472/500kHz transverter FINISHED

Today I completed the rev E version of my 10W transverter. In the end I reverted to a double balanced mixer and this immediately solved my issues with mixer stability that I had with the transistor mixer design. Air testing this evening, I am getting plenty of reports but a slight drive is noticable in the reports, probably as I am using a small plastic box and the PA heatsink warming is causing the 3.2MHz crystal to move about 1Hz during the WSPR TX cycle. It really needs a bit bigger metal box, but it will do.

The lastest transverter schematic (there may be value errors)

WSPR reports 20.9.12 with the above transverter and 6m long antenna

The desktop 472/500kHz station, ATU (don't laugh!) and antenna current meter

Japan Ham Fair 2012

http://onjapan.net/2012/hamfair/icom-kenwood-yaesu.html

The recent Japanese ham fair in Tokyo showcased the latest products about to hit the market in the coming months. Included was the IC-7100 all-mode, all band (including 4m) 100W mobile. What was not there was the long awaited FT-817 replacement.  A product I have not seen mentioned yet is the Yaesu FTM-400D digital VHF/UHF radio. I don't think this is a D-star radio, so what form of digital modulation does it use? Is this a Japan only product?

WSPR for the iPod Touch

Like many these days, I've an Apple iPod Touch and use it every day for web browsing. When watching the TV or reading the paper it is handy to be able to check my WSPR spots with a quick look at the iPod Touch.

The Apple iPhone, iPad and iPod Touch do not have that many amateur radio apps. There are a few very useful ones like an audio spectrum analyser, an oscilloscope, Echolink and a repeater database, but what I would really like is a full WSPR interface for the iPod Touch.  Does anyone know if such an app has/is being developed for Apple or Android products? Even Apple OS PCs seem to be less well catered for with regard to amateur radio software.

Further WSPR development?

On the LF reflector recently there's been discussion about how to make weak signal modes decode at even lower S/N ratios. Joe Taylor K1JT, who created WSPR, was approached by Stefan DK7FC, a very well known LF DXer, to see if WSPR could be further developed to achieve this.  One idea is a slower version of WSPR with a 4 or 8 minute time slot instead of the current 2 minute period. Theoretically it should be possible to get successful decodes with much weaker signals. Joe is currently busy with other work, but took kindly to Stefan's suggestion and said he would take a look later in the year.  With WSPR performance roughly equivalent to QRSS10, such a move would be welcomed by many of us trying to get reports on VLF, LF and MF with QRP.

472kHz transverter - real progress

Since reverting to a passive double balanced mixer based design, the circuit is now behaving properly with no signs of oscillation and a good clean signal from the PA. Although I have used an SBL1 mixer, it will work with any similar mixer package. Tomorrow I may try the design with an NE602 as this would allow the separate oscillator to be removed. With an NE602 it should be possible to do the complete TX-RX transverter with 1 IC, 2 transistors and 1 FET.  Now THAT would be neat.

472kHz transverter "progress"?

This afternoon, after a break of a few weeks, I went back to my 10W 472kHz transverter design. The intention was to simply build a second sample to prove repeatability. As is often the case, things didn't quite work out that way: instead I discovered an MF oscillation when drive was removed in some situations. Despite trying all the usual tricks so far, I've not managed to fix it yet. It is not the PA: driving it and the squarer stage directly with a 472kHz signal all is well. It looks like a problem around the oscillator and mixer but so far I have not managed to tame it. Also, and this is probably the same issue, on RX there is a wideband noise resulting in desensitisation. For this evening I have stopped work and will take a fresh look tomorrow. Maybe the double balanced mixer in my original 2010 circuit was not such a bad idea after all.

This is a classic situation when a spectrum analyser would really help as I could see in an instant where the trouble was by poking around with an RF probe and observing the spectrum on the analyser.

Bitsbox - excellent service (again)

A few days ago I decided to order some electronics components to replenish my stocks - resistors, common capacitors, trimmers, FETs etc, so I placed an order with Bitsbox, my favourite UK supplier. The order was acknowledged immediately and the goods arrived next day by first class post. Bitsbox prices are very sensible (resistors 1p each in 50 offs for example) and they charge a fixed £1.75 delivery charge per order for UK first class post.  I've now used this company several times and cannot fault the service. They stock a wide range of parts - certainly most of what I need for VLF-VHF experimental building - and the delivery is super fast. 

G3XBM recommends Bitsbox.

WISPY reports and a red kite

For the last month we seem to have been away from home half the time. The last few days we have been in Yorkshire for a sibling reunion with my wife's brothers.

On the way back home we had a REAL surprise driving along the Leeds ring road. I could not believe my eyes when I saw a red kite flying quite low overhead. These fine forked tailed raptor birds were once confined to a small part of south central Wales but following selective reintroduction they are making a comeback all over the place. We see them near Newmarket quite often, but I was totally surprised to see one driving through urban Leeds!

When I got back home I switched on the WIPSY beacon and was rewarded with a string of reports including a +6dB S/N from Germany - not bad for 100mW. The now regular  report from EA8FF was not long coming as was a report from F5VLY and several other DL stations and G8KNN not far away.

WISPY TX gets better (and even cheaper!)

Today I did a rebuild of the TX only version of the WISPY 10m WSPR beacon to improve it in several ways.  Switching to germanium diodes helps produce a much better looking DSB signal out of the mixer. With silicon diodes there was not quite enough drive. The second change was to remove the 2N3866 PA and replace it with a couple of paralleled up 2N3904s (each with a small emitter resistor so they share current properly). A 2N3866 is around £1.50 whereas a couple of 2N3904s are about 6 pence.  Output is now a clean DSB signal, even without the low pass filter, with a conservative 200mW DSB out (100mW equivalent SSB signal in the WSPR band). This is now a very pleasing little design that can be built for even less.  Within 5 minutes of turning it on it got a remarkable -3dB S/N report from EA8FF over 3000kms away.

The first UK broadcast station

The first public broadcasts in the UK were not by the BBC but a few years before in 1920 from the station 2MT in Writtle, Essex. It was known as Two Emma Toc.

The book "2MT Writtle – The Birth of British Broadcasting" by Tim Wander gives the history of this first station. It is available from Amazon for £18.95.