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Announcing the death of ugly AM radio sound!

Welcome to the world of AM high fidelity and meduci wideband AM stereo quality sound, day and night.   The future of radio is now.   Better reception.   Better sound.   At meduci, we are very passionate about good quality sound. meduci has AM stereo radios for sale.

Many radio manufacturers are leading you, the consumer, to believe that AM radio sounds literally abysmal!   Radio manufacturers have, by cutting corners and costs, tossed aside a medium that can sound as good as FM radio broadcasting, and reach a farther listening area.   In many communities, an AM station is the only LOCAL live media!   It deeply angers meduci that public perception of what AM "sounds" like should be garbage, when in actuality- its potential goes far beyond what most people have ever heard!   We hope that when you hear a good AM stereo station proudly speaking about their "sound" that you realize it is your current RADIO product that limits the quality of what you hear, not the AM medium wave band itself!

America's economy is driven by purchases, and purchase price is certainly a determining factor.   However, that DOES NOT mean that saving a few pennies here, or a dollar per unit there, to improve the quality of AM sound in radios, would break the manufacturer, or the consumer.   This explains why we did not cut corners when designing and manufacturing our own AM stereo products.

We have adopted Motorola's C-QuAM®™ analog stereo AM technology, and are proud to offer the latest integrated circuit decoder technology available for C-QuAM™ stereo tuners, to provide optimum and accurate AM stereo performance.   We re-launched AM Stereo in October 2005, and we gave C-QuAM™ a second chance in the marketplace by introducing four new AM stereo products since then.   These AM stereo products cannot be purchased anywhere else.   Customers are very satisfied with their meduci tuners.   Satisfaction is so high that meduci tuners are not re-sold on eBay.   Each meduci product is also backed with one-year warranty against defects in material and workmanship.   We use ORIGINAL McCoy Motorola IC chips and other prime components in every meduci AM STEREO product.

There are many AM medium-wave stations broadcasting wideband full fidelity sound in different parts of the world.   When received using an appropriate wide band high fidelity AM stereo receiver or tuner under good conditions in the reception environment, using a good external indoor tunable loop antenna, the recovered noise-free high definition sound is virtually indistinguishable from many high quality FM stereo broadcasts!   Hearing is believing!   Sample one of our high definition AM stereo products, and judge the enhanced audio fidelity for yourself.

model: AM_ST model: AM_ST_backa model: AM_ST1a model: Moto




This high-quality and low-cost solid state add-on after-market AM stereo decoder printed circuit board circuitry is assembled and tested (not a kit!), with new attractive green printed circuit board, new ceramic resonator offering wider stereo lock-in range, and the circuitry is based upon the popular third-generation Motorola MC13028AD stereo decoder chip.  For the do-it-yourself person, this 1.675" x 1.5" (42.5mm x 38.1mm) sized board will easily and economically convert your own tired sounding AM mono electronic digital-tuned (ETR) donor receiver to stereo reception using the Motorola C-QuAM broadcast AM stereo standard (where available).   This board accepts the signal from the 450 kHz I.F of AM receiver, and decodes stereo medium-wave MW broadcasts.  It operates at +10 to +15 Volts D.C input, and provides standard line level left and right audio outputs, for direct connection to the receiver's audio amplifier.   It may be used to support 30Hz to 15,000Hz audio frequency response; however, much will depend on the bandwidth of your AM receiver's front end strip.   Instructions are included for typical installation to AM receivers.   There is also an on-board eight-volt linear-mode I.C voltage regulator included.   BONUS:To widen the audio bandwidth in your donor host AM radio, one new muRata CFU450B black ceramic filter is also included pre-installed on-board the AM_ST decoder, free of charge, with each new purchase.   Good news is that this wide bandwidth filter will dramatically increase the recovered audio bandwidth from your AM_ST decoder.   As shown below, previous AM stereo conversions required that the existing tuner's low bandwidth tuner filter to be unsoldered, and then removed.   And the new replacement wide bandwidth filter to be installed on the tuner board, in place of the existing filter.   This would bypass the existing narrow bandwidth I.F and allow for better overall high frequency response from the converted AM medium wave tuner or receiver.   However, during the actual conversion to AM stereo reception, sometimes it was difficult to get access to the bottom side of some of the tuners.   Now you simply tap off prior to the input to the existing I.F filter, usually at the output of the last I.F transformer, from the yellow wire on the AM_ST decoder board.   Having the new ceramic filter on the AM_ST decoder makes for an easier conversion, and also reduces or eliminates some stray out-of-band interference from shortwave and other stations.   Simply bypassing the on-board 450kHz ceramic filter will facilitate 455kHz I.F input and operation from this AM_ST decoder module.   In addition, Forced Mono feature is included on-board.   Schematic diagram and details are also included with each purchase.   We provide free technical guidance for one conversion per each AM_ST decoder purchased, and include web page hyperlink to an eight-page comprehensive instruction manual with every order!   We want you to succeed with your AM stereo conversion project.   You can send us e-mail ahead of purchase to see if your tuner is compatible with this AM_ST decoder board.  

