The REALISTIC DX-375 -- a great MW Long Distance Sangean-made Radio

As any radio enthusiast in the U.S. knows, for years Radio Shack was the place to buy radios if you were into long distance radio listening. Most of their radios were very good performers for the money and they usually had more than one model to choose from. Before the 1990's many of Radio Shack's radios were custom made in Taiwan and Japan. Around 1989-90 they began to carry Sangean radios, and placed the "Realistic" badge on the front.

The DX-370 radio, tuned to KFNQ 1090, a local Seattle area sports station that carries the CBS Sports Radio network.

The Realistic DX-375 is unique, in that at first look isn't clear whether the radio is a Sangean or not. It looks like a Sangean radio, with its build quality and the slightly rounded case in front of the speaker (similar to the Sangean ATS-800A). However, unlike many other Radio Shack portable radio models, the DX-375 was not a re-badged, popular Sangean radio available elsewhere under the Sangean name. For a long time, it was a mystery sourced radio.

There are some DXers online who claimed this radio was possibly built by Tecsun, a well known Chinese radio brand.

However, internal evidence (as well as an email back from Sangean) shows that that DX-375 is a Sangean radio.

IT'S A SANGEAN RADIO -- MS-305A

I've taken the back off my DX-375 twice, to hit the volume control with some lube. The second time I had the back and front off, I looked over the radio and took pictures. I noticed it had a large MW loopstick, and I also noticed the factory model number, which is clearly seen underneath the speaker cut-out.

As shown below, the PCB on my DX-375 says 20-212 (the Radio Shack catalog number) and "MS-305A", which is apparently a factory model number. The "MS-" prefix is a Sangean radio prefix (a Google search brings up a Sangean MS-112, MS-101, and MS-103L). So the MS- number is evidence that this radio was custom built by Sangean for Radio Shack. Other factors, including similarities in the circuitry of this radio to the Sangean ATS-305 (same IF chip, same coverage, same switching transistors, similar PCB#, similar RF amp transistor used in the SW-MW chain, etc.), also hint that the DX-375 was made by Sangean.

The Sangean factory model number "MS-305A" and Radio Shack catalog number "20-212" can both be seen in this pic. Up above the two numbers is the FM front end chip, which amplifies FM coming off of the whip antenna.

SANGEAN CONFIRMS THE DX-375 IS A SANGEAN RADIO

After suspecting that the DX-375 was a Sangean radio, I emailed Sangean. I described the radio, told them about the "MS-305A" model number on the PCB, and sent them some pictures, both of the inside and outside of the DX-375.

They confirmed that yes, the DX-375 is indeed a Sangean radio.

When the DX-375 first came out, it had the traditional "Realistic" brand name on its front. Some time before they quit selling this radio, Radio Shack started branding the DX-375 with the less classic-looking "Radio Shack" badge on the front of it. Presumably, the guts and perfomance of the radio were identical (this was during a time other radios, like the DX-390 and 392, were also being re-badged).

A closer look at the back of the DX-375's PCB, showing the "MS-305A" factory model number at top, the thickness of the loopstick, and the TA8132 IF chip, which is the small chip in the center of the pic.

The DX-375 tunes the SW bands, receives FM in stereo (there is only one speaker, but FM is in stereo through the headphone jack) and also receives the MW/AM band. It is decent on SW, as long as you direct tune with the keypad, as scan tuning is a bit tedious (as will be described later here). It has decent sensitivity off the whip antenna on SW.

The radio is made in China, and has good build quality.

A diagram showing some of the Sangean ATS-305's components, showing the RF transistor serving MW as well as SW. The IF chip, TA8132 (same as used in the DX-375) can be seen to the right of the RF transistor. It's possible the RF section of the DX-375 is a similar design to that shown on this diagram.

