Asymod™ IIIs Modulator Board


Asymod IIIs

Asymmetrical Hi-Fi AM modulator

Asymod Asymmetrical Hi-Fi AM Modulator for use with mobile or base CB & HAM radio transmitters and transceivers.

Be sure to see the Stryker SR-955HPC in Hi-Fi action with the NEW Asymod IIIs in this highly requested real-human-voice demo and the Asymod III with the Cobra 29 LX BT & Galaxy DX-939 real time demos.

Got questions? Visit the new Asymod related FAQs and get answers to the most frequently asked questions and lots of valuable information related to Hi-Fi communications.

Sound Pro mobile or base with the Asymod Asymmetrical Hi-Fi AM Modulator. Get the Hi-Fi audio you want with this compact unit. With this setup you will save in time to come as there will never be the need to upgrade again.

The Asymod compact design makes it ideal for mobile and base operation and allows for internal mounting and simple installation in the transceiver with the included hardware and only requires a 12 Volt supply. The Asymod expands the transmitter’s audio bandwidth from the stock 3 kHz to well over 10 kHz. On board preset active and passive low pass filters can be set to 6, 8 or 10 kHz roll offs. This allows for the entire selected audio bandwidth to be transmitted.

The asymmetrical functionality controls the audio loudness level and provides for amplitudes in excess of +300% modulation while not exceeding the negative peaks at -100% without the use of negative peak limiting or clipping methods which produce squaring of the modulation envelope and provides for increased spectral density. The Asymod is compatible with most transceivers and it is fully adjustable via the onboard controls and accepts microphone and line level inputs. It offers the flexibility to use a stock hand mic to a high end processing audio chain using a broadcast microphone. This unit will work with all High Level Modulation transceivers by direct coupling to the driver and final’s collectors via the existing transceiver's onboard RF chokeswithout the need for a heavy, costly and large modulation transformer. Low Level Modulation transceivers will require some modification. Instructions for specific multiband HF transceivers is available upon request.

The Asymod produces modulation levels well above the norm and broadcast levels without distortion, allowing for your station to sound loud and clean. With the Asymod connected to your audio processing chain and a transceiver of your choice, your mobile or base station will sound just as or better than commercial broadcast stations.

To achieve optimum results and to make the most of the Asymod, adequate audio processing catered to emphasize on your natural voice is necessary.


Read through all related documents, including the Asymod FAQs and manuals to see the requirements for an effective Hi-Fi setup before committing to purchase. All sales are final and there are no returns. If the unit breaks, please send it back for repair. All repairs are free within the first two months after the sale.

Read through all related documents, including the Asymod FAQs and manuals to see the requirements for an effective Hi-Fi setup before committing to purchase. We are not responsible for others selling copies of Asymod products using the Asymod name, oscilloscope images and descriptions. The Asymod II and III has been discontinued and are no longer in production. Original Asymod products are manufactured by BluThunder Tecnologies and sold on this site, on and on eBay by member Myspin and carry the BluThunder logo. “Asymod” is a registered trademark and may not be reproduced or used by any means or in any form whatsoever.

The transceiver/radio is only the exciter and should not be expected to generate high levels of RF power, it should be expected, however, to generate a clean, perfectly modulated wide-band Hi-Fi audio RF signal well within the limits of the headroom available without pinching or clipping at the crest or troughs of the modulation envelope which can be later amplified with a class AB, RF power amplifier and is best heard or monitored on a good quality receiver equipped with a 6 kHz AM wideband filter and monitored on an oscilloscope.

The Asymod is not an audio processor, but it does allow for full bandwidth control with the use of Pro Tools, a combination of rack gear, or a broadcast multi band compressor / limiter.

Audio processing and a high quality microphone is necessary for optimum performance.

Audio processing for mobile or base operation is possible with the use of the iRig PRE or iRig PRO interface using the companion IK Multimedia's VocalLive Vocal Processor app (not the free version) on your iOS device.

Audio processing for base operation is possible with the use of rack audio processing gear or computer based processing such as Pro Tools for PC or Mac along with its companion interface such as the Mbox 2 Mini or newer. Pro Tools is the best choice and is highly recommended. Pro Tools sessions are free and available for download.

The Asymod is NOT designed to give transceivers more RF power, more swing, or loud distorted modulation. It is however, to be used with the appropriate audio processing to produce a broadcast quality transmission.


Recently added features to the new and improved design of the Asymod Include on board passive and active selectable low pass filters which provide preset roll off points, remote control operation via the on board Solid State switch which provides mode switching for ease of installation on multimode transceivers. Enhanced RF suppression circuits have been added and board layout design has been optimized to eliminate and avoid any stray running currents due to RF interference. Single supply operation provides for a very low noise and quieter operation. New onboard unbalanced audio preamplifier with independent input and output to be used in any installation where audio levels need to be matched as it applies to the SSB Balanced Modulator input levels for eSSB operation or as a microphone preamp.

The Asymod compact design allows for easy mounting inside your transceiver and offers all the combined features comparable to high end, very expensive broadcast gear and other available Hi-Fi mods upwards of $1000, and makes for the most important part of a Hi-Fi AM station. Hi-Fi Audio is very thought after by many radio operators nowadays and the Asymod delivers all the necessary functionality and stands as the backbone of the station.