Assembled and tested decoder board:
New prices effective now: $35.00 USD each (to domestic USA address, with free first class shipping service), or $45.00 each to any PayPal confirmed shipping address virtually anywhere else within the world, with free first class shipping service.  Tuner/receiver is NOT included with your purchase.  Prior to purchase, please ensure that there is adequate space inside your host donor receiver to be converted to AM stereo.  There are six internal connections to be made to your receiver (>+10-volt D.C power, chassis ground, 450 kHz I.F input, stereo LED driver output, left channel audio output, and right channel audio output).  
Purchase details are located here>> meduci AM_ST C-QuAM DECODER CONVERTER ADD-ON BOARD .

Scan QR code to make purchase.

This is a stocked item, and is available for immediate shipment after your PayPal payment clears to our financial institution account.  This decoder is new and directly sold from the manufacturer.   Assembled in the United States of America from U.S.A and globally-sourced parts.

new For AM Stereo Stand-Alone AM_ST Decoder Owner's Manual, please click on this link.


  • Carver TX-2
  • C.Crane CC Radio-SW
  • Delco 16194955
  • Delco 16138062
  • Denon TU-1500RD
  • J.C Penney MCS3050 (Model Number 683-3050-00 - Catalog Number 853-6641)
  • Kenwood TS-140S
  • Kenwood KT-727
  • Kenwood KT-6040
  • Kenwood BASIC T2
  • Marantz ST-6000
  • Marantz ST-6001
  • McIntosh MR7084
  • McKay-Dymek AM 5
  • Onkyo T-422M
  • Onkyo R-805X
  • Panasonic SA-AK33
  • Pioneer SX-5
  • Pioneer SX-6
  • Pioneer TX-950
  • Pioneer F-227
  • Redsun RP2100
  • Sansui TU-X1
  • Sansui 5050
  • Sanyo M7850K
  • Sony STR-DE525
  • Sony STR-GX47ES
  • Sony ST-JX430
  • Sony ST-JX220
  • Sony ST-S311
  • Teac T-H500
  • Yamaha TX-492

  • PayPal Proposition 65


    Pioneer F-227_1

    In this corner, we will spotlight current projects for our meduci AM_ST outboard decoder module!   Richard Prinsloo from Johannesburg, South Africa wanted to convert his Y2K model Pioneer F-227 AM/FM PLL tuner to AM stereo reception with the meduci AM_ST converter board.  Richard did not have the tuner's service manual; however, meduci was able to locate four poorly scanned, though readable, pages online- as taken from the actual Pioneer service manual.  Even though these four pages were incomplete, there was enough information to make a decision on how easily it would be to add the AM_ST decoder card in Richard's Pioneer host donor medium-wave AM receiver tuner.

    This tuner board seemed to be planned for some future AM stereo implementation, as there is a vacant six-pin header labeled "J3" next to an "AM STEREO" caption.  This appears to be a provision for connecting a future AM stereo module.   Four pages of the scanned service manual did not show nor address how this "J3" header connection was to be provisioned (shown below):

    Pioneer F-227_1a

    During Richard's tuner modification, he successfully replaced the existing stock ceramic filter.  He unsoldered and removed this small one-piece integrated white component from the bottom side of the tuner board, and separated the filter from the I.F transformer can:


    He re-installed the I.F transformer and replaced the stock ceramic filter with muRata black CFU-450B filter. Richard did not need to make use of the empty "J3" header when following our simple AM_ST decoder installation instructions:

    Pioneer F-227_2

    Richard writes, "Good news!!   I have successfully installed the decoder, following your detailed instructions.   I now have AM Stereo on my Pioneer F-227 Tuner.   The "STEREO" indicator even works on AM now.   I installed the new I.F filter first and tested the tuner after that.   All was still working fine.   Then I made all the connections to the tuner, and cut the audio path after the capacitor."

    Pioneer F-227_3

    It was evident that frequency response did improve using our AM_ST decoder, since the Pioneer F-227 tuner's internal audio filters were bypassed after the successful modification was performed.  Ultimately, the overall response was initially limited by the stock 450kHz I.F ceramic filter used within this tuner prior to AM stereo modification.  Since so many existing AM mono receivers were sold with low audio bandwidth (on the order of ~3kHz), we included one new muRata CFU450B black ceramic filter with Richard's new AM_ST decoder purchase.

    Pioneer F-227_4
    Pioneer F-227_5
    Pioneer F-227_6



    Bent Kyllesdal from Norway made his Sony ST-S311 FM stereo/medium wave AM monaural tuner sing much better thanks to economical meduci AM_ST card.  Convenient tap-off points are present on the Sony tuner main board.

    During Bent's tuner modification, he successfully replaced the existing stock ceramic filter.  He used one new muRata CFU-450B filter that was provided free of charge with his AM_ST decoder purchase.  This black ceramic filter dramatically widened the recovered audio fidelity, compared to the previous sound heard from the stock ceramic filter:


    This is the underside of the tuner board showing the left and right audio connections to Sony audio pre-amplifier I.C chip:

    You can watch Bent's video from here:
    playback button Play the video by clicking here>> After AM stereo modification to SONY ST-S311 tuner.


    Denon Inside

    Bent Kyllesdal from Norway made his Denon TU-1500RD FM stereo RDS/medium wave AM monaural tuner sound much better after his AM_ST card was mounted inside. Full C-QuAM stereo fidelity was realized from his AM stereo transmitter. He was also very pleased with the customer support he received from meduci, LLC.  We were there every step of the way to answer Bent's questions. We provide free technical guidance, and provide full conversion instructions with every meduci AM_ST decoder purchase; one conversion for each purchase. We want you to succeed with your AM stereo conversion projects.

