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Old 11th May 2021, 10:40 am   #41
agardiner
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Default Re: 'Proper' DAB conversion for valve radios

Review Part 1

OK, so the module arrived and I couldn't wait to open the parcel and install it.

First impressions; the unit is very well made and consists of a shrink wrapped module connected to a small unit which is mounted on a suitable valve plug. There is a flylead connected to a crocodile clip and a screened lead to an aerial socket. This teminates in an F plug, and a coax adapter is included which is a nice touch. Also included are installation instructions and a seperate operational guide which can be given to the end user if the set is not yours.

Remember, these are made for your specific radio. I suspect that the 'module' is the same every time, and that any changes to suit your radio would be on the valve plug board. Mine therefore included a suitable resistor to take the place of the series valve heater. Perhaps on some, the crocodile flylead would not be needed.

Installation is easy. Removed the mixer valve and insert the board. The flylead needs clipping to a suitable anode supply rail. You can of course remove the crocodile clip and solder the wire, but the idea is that the conversion is easily reversible. I noted that the crocodile clip is a good quality and will happily 'stay put'!

The construction of the unit appears to be very well made and the PCBs are excellent quality. I have removed the shrink wrap to take photos and see the construction, (as well as checking connections, see later). A quick reminder; while the set warms up, the unit scans for DAB (and DAB+) stations and stores a max of 100 in its EEPROM. Once stored, the unit only checks for new stations and there is a simple procedure for clearing the EEPROM if needed to start a fresh scan. The micro then spaces the stations out along your AM dial and you select them by 'tuning' your radio as before. The entire radio is used as the unit outputs IF.

I have some teething problems getting the unit to find stations which I am discussing with the developer; more later. However, the unit also generates 'static' hiss, which it inserts between stations. This is actually a nice touch. I also noticed a slight 'birdie' sound while tuning up and down. The whole experience is nice and tactile and the radio feels authentic.

The developer/engineer is Herbert, and his support is excellent, although he is not tied to his emails 24/7! I am working with him to resolve a tuning issue, so this concludes part 1 of my review. Part 2 will follow when it is working properly and I can give an overview of performance.

In a nutshell, despite having a good DAB signal where I am, the unit did not find any stations. After removing the shrink wrap and trying an aerial connection directly to the DAB tuner module, it did find some. It appears that the isolation transformer attenuates the signal too much where I am. I had even tried an external aerial. I will report further once this has been resolved.

Overall though - I am impressed so far, and for some, this will be an interesting adaptation to a vintage set. I have attached a few pictures of the unit.
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Old 11th May 2021, 11:00 am   #42
stevehertz
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Default Re: 'Proper' DAB conversion for valve radios

Hmm. "the unit did not find any stations", "I am impressed so far". ?

For me - and I'm interested in this unit if it works - I'd need more assurance than it being of a good build quality. I'd want it to pick up DAB stations (in a good signal area) better than it appears to at present.
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Old 11th May 2021, 1:36 pm   #43
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Default Re: 'Proper' DAB conversion for valve radios

Indeed. Of course it ultimately needs to work. However, I am not surprised there are teething problems given that I am apparently the 1st customer in the UK.

I don't have any spectrum analyzer to hand, so it is difficult to know exactly how much DAB signal there is at home. Being digital of course, it either works or doesn't. My DAB radio indicates good strength, but that doesn't necessarily mean much.

I do think the issue is losses in the isolation transformer, and am just waiting for Herbert to get back to me after my most recent tests. Perhaps a proper outdoor, frequency matched DAB aerial would have worked straight away, but being used to telescopic aerials on portables, a wire aerial would be most convenient.
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Old 11th May 2021, 2:15 pm   #44
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Default Re: 'Proper' DAB conversion for valve radios

Is this a DAB+ only receiver?

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Old 11th May 2021, 4:16 pm   #45
agardiner
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Default Re: 'Proper' DAB conversion for valve radios

I don't believe so, I think it is DAB and DAB+. Nothing else though.
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Old 11th May 2021, 8:55 pm   #46
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Default Re: 'Proper' DAB conversion for valve radios

I don't think there is a chipset that does DAB+ that doesn't do DAB(normal). It would be a rather silly move for marketing the radio, the Beeb (and many others) does DAB(normal) only AFAIK.
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Old 13th May 2021, 2:27 pm   #47
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Default Re: 'Proper' DAB conversion for valve radios

Making progress - appears that the design requires a particularly good aerial, it is certainly not going to work with just a piece of wire.

I have ordered a few different aerials to play with and hope to provide the 2nd part of my review in a weeks time.
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Old 17th May 2021, 10:41 am   #48
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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.
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Old 21st May 2021, 10:15 am   #49
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Default Re: 'Proper' DAB conversion for valve radios

Thanks for the review Adrian. Very interesting reading.
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Old 21st May 2021, 12:43 pm   #50
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Default Re: 'Proper' DAB conversion for valve radios

It would be great if the converter could work on a radio with push button tuning. Does the scan on startup function change the order and spacing of the stations at each startup?
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Old 26th May 2021, 12:38 pm   #51
agardiner
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Default Re: 'Proper' DAB conversion for valve radios

Quote:
Originally Posted by steve102 View Post
It would be great if the converter could work on a radio with push button tuning. Does the scan on startup function change the order and spacing of the stations at each startup?
Interesting. I see no real reason why this wouldn't work, except the way that DAB stations move around. Once the unit has stored stations that it has found, its start up scan only 'adds' any new stations to the list. This would affect the spacing of stations on the dial and thus push out any pre-set buttons. However, during periods where no new stations are found, the buttons should work as intended.
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Old 26th May 2021, 3:33 pm   #52
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Default Re: 'Proper' DAB conversion for valve radios

Quote:
Once the unit has stored stations that it has found, its start up scan only 'adds' any new stations to the list.
If (a big if) it has a dedicated EEPROM for storage a switch could be added to stop writing to said EEPROM. I wouldn't be surprised if the designer was willing to add such a feature, more sales!
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Old 26th May 2021, 6:17 pm   #53
steve102
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Default Re: 'Proper' DAB conversion for valve radios

Quote:
Originally Posted by merlinmaxwell View Post
Quote:
Once the unit has stored stations that it has found, its start up scan only 'adds' any new stations to the list.
If (a big if) it has a dedicated EEPROM for storage a switch could be added to stop writing to said EEPROM. I wouldn't be surprised if the designer was willing to add such a feature, more sales!
That would be useful feature as it would allow the user to decide when to scan for new or changed stations.
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Old 26th May 2021, 7:05 pm   #54
agardiner
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Default Re: 'Proper' DAB conversion for valve radios

I doubt this would be possible. It looked to me like the 'brains' of the DAB aspect were on the DAB module which was one of those standard all in one receiver boards. Clearly the developer has uploaded his own control firmware, but the whole point of this unit is to be seemless in the radio, without any additional controls.

I suppose it might be possible to change the firmware so it only scans when the 'oscillator frequency' is below a certain level, such that switching to a redundant LW band would trigger the scan? Assumes a dual band radio of course.
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