SHORTWAVE PERFORMANCE -- GOOD OFF THE WHIP, SLOW BANDSCAN TUNING

The DX-375 has good sensitivity off the whip on Shortwave, and is a good performer with one drawback: the tuning across the band is slow. When tuning across a SW band you have about a one second lag between channels. If you're in a high signals area, you can watch the red tuning LED and it will immediately tell you if there is a strong signal even if you can't hear it yet because of the muting (see below).

If you're in a low signals area (as I am), it will help to add a length of wire to the whip antenna to boost signals to the radio. I use a 25 ft. indoor wire (about 7-8 meters), which I attach to the whip with an alligator clip. It makes it easier to use the DX-375 because I can tune across a SW band more quickly and keep an eye on the red LED tuning indicator to check for SW stations. In a high signals area, using the the whip might work O.K.

Because of the tuning lag, I usually use the DX-375 on SW by tuning to several stations I already know by heart: 5025 khz Rebelde, 11780 khz and 6180 khz Radiobras, 6160 khz CKZU Canada, etc. I generally tune into those stations by directly entering their frequencies using the buttons on the front of the radio. I also will program stations into the 10 SW memories and listen that way. Sometimes I'll tune around and keep an eye on the red LED indicator. But mostly if I bandscan the SW, I'll use a different radio (usually my DX-370 or Grundig G2).

If it seems to be a good night for SW I'll go ahead and tune across the 49 meter band, which is the most crowded SW band here in the NW, especially in the morning when Asia comes in. With some stations, the internal loop (designed to receive SW as high as 7.3 Mhz) will bring the stations in. One morning I heard the China Radio Russian station coming in just off the loopstick, which was cool. I've also nulled out Radio Rebelde on 5025 khz with it.

THE DX-375 REALLY SHINES ON MW

Although it works well on FM and SW, it is on MW/AM where the DX-375 radio really shines. It has really good sensitivity for a non-TRF portable, and the selectivity is good enough for DXing. When I A-B it with a Superadio II the DX-375 sounds like it's about 1 db or so weaker on very weak DX channels (depending on how good conditions are. PS -- I live in a low signals area). The DX-375 doesn't have a tuned RF stage and 200 mm loopstick like an SRII has, but considering its circuitry and antenna, the DX-375 is an excellent performer. I usually use mine with an external loop -- which I do with all my radios, including the SRII and PR-D5 (when needed).

On MW it sounds like the bandwidth is around 6-7 khz wide, but it's adequate for separating a weak station from a nearby local station.

There is a tone switch on the side of the radio to reduce the treble which helps reduce some splatter on the AM and SW bands, as well as smooth out the highs on FM when listening through the speaker. There is a "DX-Local" switch on the other side of the radio that I never have used. The radio has a 3V in jack, for a plug from an AC adapter, but the radio does so well on C Cells an AC adapter really isn't needed.

The only negative sound-wise with this radio is that the AM band could use a bit more bass response through headphones. There is apparently a 'bass cut' adjustment off the IF chip somewhere and in my view that bass cut isn't needed. It still sounds good -- I just prefer a bit more bass response on AM when DXing.

The DX-375's AGC (Audio Gain Control) is just about right -- low signals are increased in volume and loud stations don't blast your eardrums once you tune into them. Unlike a couple of Radio Shack's more popular digital portables (like the DX-398 and DX-390, also made by Sangean) the AGC doesn't pump; and overall sound through headphones is good enough for DXing for longer periods.

The DX-375 has a decent, full sound through the speaker on AM, and an even fuller sound through the speaker on FM. Through headphones the radio isn't midrangy or shrill like some DX radios -- it is smooth sounding audio, with a much better sound than the more expensive DX-398 on headphones. There is no listener's fatigue with a DX-375.