    Convenient tap-off points are present on the Denon tuner board, so it was a very simple conversion for Bent.  Much of the stock tuner was retained.  One leg of the existing audio coupling capacitor (C141) was snipped on the tuner board, that came from pin 12 of IC101 (AM tuner I.C chip), to pin one of IC102 (FM MPX stereo decoder I.C chip), to disable the monaural AM audio output path.   Two series resistors were added from the AM_ST decoder left and right audio outputs to the tuner's audio amplifier I.C chip.   Switched B+ D.C voltage from the AM tuner I.C chip was also a convenient source to power the AM_ST decoder.   This ensured that the AM_ST decoder was powered down when tuner was switched to FM band.   Therefore, any stray audio would not be present from the AM_ST decoder to leak through when tuning FM stations.

    During Bent's tuner modification, he also successfully replaced the existing narrow bandwidth stock ceramic filter.  He used one new muRata CFU-450B filter that was provided and included free of charge with his AM_ST decoder purchase. This black ceramic filter dramatically widened the recovered audio sound stage, compared to the previous sound heard from the stock filter (shown on the right side below):


    Denon's TU-1500RD microprocessor "locked out" or failed to read the "ST IND" pin from Bent's AM_ST decoder when in AM medium wave mode.  Unfortunately, this is very common with many tuners.  To overcome this tuner design limitation, Bent added a separate light emitting diode (LED) underneath the front panel display window for AM stereo indication.   Bent also discussed his phenominal achievement on Facebook.

    You can watch Bent's videos from here:
    playback button Play the video by clicking here>> DENON TU-1500RD tuner.
    playback button Second video is here>> Another video for DENON TU-1500RD tuner.


    McKay Dymek AM5 tuner

    XRAYTONYB from Volant, Pennsylvania USA was up to the challenge to modify his customer's McKay Dymek AM5 solid state medium wave band tuner to receive C-QuAM AM stereo broadcasts, using the economical meduci AM_ST decoder.   This high-end AM-only tuner, very popular during the mid-1970's, has a very large intermediate frequency (455kHz) output level, which needed significant signal attenuation (or "padding"), in order to properly drive the composite baseband input to the AM_ST decoder, without overloading or "swamping" the module's I.F input.   Fortunately, this McKay Dymek tuner also offered other simple and convenient tap-off points for power, audio, and stereo indication.   XRAYTONYB added a blue stereo LED indicator that glows inside the front panel S-meter.

    Fun stuff Fun staff again
    You can watch the entire XRAYTONYB video from here (without commercial advertisements):
    playback button Play the video by clicking here>> AM stereo modification to McKay Dymek AM5 tuner.

    In this video, XRAYTONYB also discusses the best antenna matching for proper output power transfer, and demonstrates tips for building the transmitter into a metal case using quality rechargeable 18650 lithium-ion high power capacity battery power supply to the Alfredo Torrejon-designed ALFREDO LITE CCUFF low-power AM stereo C-QuAM test transmitter.   This is a low power type of C-QuAM signal source.   Without having antenna on hand, matched and resonant to the transmitter's R.F output, the listening range was limited to a few feet.   We have two such part-15 compliant type AM stereo C-QuAM test transmitters, and the range is also limited from either transmitter to the receiver's AM external tunable loop receiving antenna.   We use our two transmitters to test our AM_ST decoder modules, prior to shipment to customers.   In order to increase this transmission range, you will need the three meter long AM medium wave transmitter properly mounted outside, connected with very short shielded cable to the transmitter's low power output, and also connected to a very healthy buried ground radial ring.   Plans are widely available on the Internet.   We cannot recommend any FCC-compliant C-QuAM transmitters and outdoor antennas at this time, though.


    Sansui TU-X1 tuner

    XRAYTONYB modified his customer's Sansui TU-X1 super integrated tuner, to add AM stereo reception using the reliable and economical meduci AM_ST decoder.   In this tuner, it was easy to tap off the interior power, audio, I.F and stereo connections.   This Sansui tuner was designed prior to the worldwide standardization to the C-QuAM AM stereo format; therefore, like other tuners during this era, this Sansui has an outboard AM stereo output jack on the rear panel. These special output jacks were meant to drive external AM stereo decoders, that never materialized in the marketplace.

    Sansui is tall. the big picture.

    This is both AM and FM model using 455kHz intermediate frequency for the medium wave band, which was an industry standard for manually-tuned (non-automotive) AM tuners.   XRAYTONYB discusses how he modified the tuner, and shows where the internal tap-off point exists for the AM_ST decoder from the Sansui tuner.   It is also an easy task to revert this tuner back to stock condition, and remove the internal AM stereo decoder module.

    You can watch the entire XRAYTONYB video from here (without commercials):
    playback button Play the video by clicking here>> AM stereo modification to Sansui TU-X1 tuner.


    Phil 'Tha Dood' from Poca, West Virginia USA purchased two meduci AM_ST decoders from eBay, knowing which products he wanted to be converted.   One of the modifications was a rather high end deluxe McIntosh MR7084 tuner (domestic model made in New York, USA). We reviewed the service manual that he provided, and we supported the modification, by providing the connection details from this host tuner to his AM_ST decoder.   And the results?   AM stereo broadcasts could be successfully received for the first time!   "I think better than the FM stations on this tuner," Tha Dood says.   "Amazing!   Whatever fidelity that transmitter is capable of, this tuner now hears it."

