A couple of months ago, there was some discussion on this list about the
cheap Tesco 113B kitchen radio performing very well on longwave (see
below).
This made me curious, particularly since it looked like a simple analog
radio, the circuit diagram of which might teach us something, so I got
myself one during my recent UK holiday.

Opening it up showed that it is not analogue at all. It's built around
an AKC6952 chip, of which a Chinese datasheet is at
+http://travelx.org/dsp6952.pdf .
This is a complete radio chip, presumably entirely digital, like e.g. the
SiLabs Si48xx series.
I knew such chips existed, but hadn't realized they were so cheap that
nowadays even the cheapest "analogue looking" radios use them, although
in hindsight it does make sense.
Technically it seems a bit silly though: tuning a nicely synthesized radio
via a mechanical potentiometer with a rather imprecise mechanical scale,
just because that's how kitchen radios are supposed to look.

I did some measurements on this radio using an AM signal generator.
It seems to tune in 3 kHz steps, and if the incoming signal isn't quite
on the tuned frequency, it seems to automatically make one such a 3 kHz
step either way. This explains why it seems to suddenly "lock" onto a
signal, as David wrote.
Its AM detector seems to be a standard envelope detector, not a synchronous
detector, judging by the distortion when I notched the signal generator's
carrier.

I don't know why it would be more immune to noise than other radios.
Its digital filters may well be much steeper than those of cheap real
analog radios, thus keeping some noise out.
Also, the google translation of the datasheet promises "Precise digital
demodulation", whatever that means...

Regards,
  Pieter-Tjerk


On Thu, Nov 03, 2016 at 05:34:50PM +0000, David Hine wrote:
> Hi Alan, I am certain you are correct, but this Tesco set is much much quieter
> than my Eton G3, which also has sync detection. There must be something else
> too in that Tesco £9 cheapie -but what is it?? I know another user of one of
> these he bought for TMS on R4 LW, and he says it's the only LW radio he can 
> use
> anywhere without any interference. Perhaps get one before they disappear from
> the shelves? I bought several, as they are so cheap, with the view to one
> day discovering this radio's 'secret'. I feel this 'secret' could be valuable
> to know for other LF applications. Perhaps someone in this group has the
> answer? Very kind regards, David.   
> 
> 
> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
> From: Alan Melia <[email protected]>
> To: [email protected]
> Sent: Thursday, 3 November 2016, 17:14
> Subject: Re: LF: Smart noise cancelling?!?
> 
> Hi David, what describe (jump to frequency as you tune a station in) sounds
> like a little bit of sophisticated radio electronics. It suggests that the 
> unit
> employs synchronous detection, somtimes called enhanced sideband detection I
> think. I dont have details to hand but it would allow a clear signal to be
> received in a much narrower receiver bandwidth than the 18kHz of the bog
> standard diode detector usually used on cheapies. It also has the advantage
> that it greatly reduces the effects of fading (apparent over-modulation) on 
> the
> audio quality.
>  
>  It may sound unlikely at first sight at that price But sophisicated MSF
> synching clocks are available for about the same price.
>  
> Alan
> G3NYK
> 
>     ----- Original Message -----
>     From: David Hine
>     To: [email protected]
>     Sent: Thursday, November 03, 2016 4:32 PM
>     Subject: Re: LF: Smart noise cancelling?!?
> 
>     Hi Stefan, Although this is a bit different, but also to do with noise, I
>     bought a very cheap kitchen broadcast radio from Tesco for £9. It has  
> Long
>     Wave on it, and I am amazed it is the only LW radio I have that can 
> receive
>     all the stations that still are on LW without any background noise once a
>     station is tuned in. It can be mains powered and next to a computer or TV,
>     and still no local noise!! The model number of this Tesco kitchen radio is
>     RAD - 113B. On tuning to a station, it suddenly 'locks on' to it with a
>     small 'jump'. Then the local noise totally disappears, leaving only the
>     required LW programme interference free!! Why is this? -could it be the 
> way
>     this very cheap radio detects the signal? If so, the detection method used
>     in this cheap radio would be very useful for LF work, in which local mains
>     noise is always a big problem. Perhaps someone here also owns this
>     Tesco radio, and can answer why it is so quiet indoors where all my other
>     Long Wave (and much more expensive) receivers are all swamped by local
>     noise when used indoors?? I hope this is useful. Regards, David.  
> 
>     
> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
>     From: DK7FC <[email protected]>
>     To: "[email protected]" <[email protected]>
>     Sent: Thursday, 3 November 2016, 13:22
>     Subject: LF: Smart noise cancelling?!?
>    
>     Hi all,
> 
>     Last night i thought a bit about noise cancelling on LF/VLF. Depending
>     on the band and distance and strength of the QRN, different settings for
>     a noise blanker are used, or optimal. Different rise times, treshold
>     levels and so on.
>     I thought about propagation changes and different shapes of QRN bursts
>     in the time domain, requiring different blanker settings.
> 
>     Is it possible to program an 'intelligent' noise blanking system that is
>     evaluating the input spectrum, looking at the shape/type of a sferic and
>     automatically sets individual dynamic noise blanker parameters for each
>     burst?
>     Or do i miss something here?
> 
>     Just a thought. I guess i'm not the first one who has this idea :-)
> 
>     73, Stefan
> 
> 
> 
> 
> 
>