View Single Post
Old 17th May 2021, 10:41 am   #48
agardiner
Hexode
 
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 484
Default Re: 'Proper' DAB conversion for valve radios

Review Part 2.

The system is now fully working. The issue was only the requirement for a suitable aerial. The designer includes a simple 1:1 isolation transformer in the aerial circuit, which allows safe use on a set with a live chassis, along with providing safety on the aerial socket regardless. As such, the aerial needs to be a suitably matched impedance, or the losses are just too great. (at least where I am anyway) So do not expect this to work with a wire aerial, telescopic aerial or any old external aerial. An external one designed specifically for DAB would be ideal, but in the end I bought a cheapo unit from ebay which worked fine. It is only a whip style on a magnetic base, but designed for the DAB band. This matched the module fine and worked even better when placed on a radiator which I suppose added a ground plane. Once this was working, I had to fine tune the units IF output to match the radio. This was very easy and facilitated by tweaking the IF output transformer on the units daughter board.

So onto the actual use and performance. The unit scans and stores stations while the set warms up. This is OK in theory, but of course the unit cannot start to function until the diode valve has warmed up enough. So in practice, it will depend on the valve line up as to whether the unit has completed its scan or not by the time the radio is functioning. In the case of my DAC90, the radio is alive before this has completed, and I have to wait around another 30 seconds. No big deal.

The stations that are found are then spaced out along the dial. Note, they will not necessarily be in the same order as your regular DAB radio; I image they are spaced in the order they are actually found. Between the stations, the unit injects a hiss, similar to what you have on an FM radio. This feels natural, and also helps when tuning as you know you are not on a station rather than on one that has been found but is silent (perhaps through lack of enough signal).

More interestingly, when you get to a station, it doesn't suddenly 'lock in'. We are used to digital being all or nothing, but not so here. The designer has made the unit so that you have to fine tune the station; when 'off tune' you get a variable amount of hiss and distortion. Very clever. You quickly forget that the radio is now DAB and it really behaves and feels like an analogue radio. The whole experience was really nice and tactile and a very authentic upgrade. Sound quality was fine, above any off air MW reception and nice and rounded.

So in summary.... This will not suit everyone. A collector will surely be better off with a pantry transmitter as this will serve more than just DAB and to more than one radio. However, if you only have a single set, or perhaps restore a radio for an end user who has inherited it, then this is a worthy consideration.

If you want to select stations using a menu, or guarantee reception of a particular station, then this is not the solution; get a modern DAB radio. But if you want your vintage set to have a good selection of modern stations then this adds an interesting dimension and achieves it while retaining the authentic vintage experience. It is also perhaps worth consideration by collectors for one set for its interest value.

Certainly the designer has really thought this product out and implemented it really well. I would certainly recommend it.

Adrian.
agardiner is offline   Reply With Quote