    Tha Dood has his own medium wave carrier-current station at 610 kHz, with FCC part-15 compliant radiating station at 1620 kHz, and a low-power unlicensed AM Stereo test transmitter from Sean Cuthbert operating on 1580 kHz.   He also operates a web site called Real Free Radio where his music play list can be found.   His current activities are also dicussed.

    For the McIntosh MR7084 successful tuner modification, Tha Dood highlighted in yellow the components affected, or changed, from the tuner board layout page, as taken from the McIntosh service manual:
    McIntosh PC board modifications

    Much of the stock tuner was retained.   One capacitor (C93) was removed, that came from pin 12 of IC2 (AM tuner IC chip), to IC5 (FM MPX stereo decoder IC chip), to disable the monaural AM audio output path.   Series resistors were added from the AM_ST decoder left and right audio outputs to the tuner's audio amplifier.   Switched B+ D.C voltage from the AM tuner IC chip was also a convenient source to power the AM_ST decoder.   This ensured that the AM_ST decoder was powered down when tuner was switched to FM band.   Therefore, any stray audio would not be present from the AM_ST decoder to leak through when tuning FM stations.   Front panel MPX LED stereo indicator was also able to be used, and was a simple connection to the AM_ST module.

    This is the interior view showing the six wire connections from the meduci AM_ST decoder to the McIntosh tuner board (tap on the pictures to enlarge them):
    McIntosh AM MPX LED Indicator

    McIntosh Interior View


    This McIntosh tuner had one stock blue muRata SFG450D ceramic filter after the tuner's mixer stage, which was capable of 10kHz recovered audio response.   Tha Dood was able to remove that SFG450D filter, and replace it with one new black muRata CFU450B ceramic filter that was included with his AM_ST decoder purchase.   It was a direct drop-in replacement.   McIntosh also made accommodation on their tuner board for a five-pin ceramic filter, and the two empty holes on the board were used as I.F output to the AM_ST decoder.

    For the front panel illumination, Tha Dood also removed the six incandescent "wheat" 7373-style light bulbs that came with the tuner, and replaced them with six white LED indicators.   This should increase reliability, and eliminate the need to replace these front panel indicators within the foreseeable future.   You can see the result below for the 1580kHz stereo station-- also showing the AM stereo MPX indicator in the lower left corner of the LED tuning display:
    McIntosh front panel with white LED

    Tha Dood is going to button up the modification.   He says, "I hope to mount the meduci board, and I believe that I've finally found a decent place to do that, just between the Tuner Board and faceplate board is a dummy foot hole, with a plastic plug in it.  " As the pictures show, this was a very successful AM stereo conversion modification project.


    Mike G. from Hudsonville, Michigan USA successfully modified his Sony STR-DE525 receiver to hear WLS-AM (Chicago, Illinois USA) and WIRL-AM (Peoria, Illinois USA) in stereo at night!

    This picture shows the successful installation with AM_ST decoder mounted flat against the outside of the existing FM/AM tuner pack inside Mike's Sony STR-DE525 receiver:

    Sony AM stereo installation

    There were five total new connections made inside the Sony tuner pack.   This tuner pack uses the Sanyo LA1837 IC chip, which is an "AM stereo friendly" design, with easy left and right AM stereo audio connections back into the chip:

    Sony Connections It's a Sony

    Mike breaked the connection between pins 22 and 24 on the LA1837 to disable the mono AM audio path.   Also, this Sony receiver's micro-processor does not read the STEREO pin voltage level when the tuner is placed on AM medium wave band.   Therefore, the front panel stereo indicator did not properly indicate when AM stereo C-QuAM stations were received.   Mike was able to ingeniously use the receiver's front panel DVD/5.1 Dolby Surround LED indicator to indicate when this receiver was tuned to AM stereo stations.   This indicator now serves duty as AM stereo, DVD, and 5.1 Dolby Surround indication.   Mike made the connection on the printed circuit board behind the front panel:


    After this installation was completed, Mike says, "Well, Jeff I got her to work!!! You were right about the stereo indicator light only working during FM operation.   So found out that where I tapped the power it was dropping the voltage to about three volts so the decoder wouldn't work.   Tap it to the tuner power and works great now.   I used 15k-ohm series resistors for audio and sounds great.   ... I appreciate the product and help."

    Mike is procuring parts to assemble his own home-made large tunable loop antenna in order to improve reception further from distant AM stereo stations.


    Sanyo Boombox Mod

    Sean Cuthbert installed his meduci AM_ST decoder board inside the Sanyo M7850K AM/FM/SW/cassette boombox radio with very good results.   He found that second hand AM stereo radios are very expensive, as sold on eBay.   To save money, Sean decided to convert his own radio to AM stereo reception.   He likes this Sanyo model, as it has two shortwave reception bands.   In order to improve the recovered audio bandwidth, Sean also replaced the AM medium wave ceramic filter with a better device, capable of 10kHz audio response.   This compares to the stock ceramic filter that allowed the AM radio portion to reproduce audio up to 4kHz (essentially telephone line quality)! Also, an integrated cassette recorder facilitates AM stereo airchecks to be saved.

    playback button Play the video by clicking here>> AM stereo modification to Sanyo boombox.


