Freeview/SKY quality

Not as daft as it sounds though... When I was I guess about 10, I had a Ladybird book called "How to build a transitor radio!" ;-)

ISTR it went through building a set in stages, starting with a basic crystal set (using a OA91 diode for AM envelope demodulation - about the last time I have used one of those), and then worked up to a regenerative design. The construction method was a little "unorthodox" with a wooden breadboard with a matrix of screws driven in, and the wires of the components trapped under screw cups. Alas the full design never did work, and I did not have access to the test equipment to trace it through correctly to work out why. (not helped by being a very old circuit design - many components were on the verge of being obsolete).

Alas the freeview can sound worse on the poor bitrate channels. With a decent bitrate channel I have found it is about as good as NICAM when fed into a prologic decoder. There also seems to be a fair variation in sonic performance between the different freeview boxes.

Comparing against analogue is a little more trickey - as you say you would have to limit your source material to mono which in many cases will also mean older analogue recordings etc.

I can vouch for this - I got a digibox for this reason alone. There is a churchyard full of very old, very tall trees near my house. The signal bounces off them causing quite bad ghosting on my analogue signal. As the trees wave majestically in the breeze so the little ghosts dance about on the telly. Anyway, the digibox has cured this and gives a perfect signal on channels 1-4 despite running off an aerial which looks like it may have been up there since the house was built in 1880. The other channels can suffer from signal degradation but they seem to broadcast unalloyed crap, so no loss there.

I will second that. Ok the DVD's are a tad sharper, but otherwse my analogue installation is almost totally free of defects and sharp and clean.

as is my FM radio...

I had an (IIRC) Radionics kit

Perspex matrix with mounted components with lugs which fitted into screws .. it sort of worked

The screening is the reason for the cable requirement. Correct cable is required even if (and probably more so) you are 2 miles from the transmitter.

Which was my point. I was just trying to explain it in simple terms....

"John Rumm" wrote | Andy Hall wrote: | > "for grown ups"). The librarian looked down her nose at me and | > suggested that I would be better off with Janet and John or Noddy. | Not as daft as it sounds though... When I was I guess about 10, I | had a Ladybird book called "How to build a transitor radio!" ;-) ... | Alas the full design never did work,

I'm glad you told me that; I had the same book but never tried making it up. Now I know it wouldn't have worked anyway, I don't feel I missed as much.

Owain

I think one of the problems was the components used were so old in design that the spec had altered by the time I managed to find examples of them. The transistors used (can't remember the number at the mo) were in glass domed cases with a black finish (about 3mm diameter by 7mm tall). It also called up things like "postage stamp" type trimmers which at the time were difficult to find (although they are available again now!).

Ahh. Red spots. ;-)

OC71 etc, though that was an audio type tranny. Nicely light sensitive if you scrapped the paint off.

When I was at the "building my first radio stage" (late 60's early

OC81 comes to mind. I had some here till recently...

Strange numbering system...followed on from the valve conventions. O was the filament coltage, and C meat it was a 'triode'....!

IIRC, OC82 was an output transistor in an ally can. OC71 was the common general purpose type.

Thinking about it, I'm sure you're right. I remember filing round the base of the glass, removing it, getting the jelly off, scraping the glass clean....lo, a phototransistor (terrible characteristic, but...)

But you got it wrong. The need to use decent (i.e. well-screened) coax cable for DTT is much more to do with keeping impulsive interference at bay, than with the loss of the cable.

At UHF most of the loss of a coax cable is 'copper loss' in the resistance of the conductors rather than dielectric loss. Thus it's mainly determined by the size of the conductors - almost always 1mm inner and about 4.6 - 4.8mm outer for the sort of cables we're talking about. There's not that much difference in loss between CT100 / WF100 type cables and single-braided coax over the length of a typical domestic downlead (at least not until you get to the really cheap & nasty cables with < 30% braid coverage) - but there is a huge difference in the screening effectiveness and that's what matters.

And the audio line-up in a good transistor radio of that era was an OC71 feeding an OC81D driver feeding a pair of OC81s in push-pull (transformer coupled in and out). For the RF side you had an OC44 self-oscillating mixer and two unilateralised OC45 IF stages.

Nostalgia...

That was the beastie....

I guess I was lucky... first got into electronics in about 1980, and lived 10 minutes walk from the one and only Maplin shop at the time. ;-)

hmmm - had forgotten that til you mentioned it.... feeling old now ;-)

Yup. Life was simple in those days. ;-)

Not always transformer output, though - high impedance speakers were fairly common.

I've got a working 'Good Companion' I bought as a kit with my first pay from the BBC. Micro alloy transistors and transfilters...