Radio Shack 200629 Synthesized World Receiver -- how to quickly fix a feedback and whistling noise issue

The Radio Shack 200629 "PLL Synthesized World Receiver", with a Panasonic external SW antenna. The silver plug is a mono-to-stereo adaptor, which seems to be needed with at least some of these radios.

I bought one of these marvels about five years ago (in 2013), when Radio Shack had them on sale. Radio Shack calls them the "PLL Synthesized SW Receiver", and colloquially they have been referred to as the "Radio Shack World Receiver", "Radio Shack Synthesized World Receiver", or by the catalog number 200629.

It's basically a new Sangean ATS-505 in a black cabinet, and with the Radio Shack badge. The audio chip is different, with a little bit more output. The tuning has no chuffing. But basically it's an ATS-505 with Radio Shack's name on it.

They're great radios. Unfortunately, Radio Shack is online only, and doesn't sell these 200629 World Receivers anymore, and Sangean unfortunately no longer makes ATS-505's. But if you find one for sale online, they are very good radios.

But there is one minor issue -- at least with mine. The issue I experienced may not be present on all of these radios. It's possible it is just a glitch with mine. But in case anyone else who has one of these radios encounters feedback when using an external SW antenna, I found a way to defeat it.

FEEDBACK AND OSCILLATION USING THE EXTERNAL ANTENNA

I hadn't used my Radio Shack 200629 / ATS-505 in maybe a year. I just lost interest in Shortwave, and had other radios that I used in my radio hobby. Seeing it on the shelf one day, I pulled it out, plugged in some batteries, and plugged in my 25 foot indoor wire antenna (which ends in a mono mini-plug).

I noticed weird sounds on the SW stations -- almost a swishing sound, like there was frequency instability. When I switched the sensitivity switch from 'DX' to 'LOCAL' it went away somewhat.

When I pulled out the headphones I noticed my Radio Shack World Receiver began acting like a theramin whenever I moved my hand close to the radio. Weird. Obviously, there was some sort of internal oscillation going on in the radio, that was caused in some way by the external antenna, and was abated somewhat by having the headphones plugged in.

It took several days of staring at a schematic and experimenting with the radio to find out that the problem was simple: the SW External Antenna jack is a stereo jack.

When I plugged the mono antenna plug all the way into the stereo EXT Antenna jack -- that was when I got the feedback.

I tried plugging my antenna plug in PART WAY, so it wasn't all the way in. No feedback, no swoosh noises, no theremin sounds.

PROBLEM SOLVED.

I then found a mini mono-to-stereo adapter out of my parts box, and plugged my antenna plug into the adapter, and then plugged the adapter into the radio. It works on SW perfectly.

SIMPLE SOLUTION: USE A STEREO ANTENNA PLUG, OR MONO-TO-STEREO ADAPTER

The 200629 does not like mono antenna plugs in the stereo antenna jack. A mono plug will cause at least some of these radios to feedback somehow, and if you aren't using headphones you'll find the radio acts like a theremin.

Whether Sangean-branded ATS-505's have this issue, I don't know. I know that the audio chip on the 200629 is different from the one used in ATS-505's -- at least the ATS-505's that were first produced. It is more powerful than the audio chips in older 505's. But the IF chip is the same, the FM front end chip is the same, and I'm guessing the rest of the basic circuitry is the same.

The EXT Antenna jack is wired stereo apparently to take the internal, whip antenna out of the picture. The radio is a fairly high gain radio on SW -- it has an FET RF amp and several FET stages of IF amplification and filtering that it doesn't have on MW and LW. Although I am a neophyte at reading schematics, it seems the whip antenna is connected to the RF amp with less resistance, and plugging in the EXT antenna with a stereo plug switches the whip antenna off, and increases the resistance somewhat.

So using a mono EXT antenna plug into the stereo jack somehow overloads the front end of the SW part of the radio. Voila! Oscillation.