    Neto Silva from Brazil installed his meduci AM_ST decoder into his J. C. Penney MCS-3050 tuner to improve the overall sound and to reduce audio distortion.   Why would anyone add an AM stereo decoder to a tuner that already contains an AM stereo tuner? J.C Penney uses the Motorola first generation AM stereo decoder chip (MC13020P).   In the third generation decoder chip (MC13028A) used in our AM_ST add-on board, a balanced full-wave envelope detector is used, which is technically better than the half-wave diode envelope detectors used in garden variety AM tuners and receivers.   This design improves audio fidelity, due to the very low total harmonic distortion encountered (typically under one percent, and inaudible to the human ear)!

    MCS3050_Upgrade MCS3050_Upgrade2

    There were six connections made from the AM_ST decoder board to the MCS-3050 tuner board. Of course, meduci provided complete and detailed installation instructions with Neto's AM_ST decoder module purchase! If you have MCS-3050 tuner, you should consider upgrading the AM stereo functionality with one of our AM_ST models.  


    decoder inside decoder outside

    Rich Modafferi built his "connect to any radio" AM stereo decoder enclosure to house his meduci AM_ST decoder board, which complements his tube-based AM stereo C-QuAM transmitter.   Rich also used his Sencore SG80 stereo generator for testing purposes.   His enclosure has inputs for 455 kHz I.F and a level control is provided for adjusting this I.F input.   There are both BNC and RCA I.F input jacks, and fixed and variable audio level outputs.   Single indicator lamp functions for "power" and "stereo", glowing dim on power, and full bright for AM C-QuAM stereo lock.



    X-FM conducted C-QuAM stereo broadcast on July 23, 2012.   Kenwood TS-140S shortwave receiver was modified by JFarley for AM stereo reception using his AM_ST decoder.   This modification allowed reception for this X-FM underground test broadcast from Redhat using C-QuAM stereo technology! This unique "music to the power of X" broadcast signed on just after 02:00 UTC with test tones at various frequencies, then X-FM identification as "C-QuAM AM stereo test transmission" followed by The Cars "Moving in Stereo" song.   Indeed, this is an appropriate song for this test! You can listen to this stereo broadcast here>> meduci AM STEREO SHORTWAVE TEST (20.2MB).

    XFM Test meduci close up

    There is some fading evident during the 43-meter single sideband shortwave test transmission.   As expected, lack of stereo lock occurred during the very deep fades.   From JFarley: "With the hardware decoder on a TS-140S, I have pilot about 50 percent of the time.   Thought there was separation during The Cars piece when you got above S9.   Kind of eerie listening and just getting a feel for this.   It's noisy tonight with choppy fades.   The meduci decoder in the TS-140S seems to lose pilot easily in a fade.   I am in and out of lock with fading, and it is sometimes a pronounced difference, sometimes it is more subtle.   But it is stereo! Reception here was around S8-S9, and that would have been enough to keep pilot lock here, I feel.   Problem was the very choppy fades down to S5.   I also noted some unlocking due to noise."

    You do not need to search high and low for a Kenwood TS-140S shortwave receiver.   Our past customers have successfully combined Redsun RP2100 with our outboard AM_ST stereo C-QuAM decoder board with very good results.   Redsun RP2100 is nearly identical to C.Crane CC Radio-SW model.   Both models tune the entire shortwave radio bands, and have the necessary 455kHz I.F output, so you do not need to open the radio, in order to install our AM_ST model C-QuAM decoder board.


    Todd's First!

    Todd Roberts (WD4NGG) converted his Delco automotive FM stereo/AM mono radio (model 16194955 - readily available on eBay) to AM stereo using his meduci outboard AM_ST decoder, so that he could hear "The Mighty 1630 KCJJ" in stereo. He also receives WLS from Chicago via skywave propagation! He added the forced mono switch to one of the mounting ears of the Delco radio! He placed the AM_ST board in a plastic box and added front-mounted AM Stereo indicator.   Todd also replaced the stock 3kHz ceramic filter in the Delco radio with new 7.5kHz ceramic filter from eBay.   This was a simple modification, since the 450 kHz I.F level from the Delco is an ideal match to the AM_ST board!

    Since muRata 3.6MHz ceramic resonators were as scarce as hen's teeth at the time, Todd used one 43uH toroid inductor resonated with a 9-50pFd ceramic trimmer in place of the stock ceramic resonator.   With continued experimentation, Todd says, "One thing I noticed using the toroid with loose turns wound over the core was it seemed to be a bit microphonic if bumped, so the turns will need to be glued in place, and the toroid probably glued to the board, to make it rock solid.   Of course there were no microphonics noticed when tapping the ceramic resonator."

    Todd's BUD Box

    Todd's most recent summer project was to relocate his meduci AM_ST outboard decoder into a small aluminum shielded BUD box enclosure, which was mounted to an aluminum sub-panel, then bolted to the front mounting ears on the top of his Delco 16194955 AM Mono/FM Stereo automotive radio.

    Todd's solution to interfacing the Delco's internal top tuning board to the outboard AM_ST decoder was to solder a printed circuit board-mounted SMA socket directly to the tuner board.   This socket was connected across the output pin from the 7.5kHz ceramic filter, and its ground pin, without having to drill any holes, or change anything on the tuner board.   Todd was then able to route the I.F signal from the Delco radio to his AM_ST decoder board using a small SMA shielded jumper cable and SMA connectors.   Todd did have to punch out one 0.5-inch hole in the top cover of the Delco radio, in order to allow the SMA socket to protude through the top cover.   Modifications were not necessary to the Delco tuner board itself, though.

