Are the Belka radios SDR based, or are they simply small conventional DSP radios?

[svenmarbles]

Are the Belka radios using SDR technology for demodulation? I’d always been under the impression that the Belkas were centered around SDR, but as I’m looking into it, I’m not actually seeing any evidence of that being true. Is it just a DSP chip based radio?

 

[prcguy]

The fact it has adjustable IF band widths and other features that would require a lot of space and components that would be costly means it has to be an SDR. An SDR will have DSP but the presence of DSP doesn't mean its an SDR. In some radios the DSP is for audio band processing only and not replacing typical hardware tasks like IF band width, AGC, demodulation, etc.

 

[ka3jjz]

The ATS909X2 has DSP, but isn't a SDR, and it has multiple bandwidths available too. Mike

 

[prcguy]

But the Sangean is big in comparison and probably has a couple of cheap ceramic IF filters. The Belka has some IF BWs that are infinitely adjustable, which can be accomplished with fixed filters and adjusting LOs, etc, but that takes space and costs $$. With SDR you can do that on something the size of your thumb nail and some fancy software.

The ATS909X2 has DSP, but isn't a SDR, and it has multiple bandwidths available too. Mike

 

[ka3jjz]

No, that's not correct. The Belka's BWs has fixed values (like the Sangean) and not adjustable. (They are selectable, which is not the same thing and likely simply a mis translation). Keep in mind that the Sangean hears MW and FM, too, unlike the Belka. Mike

 

[ka3jjz]

Also the Belka has a standard audio amp - it says so on their website. A SDR wouldn't use this. Therefore I suggest that this is a DSP, not SDR, radio. Mike

 

[ka3jjz]

For those that don't know what is being discussed here...

Belka DX and DSP Receivers - The RadioReference Wiki

wiki.radioreference.com

Onward....Mike

 

[svenmarbles]

They’re defined filtering steps, not variable, but there are a lot of them. 12 in total, and I’ve never had a radio with low cut off before. My Drake R8 doesn’t have it. Frankly, I’m not even sure what you do with low cut-off filters lol.

 

[ka3jjz]

This article from Fenu Radio (Switzerland) has a short user review of both the older DSP unit and the DX, and most importantly a block diagram of each radio...

Fenu-Radio - Belka-DSP -- Belka-DX

www.fenu-radio.ch

Mike

 

[KE5MC]

Also the Belka has a standard audio amp - it says so on their website. A SDR wouldn't use this. Therefore I suggest that this is a DSP, not SDR, radio. Mike

Why does a std. audio amp exclude it as an SDR radio?

 

[ka3jjz]

Because a true SDR recovers audio very differently from a superhet design, as I understand it....and as an aside, the block diagrams show that this is clearly a DSP radio....Mike

 

[KE5MC]

I whole heartily agree the technology to recover the audio varies greatly. I was interested in your comment that the end stage (audio) defines the front end technology. The audio stage will likely be tailored (high frequency rolloff) to deal with digital artifacts introduced in direct sample SDR or wherever the DSP comes into play. Clearly a good block diagram will identify the radio type regardless of the last stage. Your comment surprised me in that most radios the end product which in this context is audio will need some level of help and isolation from the other circuit to be useful for headphones or speakers.

 

[ka3jjz]

One other point - I see no ADC (analog to digital converter) on the block diagram. Mike

 

[krokus]

Because a true SDR recovers audio very differently from a superhet design, as I understand it....and as an aside, the block diagrams show that this is clearly a DSP radio....Mike

An audio amp is still needed for an SDR, to drive the speaker, if the audio decoding/recovery is in a standalone radio. If recovery function is being handled inside a PC, then the PC provides the audio amp.

 

[prcguy]

Looking at the block diagram the Belka is an SDR, plain and simple. Some of the criteria for an SDR is IF filter band widths and demodulation is handled by digitizing the RF and these functions are then handled by software simulation of hardware components. That is what the Belka is doing and its a superhet that converts to a low IF or baseband then to an IQ demodulator then the I and Q are digitized and DSP is taking care of all other receiver functions. Its an SDR, no question and no different that some of the first SDR receivers developed.

Because a true SDR recovers audio very differently from a superhet design, as I understand it....and as an aside, the block diagrams show that this is clearly a DSP radio....Mike

 

[ka3jjz]

But there's no ADC or DAC converters, at least in the block diagrams...Mike

 

[KE5MC]

This is the block diagram I think prcguy is looking at from a link in an earlier post. It lays out like he saids, as a superheterodyne just not like we are familiar with in old school pre digital days. Symbols and names have been changed to protect the innocent or confuse the rest of us.

 

[prcguy]

Yes there is, right before and after the DSP. The final frequency conversion is done with an IQ mixer and that looks like its providing a baseband I and Q output. These In Phase and Quadrature signals contain all the amplitude, frequency and phase information needed to reconstruct the signal in the digital domain. The I and Q signals are then fed to an analog to digital converter, processed by the DSP and when I say processed they are further filtered digitally in band width, demodulated, AGC is applied somewhere then a final digital to analog converter gets you the resulting processed and demodulated analog audio from the receiver.

Look at the block diagram and you will see what I described and also the lack of a hardware IF, no hardware IF filtering, no hardware demodulator, its all broad band RF until the final mix down to baseband before digitizing and DSP. Its an SDR and if the mfr wanted to and there was enough on board memory, they could diddle the internal software to give you more or different IF band widths, add another waveform (a mode like WBFM or P25 or anything else) and it would use the exact same hardware.

But there's no ADC or DAC converters, at least in the block diagrams...Mike

 

[ka3jjz]

Yep you're right - just didn't see the symbols. A SDR it is - and in such a small package too. Mike

 

[svenmarbles]

Thanks for going to the trouble to dig into this to the degree that you guys have. All of it being WELL beyond me, but my original question has been answered.
Thanks again.