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Ultralight Radio AM-DX Shootout-- Round One


Ultralight Radio AM-DX Shootout-- Round One
updated January 3, 2008

Introduction
Recently, perhaps out of nostalgia for a bygone youthful era, the reviewer purchased a Sony SRF-59 Walkman, a tiny analog AM-FM Stereo radio that looked almost exactly like the portables of old. With very low expectations, the reviewer proceeded to test it out … and was absolutely astonished! The unit not only had outstanding sensitivity and selectivity, but was almost entirely free from images and birdies, right from 530 to 1700 kHz. It had superior AGC and audio. As if this was not enough, the price was only $17.00! In over 40 years of medium-wave DXing, the reviewer had never experienced such a phenomenal small radio. Within a few days, it was used for multiple TP contacts (a thrilling experience, and hopefully the start of a pocket-radio trend). Strictly by accident, the resulting adrenaline rush caused the reviewer to mistakenly send an email reporting this exciting experience to Colin Newell, the administrator of the excellent dxer.ca website, who not only encouraged a full review of the SRF-59, but also honored me by offering to post the entire review on his innovative web site.

The Contestants After discussion of the SRF-59 started on the IRCA list reflector, it was suggested that other pocket portables have performance equal to (or surpassing) this surprising performer. Always eager to find an excuse to purchase more new radios, the reviewer chose three additional highly-recommended AM –DX portables to participate in this Ultralight Radio AM-DX Shootout: the Sony SRF-M37V and Sangean DT-200VX digital units, and the Sony ICF-S10Mk2 analog unit. These would be thoroughly tested for sensitivity, selectivity, image and spurious signal rejection, AGC, audio, and TP/TA reception ability (if any). Following basic descriptions of each of the units, the tiny radios will be tested in a competitive live-signal “shootout,” to be followed by a thorough analysis, critical judgment, and the pronunciation of a final verdict for each unit.
Sony SRF-59
This tiny analog AM-FM Stereo unit was the subject of an extensive 4-page review recently written for Colin’s excellent dxer.ca website, and the IRCA Technical Column. The review includes detailed information on the construction, circuitry, performance (in relation to the ICF-2010, ICF-SW7600GR and ICF-S5W models), and also a section on pocket-radio TP-DXing tactics. Readers are encouraged to read the posted review for full information on this highly respected pocket portable, which the reviewer has used for multiple TP loggings. It retails for $16.08 at Amazon..

Sony SRF-M37V This digital TV/Weather/AM-FM Stereo headphone-only unit is extremely compact (83 x 63x 32 mm, or 3.4 x 2.5 x 1.3 inches), and weighs only 94 g (3.3 ounces). It has a clock, 25 memory presets (5 for the AM band), and most importantly, the critical ability to tune the entire (530-1710) AM band in either 9 or 10 kHz steps. Besides the 87.5- 108 FM coverage, it also can tune TV channels 2-13 and Weather channels 1-7. It includes a basic set of stereo headphones (acceptable for AM-DXing, but not recommended for FM-stereo enthusiasts), and a belt clip. It requires a single AAA battery (not included), which is reputed to last 54 hours on AM, and has an attractive black case with silver dial trim. The case has a curved bottom edge, with the memories accessed by five front-panel push-buttons (that could conceivably be distinguished in the dark, by a DXer on an ocean beach). The unit retails for $34.99 (Amazon). Needless to say, the combination of 9 kHz split capability, digital tuning and memories makes this radio the uncontested leader in AM-DX tuning convenience among the contestants.

Disassembly of the compact SRF-M37V (by removing the four back-panel screws, two of which are in the battery compartment) reveals two circuit boards—the front surface-mount digital board containing the front-panel clock/display, and various pressure-sensitive switches (Power, Clock, Band, memories, and Tune/Time set inputs) and a lower-case discrete-component RF/AF amp board, containing the 51 mm (2 inch) ferrite bar antenna, tuning coils and IF circuitry for various bands, the volume control and headphone jack, audio amplifier circuitry, etc. The ferrite bar antenna is curiously located in the center of crowded components sandwiched between the two circuit boards—hardly an ideal position for optimum RF patterns, or nulling capability.