    Using a spectrum analyzer, Todd determined that using this very short length of small SMA shielded cable did not affect the I.F filter's passband or ripple.   This re-packaged combination also eliminated the stray shortwave station interference that Todd had previously encountered, sometimes when listening at night, when using his AM_ST decoder mounted in an unshielded plastic box.

    Hopefully, these modifications provide inspiration for project creations using your own meduci AM_ST decoder board.   Please send us your AM stereo decoder conversion pictures, experiments, and descriptions using your AM_ST decoder! We will display the pictures and describe your project in an upcoming meduci web site update.

    History of AM Stereo

    Analog AM stereo technology has claimed its roots almost since the beginning of conventional monaural AM broadcasting within the United States.   Later, four different competing AM stereo systems were placed on the air in the early 1980's, including systems from Motorola (C-QuAM™), Magnavox (PMX), Kahn-Hazeltine (ISB), and Harris Broadcast (Variable Angle Compatible Phase Multiplex, or V-CPM).   Eventually in 1993, Motorola's C-QuAM technology achieved the exclusive standard for AM stereo broadcasting within the U.S.A. During this time period, Australia, Japan, and other countries were also exclusively using the Motorola C-QuAM system, making C-QuAM the essential de facto world standard for AM stereo broadcasting technology.

    All of the AM stereo systems share in common the addition of a stereo exciter to the existing monaural AM transmitter.   This exciter typically has two outputs: the monaural L+R audio, which is time delayed and fed to the transmitter's normal audio input; the second output is the R.F carrier, which replaces the signal from the transmitter's normal quartz crystal oscillator stage.   This signal also contains the necessary time delayed and phase modulated (quadrature) information.   Because these stereo exciters are retrofitted onto transmitters which were never designed for AM stereo operation, they also must contain corrective equalizers and adjustable delay networks, to insure that all of the relationships are correct through the transmitter modulator, power amplifier, and ATU/antenna system.   Decoded stereo separation suffers if the timing and phase relationships are not correct at the receiver.

    Motorola's C-QuAM system is covered in several U.S. patents written by the late Frank H. Hilbert and the late Norman W. Parker of Illinois. Norman Parker invented the C-QuAM system, per written correspondence from his wife, Margaret Parker.   Margaret also wrote all of the patents.   Patent number 4,218,586 was applicable to the basic system.   Several other patents included 4,406,922 and 4,192,968.   Delco Electronics Corporation (now known as Delphi) later introduced many adaptations and new C-QuAM inventions, covered under various additional U.S patents.

    About us

    meduci, LLC is a highly entrepreneurial, creative, and innovative research and development organization that specializes in custom free-lance engineering, research, electronic design, development, and production of electronic products, from conceptual ideas through to finalized products, in prototype quantities, up to large scale manufacturing.   We also design low frequency (class A, class AB, class D) audio power amplifiers, class C power R.F amplifiers, and R.F front-end (amplifier, mixer, oscillator), using National Semiconductor, Motorola, and other custom ASIC chipsets and discrete components.   We strive for quality and excellence in workmanship.   Our products are designed for faithful sonic reproduction of the on-air source material.   For customers with specific requirements, you could always count on us to produce innovative solutions in a time effective and cost efficient manner.   Our customers are benefited by better pricing, quality warranty, and excellent technical support.   Contact us for a free quotation -- we appreciate your business.   Our goal is to meet the needs of our buyers, distributors and dealers, and we can work on an ad hoc basis. amstereo'AT' (replace 'AT' with the @ sign).
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    12 March 2020

    Dear valued customer,

    meduci, LLC is diligently working to manage through this worldwide, daily evolving novel Coronavirus (COVID-19) emergency pandemic crisis situation that we all currently endure.   Pursuant to guidelines issued by the U.S Cybersecurity and Infrastructure Security Agency (CISA), and U.S Department of Homeland Security (DHS), meduci, LLC is part of the essential critical sector infrastructure, and is required to remain open for business as an essential service, to continue to receive raw components and supplies, to manufacture electronics products, and to ship these products to the end user sector.

    We continue to ship globally, with our highest priority being our internal and external customers.   We do not ship UPS Red Next Day service, nor any other expedited delivery service at this time.   Shipping guarantees are NOT being made from the carriers.   Refunds are also not being granted from these shipping carriers for delivery delays.   There is a huge increase in volume, as more people are shopping online, due to COVID-19 restrictions.   Unfortunately, this means your parcel delivery will be delayed.   For domestic shipments prior to 03/12/20, it would take a few days to one week for delivery.   These domestic deliveries are now taking weeks to complete.   For international shipments from USA, previously it would take weeks for delivery.   These deliveries are now taking months to complete.   This is being caused by limited domestic and international airline flights, significantly reduced airline capacity on those flights, local route restrictions, delivery controls, flight disruptions/cancellations, government restrictions, border closures, and increased safe distancing requirements.   Delivery companies are now operating with split shifts, ensuring clean disinfected work areas and stations between shifts.   Rest assured, that we are doing everything we can do to minimize order processing and delivery delays.   We will provide updates as they arrive, and we will continue to monitor the ongoing situation.

    Notice of Force Majeure-- meduci, LLC is fully operational to help with your end user product needs as an essential manufacturer, despite some of these recent world struggles.   We will inform you via e-mail the current status for your submitted orders to meduci, LLC.   We will also provide shipment tracking numbers when orders ship from our facility.   Some international delivery services are no longer available, due to COVID-19 response.   Thank you for your patience during this difficult time.

