Roberts Sensitive Sangeans

A couple of Roberts branded Sangean sets that are both faulty, but still manage to bring in the DX. I already have the R816 (ATS-909) so my curiosity got the better of me to see how the lesser models from that era perform.

Roberts R617 is the Sangean ATS-606, early version with a DISPLAY button. The later models have a FINE tune in this position instead which allows 1kHz tuning steps. This one runs OK for a while and then the PLL circuit will lock up. At present, proving elusive to find the cause.

Roberts R809 is the Sangean ATS-808. This one came to me faulty as it's obviously suffered display damage. Also had a 1kHz tone present on all the LW/MW/SW signals. Applying an unmodulated test signal, the tone got louder as I increased the RF level! After testing some suspicious capacitors around the PLL circuitry and finding them to be OK, I found contamination in various places on the microprocessor/keypad board which I've cleaned up and it now works. Another parts donor is on the way.

Given the difference in sizes, the electronic design seems to be very similar. Both of these sets have poor front-end selectivity on MW - I found a signal on 576kHz which, after the initial "a new station!" excitement, turned out to be an image product of CWR on 1476kHz! (twice the second IF 450kHz). Happy to say that I don't notice that on the R861. They also accept an external antenna for LW and MW.

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Tecsun R-9700DX Teardown

I've seen a lot of favourable comments on this analogue SW radio via various YouTube channels, along with it's sibling the R-9710. Sold in some (USA?) markets as the Grundig Yacht Boy 250. Exact specifications and schematics have evaded me so far, however I did find a teardown and comparison at RadioIntel.com from which I've borrowed this photo: Photo from http://www.radiointel.com/review-review-tecsunr9700dx.htm It appears to use dual-conversion on shortwave with a fixed crystal local oscillator (see the 10 crystals above the bandswitch). One feature is that the tuning on the short wave bands tune the opposite direction to the AM and FM bands. Here's my (incorrect) guess of how it works. AM band IF is 450kHz (from the orange block filter) AM local oscillator tunes 975kHz - 2160kHz. The image of the AM band (1425kHz - 2610kHz) is used as a tuneable first IF for the shortwave bands. Each band is 600kHz wide so it probably uses 2000kHz - 2600kHz. The SW ba

Tecsun R-9710 Teardown

Although I've been itching to get my hands on the Tecsun R-9700DX, I wasn't really aware of it's smaller sibling, the R-9710 until I saw this review on the Two Hands and a Radio YouTube channel. Two Hands made the observation that the shortwave bands tune in the opposite direction to the AM and FM bands, which made me go and do a quick check other Tecsun analog radios. I found the R-9700DX also has this inverted tuning feature so some Googling later and I've located a teardown of the R-9710 plus other sets. The original article is in Chinese but you can view it through the magic of Google Translate . R-9710 teardown from http://www.leowood.net/sbdp209.htm Note it has eight crystals around the bandswitch for that fixed-crequency first local oscillator. Add the schematic found at http://www.fmdiy.com/ReadNews.asp?NewsID=305 More dead links to maintain unfortunately.

Tesco RAD-108 AM/FM/Shortwave portable radio review - American Style

I sent one of the RAD-108s over to Two Hands and a Radio for a YouTube review. Update - looks like 2H has taken his YouTube channel down so this is no longer available. Here is mine, a poor substitute. It didn't do too well on the American AM broadcast band, probably due to tuning in 9kHz rather than 10kHz steps!

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