Review: Tecsun PL-360 "EMI" receiver

-March 19, 2014

The $50 Tecsun PL-360 AM/FM/SW receiver has been out for a while and is considered by the short wave listener (SWL) community as a pretty fair receiver for the size - beating out several other recent models out of China. The guts of the receiver is based upon the Silicon Labs Si4734 DSP IC, which tunes all the major worldwide AM/FM and shortwave bands. It is also quite unique in that it continuously reads out signal strength in dBuV - something that would catch the eye of an EMC engineer! It also displays signal to noise ratio in dB.

Figure 1 - The Tecsun PL-360 AM/FM/SW receiver with external AM loopstick antenna.

The form factor is quite different from most multi-band receivers, as it’s about the same size as a thick TV remote control. This better accommodates the telescoping antenna, which is used for FM and SW. Besides making a handy broadcast receiver for travel, it should also be useful for tracking down low-frequency EMI emissions, from things like switching power supplies and the myriad of CFL and LED lighting that’s becoming much more prevalent these days.

The AM band picks up the stronger stations OK, as is. However, the receiver is provided with an external ferrite “loopstick” antenna that can rotate for best reception. I use this to boost the sensitivity in locating noise emissions from these low-frequency sources. Very often, you can tell by the sound what the source may be, as well as the emission characteristics. The loopstick antenna is also sensitive enough to couple into, and follow, conducted noise in wiring - for example, in a factory or other building.

The receiver, when tuned to AM, also makes an excellent ESD detector. It is senstive enough to pick up ESD events from several feet away. See the links below for more ESD-related applications.

You’ll also note during your sleuthing for interference, that many products that are turned off are not really “off” and are continuing to contaminate power lines. This might be a great application for the receiver in environments that need to be “RF quiet”.

Figure 2 - Using the Tecsun PL-360 to identify a very noisy DVD player - even while turned “off”. Note the very strong 44 dBuV received signal.

Primary Features
  •  Worldwide FM band support (64–108 MHz)
  •  Worldwide AM band support (520–1710 kHz)
  •  SW band support (2.3–26.1 MHz)
  •  LW band support (153–279 kHz)
  •  Advanced AM/FM seek tuning
  •  Automatic frequency control (AFC)
  •  Automatic gain control (AGC)
The receiver has several convenient tuning methods. The “Easy Tune Mode” (ETM) will automatically tune through the selected band and save the stronger stations in memory channels. These channels can then be selected with the Tuning thumbwheel on the side. Alternatively, you can place the receiver in manual tune and the Tuning control will adjust the frequency up or down in steps of 1 kHz. If you tune the dial quickly, it tunes in 10 kHz steps. In between the common shortwave broadcast bands, the tuning is in 5 kHz steps. Frequencies may be manually saved in up to 450 memories.

Figure 3 - A block diagram of the Silicon Labs Si47354 receiver IC.

As you can see from the block diagram, RF energy enters a low noise amplifier (LNA), where the automatic gain control (AGC) is adjusted and proceeds to the mixer. The in-phase and quadrature (I/Q) signals are then digitized and band-limited in the ADC circuits. From this point, the 24-bit (48 kHz) digital signal processor (DSP) controls the received bandwidth and demodulation. The digital to analog converter converts the digitally-processed signal to audio for additional power amplification to the speaker. One unique feature is that the AM front-end has the ability to automatically tune most any type of inductive AM loop antenna, as the capacitance will tune from 7 to 590 pF. This allows a variety of antennas to be connected.

One other unique feature of the Si4734 chip is that it includes a peak detector after the LNA. A separate DSP function (not shown) uses the detectors to set high and low thresholds to incrementally adjust gain. If the received signal strength indicator (RSSI) does not track the change in gain of the LNA (in 1 dB RSSI per dB gain) then a flag is set indicating possible intermodulation distortion. The chip can correct the situation by reducing the amplifier gain, thus reducing the chance of intermod issues. There are many other subtle operational features that make for a pleasant listening experience.

One drawback is that the receiver has no input port for the FM and SW bands, relying only on the built-in telescoping antenna. This would preclude plugging in near field probes or current probes. However, the AM band does have a standard earphone jack-sized port for this purpose. The unit runs on three AAA cells and if chargeable cells are installed, has a standard USB-mini charging port. The unit seems well-constructed and comes with a protective leatherette pouch (but won't fit the external AM antenna). I find it slips nicely into my main EMI troubleshooting kit.

The PL-360 is available from Amazon and a few other Chinese dealers. An earphone and clip-on wire antenna for better SW reception is also supplied. Delivery from Amazon was very quick. The street price was just $46.

For more:

Tecsun PL-360 receiver (Amazon)

Detecting ESD Events

An EMC troubleshooting kit (detecting ESD)

An EMC troubleshooting kit (emissions)

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