The DX-375 picking up Radio Rebelde on 5025 khz using just its internal ferrite loopstick antenna. As you can see, it is receiving Rebelde strong enough to light up the tuning signal LED -- the DX-370 below, which is not designed to receive SW on its loopstick, is receiving the station but extremely weak -- it's not even triggering the DX-370's LCD tuning indicator. I've found that the DX-375's loopstick -- used with or without the whip antenna -- can in some cases reduce RFI on SW -- but not by much. Household RFI is just too powerful for the vast majority of SW listening.

TUNING LAG, BUT THERE IS A WORKAROUND

If you tune with the up and down buttons there is almost a one second lag in tuning steps (due to muting), which makes it a bit time consuming when you want to scan through a SW band -- it's not so much of a problem on the MW band or FM band, where there are many more signals.

If you 'auto-search' on SW (press an up or down button and hold it) the radio will sometimes skip over audible stations instead of stopping on them, because the SW station's strength may not be above the radio's search threshhold. If you press the up or down key repeatedly, you can toggle through the channels, but on some SW bands that can be time consuming.

DURING AUTO-SCAN, OR TOGGLING UP THE BAND, WATCH THE RED LED

But because the tuning increment works slowly (about a second), it's best to watch the red LED indicator, because the LED indicator will light up on stations that don't stop the auto-tuning, and it will also light up before the sound breaks through the muting.

On AM the DX-375 is very good, coming surprisingly close to a Superadio in performance (maybe 1 db weaker on weak MW channels), considering it has a shorter, smaller loopstick antenna and isn't a TRF design. It's good because the IF chip is high gain and the radio has a very good loopstick antenna (140mm x 9 or 10mm -- the thickness is hard to measure accurately, but it's over 8 mm), which is large for a portable. I believe the loopstick is larger than the one used in most of the Sangean 800- and 900-series SW radios

The slow tuning of this radio isn't as big a deal on the MW/AM band because usually every channel has a station on it, and most times I just use the keypad if I want to jump up the band. And usually when tuning the MW band I listen to each channel to see what's on, anyway.

The DX-375 has a TA8132 IF chip, which is a fairly high gain chip, which also adds to the radio's performance. Although I can't find a schematic for this radio anywhere online, the similar ATS-305 has an FET in the SW-MW IF chain, and there are a couple FET's in the DX-375's parts list. So it's probable that an FET in the IF amp chain adds to the DX-375's performance on the MW band.

It has an FM RF/IF front end chip (TA7358) but it doesn't quite pull in FM stations as strongly as my Realistic DX-370. I don't know why that is -- technically, there shouldn't be much of a difference.

A plastic shim inside the back cover of the battery compartment can help extend the life of C Cells in a DX-375. The spongy material breaks down over time, and sometimes isn't sufficient enough to keep the batteries tight in place. The plastic shim I made from the top of a protein shake bottle can be seen inside the battery cover in the picture above.

USE A PLASTIC OR CARDBOARD SHIM IN THE BATTERY COMPARTMENT TO GET MORE OUT OF YOUR BATTERIES

The DX-375 runs on two C batteries, and they last a reasonably long time. I've had decent results with heavy duty batteries, especially if I use headphones. The batteries last a while because the radio has no clock, so when the radio is 'OFF', it's actually OFF! (well -- there still is a tiny bit of current drain to run the power switch -- but you get the idea!). The low battery indicator will come on when the radio hits around 2.0-2.4 volts, then -- after a bit -- the radio simply cuts off.

The batteries last longer on MW/AM than they do on FM or SW (according to the specifications the radio uses about 25% less power on the MW band). I have noticed that when the batteries get down around 2.4 V or so the battery indicator will flash on SW and FM, but the radio will still operate normally on MW for a while longer.

I usually can tell when the batteries are lower than 3 volts because after a while I'll have to press the power switch two times to switch on the radio. It's been that way since the radio was new. This happened a lot more often before I discovered the benefits of adding a plastic shim beneath the battery compartment cover, which presses the C cells together better.

