Posted 20 hours ago

SIHUADON D808 Portable Radio Transistor AM FM SW LW SSB Air Band Multiband Radio Loudspeaker Alarm Clock Sleep Timer Black

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The XHDATA D-808 FM Stereo/LW/MW/SW-SSB AIR RDS Synthesized Receiver is supplied with a succinctOperation Guide that may not cover all the details of the radio operation behavior. Initially I thought that this behavior wasrelated to a defective component,but now that I have my unit (new version 2021), I am not so sure.As the volume is a pure analog potentiometer, the noise must be generated inside the CS4863 (LM4863 equivalent) audio power amplifier IC. Looking to the publicly available pictures, extensive changes were made in the circuit diagram and PCB layout of the Receiver board. Power supply issues - Power ON key fails to turn the radio ON, or else it power Off by itself, even with a fully charged battery, several causes for this, one being the use of inappropriate batteries (physically incompatible with the battery holder terminals). Gone is the RF front-End with the 4-Sub-Bands pre-scaler using four LC trimmers for proper alignment and better spurius strong signals rejection, being replaced by common LCR fixed values networks using SMD components.

Due to product quality problems within 1-3 months of receiving the product, we can replace it with a new one, but the customer pays for the logistics costs incurred.The above reasoning is supported by the fact that this model's sensitivity is on pair with similar radios of other brands, because doing a manual tuning or entering the RF frequency directly will acquire the RF signal without issues, while the ATS and the Auto Scan features fail to capture that RF signal. Some have reported that the squelch is not fast enough to unmute resulting in loss of the initial conversation. I can confirm this to be true, but it loses just a small fraction of a second, not really an issue. LW band seems to show poor sensitivity on DSP radios like this model category, due to a poor design of the RF analog passive components that favors the MW band. The design choice used on the D-808 was to save costs on the audio pre-amp and simply configured theCS4863's OpAmp1A andOpAmp2A with a very high bridged mode differential gain of 77 (!) My 2021 unit present these transitory noises. I wonder if the muting system is not being enabled by the MCU firmware. Bug or hardwaredesign fault?

Functional: Alarm function, sleep mode, and the time can be set and displayed in the off state. The sleep timer setting can be automatically turned off according to your lifestyle settings. R108 radio can be placed on the bedside, get up in the morning, enjoy the wake-up service of the radio, and watch the time with an open eye. When you brush your teeth, you can listen to the radio and keep up to date with the news. So the manufacturer have cut production costs by eliminating costly LC trimmers and active components of the Pre-Scaler and DC-DC converter, reduced the alignment requirements at the assembly line, and potentially have reduced some internal noise coming from the MCU/Display into the DSP, at the cost of offering a radio with lesser ability to reject strong spurius RF signals. The squelch also works adequately in my opinion. Set it level 1 and it will not mute the audio due to the noise floor inside house (around 12dBu), but at level 2 it would mute it; then the radio is able to unmute the audio for signals as low as 25dBu. The DC-DC converter was not properly shielded in the previous versions, being a source of RF noise. Other better radio brands, even ones using the same basic chassis, use shielded DC-DC converters.On the other hand, the AVDbridged mode differential gain configured on the D-808 is too high, generating lots of noise, and that may also be increasing these shudown/turn-on noises as well. Doingmanual tuning across RF bands results in muting/chuffing sounds when changing eachRF step.This seems to be a design characteristicof DSP based radios. In this model the volume drop can be reduced by seleccting the Slow tuning mode. In my 2021 unit, I can not confirm this behavior seen in the older original model of 2018. The radio is able to find signals with just 30dBu and 4dB S/N ratio. 30dBu may look like a high level signal but the radio is by the window inside the house using the telescopic antenna and the noise floor here is around 20 to 25 dBu. My 2021 unit came with 3.81V in the battery (still a XHDATA 2000mAh device) and the battery level indicator had 2 bars.

I am currently located in the Northeast of Portugal, at an altitude of about 1000 meters, and I can receive radio transmission signals from the various passenger planes that fly over the area, using the telescopic antenna and being indoors at the window.The audio components section was rearranged and the DC-DC converter to supply voltage to the Pre-Scaler varicap is not visible anymore, so it seems it was simply eliminated. Due to product quality problems within 3-12 months of receiving the product,we can repair it for free, but the customer pays for the logistics costs incurred. If the MCU firmware is shuting down theCS4863 to avoid these nasty noises during band switching and fetching memory preset stations, as it should, then probably would be possible to fix it by following the Texas InstrumentsLM4863 datasheet. Telescopic antenna - Last section (with tip) detached from the rest. Also, the antenna mounting seems to be fragile, requiring great care when rotating it, as it can break the plastic support. Allegedly, the Auto Tuning and Store feature seems to only find the stronger RF signals, probably because the firmware was set to use a too high threshold detection level, and there is no user setup to change it.The same behavior happens for the Manual Scanfeature, by presssing and holding the Up or Down keys for 2 seconds.

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