  Users of Instant Radio benefit from access to the latest firmware.

Further reading

Gadget tunes in to FM via USB

Instant Radio for distant FM reception

Instant Radio satirical shootout

Instant Radio slideshow

Radio recording saved the radio star

Silabs Radio DLL

* Standard DIN sensitivity specifications, tested with THD 3% & S/N of 26 dB. Official data, sourced from manufacturers. Lower numbers (approaching zero) indicate the best FM sensitivity. The Elad FDM-S2 sensitivity is measured differently from conventional tuners. This SDR offers better than 2 microvolts using the 12dB SINAD measurement on the extended FM band.

As always, the writer has no affiliation with any retail merchant or product manufacturer. This entry is NOT intended to be construed as an endorsement of any particular model. Prospective buyers should carefully make their own enquiries according to their particular needs and circumstances.