Many thanks for this very instructive video. It's kind of funny that so much control of these DSP chips go over analogue voltage values. I would have expected some binary values over a number of pins. Maybe that would require too many pins? I see that some version operate over a command/response protocol through a serial I2C-style connection. i see that all the resistors are 1%. One has to hope that the ones they put in these cheap radios are indeed precision resistors of high quality that will not drift with time.
Thank you for sharing your findings and the inside of the D-219. Concerning the 9/10K stepping on AM (MW) band, as the design uses aa series resistor ladder, changing a single resistor value would require to change all other resistors above in the ladder in order to maintain the correct resistance values for each RF band as specified in the application note. As the MW band resistor value is located lower in the series ladder, it seems that most of the resistors need to be replaced. As for the circuit diagram and components for the PCB ref. D-219 20221023: U1 D2822M Audio Pwr Amp 8-pin dip U2 Si4825A10 DSP 16-pin dip Y1 xtal 32768kHz Q1 J6 3-pin smd SOT-23 S9014 NPN Q2 R25 3-pin smd SOT-23 2SC3356 NPN RF Q3 J6 3-pin smd SOT-23 S9014 NPN Q4 M6 3-pin smd SOT-23 S9015 PNP Q5 R25 3-pin smd SOT-23 2SC3356 NPN RF D3 A7 3-pin smd SOT‑23 BAV99 D4 M7 2-pin smd large VR1 Volume pot VR? Tuner pot R100K It seems this radio is a textbook implementation of the Silicon Labs Si4825A10 DSP chip for all RF bands, so no fancy RF front end pre-scalers here, but at this price we do not expect to see it being deployed as that would be what the D-808 uses. However I see some form of a basic active RF front end/filter, probably for the SW band and less probable for the FM band, in the form of a few capacitors, resistors and at least one inductance close to a couple of transistors. The SW (shared with FM) antenna signal is limited by a pair of low capacitance diodes (D3, A7/BAV99) before being passed thru some RLC filters to a couple a RF transistors (Q2 and Q5, R25/2SC3356). Then the SW RF signal is passed to the DSP chip. As for the FM signal from the antenna, as per the application note it is simply passed to the DSP chip dedicated input pin, as seen in most of the designs, even at higher price range. However, as two RF transistors are used in this design, both SW and FM bands are probably using active front-end stages. Further checking of the PCB traces would be required to confirm this hypothesis. The other 3 transistors (Q1, Q3, Q4) are not really suited for RF applications as these are NPN and PNP general usage devices, most likely used as switches or current/voltage regulators. Update: Looking to the PCB traces, it seems that the FM band uses the RF transistor Q5 as a front-end, while the SW band uses Q2. So the antenna signal is fed in parallel to both RF transistors using dedicated RLC networks. Diode D1 allows to switch between MW and SW bands.
Thanks for working that out! Figuring out the RF amplifier is beyond my pay-grade. I had quickly looked at the data sheet to see if the resistors could be easily changed on the resistor ladder, and came to the same conclusion you did.
I'm not sure that is correct. If you increase one resistor (i.e. one step) by 10K and then you decrease the next one in the ladder also by 10K, then the total remains the same, and all the other steps on the ladder are at their original values. I may grab another D-219 and have a play with this idea.
On the D-219 you might get more value from playing with Pin 1, the LNA_ENA pin as this would let you switch in the wide band SW bands. I suspect it is grounded, looking at your pictures of the PCB, but if the grounding was removed and it was tied to VCC through a switch and a 10K resistor (per the example in the datasheet) you should get the alternative SW bands. You could also play with the other values in the resistor ladder to gain access to the remaining SW bands.
Many thanks for this very instructive video. It's kind of funny that so much control of these DSP chips go over analogue voltage values. I would have expected some binary values over a number of pins. Maybe that would require too many pins? I see that some version operate over a command/response protocol through a serial I2C-style connection.
i see that all the resistors are 1%. One has to hope that the ones they put in these cheap radios are indeed precision resistors of high quality that will not drift with time.
Thank you for sharing your findings and the inside of the D-219.
Concerning the 9/10K stepping on AM (MW) band, as the design uses aa series resistor ladder, changing a single resistor value would require to change all other resistors above in the ladder in order to maintain the correct resistance values for each RF band as specified in the application note.
As the MW band resistor value is located lower in the series ladder, it seems that most of the resistors need to be replaced.
As for the circuit diagram and components for the PCB ref. D-219 20221023:
U1 D2822M Audio Pwr Amp 8-pin dip
U2 Si4825A10 DSP 16-pin dip
Y1 xtal 32768kHz
Q1 J6 3-pin smd SOT-23 S9014 NPN
Q2 R25 3-pin smd SOT-23 2SC3356 NPN RF
Q3 J6 3-pin smd SOT-23 S9014 NPN
Q4 M6 3-pin smd SOT-23 S9015 PNP
Q5 R25 3-pin smd SOT-23 2SC3356 NPN RF
D3 A7 3-pin smd SOT‑23 BAV99
D4 M7 2-pin smd large
VR1 Volume pot
VR? Tuner pot R100K
It seems this radio is a textbook implementation of the Silicon Labs Si4825A10 DSP chip for all RF bands, so no fancy RF front end pre-scalers here, but at this price we do not expect to see it being deployed as that would be what the D-808 uses.
However I see some form of a basic active RF front end/filter, probably for the SW band and less probable for the FM band, in the form of a few capacitors, resistors and at least one inductance close to a couple of transistors.
The SW (shared with FM) antenna signal is limited by a pair of low capacitance diodes (D3, A7/BAV99) before being passed thru some RLC filters to a couple a RF transistors (Q2 and Q5, R25/2SC3356). Then the SW RF signal is passed to the DSP chip.
As for the FM signal from the antenna, as per the application note it is simply passed to the DSP chip dedicated input pin, as seen in most of the designs, even at higher price range. However, as two RF transistors are used in this design, both SW and FM bands are probably using active front-end stages.
Further checking of the PCB traces would be required to confirm this hypothesis.
The other 3 transistors (Q1, Q3, Q4) are not really suited for RF applications as these are NPN and PNP general usage devices, most likely used as switches or current/voltage regulators.
Update:
Looking to the PCB traces, it seems that the FM band uses the RF transistor Q5 as a front-end, while the SW band uses Q2.
So the antenna signal is fed in parallel to both RF transistors using dedicated RLC networks.
Diode D1 allows to switch between MW and SW bands.
Thanks for working that out! Figuring out the RF amplifier is beyond my pay-grade. I had quickly looked at the data sheet to see if the resistors could be easily changed on the resistor ladder, and came to the same conclusion you did.
I'm not sure that is correct. If you increase one resistor (i.e. one step) by 10K and then you decrease the next one in the ladder also by 10K, then the total remains the same, and all the other steps on the ladder are at their original values. I may grab another D-219 and have a play with this idea.
On the D-219 you might get more value from playing with Pin 1, the LNA_ENA pin as this would let you switch in the wide band SW bands.
I suspect it is grounded, looking at your pictures of the PCB, but if the grounding was removed and it was tied to VCC through a switch and a 10K resistor (per the example in the datasheet) you should get the alternative SW bands.
You could also play with the other values in the resistor ladder to gain access to the remaining SW bands.
Stred i think you can get a XHDATA D_219 mw band that goes 16000 to 17000
Yes, there's been a North American version out for a little while. It's now available here in Canada. I just haven't got around to ordering one.