Sony’s proprietary IC is apparently the shielded dark gray-colored IC located between these two boards on the reverse of the front surface-mount board, although this was not verified. Finally, experimenters are unlikely to be enthused by the cramped construction of this unit, which obviously was designed by Sony to cram every possible component into the smallest space. Although the unit’s disassembly proceeds logically without surprises, even a confident hobbyist may feel like he is entering the watch repairman’s domain. The tricky fourth micro-screw (located in the recessed area of the battery compartment), for example, can only be reinstalled by placing it vertically on your micro-screwdriver, turning the radio upside down, and “threading the needle” with nerves of steel.

Sangean DT-200VX This innovative, attractively styled TV/AM/FM-Stereo radio is slightly larger than the M37V at 107 x 63 x 19 mm (4.2 x 2.5 x .75 inches), and weighs 106g (3.8 ounces) without batteries. It offers the choice of headphone or speaker operation, and has many features such as 19 memories (all of which can be used on AM), auto station scanning, TV channel 2-13 audio, 60-minute auto shut-off, a base-boost circuit, function lock, and FM-mono capability. The DT-200VX is fully capable of tuning in either 9 kHz or 10 kHz steps, and can be switched very easily as follows: For 9 kHz step operation, with the radio OFF, hold down the TUNE DOWN button until the screen flashes "StP 9" three times, and audio comes up. To reverse back to 10 kHz, follow the same process but use the TUNE UP button. The screen will flash "StP 10" three times, and the radio will come on with the 10 kHz step system. The DT-200VX FM sensitivity and selectivity is clearly the best among these portables, and when combined with the versatile scanning and memory functions, makes this unit the obvious choice for an FM enthusiast. It requires 2 AA batteries reputed to have 30-40 hour run time, and comes with a belt clip, stereo ear buds, and trailing antenna. Having an ergonomically pleasing black case with gray push-button controls, it retails for $49.99 at Amazon.

The DT-200VX is one of those tight-fitting portables that requires some prying persuasion to disassemble, even after the three rear screws are removed (similar to the SRF-59). Disassembly also causes the top panel, the small Lock and Stereo/Mono/Speaker switch plates and the DBB switch control to fall out, which may deter casual hobbyists from proceeding. The main circuit board, located on the radio’s back side, contains both surface mount IC chips on the back-facing side (a large 24-pin TA8132AFG and two smaller IC’s, one of which is presumed to be an audio amp because of speaker connections) and discrete components facing the radio’s front side (a 56 mm or 2.22 inch ferrite bar antenna, tuning coils and IF circuitry for various bands, the volume control, headphone jack, and the input/output connections for the previously mentioned IC chips). The ferrite bar loopstick, though well isolated physically, is curiously located at the bottom edge of the radio.

The second, smaller (surface-mount constructed) circuit board, attached to the front of the unit, contains IC’s and circuitry for the display, tuning and band switch inputs and outputs, memories, and the power switch. Finally, the tiny 35mm (1.4 inch) 4-ohm speaker is one of the smallest the reviewer has ever seen, and seems unlikely to win any audio awards. The hobbyist attempting to reassemble this unit has the enjoyable task of fitting the front and back together while pushing in the top panel, simultaneously juggling the Lock and Stereo/Mono/Speaker switch plates, all the while pushing in the DBB control lock lever. Success in this ultimate challenge, if attained, makes you feel like you’ve just built a Heathkit.


Sony ICF-S10Mk2 This very basic analog AM/FM Mono portable looks like something straight out of the 60’s, and seems designed for the growing (read: growing older) nostalgia group. The silver-colored retro-radio tunes only to 1605 on AM, and at 71 x 118 x 30 mm (2.9 x 4.7 x 1.2 inches) while weighing 202 g (7 ounces), is the largest and heaviest unit of this group. Taking 2 AA batteries (45 hours run time), it features a speaker, a LED for tuning, carrying strap, and very little else. At $9.99 (Amazon), what did you expect?

