Low cost signal generators for QRP

Elecraft's XG3 signal generator

Although I have a couple of (loaned from friends) signal generators, these are rather large in a small shack. There are times when something small but calibrated is useful. Elecraft sell the XG3 signal generator which can be PC programmed to give a number of fixed output levels on a wide range of HF, VHF and UHF frequencies. It is the same (small) size as the T1 auto ATU i.e. about the same size as a packet of cards.

The Norcal S9 signal generator

Norcal also sell a kit for a small fixed frequency signal generator called the S9 Signal generator that can provide a fairly well controlled range of output levels. Currently it is out of stock, but the circuit is simple and could easily be built from scratch "dead bug" style.

Writing for radio magazines

In recent years I've written articles on a wide range of subjects, from VLF to optical, for several different radio magazines around the world. Now I don't do it for the money as I have a pension that covers my needs adequately, but I am surprised how poorly radio magazines do pay authors. This may be one reason why they find it hard to find new authors.  I won't quote figures here as I don't want to embarrass anyone, but you have to write articles for the pleasure of doing so and not for the financial rewards, especially when tax is deducted.

One of the lowest payers appears to be the ARRL, which I find particularly surprising considering that QST must have one of the largest circulations in the world. Considering how long it takes to put a decent article together  with illustrations and schematics (very many hours), the rewards are probably better if one stacked shelves at a local supermarket or worked on the local dustcart.  It doesn't exactly encourage budding authors.

Times are hard and revenues in amateur radio magazines from adverts is probably falling, but reading QST, Practical Wireless and RadCom I see pages and pages of adverts that must bring in a decent amount. Maybe they'd get, and keep, more readers if they encouraged people to write interesting articles by paying a little more?

Royal Mail - postal/packet costs

I'm frustrated and actually quite annoyed with Royal Mail.  Have you visited the barely understandable Royal Mail website recently?  All I wanted was to find out how much a small parcel (a book - the Scatterpoint compendium sold on eBay) would cost to send to Germany on Tuesday. It appears you now need a PhD to navigate the darn website and understand all the options. It is nearly as hard as trying to find a utilities tariff.

Having done a bit of eBay trading this last few weeks, I'm surprised how expensive it now is to send a small packet by post using Royal Mail or Parcel Force, even more so if sending it abroad. Unless I have misunderstood the incredibly confusing information on how to send a small packet to Germany, one weighing 760g costs an astounding £6.62. Go above 1kg and the rates are extortionate.

Thankfully we still have a helpful local post office staffed with people who try to sort this out for you. Not having receiving my doctorate yet, so unable to navigate the Royal Mail website, I'll have to ask the nice lady at the local PO for the price and a stamp.

Why can't we have a SIMPLE postage tariff based on weight and whether it has to go surface or by air? OK, add a few options if you want a guaranteed delivery.

More Chinese QRP radios/kits

Chinese QRP kits and ready built radios seem to be everywhere. For example, see the KN-Q7A kit from http://www.crkits.com/ . This little 40m 10W or 20m 5W QRP SSB transceiver was designed by BA6BF.   Reviews on eHam.net are good (4.9/5 with 8 reports) so this is no toy radio.

http://www.crkits.com

I have the feeling this is an enterprising Chinese amateur making a bit of money selling a few kits rather than a major Chinese manufacturer, gearing up for the big time. However, this IS coming. Unless the big boys like Yaesu and Icom move to low cost manufacturing locations like China for the bulk of their products then their days are numbered. Honestly. 

Amateur DX Europe to Alaska on VLF?

There has been some excitement over the last few days as Lawrence KL1X has seen a signal on 8.9700kHz when the noise was low that just could be coming from Uwe DJ8WX near Hamburg. He has tried to find out if this is a locally generated artifact, but it seems not.

KL1X grabber monitoring 8.270kHz for intercontinental amateur DX

In the coming weeks DJ8WX is moving his continuous carrier VLF transmitter (a long carrier is needed to be visible in the incredibly narrow bandwidths needed to see anything at all) down to 8.270kHz which is a clear frequency in Alaska. The Alaska VLF grabber is already active and, as soon as Uwe starts up, we hope to see a weak signal appear. If this happens this will be the very first confirmed reception of an amateur VLF signal from Europe in North America. The VLF receiver Lawrence uses is a small E-field probe antenna high up in a tree in a birch forest.