    We are keeping meduci, LLC members safe from the virus, with every possible preventative and protective measure put into place.   Out of an abundance of caution, and in adherence with guidance provided by local authorities, we have created policies to slow the virus spread internally within our organization.   We have limited travel, canceled meetings, restricted outside visitors, encouraged sick people to stay away, and have enhanced our cleaning and disinfection procedures in order to maintain a safe working environment.   Essential operational fulfillment and production support areas of the business continue under greatly enhanced procedures for sanitation, social spacing, and six-feet (1.828 meter) safe distance.

    Thank you for your continued support.   Stay healthy and safe.   We will all prevail to get though this difficult time period together.


    Model: MW2 PLL Tuner Front

    If you are a frequent visitor to this web page, then you know that we have been re-designing the MW-2 PLL tuner, to offer a new dimensionality in sight and sound, using the advanced new old stock Motorola MC13027/MC13122 C-QuAM combination chipset, to meet the EIA/NAB AMax requirements.   We wanted the highest performance achievable out of this analog chipset, the last AM stereo decoder released from Motorola.   This chipset has superior performance, especially with respect to noise limiting, and blanking, and is not your typical run-of-the-mill design.   To date, we have been encouraged by the response.

    Unfortunately, the MW-2 PLL tuner is still not currently in production.   There are a few obstacles that remain, and still need to be overcome.   As you well know, really good receiver design is very difficult indeed; however, it is necessary for the revitalization of AM radio, and for C-QuAM stereo in particular.   We are taking our time effectively designing this tuner, and not rushing this to market.   Further progress update details are forthcoming below:

    One obstacle that we encountered was attempting to get the local voltage controlled oscillator (VCO) in the superheterodyne tuning circuit to accurately track the RF front end pre-selector circuit across the entire AM medium wave broadcast band- to increase selectivity, and to reduce image frequencies.   Aside from the top end of the band, that was not possible.

    Over many months, we started looking at other tuning circuits, and realized that virtually ALL existing tuners and receivers have this large tracking error deficiency.   They do not track well, especially on the lower end of the band.   Having a good RF front end pre-selector stage that tracks well with the VCO is not trivial to implement over the entire tuning frequency band.   Compounding our effort here was that the VCO in the AMax chipset runs four times higher than standard receivers.   This higher VCO frequency inside the MC13027 tuner chip is designed to further reduce the phase noise generated from the VCO, decreasing for C-QuAM stereo stations.   So we are going back to the original MW-2 PLL design that requires a two-step tuning process.   You first rotate the front panel coarse tuning knob, until your desired AM medium wave station appears on the front panel LED station frequency digital display.   Then you fine tune your AM external indoor loop antenna, until the green dot appears on the same display in the upper right corner.   This dot assures that your loop antenna is center tuned and locked to the desired station.   End user may also prefer a front-panel mounted variable fine tuning knob, that is adjusted for maximum sensitivity on their AM medium wave station after the coarse tuning knob is rotated to select the desired station.

    Second order of business was to further reduce the phase noise from the recovered audio in stereo mode.   Designing a good frequency synthesizer charge pump was essential to good performance, as well as driving the tuner's front end VCO stage.   Using the MC145151 PLL circuit exactly as shown in the MC13028 data sheet did offer tweets at multiples of the R counter (say 10kHz and 20kHz) and other phase noise artifacts were observed.   Much of this could be knocked down in post-decoder filtering, which most consumer AM stereo radios already achieved (notably tuners from Carver and Denon, etc).   It is better to handle it between the phase detector output and VCO, though.   We succeeded on that front.

    Another item noticed during bench testing this Motorola MC13027/MC13122 AMax chipset was the function of the signal quality detector circuit that controls variable-Q twin-T notch filters for adaptive audio bandwidth, stereo audio blending to mono, and inter-carrier whistle reduction.   This circuit takes the received signal strength voltage, and accordingly adapts the audio frequency response to the signal path conditions.   During testing, local AM stations enjoyed very wideband audio high frequency response.   Anything less than a locally received signal reduced the high end recovered audio frequencies from the stereo decoder.   So weaker stations were given less audio bandwidth.   Under these less than ideal reception conditions, the AMax chipset started rolling off the audio before 3kHz.   This testing did nothing to improve the selectivity of the set, to reduce the "monkey chatter" sound heard from first adjacent stations.   It seems that it would be better to first make this decision immediately at the I.F level, rather than further and deeper inside the decoder processing stages.

    GM Delco used this identical adaptive bandwidth circuitry in their C-QuAM automotive radios manufactured from 1993 to 1997, found primarily in GMC Jimmy, Chevrolet Blazer, Chevrolet S-10, GMC Sonoma, and other vehicles of that time period.   Based upon past experience listening to these Delco radios, we were not initially sold on this variable-Q design.   However, fast forward into the next two decades (yes, it HAS been that long)- new listeners to the AM medium wave band do not like to hear background hiss, that is most prevalent on any AM tuner capable of very wideband (beyond 7.5kHz) audio frequency response.   Motorola's engineers had foresight to design their patented variable-Q adaptive bandwidth circuit into the MC13027/MC13122 chipset, in order to reduce this background hiss during less than favorable reception conditions.   Future generations of listeners will definitely enjoy this feature.   For this reason, we are leaving Motorola's adaptive bandwidth circuit intact.