Now you can make your mobile or base station sound like you always wanted it to at an affordable price. If you are tired of spending on expensive gear or trying different combinations and still don't have the Hi-Fi audio you want for your CB or Ham AM radio station setup this is the way to go. With this setup you will save in time to come as there will never be the need to upgrade again.

  • Mobile or base operation, ease of use and simple installation; only a 12 Volt, 5 Amp power supply is required.
  • Rugged design built on a tough PCB to provide years of continuous use.
  • Audio gain control allowing for proper drive from the microphone and line level input.
  • Modulation Level control allows for final audio control and is set in combination with the Carrier and Asymmetry controls to achieve the level on modulation desired.
  • Carrier controls sets the reference carrier level (dead key) to set the modulation and asymmetry levels.
  • The Asymmetry control maintains the negative peaks at -100% modulation while allowing for positive peaks of excess of 300% without pinching or clipping.
  • Preamplifier gain control to allow matching of audio levels.
  • Remote ON/OFF control.
  • Power status LEDs for the 12V and onboard 24V supply.
  • Input voltage polarity protected.
  • Modulation peak indicator.
  • Convenient mount holes.
  • Heavy duty screw terminal block connectors for the line in, power in, modulator output, pre-in and pre-out connections.
    TO-220 and TO-247 onboard compatibility for mounting single or dual modulating stage transistors.

Modulator Configuration

The Asymod III may be set up in any one of the three following configurations:

A- Single MJE3055T transistor (Q2) with a maximum collector current of 10 Amps.

B- Dual MJE3055T transistor (Q2 & Q3) with a maximum collector current of 20 Amps. (Request)

C- Single TIP35C transistor (Q4) with a maximum collector current of 25 Amps.(Request)

Although configuration A will work fine with most 4 watt transceivers, for heavy use or higher output transceivers, such as dual final transceivers, configurations B or C are recommended which withstand higher duty cycles at lower temperatures and are available upon request.

Be advised that the Asymod appearance will vary depending on the requested configuration and combination of modulator final output stage transistors used.

The Asymod will arrive pre adjusted, however, in some cases it might require some fine tuning to perfectly match your particular setup. This unit requires basic electronic skills to install and adjust. It is recommended to use an oscilloscope to do all the initial adjustments. Refer to the Asymod Installation Manual and Asymod Operation & Troubleshooting Guide for details.

• +12 volt supply @ 5A
• Heat Sink for final stage modulator transistor/s.
• Enclosure if not mounted inside a transceiver.

Absolute maximum ratings:
• Audio input: +4 dBu, 1.74 VPK or1.23 VRMS
• +15 volt supply @ 5A

Remote control sensitivity:
• +8V ~ +12 V

Audio Input Range:
• Audio input: -30 dBu to +4 dBu

Frequency response:
• Input: 20 Hz – 11 kHz.Expandable to 20 kHz.
• Output: 20 Hz – 11 kHz.Expandable to 20 kHz.

Total System Distortion(@ 300% modulation):
• <0.01% THD 20 Hz – 1 kHz
• <0.02% THD 1 kHz – 5 kHz
• <0.03% THD 5 kHz – 14 kHz
• <0.05% THD 14 kHz – 24 kHz

Input & Output Passive Low Pass Filter:

Selectable: 5 kHz, 8 kHz, 11 kHz or 20 kHz

Preamplifier Active Low Pass Filter:

Selectable: 8 kHz, 16 kHz

Modulator Output:

*The following values were recorded using configuration A, modulating an AM transceiver manufacturer rated at 4W carrier and 16W peak with a 1 KHz tone.

Refer to the captured oscilloscope pictures in the Asymod Operation & Troubleshooting Guide.

• @100 % modulation: 3W carrier, 12W peak. (4X carrier = 100% modulation).
• @200 % modulation: 2W carrier, 16W peak. (8X carrier = 200% modulation).
• @300 % modulation: 1.0W carrier, 15W peak. (15X+ carrier = 300% + modulation).

*The following values were recorded using configuration B, modulating a CRE-8900 transceiver with one IRF-520 driver and two IRF-520 finals with a 1 KHz tone, manufacturer rated at 12W carrier, 48W modulated.

• @100 % modulation: 15W carrier, 60W peak. (4X carrier = 100% modulation).
• @200 % modulation: 7.5W carrier, 60W peak. (8X carrier = 200% modulation).
• @300 % modulation: 4W carrier, 60W peak. (15X carrier = 300% modulation).

*For higher RF output power levels use a class AB amplifier. It is best to generate your original modulated signals at lower levels and use the amplifier to amplify your output to the desired level.

Shielded cable should be used in all audio connections and RF bypass capacitors where ever possible.

The Asymod comes with:

Description Manual
Installation Manual
Operation & Troubleshooting Guide
Asymod FAQs
• Mounting hardware
• TO-220 / TO-247 Thermal Silicone Rubber & Fiberglass Composite Insulator
• Single MJE3055T transistor (T2), configuration A. Configuration B or C available upon request
• Downloadable Pro Tools sessions

For advice on Hi-Fi audio processing you may visit

**This design is based on the oldest technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker, or the light intensity of television pixels. This technique contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied.

Asymod - Patent Pending

Please Read Before Buying:

Please do all research and ask all questions before buying.

Take a look at the pictures and the oscilloscope captures for actual results, browse through the manuals and ask questions as needed.

Unit ships out within 1 to 3 business days of cleared payment if unit is ready otherwise as soon as the unit is ready.

*EV RE20 microphone shown in pictures is not included.