ATS25 Radio with Touchscreen
SI4732 Radio Version 2.0.
A Short Review from the Editor’s Shack
In the December 2021 issue of this magazine (RadioUser, December 2021: 40-41), I took a look at the simple ATS-20 SI4732 radio, named after the chip upon which it is based. Well, Father Christmas has been kind and sent me the successor model too.
This new ATS25 radio is constructed around the Silicon Labs Si4732 M/FMSW/LW/RDS receiver IC, like its predecessor. Upon switch-on, the first (blue) screen on my review radio showed the following message – presumably the callsigns of the software developers and PCB builders of the device, and the software version: AT25 RADIO DSP; SOFT PE0MGB-BD7JPY; PCB BY BD7JPY; SI4732: 63.
Our brilliant Aerials Now columnist Keith Rawlings was kind enough to lend me the review unit. Keith has been busy putting together a much more in-depth assessment for the 2022 edition of the World Radio TV Handbook (Vol. 75). My thanks go to him, as well as to our colleague, the WRTH editor Nicholas Hardyman at WRTH Publications Limited in Oxford.
This iteration of the SI4732 chip radio is larger than the previous ATS-20, measuring 120 x 115 x 48mm – without the sizes of protruding parts and the plastic tuning dial. Its official designation is ‘ATS-25 Si4732 Full-Band Radio Receiver DSP Receiver FM LW (MW And SW) And SSB With 2.4" Touch Screen’. Bit of a mouthful there. Frequency ranges are 64-108MHz (FM, with RDS); 153-500kHz (LW); 520-1710kHz (MW), and 1730-30000kHz (SW). The radio offers FM (RDS), AM, SSB modes
The touch-screen, which I found to be at just the right level of sensitivity, measures 40 x 55 mm, and 6.5 cm in diameter (2.4’); once again, you might consider putting your glasses on to read and operate this. I found that using the touchscreen pen I normally use for my laptop, works wonders here – in fact, one of those should be included in the pack as an accessory.
FM reception includes RDS, which appears in small writing under the main frequency display, flashing as it does so. On FM (only), the ATS-25 offers a nifty ‘search’ function (go to the second screen of the user interface, under ‘next’).
In use, I would say that this radio was pleasant and easy to operate, without recourse to the manual. The in-built Lithium-ion battery (3.7v /2000MA) offers a long battery life once charged via its TYPE-C charging interface, at a maximum 1.5A charging current.
Or you can run it off a portable (in my case, a TalentCell YB1203000-USB).
As in the case of the predecessor model, the ATS-20, a good external aerial is a must. On FM, your headphone wire acts as an aerial too, through the 3.5 mm audio-out jack. I tried several telescopic ones on the BNC aerial connection, as well as my Reuter RLA-3 indoor crossed loop and the Wellbrook ALA1530.
Surprisingly, the little receiver was not fazed by any of them, the Wellbrook bringing in the best results on medium- and short wave during the day, for example on Radio Cumbria (837kHz). The (ribbed) tuning dial is larger than on the ATS-20, and it seemed to be marginally more solid.
Output via the inbuilt speaker is 1.5W, and sound on FM is, in my view, slightly worse than on the ATS-20. This may be my hearing, but several early reviewers have also commented on this.
(October/ November 2021, YouTube).
Data / SSB Reception
On SSB, I tried the ATS25 first – you will not be surprised to hear, given my interests – on weather data, both Radio Facsimile (WXFAX) and Radio Teletype (RTTY) signals. In the case of RTTY, I was surprised about the relative accuracy and stability this cheap device delivered to my soundcard and PC.
The images in Figs. 3 to 5 are of RRTY signals from Seewetterdienst Hamburg, the German Weather Service (DWD) on 7646kHz (actual setting: 7645 USB DDH 7, 00.00 - 24.00 UTC, 1 kW F1B 50 Baud + / - 225Hz) received here in the Northwest on 11 December 2021; Fig. 3 shows the ATS25’s (rather cumbersome, please send me more cables and adapters!) connection to my soundcard.
In terms of some weather fax data reception on USB, I was even more taken aback. The screen grabs in Figs. 6 and 7 are from a session on the same day, 11th November 2021, showing ice map data. This came from 7880kHz (actual setting7879kHz with BFO on 525 Hz; DDK3 10,0 kW F1C; white + 425Hz, black - 425Hz). This is the main European DWD weather fax frequency.
Maybe it’s the fact that I have only recently started using a much better (192kHz, 24-bit resolution) sound card setting, but this is an impressively detailed result that I would otherwise only expect from much bigger receivers, such as my general workhorse AOR AR7030. From Northwood too (JOMOC, these days), I got 8040kHz (actual setting: 8040; 1500Hz BFO), and the images came in crisp and clear.
Your settings on the ATS25 will almost certainly be different; it is all a case of trial and error, especially with some of the bandwidth settings on the radio (Fig.8) – but therein lies all the fun! For RTTY and Fax reception, the little radio’s longer-term stability was acceptable, yielding some useable maps and imagery.
In all cases in this section, I worked with the ATS25 connected to my Wellbrook ALA 1530 Loop or Reuter RLA-3 Indoor Crossed Loop, and the radio did not baulk at this. A simple long-wire aerial will just mean that you can use this as an FM radio with a few AM/ HF catches from stronger stations.
My current soundcard is a Behringer U-Phoria UMC202HD (which I normally use for VLF experiments), and the decoders were SeaTTY (pictured) and Zorns Lemma 11.41. I relied on Friture and the Darkwood Designs Peak Level Meter for visualisation.
In all instances, I had turned the volume up fairly high on the ATS25 and found a happy medium using the volume controls on the sound card too. In terms of the relatively simple kind of data signals, I am interested in, this little radio did the job, and I could just leave it on all day.
No, it is not professional level, but it works just fine for me, as a stand-alone little setup. It keeps the weather maps coming and frees up the ‘big’ HF receiver for broadcast and HF Voice/ Amateur Radio listening, frequency-checking, one-frequency monitoring and other things.
Rawlings, Keith (2021) ‘ATS25 Si4732’ in Hardyman, N. (ed.) World Radio TV Handbook (WRTH) Vol. 76 (2022); WRTH Publications Limited: Oxford: 22-3 (Fig. 9).
Table 1: ATS-20 SI4732 Radio Features:
Fig.1: The SI4732 ATS-25 Radio with touchscreen. Use a stylus!
Fig. 2: The connections at the back of the SI4732 ATS-25.
Fig. 3: Receiving weather-related RTTY from the DWD on 7645kHz, or thereabouts.
Fig. 4: Zorns Lemma 11.42 ‘translates’ the synoptic data received into pictures of the sources of the data.
Fig. 5: Visualising the signals with Friture (right). Zorns Lemma 11.42 is on the left.
Fig. 6: Receiving DWD weather fax signals on 7880kHz.
Fig. 7: An ice report on 7880kHz on the day.
Fig. 8: The bandwidth-selection screen of the ATS25.
Fig. 9: The ATS25 reviewed in the 2022 edition of WRTH.