    We are also leaving the wide band/narrow band selection at the I.F stage preceding the stereo decoder, using two different ceramic filters.   Narrow mode will increase station selectivity, and roll off decoded audio approximately ~4.5kHz (at -6dB).   This frequency response also comes very close to mirroring the USA NRSC audio de-emphasis curve.   Wide mode will have top end to 10kHz, which will effectively reduce the inter-carrier "whistle" sounds prevalent at night.   Speaking of inter-carrier "whistle" sounds, we also experimented with different circuitry to eliminate this artifact, without affecting the remaining audio spectrum.   We hope to continue with significant development efforts in this regard.

    Then we addressed the time period taken to trip the decoder into stereo mode, and automatic blending to mono, after stereo decoding has occurred- both are functions of the signal quality detector stage.   Stereo decoding takes approximately ten seconds to lock again after loss of 25Hz pilot tone, either intentional from the encoder, or during fading signal conditions at night.   You can force the stereo acquisition faster by toggling the front panel auto stereo/forced mono switch, or tuning away from, and back to the C-QuAM station.   So we are retaining this stereo/mono switch on the front panel, as well as the NRSC de-emphasis enable/disable switch, and wide/narrow I.F bandwidth switch manual selections.   Let the user decide how they want their sound presented, via a manual toggle switch (or three).   However, automatic blending to monaural feature will also be retained during very weak reception conditions.

    Since the last meduci PRO1k+ tuner was produced, we were discouraged to build another true high fidelity AM stereo radio.   We designed our tuners to equal the performance of the Carver TX-11a/b tuner models, which during their production run, were perhaps the widest wideband C-QuAM stereo tuners available during that time period.   We always felt that Carver was the benchmark that other AM tuners needed to be compared.   Logging hundreds of hours listening to our TX-11a tuner more than 25 years ago on very well managed and engineered local AM stereo stations (WJR, WMNI, and others), meduci was not sold on building a typical run-of-the-mill AM stereo tuner out of the gate, either, that only sounded as good as all of the other non-Carver tuners available at the time.   We asked the stereo enthusiasts on Facebook- do you really want a wideband audio tuner? And the answer plain and simple was YES!   Jacob Hammond says, "Yes to wideband! ... I believe these other tuners get more attention, simply because they are more plentiful, and less expensive than the Carver." Others say that the Carver TX-11a was not perfect, and had issues, such as low frequency stereo performance (recovered audio from 50 Hertz to about 90 Hertz suffers from loop following, which causes audio distortion in the bass response).   Quartz-based crystal oscillator would have been better than the ceramic resonator that was used inside the Carver TX-11a/b tuner.

    Prior to this audio discussion on Facebook, the general consensus from AM stereo enthusiasts was that the Realistic (Radio Shack) TM-152 model, and any of the Delco AM stereo automotive radios were still desired by many AM stereo enthusiasts, for their price, and sound quality.   TM-152 used one muRata ceramic filter specified with 4.5kHz audio response (at -6dB), and the Delco radios used two muRata ceramic filters, each with 6kHz audio response (again at -6dB).   We could easily build stereo AM tuners that sounded identical to the Realistic and Delco models.   That would have certainly cut down on the high frequency noise within the upper audio passband coming from the PLL synthesizer and external sources.   This is how many manufacturers in the day did it for their analog AM stereo implementations.   After further review, we decided not to take that design route.

    We also asked AM stereo enthusiasts for their preference for antenna selection- either internal or external, and whether it should be tunable.   AMax standard does call out to use an external antenna input connection for home AM receivers and tuners.   So we already had that covered in previous meduci tuner releases.   We will indeed have one antenna connection on the rear panel, that will adapt to many different external connectors (PL-259, F, BNC, PAL, RCA, etc.) via pigtail.

    We also received some feedback that users would like to see their stereo tuner come back to its previous reception state, after the power is totally removed, and then restored to their devices.   Some use a switched power strip that removes all power at once- tuner, audio amplifier, etc.   Remembering the last station is not usually an issue with using a non-electronic manually-tuned receiver, as the tuning condenser usually stays fixed in place, until physically moved by the user.   We are asking for an electronically tuned radio to come back to its previous reception state, after the power is totally removed, then restored.  Implementing this request will be a bit more challenging.

    Linearity, signal-to-noise ratio, and dynamic range are also important considerations in the RF amplifier stages over very wide signal inputs.   AMax chipset addresses this well, using a very wide AGC feedback loop in the decoder.   This AGC loop can be tied back to the front end.   Motorola says that wideband filtering insures phase linearity to a greater extent.   However, you also want a narrower bandwidth for weaker signal work.   A wideband medium wave receiver should also be followed by appropriate (via manual toggle switch defeat) audio de-emphasis circuitry, after the audio detection recovery. De-emphasis should be able to be defeated, since not all stations use audio pre-emphasis prior to transmission. Users can decide what sounds better to them.

    Stay tuned, and watch this space for additional updates.   We would like to get this MW-2 PLL tuner released, as much as you are anxiously awaiting to see it.   We will let you know when our new MW-2 PLL tuner is available.   We are striving for the highest performance possible, better than any past consumer produced AM stereo radio.   Thank you all for your support, patience, and feedback.

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    This web page was updated on Sunday, October 25, 2020.

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