Tesco RAD113B

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Julian Hardstone
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Tesco RAD113B

Post by Julian Hardstone » 20 Nov 2016 02:05

I had heard that this £9 portable LW/MW/FM radio had unusual properties including unusually good quality listening on R4 LW so I rushed out to buy one.

At this ridiculously low price I wasn't expecting much and it is certainly not a dx machine, but it is remarkable value and an unusually good kitchen or workshop radio. It is clearly using DSP of some sort on AM and FM and the immediate impression is that it does not tune in any way we are accustomed to from an analogue-tuned receiver.

On both AM and FM it appears to 'capture' all strong signals as you tune across the band, and it demodulates the full bandwidth of the transmitted signal so it is not possible to tune for minimum treble (AM) or minimum distortion (FM) in the customary way. The stronger signals just pop up fully resolved, with very great backlash on the tuning, as though there is strong AFC on all bands. Once locked on, there is unusual immunity to QRM, QRN and selective fading on AM, and to the dreaded multipath distortion on FM

So, what's inside? Not a lot, for sure! One small PCB does everything, but the tuning knob seems to be glued on strongly so the board cannot be removed without demolishing the case. The tuning device is a potentiometer, and on AM the antenna is provided by separate small ferrite rods for MW + LW. I presume they are not tuned because of the flatness of the audio response, which would not be possible with the conventional tuned ferrite rod. Each is only 50mm long but the sensitivity is adequate for all the stronger stations which are what it readily 'captures'. Weaker signals can also be resolved with care. With the tuning scale being only 50mm and with the backlash being equivalent to about 5% of that it requires care and a knowledge of the band to find the weaker signals between the big signals, but if you turn the volume to max and tune slowly the DSP will slowly resolve any channel with anything on it.

It runs on mains or batteries. Current consumption is 50-100mA depending on audio volume, so running on the 3 × D-cells should give me a year or two of intermittent listening around the house and garden, where the freedom from multipath will be an emancipation (we use mains-powered DAB radios everywhere else :) and if you like to listen to RTE or the French stations on LW then for the price of 3 pints you will have the best portable you ever owned. Now we just need someone to remove the PCB for a look at the device which does all the work. There is no clue as to the Chinese manufacturer but I would expect it must be one of the big receiver specialist companies.

http://www.tesco.com/direct/tesco-113b- ... d=213-3319

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Julian Hardstone
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Re: Tesco RAD113B

Post by Julian Hardstone » 15 Jan 2018 15:48

I called into Tesco to see if they have those clever AM/FM/USB radios that Pe1etr was describing (they didn't and I don't know if there is another UK supermarket that might have them). I saw they still have the RAD113B (now £10).
As I said before these are not a dx machine but I love the freedom from FM multipath distortion for domestic listening. As an update I have discovered that the DSP device is the 6952, the manufacturer seems to be AKC. The datasheet is all in Chinese but shows it tunes LW, MW, FM 64-108MHz and TV sound 56-92, 174-222MHz. I do not understand the architecture of the device but it does not seem to use a Local Oscillator or have hardware IF filtering. The device has FM stereo outputs.

KPC850
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Re: Tesco RAD113B

Post by KPC850 » 18 Jan 2018 09:59

Julian Hardstone wrote:
15 Jan 2018 15:48
. I do not understand the architecture of the device but it does not seem to use a Local Oscillator or have hardware IF filtering. The device has FM stereo outputs.
On FM there IS a local oscillator which is approx just 0.125 MHz away, above or below, the received frequency, on these type of receivers ('low IF' for FM). Leakage out of the set would be extremely weak, a narrowband scanner very near the radio will probably receive it. The 4th harmonic of the LO would be more easily received (on a nearby scanner)

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