Disassembly (by removal of two different-sized screws) reveals a geared tuner, with separate geared plastic linkage in a front-panel slot, connected to the dial needle (exactly like the SRF-59). This also makes the radio tricky to reassemble (again, like the 59). The very limited circuitry (mounted on the back side of a discrete-component circuit board) features a 50 mm (2 inch) ferrite bar antenna at the top of the radio, a 30-pin master IC, and other basic components exactly like the radios of the 60’s. The 58 mm (2.25 inch) speaker also plays the retro part, and after viewing this very modest circuitry, the hobbyist will have the pleasant task of attempting reassembly (by aligning the tuner gear with the geared dial linkage, making sure both match in frequency, and don’t bind).

Shootout Day Arrives It was a cold, harsh December morning in Puget Sound, when these four gallant contestants gathered together to decide their fate. Noontime conditions were somewhat below average, adding to the somber mood. For the sensitivity tests, the radios would compete to receive KONA-610 (160 miles), CFAX-1070 (110 miles) and the KVRI/KOHI-1600 mix (125/100 miles). For the selectivity tests, they would compete to split off KPQ-560 from KVI-570 (tough), CHMJ-730 from KIRO-710 (moderate) and KARR-1460 from local KSUH-1450 (extremely tough). Following these live-signal “shootouts,” each radio would be evaluated for images, spurs, AGC and audio quality. Any individual defects would also be noted. In the following tables, “5” is excellent, “4” is very good, “3” is average, “2” is fair, “1” is poor, and “0” is extremely poor. This judges the accomplishment of the specific task only, not the overall radio performance.



Sensitivity: KONA-610 CFAX-1070 KVRI/ KOHI-1600
 
SRF-59 steady weak audio (2) moderate audio (3) moderate mix audio (3)
SRF-M37V weak mumbling audio (1) moderate audio (3) strong mix audio (4)
DT-200VX weak mumbling audio (1) moderate audio (3) moderate mix audio (3)
ICF-S10Mk2 no reception (0) no reception (0) no reception (0) Sensitivity Summary:

The three top units have roughly similar sensitivity from the bottom to the
top of the band, with the SRF-59 having a slight edge on the lower frequencies, and the
SRF-M37V having a slight edge at the top of the band.
The ICF-S10Mk2 is hopelessly outclassed, failing to detect a trace of any of these test stations.

 
Selectivity: KPQ-560 CHMJ-730 KARR-1460
 
SRF-59 moderate KVI slop (3) no KIRO slop (5) moderate KSUH slop (3)
SRF-M37V all KVI slop (0) strong KIRO slop (2) all KSUH slop (0)
DT-200VX all KVI slop (0) weak KIRO slop (4) all KSUH slop (0)
ICF-S10Mk2 all KVI slop (0) all KIRO slop (0) all KSUH slop (0)



Selectivity Summary: The SRF-59 has a strong selectivity advantage across the band. The
DT-200VX is much more selective than the SRF-M37V, which is slightly superior to the ICF.

Individual Issues

SRF-59: No images; insignificant spurious whistle on 730

SRF-M37V: Strong KSUH-1450 image on 550; poor selectivity adjacent to

locals, i.e. KKOL-1300 covers 1280-1340, KSUH-1450 covers

1410-1500, and is weakly heard up to 1640; spurious mix of

KSUH-1450 and KZIZ-1560 heard on 1610

DT-200VX: No images; insignificant spurious whistle on 750

ICF-S10Mk.2 Strong KSUH-1450 image on 540, and strong KZIZ-1560

image on 650; poor selectivity, poor AGC, multiple spurious
whistles across band; extreme background noise across band


 

Shootout Final Summary The top three units were very competitive in the sensitivity tests, but when overall DX capability is evaluated, only the DT-200VX excels in total performance. The SRF-59 is clearly far superior in selectivity, but most DXers would consider its analog tuning system (and a rather touchy tuning dial) somewhat burdensome. The SRF-M37V has superior digital tuning convenience (with memories), but it has a serious selectivity issue. Only the DT-200VX has good selectivity with great tuning convenience (with the most memories), and as such, it deserves the title of the best digital Ultralight radio in this shootout. The SRF-59, because of its superior selectivity and nulling ability, would still be the choice of the analog enthusiasts who are willing to tolerate (and even enjoy) somewhat touchy thumb wheel tuning.

