Superdrug £3 radio

I received a tip-off from Tony Saunders G4LLW about a Superdrug special offer.

A 10-band radio for £2.99. Naturally I rushed off to buy one.

This is a neat little radio, featuring:
Digital clock/alarm with backlight
4 digit frequency counter
MW/SW1-SW8/FM
Telescopic antenna
Runs off 2x AA batteries (not included)
Integral 8-ohm 0.25W loudspeaker
Power LED, Tune LED

Sensitivity spec according to the information sheet is:
FM <= 20uV,
AM <= 4mV/m (what does that mean?),
MW <= 20uV..

That's confusing since the 10 bands they mention are FM, AM, SW1-SW8 ; but the sensitivty specs are FM, AM and MW. So what is it, MW or AM?

I haven't yet played with it much but I did open it up. Inside is a single 24-pin SMD IC, with markings:
CHMC S5504
D1191

The Superdrug 10-band radio

I'm not sure if any of these constitute a recognisable part number?
There are also 6 discrete transistors near the audio end of the board. There is a ribbon cable to the LCD/buttons board, which presumably has another IC to take care of frequency counter and clock functions.

Apart from the SMD IC, the rest of it is non-SMD. There are several canned IF transformers and a plastic-cased 465kHz ceramic filter. Tuning is via a polyvaricon variable capacitor, i.e. this radio is not synthesised PLL. The digital display must therefore be a proper frequency counter.

I imagined it would be relatively easy to adjust the 8 SW bands to cover some ham bands. But testing reveals even that isn't necessary, contrary to the band limits specified in the information sheet. Band coverage as displayed on the frequency counter:

FM 86.6 - 108.7
MW 523 - 1657 kHz
SW1 5.81 to 6.56
SW2 6.74 to 7.58 (incl whole of 40m)
SW3 9.29 - 10.35 (incl whole of 30m)
SW4 11.85 to 13.03
SW5 12.93 to 14.20 (incl lower part of 20m)
SW6 15.21 to 16.63
SW7 16.63 to 18.14
SW8 20.94 to 22.54

The tuning knob is not geared, so tuning CW could be tricky unless the band could be narrowed somewhat. The frequency counter resolution is 10kHz, I don't know if this could be altered.

IMPORTANT! How to open this radio without breaking anything (remember, it did only cost £3, it isn't very strongly made!):

On the back there is a flap of plastic which flips out and allows the radio to stand up on a table. When the flap is flipped, there is a small screw behind it which must be removed. Next, notice a small switch on the righthand side of the radio, next to the tuning thumbwheel. It says Low<->High: I think it means AF bandwidth, that's CW/SSB to you and I! The switch pops off using a small screwdriver, knife, paperclip or whatever.

Finally, the two halves of the case have to be unclicked: gentle pressure with a screwdriver or small knife to prise apart the two halves should be applied to the clip points which are on the top and bottom of the radio (the long edges of the rectangle). That's it. When putting it back together: be sure to align the slider switch knob with the actual switch inside; also, be very careful not to overtighten any screws since the plastic posts they screw into are very soft plastic and will easily split.

I tuned around at 2215Z this evening and could hear many CW stations in the lower part of 40m. Well I say "hear": not proper tones, but a hiss as you do when trying to receive a carrier in AM. To properly demodulate CW or SSB will need a BFO, somewhere offset slightly from the 465kHz IF.

Here are the pictures: http://www.hanssummers.com/radio/superdrg/

(I intentionally didn't spell Superdrug correctly, because there are site scanning 'bots' out there which find any sites with "drug" or "pharmacy" in them and ban them for some corporate users etc).

I know that Tony G4LLW is building a BFO with it - hopefully others will experiment too.

Happy experimenting

72/3 Hans G0UPL
http://www.hanssummers.com/

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