Most new shortwave receivers let you enjoy synchronous detection. It is an important and very useful feature if you listen to AM broadcasting on medium and short waves. Let’s find out more.
When I returned to shortwave listening around twenty years ago, I discovered a new feature had been added to leading desktop receivers. Now, they let me enjoy synchronous detection when tuning AM stations on medium and short waves. And boy, what an improvement it provides.
Some of the first modern receivers to provide this feature during the 1990’s were the Drake R8, Japan Radio NRD535 and AOR AR7030, shown above. Later versions of the R8 also let you select which sideband you wanted to tune, as did the NRD535. This was possible because synchronous detection uses a product detector, like that used for sideband reception. To select between sidebands on the AR7030 synch detector you needed to use the passband tuning. Initial synchronous lock-up delays in the AR7030 were fixed in later firmware.
AM Synchronous detection goes by many names: coherent detection, exalted carrier and exalted carrier selectable sideband. That’s what the ECSS on the NRD535 and NRD545 front panel stands for. Incidently, the AMS on the front panel of the NRD545 did not stand for synchronous detection. Rather, it was for AM Stereo using Motorola C-Quam.
Perhaps the earliest form of shortwave synchronous detection was achieved with something called the Q-Multipler, which used phasing to boost or reject signals in the IF chain. Old 1950’s radios from Hammarlund had a Q-Multiplier. You could use this device to boost the level of an AM carrier to get better demodulation.
Unfortunately, while modern ham receivers are very good to shortwave DX, very few have supported synchronous detection until recently. The same has been true for portable receivers, but that is changing fast. Most of the new Tecsun and similar portables now sport AMS. The legendary Sony ICF-2010 was a pathfinder in 1985.
Enjoy Synchronous Detection – What It’s About
Stay tuned as we describe synchronous detection, how it works and why it performs better than traditional AM detection. But the basic idea is this. AM signals are comprised of a carrier and sidebands. All of the audio is in the sidebands. A proper ratio or relationship between carrier and sideband power is needed for good demodulation. Especially on short wave, the carrier strength varies considerably, fading up and down. Distortion results.
Synchronous detection in its various forms boosts the transmitted carrier or replaces it with a strong local carrier. Resulting demodulation can be improved significantly.