Phasing direct conversion receivers

What I think is quite an old paper turned up in my browsing today: http://www.norcalqrp.org/files/austinnc2030presentation.pdf . In it, Dan Tayloe N7VE describes how a direct conversion design with phasing to cancel out the unwanted sideband can be a truly excellent receiver. I have never tried this approach myself, but think it would be worth it for, for example, a WSPR receiver where the phase accuracy has only to be maintained over a 200Hz audio bandwidth. Over such a small audio bandwidth a very simple phase shift network would work.The same applies on TX where a very simple final frequency phasing TX could produce quite good sideband suppression with very few parts.

The current G3XBM (operating) shack

G3XBM QRP shack in a bedroom corner

Thought readers might like to see what the G3XBM station consists of currently.  In the photo I have annotated most pieces. The little silvery box to the right of the SignaLink interface was a VX2 programmer (software for which crashed my PC a year ago), but this box  is to be used to house my WISPY 10m WSPR beacon transceiver. The K1 was last used yesterday and the FT817 gets almost daily use, with the very nice audio speech processor underneath. Not shown are the lightbeam kit or the LF and MF tranverters for 136 and 472kHz which are housed elsewhere close the the earth-electrode antenna feed. There are also several homebrew rigs in drawers that get brought out from time to time. For the time being, the Elecraft K1 is not being sold.

The maximum power I can run currently is around 7W from the K1 and about 12W out on 472kHz from the transverter (about 5-10mW ERP) and 30W from the 136kHz transverter (about 50uW ERP). I have no great desire to run much more power. The FT817 is only used at 2.5W or less.  

RaspberryPi WSPR TX

This means little to my software incapable brain, but may be of interest to some readers: a Raspberry Pi mini-computer used as a basic 10mW WSPR TX up to 250MHz with a suitable low pass filter on the output. I know my old colleague Bob G3WKW has done something similar. I am impressed.

See https://github.com/threeme3/WsprryPi

KW Vanguard

Alan's KW Vanguard

Memories of when first licenced were stirred this evening with an email from Alan McWhirter near Edinburgh who is restoring an old KW Vanguard (CW and AM transmitter) to working order. My first ever outings on HF were with my old G8 callsign operating under the supervision of Bill G4PJ. On a Sunday morning he would let me loose with the Vanguard and we'd work several locals on 80m and some Europeans on 40 and 20m, all on AM in 1967.

A reminder to Alan and others that most 10m AM activity is between 29 - 29.1MHz. In recent months there has been plenty of activity on AM when the band has been open across the Atlantic. Great fun.

QSOs with the Elecraft K1

As I am considering selling my Elecraft K1 rig to fund some other purchases, I decided to fire it up this afternoon to see that all was well. It turned out to be a very pleasant QRP session with 8 QSOs in 8 countries in the log at 5W on 40m and 20m in a casual hour or so of operating. In addition, there is a page full of reverse beacon spots for the CQ calls that didn't get answered. With the Par 10/20/40 end-fed antenna it doesn't need much to match the antenna: in fact without the auto-ATU it should match well on 40 and 20m, although with the internal auto-ATU I can also match this on 30 and 15m.

I still have mixed feelings about parting with this rig: it doesn't get used much so really would be better with someone who would make full use of it. On the other hand, when I use it I get good results and plenty of QSOs. We'll see if it goes or stays in the coming days. It will be on eBay if being sold, but not until I've carefully thought about it.

Low cost netbooks and ReadyBoost

http://content.hwigroup.net/images/products/xl/132431/asus_eee_pc_x101ch_black.jpg

At the moment www.amazon.uk has a very good deal (£173) on the little 10 inch Asus X101CH netbook.  Reviews are mixed, but overall this may fit the bill for a small second PC that can be used to run simple (Windows software) tasks without much multi-tasking.  It should also be able to run WSPR or Spectran as long as nothing much else is required at the same time. There is a lot of bloatware supplied which probably slows it down for most novice users. With ReadyBoost installed on an SD card I think the 1GB of RAM should be less of an issue.

