Nick B's SWL Blog

   New toy for this summer. Order placed with Anon-Co on 21st April with expedited shipping (which included the battery), delivered on  28th April. Arrived with a UK Royal Mail postage label and a return address in Manchester, maybe it was shipped from stock already in the UK? I paid $71.44, inclusive of shipping and tax, which worked out at 53.44 of my British Pounds. Undocumented functions Press and hold 3 with power on: CH-S displayed selects whip antenna, CH-A displayed selects internal ferrite bar antenna. Press and hold 7 with the power on: Sets maximum volume for selected band using volume knob. Press and hold 9 with power off: Alternates between ON and OFF. Unknown. Press and hold 9 with power on: Number adjustable between 1 and 30 using tuning knob. Unknown. Press and hold VF/VM with power off: Segment test followed by firmware version. Mine is 3305.  I'll update the article when I figure out what they all do. Performance Early days but initial performance o...

After carrying out the external antenna connection modification to the PL-310ET, I built an external antenna coupler for MW and LW.  The coupler uses (obsolete) Toko 10mm inductors which are tuned on the primary side by the varicap diode on the SI Labs IC. The secondary side provides a low-impedance coupling to an external antenna. MW uses a Toko RWR331 230-300μH primary, 1.75μH secondary. LW uses a Toko 98299 2.9-4.0mH primary, 46μH secondary. Some excellent results have been achieve, particularly on Long Wave.

Over at the RADIO_TIMETRAVELLER blog there are some excellent articles about connecting loop antennas to Tecsun or similar portables. This ought to be my next step after tinkering with the larger ferrites. I need to study the SI labs data sheets for these radios again to see if it is possible to add a loop to the shortwave antenna connection, for use on the Tropical Bands . The SW input doesn't have a varicap tuner so it would probably require an additional variable capacitor to tune manually.

As the PL-606 has the same antenna jack as the PL-310ET I though I'd take a look and see how easy it would be to carry out the modification. Actually more straightforward on this set. Unfortunately, when I removed the rear cover, I found the internal ferrite bar in two pieces. I've repaired this using superglue which has worked for me on other ferrite rods. The end results on LW are as impressive as the 310. On MW, despite trying two different coils (500µH and 200µH), results at the lower end of the band showed an improvement but at the top end the performance appeared worser than the internal ferrite bar. Conclusion? Definately needs the mod for LW but quite adequate for MW.

So I decided to try the mod originally documented by Laurie Mann to utilise the spare connections on the antenna jack to bypass the internal antenna when an external one is plugged in. I suspect this is how the Tecsun PL-360 works which has the option of internal or plug-in external ferrite antennas. The PL-606 also has the external antenna jack so maybe it is mod-able too. Rather than remove the rod and swap wires, I drilled a hole and mounted a 1.3mm pcb pin to use as a solder point for the wire from the ferrite rod. Run the first wire: Then the second wire to the new PCB anchor point: Showing the new wiring in position: Don't forget to cover the base of the whip antenna with some insulation tape to prevent it shorting across the new connections. So now I can connect my new external ferrite monster rod, with a selector switch for MW and LW sections of the coil. I found that it was necessary to change the coil switch before the Tecsun MW/LW band change othe...

Compared to other DSP radios of similar size (PL-380, R-108...) I find my PL-310ET to be extremely deaf on MW (AM broadcast band). The longwave band is even worse. So let's take it apart and see what can be done. The poor-quality ferrite bar is shaped like a banana. I borrowed the ferrite antenna from a rotating loop desing I buit a few years ago. After removing the connections to the internal loopstick, I found it worked quite well on the LW coil section. So I ordered a larger 10-inch monster rod which seems to work quite well on MW. Manx Radio on 1368kHz is a good daytime test signal, at the lower end of the band I can hear Carolone 648kHz and Spectrum 558kHz. The radio design has been around a few years so I'm sure someone else will have tried this. There are certainly some mods documented for the PL-380. Sure enough, I found an article on the Ultralights group showing how the spare contacts on the antenna socket can be utilised to switch out ...

This radio is a one-chip wonder! The main active device appears to be a Sony CXA1691BM IC which was originally designed for radio-cassette recorders. Here it is with a strong signal from Pyongyang on 12015kHz. This particular one is a Kaito-branded model which I purchased from Universal Radio of Ohio whilst in the US And here is the schematic:

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.

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...

I used two Tecsun radios for this experiment. On the left, a PL-380 tuned to 13760kHz; on the right, a PL-310ET tuned to 15245kHz, tuned to this evening's English Language program from the Voice of Korea. Fed into the left and right channels of a Tecsun ICR-100 which I'm using as a MP3 recorder. Both Tecsuns are set for a bandwidth of 3kHz and the volume at 10. The difference in propagation is noticable. Sometimes 13760 is better, other times 15245. Overall I'm hoping nothing is lost in the fades, listen for yourself to decide! Probably some of DPRK's more easy-to-listen-to music followed by the broadcast schedules for the English Languare service. If you cannot see the audio controls, listen/download the audio file here