A very good radio, with a good selection of bandwidths and step sizes. Can be computer-controlled and it has a discriminator output on the AUX connector. Also has a 10.7 MHz IF output on the back.

A fairly good performer, although mine could use a speaker mod to eliminate the audio cutting in and out that can occur.

Like many owners, I'm looking for the Service Manual for this rig. So far all I have are the schematics.

Four-channel scanning in the VHF band.

ICOM bungled the release of the control protocol, but it's been reverse-engineered and is available on the Internet.

As with any receiver, it's important to have the right antenna for the frequencies you're interested in.

I recently purchased a UT-106 DSP Unit and will install it when I have some time.

Unfortunately, it's discontinued. It's a neat design -- a GRE receiver board interfaced to a computer-control board (controlled via a Winbond 8051 microprocessor).

Opto had planned to offer a series of add-ons to the receiver, but eventually had trouble getting boards from GRE in the small quantities that sales numbers dictated.

Very good sound from this receiver.

This radio is still in the original box.

Support documents can be found on Radio Shack's support web site, here.

Support documents, including a manual in Adobe Acrobat (PDF) format, can be found on Radio Shack's support web site, here.

This radio is identical to the Sangean ATS-909.

I have a little more information about this scanner here.

I have more information about this scanner here.

Covers 550 kHz to 30 MHz.

For more information and photographs, click here.

You can read more about this model here.

For more information and photographs, click here.

Coverage: 118-136 MHz and 144-148 MHz.

Coverage: 29-50 MHz, 144-148 MHz, and 410-512 MHz.

Click here for more photos.

• Beacons: 175 to 400 kHz
• AM Broadcast: 550 to 1600 kHz
• Marine: 1.6 to 4 MHz

This model originally came out around 1971.

Covers the following bands: 33-47, 118-136, 154-164 and 450-512 MHz.

Full coverage (less cellular) TrunkTracking handheld scanner. Capable of computer control.

I bought this unit at a garage sale. When I plugged it in, instead of channel numbers, the two-digit display showed 'L'. I hit the [WX] button and immediately heard the local NOAA weather radio transmission. Hitting [SCAN] after that caused the scanner to run through all sixteen channels.

Apparently there are folks out there who get the 'L' display and are unable to proceed. If the [WX] doesn't work, try programming one of the 16 channels with a known frequency (NOAA weather frequencies are good for this: try 162.400 and 162.550 first). After receiving a good signal, manually step thorugh each channel - you should hear static if the squelch is set correctly.

I'm looking for computer control and cloning commands beyond the few CAT messages described in the manual.

I need to get a spare set of tubes for this unit.

Does anyone have a good source for tubes, especially the 1L6, that aren't at a ridiculous price?

Brief documentation is available from Radio Shack's support web site at here. The September 1998 Hints newsletter from the American Radio Relay League (ARRL) has the following modification:

Louder DSP with the RS 21-543 Box

Michael, N4TMI, has a quick fix for anyone trying to get more volume out of a Radio Shack 21-543 DSP box:
The cure is simple. The gain of the audio amplifier can be doubled by soldering wire jumpers across R54 and R57. These are clearly labeled 100-ohm chip resistors on the underside of the circuit board. According to the manufacturer's data sheet, the KIA7227CP audio amp chip does not require these components. Their only purpose is to reduce gain, apparently a bad idea in this situation. After the mod, it's much easier to get room-filling volume from a speaker. Sound quality is excellent, and digital signal processing is unaffected.
--Michael A. Covington, N4TMI, 285 St George Drive, Athens, GA 30606; e-mail mc@ai.uga.edu