My question is have readers of this blog any experience of using ReadyBoost to speed up sluggish netbooks? Also, have any readers actually got an Asus X101CH and, if so, any views on its suitability for (single task) use with WSPR, Spectran or similar?

8.5km "over the horizon" on 481THz tonight

This evening I ventured further afield with the optical kit to see if I could copy my QRSS3 beacon signal in the village of Stow-cum-Quy which is 8.5km from home . This is non line-of-sight and nearly twice as far as my previous tests last week.

Path covered this evening NLOS

Success! After quite careful searching both horizontally and vertically, the signal was copied and recorded at around 14dB S/N (at best) pointing just above the horizon. After searching for a stronger signal, the sky became increasingly "murky" and I was unable to find the signal again, so I came back home.

1W LED TX in 100mm optics, SFH213 detector in 100mm optics

This range is about the practical limit: aiming is very difficult and I find it is hard to get back to the same direction/elevation if I move anything. I need a tripod that is far more stable with some sort of degrees marking (both horizontally and vertically) so that I can go back to the best settings with confidence. At the moment it is a bit "suck it and see" to find the best aim and nearly impossible to get back to those settings easily if the tripod gets knocked.

This was clear air scattering as there was hardly a cloud in the sky. I have still to try cloud-bounce with real low level clouds.

To see the signal play this recording through Spectran with it set to 572Hz in 0.34Hz bandwidth. QRSS3 signal will be clearly visible.

There is a chance that I may try a much longer 27km NLOS path before too long. Looking at the map, this should be a possibility but I may need another 6-10dB from a Phlatlight LED and a MUCH more stable tripod!

My books on eBay

This week I have 8 items for sale on eBay including a few radio books. I am trying to de-clutter ahead of our house move in a few months time. It is proving harder than I thought to get rid of things and in fact I am still collecting more things than I am disposing of!

The radio books are QRP Basics by George Dobbs. This is an essential guide to low powered radio operating. As I have the newer edition, this first edition version is for sale. Highly recommended book.

The next is LF Today by Mike Dennison G3XDV which is the first version of the guide to LF operating especially on 136kHz, although invaluable for 472kHz too. I used this version extensively when first setting up to TX on 136kHz.

The next is The Comprehensive Radio Valve Guide which is a Babani series book listing every radio valve since 1956. As a semiconductor man I hardly ever looked at it.

Another book is the 6 Metre Handbook, a guide to the magic band by Don Field G3XTT. This book is really aimed at 6m DXers and I was a bit disappointed that it didn't say more about using the band for simple local communications.

There are also a few other good books listed and a mock marble fire surround which my local builder tells me should sell for over £100.

You can find all 8 items for sale via http://myworld.ebay.co.uk/rlapthorn .

Get bidding if you are interested as they are sure to sell.

100 subscribers - thank you

Just noticed that the number of people who subscribe to this blog has now reached 100 for the first time.  Many people just drop in from other links, but it is good to see that so many people actually subscribe.  I try to post things that interest me, and I hope interest you too, here.  Please let me know if the blog can be improved in any way.

Things (such as designs) that are of longer term use are added to my main website www.g3xbm.co.uk so check there too if you've not visited it.

Android and iPod WSPR

WSPR on the iPod Touch 4g

To the best of my knowledge no-one has (yet) produced apps for these devices that allow them to be used as WSPR mode terminals.  Not being a software expert (at all) I am rather surprised at this: these are now very common platforms that a wide variety of people have. The number is growing daily. How much more convenient it would be to use my little iPod Touch 4g, for example, with a simple QRP WSPR transceiver, than with a PC or laptop. Are there any technical reasons why such apps haven't appeared?

If anyone knows if this has/is being done please let me know. I am aware of WSPR watch but this is NOT a WSPR terminal, just a neat reporting app.  The picture shows what WSPR might look like on such a device - I wish!

I wrote to Joe Taylor to find out if the creator of WSPR knew of any attempts. This was his reply:

"Hi Roger,

No such effort has been attempted, to my knowledge.

   -- Joe, K1JT"