USING A STEREO ANTENNA PLUG OR A MONO-TO-STEREO ADAPTER = HAPPY RADIO

Either way, if you use a mono EXT antenna plug on a Radio Shack World Receiver, you can get oscillation, feedback, and theremin like hand capacitance effects, especially without headphones plugged into the radio.

Use a stereo plug, or a mono-to-stereo adapter, or if you have to, just engage the mono plug enough to where it is halfway seated -- that also works. Then you can spend time DXing with your 200629 / ATS-505 without extra oscillation and theremin-like stuff going on. :-)

So if you have a Radio Shack PLL World Receiver 200629, and you have weird oscillations when using an external antenna, make sure to use a stereo input jack, or -- better yet -- a mono-to-stereo adapter.

You can also just clip an external wire antenna to the 200629's whip antenna. The connection to the radio's circuitry is more or less the same. I've never had whistling issues clipping my indoor wire to the whip antenna, though.

Not all Radio Shack 200629's may have this issue. I really don't know. My radio works normally otherwise, and with the adapter, it's working well with the external antenna now.

I will probably post an article on the radio itself soon.

Until then, hope those of you in the Northern Hemisphere are enjoying the last of Winter, and Winter DX season.

SOME DECENT CATCHES ON SHORTWAVE

MW has been fair-to-middling here at my location recently, but a few early mornings I've heard some decent catches on the 49 and 41 shortwave meter bands -- including the BBC in Urdu, Pashto and Dari towards South Asia on 7485 and 7465 khz, broadcasting from Kranji, Singapore -- both catches I heard on the 200629 Radio Shack radio with a 25 ft (10 meter) indoor wire, a few mornings ago around 1500-1600 UTC.

Lately shortwave propagation conditions have been mostly mediocre, but there have been a few mornings that the pipeline to Asia has been open, and that was one of those mornings. :-)

CC 2-9-2018

 

ADDENDUM, August 31st, 2023: 

After having to repair the connection between my whip antenna and the 200629's main PCB, I took a second look at the 200629's schematic diagram and the way the EXT antenna jack is wired. I'm not sure if it's a stereo jack or not, but the stereo plug did help when I used an external wire with the radio.

Then I lost the mono-to-stereo adapter. So I started clipping the 10 meter / 25 ft. indoor wire to the whip. That worked great. Then it started cutting out. I took the back off. The whip is connected to the PCB with this little prong device, and it's one of Sangean's weak points, they made connections like this with some of their other radios, and those connections would eventually get wiggy. My DX-390 needed hard wiring, and so did my DX-440.

Now it looks like my ATS-505/200629 needs its whip hard wired to the PCB as well. Live and learn. :-)

The EXT jack still acts odd if the mono plug is pushed all the way in. I think that either a) my previous conclusion in this article is correct -- it's a stereo jack (it just doesn't say so in the manual!), or b) my EXT antenna jack is defective. 

After I fix and hard wire the whip antenna connection, I may write up another article on the 200629 and the antenna issue.

And, just in case any new 200629 owners are reading this article by chance and wondering about a loud whine on 9820 kHz, yes, there is a 'Birdie' in the middle of the 31 Meter band, on 9820 kHz. Birdies are fairly normal on PLL radios. Luckily for SWLs there aren't many of them. 

And all this said, I still think the 200629 / ATS-505 is a terrific SWL and MW DX radio. Great sound through headphones. Enjoy. C.C.

ADDENDUM, June 12th, 2024: I made a couple minor edits, including adding a line stating that if you clip the wire antenna to the whip, using an alligator clip, you don't get the whistling / oscillating issues -- at least I haven't in the 2 years I've just been using my wire antenna that way -- clipping it to the whip antenna. Looking at the schematic, there may be an internal wiring connection that makes the radio dislike mono plugs in the EXT antenna jack. But right now, that's just a guess. 

TL;DR: just clip your wire antenna to the whip. :-)