SRF-59 Verdict This radio is far superior in RF performance, not only considering its selectivity advantage, but also its astonishing nulling ability. It can easily receive stations next to (and actually on) local frequencies, including many that the other units have no hope of receiving. It has superior AGC and audio. But the reviewer is fully aware that analog tuning is burdensome to many, and that the digital revolution has increased our expectations for tuning convenience. Each individual DXer must decide for himself whether analog tuning is preferred, acceptable, barely tolerable, or a deal-breaker. For those who love analog tuning (or can tolerate it), the SRF-59 is truly a DXer’s Dream Machine. For those who are allergic to analog tuning or addicted to memories, the reviewer recommends either the SRF-M37V or DT-200VX, depending upon whether you are a transoceanic or domestic DXer, respectively. Urban DXers with many locals may wish to consider this well-behaved unit, even if analog is not their first choice.

SRF-M37V Verdict This unit is a wonderful achievement in digital tuning convenience, memories and 9 kHz split capability, and if not for its serious selectivity issue, would have been the obvious choice for transoceanic DXers. Even with this limitation, both the reviewer and another DXer have used it for TP reception, and its ability to store 9 kHz split frequencies in memory is a tremendous advantage, when propagation peaks occur. The selectivity problem presumably would be less troublesome in isolated, rural locations, and a DXer on an isolated beach could really have fun with this radio’s sensitivity, and tuning convenience. But the cold fact is that urban and suburban DXers have way too much unwanted RF in the air, and this radio is only too happy to spread it all over the dial. A typical example is when I was sure of a Korean HLAZ-1566 logging, until I heard the same Korean voice on 1548, 1539... and all the way down to my Korean local, KSUH-1450. On the other hand, if a DXer views these Ultralight radios as simply a fun curiosity and is willing to take the chance of local slop covering their TP or TA, this may be the radio for those who need memories, split capability, and decent sensitivity. For urban DXers, however, the SRF-M37V’s poor selectivity (and image susceptibility) should properly be considered unacceptable. With good AGC and audio, it’s like a great puzzle missing one important piece.

DT-200VX Verdict This innovative radio is great fun to use, and has digital tuning convenience surpassing that of the SRF-M37V, with far superior selectivity. It would be an excellent choice for both domestic and transoceanic DXers, and for usage as a very lightweight travel portable, with class-leading memory capacity. It has great AGC, fine audio, a very well-behaved receiver almost completely free from images and spurs, and has the auto shut-off function. FM enthusiasts would also love this radio, which is clearly superior in FM sensitivity and selectivity. Urban DXers may also wish to consider this radio because of its immunity from images, and serious spurs (in my moderate-RF environment).

ICF-S10Mk2 Verdict In the harshly competitive world of a shootout, absolute honesty is imperative. This unit was replaced before the competition, because the reviewer thought it might be defective… but both units had the same performance. The opinion of the DXer who recommended this unit is very well respected. However, Sony has apparently either stripped down the AM section in this latest unit, or changed it entirely. This radio’s sensitivity and selectivity are very poor. It could not receive any test stations, either for sensitivity or selectivity. It has multiple images, and more “birdies” than an aviary. As far as TP ability, a DXer in southern California might be able to receive Santa Catalina Island… on a good day. I don’t think Sony intended this radio to be a serious DX performer, and it should be avoided, except to receive your locals.

 


Gary De Bock wishes to express sincere appreciation for the very generous assistance and support from Nick Hall-Patch, in the drafting of this review. Sincere thanks are also given to Colin Newell, whose interest in the Ultralight radio concept truly made the SRF-59 review possible. {mos_sb_discuss:12}

 

 

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