Batteries will last longer in the radio with the plastic shim in the battery compartment. I've found that the battery compartment is larger in diameter than some brands of C cell batteries. Consequently, without a shim, the battery indicator may come on earlier than necessary, and you can possibly get lower battery life because of it.

I cut a shim from the lid to a big plastic bottle, and then shoved it in between the batteries and the battery compartment cover. C Cells last longer in my DX-375 now. I still have to press the power button more than once when the batteries are weak, but not as much as I used to. And I get longer battery life with the shim, than without.

OTHER PECULIARITIES

Sometimes I get an image on the DX-375 high up in the MW band, and sometimes another one in the low band -- but they're not always there. They don't get in the way of DXing with the radio, though.

The only 'maintenance' I've had to do with my DX-375 was squirting some DeOxit into the volume control. There is a convenient, very small hole near the side of the radio's PCB that allows for you to squirt some lube into the control -- if you take the back off the radio.

The DX-375 with the back off. The loopstick is fairly large, as can be seen (along the top side of the radio). The tiny hole that makes it easy to lube the volume control is near volume control's upper right solder pad in this picture (hard to see ). Whether the hole is intended to be there or not, I don't know -- but it works.

You can also squirt lube with the radio's back case left on, by squirting it down the side of the volume control knob, but not all of it will get inside the control where it's more useful.

The only glitch with this radio is on rare occasions the microprocessor can apparently wig out. You reset it by taking the batteries out and putting them back in a few minutes (or even a half hour) later. I've had mine for over a decade and the radio's never wigged. So this problem is fairly uncommon.

The DX-375 has built in back-to-back diode protection for the whip antenna (the diodes are on the component side of the PCB, near the FM RF amp chip) which means if you happen to touch the radio with a static charge in Winter, it probably won't zap the RF amp transistors.

The memories are extremely easy to program, and work quickly. It has a 'memory scan' feature in which the radio will search through each memory location and stop when it 'sees' a strong enough signal. I've never used this feature, but I can see where it could be useful with SW, and maybe even with MW. Once again, the red LED will light up long before the scan stops on a channel.

The DX-375 with the front off. The buttons are discrete buttons, similar to those used in some Panasonic radios -- as can clearly be seen in this pic. They have an excellent tactile feel to them.

The buttons on the DX-375 have a positive feel, and the radio is well built. Mine took a dive to the floor within a year after I got the radio; the dive left a small dent in the whip antenna -- the radio has worked fine ever since.

A GOOD DXer, POSSIBLY A DECENT PREPAREDNESS RADIO, TOO

If you happen to find a DX-375, they are excellent for MW DXing and pretty good for SW listening, and FM is in stereo through the headphones, which is always a plus. :-)

Although the DX-375 doesn't have the extended battery life of a GE Superadio, Sony SRF-59 or Sony ICF-38, it has better battery life than other digital SW radios, like the DX-398 and more recent Radio Shack ATS-505/200-629 World Receiver (both of those are good radios, but both of those radios eat batteries). A set of two C cells is relatively cheap and they will last a couple weeks or more in a DX-375 depending on how much it is used. And, naturally, if you use headphones, the batteries will last much longer.

For emergency preparedness I'd choose a DX-375 over a Grundig G2, Tecsun or other recent model radio that has a rechargeable battery, as there is little you can do when the power is out for an extended period when rechargeables go dead (unless you charge them in your car, which can apparently be done, if you want to run your car's battery that long. My G2 takes 4-5 hours to charge from the AC adapter). C Cells are easy to pack away in a drawer or closet, and are relatively cheap.

NO LONGER IN PRODUCTION, BUT AVAILABLE USED ONLINE

The DX-375 is no longer made, they are available on the used market, and I've seen them for as low as $40 on auction sites online.

A lot of DXers might even have one of these radios around and haven't thought about using one to DX the MW band with. If you have a DX-375 and are into MW distance listening, they're definitely worth trying out. Place an external loop next to one and it will give a Superadio a run for the money.