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Reviews Categories | Receivers: General Coverage | Radio Shack DX-300 Help


Reviews Summary for Radio Shack DX-300
Radio Shack DX-300 Reviews: 12 Average rating: 3.1/5 MSRP: $$399.99 (in 1980)
Description: The DX-300 is a DC to 29.999 MHz general-coverage short wave radio.
Product is in production.
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EX-W6BC-REMOVED Rating: 5/5 Dec 6, 2003 16:14 Send this review to a friend
Great General Coverage Radio  Time owned: more than 12 months
I have had my DX 300 since 1980 and have been very pleased with it. The DX 300 performs exceptionally well thanks to its "Wadley Loop" tuning system. The Loop system uses a single 1 MHz crystal to generate harmonics at 1 Meg intervals, a double mixing process with a tunable 45.5 to 75.5 Mhz oscillator providing 30 tunable ranges from 500 Khz to 30 Mhz.

Pros: Great AM sound, 20 & 40 meter reception very good with simple dipole
 
N5NSL Rating: 3/5 Jul 19, 2003 21:52 Send this review to a friend
OK Radio, but needs to be understood to use.  Time owned: 0 to 3 months
I remember looking on the DX-300 and DX-302 when I was about 14 or 15 and remember liking the radio at the time as a general coverage receiver. At a period where I was too young to earn a $3.00 minimum wage, the $399 radio was out of the question at the time. There are a few DX-300 and DX-302 radios floating around ebay and I decided I'd reacquaint myself with the old radios. The DX-300 model I received was apparently an attic-resident from the estate of a ham who had SK'ed. I cleaned up the radio's physical dirt and dust, reset and re-lubed the RF preselector, wiped most of the accessible contacts, and partially realigned the rig with a frequency counter and a reference radio. (It didn't need much alignment.) After all this it behaves exactly like a cleaned up December, 1978 (12A8) vintage DX-300.


The Good:

The radio controls are easy to operate and the displays are easy to read. The large five-digit display in the upper middle of the radio's face is easy to display and instantly responsive to any movements of the kHz display. If the kHz knob is spun, the display will display the usual 8 pattern as the numbers increment or decrement faster than the eye can perceive. The sound quality is passible and somewhat adjustable with the "Audio" switch ("Wide", "Normal", and "Narrow", referring to the AF tone or AF frequency response). In the DX-302 the "Audio" switch was replaced by a "Sensitivity" switch, which toggles an IF filter in and out. The AM mode also has an ANL circuit to reduce the effects of static, and SSB and CW reception is good, but CW reception is wide (and tuning is fast) and requires an external AF notch filter or equalizer to pick out individual stations in crowded bands. There is no BFO per se as in the DX-302, but a "Fine tuning" knob rotates 360 degrees and proportionally offsets the radio's tuning +/- .5 kHz when rotated 90-degrees off it's knob-mark-impled "center" (knob mark pointed "up"). The radio is three-way powered by 120VAC, 12VDC into a male coaxial power connector on the chassis, or eight "C" cells in a two-row bay on the radio's backplane. On A/C power and 12VDC power the display and backlights both illuminate continously. On battery power, only the LEDs illuminate unless the "Light" front-panel switch is set to "On".

It has two 1/8" mono jacks (outer one's for an external speaker, inner one's for a morse code key which keys an oscillator through the speaker for code practice). It also has a RCA phono jack marked "Tape" for line-level output to a recording device (assumed to be a tape recorder). The radio also has a PL-259 coax connector and a screw-tapped connector for a twin-lead antenna (or an antenna and a ground wire). The radio also has a mute function accessed by either shorting the "Mute" tap screw to the adjacent "Ground" screw, selecting the "Standby" mode from t On the DX-300 it increases/decreases speaker circuit capacitance. The modulation mode selector, or rotating the "MHz" tuning knob until the "Mhz" portion of the digital display blanks.

Physically the radio is in a black face with a black face. The LED display is the most outstanding feature of the radio after the two large tuning knobs. While insufficient for nightlighting, but radio is extremely easy to view at night or in a low-light environment.


The Interesting:

This radio basically uses three tuning devices to acquire a signal and in operation can tune from DC to 30.000 MHz. To acquire a signal (after the RF-Gain is properly set), the user has to set the MHz knob then set the kHz knob to get to an indicated frequency, set the RF preselector to notch-in sensitivity (and some selectivity) for the given frequency) while watching the signal strength meter for the point of greatest gain, then sometimes adjust the MHz knob very slightly to "peak up" the sensitivity even further. Often but not always on this method, you'll arrive right on the indicated frequency.
I set the radio to tune to DC (0.000 MHz indicated and actual), and it went to full-signal and was resolving the vibrations from the chassis if I tapped hard. At 0.000 MHz, the DX-300 very vaguely acts like a really insensitive microphone.

