18 August 2018

Real-World Amateur Radio: WSPR - Choose your magnetometers with care.

Interesting article on  MW1CFN amateur radio blog on the availability of magnetometer data for radio propagation studies. I was looking for this type of data as signals from North Korea and Japan to my location in the UK take the high latitudes somewhere over Finland.



Real-World Amateur Radio: WSPR - Choose your magnetometers with care.: I'm currently running a longer-term WSPR campaign, with a focus on the auroral zone. I'e been scratching my head in trying to rela...

15 April 2018

Blast from the Past - Sony ICF-7600DS






This was my first Sony portable. It was pushed into second place behind the ICF-2001D but it provided excellent service as my alarm clock prior to selling it in 2003. I do own the final model in the 7600 line, the ICF-7600GR which has the synchronous detector feature.

Lots of information on the 7600 series can be found over at Stephan's excellent website http://stephan.win31.de/sony7600.htm

Blast from the Past - Sony ICF-2001D


This is my Late Sony ICF-2001D. The station is BBC Radio Scotland 810kHz and the location is Embo, Sutherland in NE Scotland.

At the time I bought this (late 1990s) the ICF-SW77 and ICF-SW55 were current models but I chose to buy one of these. It served me well for many years (even as my daily alarm clock!) until it suffered terminal battery corrosion after being left in extended storage. The culprits were actually Duracell branded D cells, not exactly a cheap brand.

I considered buying a replacement but with the price these now fetch on the second-hand market and the abundance of modern portables, I am reluctant to spend the money and risk being disappointed.

The moral of the story - make sure your remove ALL batteries before placing in storage or if you're not going to operate for an extended period.

4 April 2018

15820kHz UNID 1138z



Not sure what this could be, sounds like some kind of pager tone, maybe it's breakthough from another frequency. Or maybe it's really here?

648kHz - 1960's style on the Dynatron Nomad




Check out those TWIN ferrite rods! Not bad performance for a radio that is almost 60 years old!

26 March 2018

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.

It didn't do too well on the American AM broadcast band, probably due to tuning in 9kHz rather than 10kHz steps!

6 March 2018

Cheapest World-Band Portable

Tesco in the UK are selling a world-band portable for £8 incuding VAT (that's $12 USD at current exchange rate). I don't normally shop there but I might have to make a special trip to pick up one of these R-108 radios for evaluation. That'll be £12 then after adding the cost of the tram ride.

It covers 12 bands:
  • Long Wave
  • Medium Wave
  • FM Broadcast 88-108
  • SW1 60 meter
  • SW2 49 meter
  • SW3 41 meter
  • SW4 31 meter
  • SW5 25 meter
  • SW6 22 meter
  • SW7 19 meter
  • SW8 16 meter
  • SW9 13 meter

Link to RAD-108 at Tesco.com

15 February 2018

Kaito WRX-911 aka Tecsun R-911


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:

14 February 2018

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


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 bands tune in the opposite direction to the AM band. To achieve this inversion, the fixed first LO crystal will have to be on the high side of the tuning range. 
  • Taking the tuning range for the 13 meter band as an example, the first LO will be 24000kHz (24MHz)
  • 24000 - 21400 = 2600kHz 
  • 24000 - 22000 = 2000kHz.
This will give a nice bandspread across each of the SW broadcast bands and the use of quartz crystals will ensure it's stability should be close to that on the AM broadcast band.

Update

Well I found a schematic on Tecsun's website and it seems it doesn't work as I first thought.
The first IF for SW is actually 10.3 - 11.0MHz.

And finally after Google Image searching, the schematic from http://www.radioscanner.ru !


I'll ammend this article when I have finished measuring the actual oscillator frequencies.