In theory it can also receive VLF (below 150kHz), but I've never heard any VLF traffic in my life (including with this radio). However, at 3 kHz with full RF-Gain and no antennas connected, it picks up it's own LED display. But with any antennas connected, it'll pick up the outside world at 3kHz.

Also, it resolves low frequency signals well (150kHz to 519kHz) with no interference, and treats 455kHz like just another frequency.

It receives AM (MW) signals well, with some interesting internal interference if a weak signal lands between 0.910MHz and 1MHz due to the nature of its implementation of Wadley loop synthesis.

Also, if the preselector and main tuning are set far enough apart amid extremely strong stations with a long random-wire, the radio may tune in those extremely strong stations with the preselector as the primary determinant in the tuning, regardless of the main tuning setting. (That is, the radio's circuitry after the preselector is subject to overloading and the notch-filtering nature of the preselector effectively becomes the radio's tuner if a signal is already extremely strong into a very large antenna). The DX-300's manual generally acknowledges this as a trait in the radio's design. Also due to this, if the main tuning is set to a strong shortwave station and the preselector is set to a strong local AM station and the antenna is large with itself a high gain, you'll hear both stations at the same time.

The radio does drift, but the indicated frequency will follow the drift. If the radio is set to a given frequency and through some means drifts 1kHz higher, the display will increment by 1kHz. If the frequency is xx.xxy999 Hz, the "y" digit will sometimes rapidly oscillate between adjacent numeral values (between 4 and 5 for example).

The range tuned by the kHz display spans over 1MHz and overlaps with other frequencies as set from the "MHz" tuning knob. If the kHz knob is set below the 000 kHz reading or above the 999 kHz reading, the kHz display will blank out. The MHz tuning indicator can also blank between MHz settings. When the MHz segment of the display blanks out as the "Mhz" tuning knob is rotated, the speaker mutes.


The Bad:

The DX-300 is passible as a general coverage receiver and hobby have-fun-with-the-radio. But it's not stable or accurate enough for really deep weak signal work. Even with the Wadley-loop design intending to cancel drift, it drifts due to thermal effects on the circuitry (mostly the coils) and internal resistence from the mostly mechanical tuner. The radio does have a predisposition to overload, but with good handling using it's RF-Gain and 20db/40db attenuator switch can handle very strong signals without distortion. A side effect of the Wadley loop design which I've read frustrates some users is that the digital display doesn't always seem to be right. This is true in that the outer tuning ring (which tunes the 1st local oscillator and the "MHz" section of the digital display) affects the "kHz" selectivity and sensitivity of the radio. If the "MHz" ring isn't adjusted properly (and what's "proper" is subjective to the "kHz" and preselector), it can detune the radio such that the digital display may indicate a given frequency, yet the radio actually may be tuned to one (or more) different frequencies. If my MHz setting is off can set my DX-300 to WWV on 10.000 MHz (indicated) with a properly connected 100-foot random wire at full RF-Gain and never hear it while my other radios have 5:9 reception and the strong audio to prove it. However, once the "MHz" ring is adjusted, the DX-300 resolves the signals with the same sensitivity and display accuracy as the other radios. The bottom line with this kind of Wadley-loop superhet design is that getting on frequency is not as easy as with a PLL or microprocessor-based rig. (On the PLL uP rigs, you can just punch in the frequency and the radio goes (and stays) there. The DX-300 isn't that way.) Also, inheirent in the design for the DX-300, the radio may have a beat between 910kHz and 1MHz (actual received frequency) if using the internal ferrite coil antenna and tuned to a weak signal. I assume for some it may be a frustrating radio if one doesn't understand how Wadley loops behave and are spoiled (like me!) on PLL uP rigs.
Often the low ratings don't seem to be because the DX-300 can't receive weak signals (it can!), but finding a weak signal and knowing the frequency can be troublesome. Also, due to the overloading, sometimes image rejection may be poor if the MHz and preselectors are not set correctly, causing a strong station to periodically reappear as a very weak image as the "kHz" knob it turned. Also, the main tuning knob's spinner is the identically the same type used on the DX-200 and DX-302, and has a similar problem with it's spinner squeaking on turns or breaking if overstressed.


Conclusion:

The radio is adequate for casual listening, but will frustrate some users who don't understand how Wadley loop superhet radios behave and need to be tuned. It will also frustrate those looking for weak signal contacts or expecting the radio to be a simple-to-tune rig. There are definitely better (and some worse) radios out there, and for some types the radio itself is fun in and of itself, but the DX-300 is OK for general casual use.
 
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