DJ8WX has been a very good signal on VLF here in the UK on my own receiving system (an 80m sq vertical loop feeding a preamp feeding a PC running Spectrum Lab with a special 424uHz bandwidth .usr file). I have not listened for Uwe recently as my loop is down but G3ZJO has copied him well in the last few weeks on his grabber.

DJ8WX's signal as seen on the G3ZJO VLF grabber

If you are interested in amateur VLF then visit https://sites.google.com/site/sub9khz/ and check out the various preamps, grabbers and DX reports. It is possible to check out activity by looking at the various grabbers (VLF receivers linked to the internet) around the world.

I've left the Yahoo KX3 group

Since its early days, I've been receiving posts from the Yahoo KX3 Group, which is a group for people interested in this Elecraft radio. It was generating a huge number of daily posts: this month people have posted 1590 messages already! As it is now rather unlikely that I will purchase a KX3 - I simply cannot justify £1200+ for a fully loaded, if excellent, QRP transceiver - I decided today to leave this group.  That still leaves plenty of other Yahoo group messages to read.

I'm not sure how others read Yahoo Group messages, but I always choose

"Web Only - Don't get notified of the latest happenings. Read messages only on the web."

I'd be unable to cope with several hundred, possibly thousands, of additional emails from groups each week. This option is always available when you join a Yahoo group, or you can do it later by editing your group settings.

Voice of America cutbacks

In my early days as a shortwave listener, the various VOA transmitters around the world were popular station targets for reports. I even copied "this is the Voice of America, Monrovia" (West Africa) on my little 4 component SW crystal set.  Now I see that the VOA is having to cut back transmissions because of the USA's budget issues. Like many shortwave broadcasters, VOA is feeling the pinch in hard times. The shortwave broadcast bands are no longer the same as they were back in the 1950s and 1960s: there are fewer and fewer English language transmissions to be heard nowadays.

As an aside, and I try to avoid political comments in this blog but feel compelled to share this, I read today that the audited costs of the Iraq war for the USA are an estimated $767bn. With ongoing healthcare and support costs the final figure will be well over $1trillion. All nations make mistakes and enter wars they later deeply regret, including the UK. What saddens me is the total WASTE this represents: Saddam was no saint, neither are the Talibhan in Afghanistan, but there has to be a better way to change nations. The phrase "swords into ploughshares" comes to mind. Jaw jaw is better than war, war. Just think how $1 trillion could have been better used.

Rectennas and solar energy

Recently I read about some interesting work on Rectennas, which are combined antennas and rectifiers used to detect microwaves and optical frequencies. The work suggested that very high efficiencies may be possible at optical frequencies (around 70%, possibly more) using nanotechnology leading to much more efficient power conversion of solar energy. The correct term for these would be Nantennas. At my new house (move coming up in a few months) I will be considering the installation of solar photo-voltaic panels, but wonder if I should wait a few years in case technical breakthroughs with Nantennas could revolutionise these?

Back from Lincoln

For the last few days we have been on holiday in Lincoln, staying at the Old Palace Hotel (I an highly recommend this) just below the marvelous cathedral. Our room was high up and looked due south and had an excellent take-off.  Sadly I brought no radio gear with me though, so was unable to take advantage of the site.

Clear air forward scatter optical kit

The schematics below are of the RX and TX used in the recent "over the horizon" NLOS 481THz optical tests. As you can see, not too much complexity involved considering the useful science that results. All parts are inexpensive and readily available. Nothing critical apart from the PIN photodiode and the 280000mcd red LED which I got from Hong Kong via eBay. 100mm optics used at the TX and RX ends.

The 481THz receiver

The 481THz beacon transmitter

Reverse beacon Network

7MHz QRP RBN spots this evening

The Reverse Beacon Network is an extremely useful resource. This evening, in addition to several QRP QSOs on CW, I got quite a few RBN "spots" proving just where my signal was reaching and at what strength. This is a bit like the WSPR database but for CW. As such signals have to be stronger to be copied than for WSPR but it is helpful.

More books on eBay

A couple more books have been listed on eBay this afternoon which may be of interest to readers. They are the RSGB's latest VHF/UHF handbook and the Backscatter Technical Compendium with articles from Backscatter (UK Microwave Group) from 2004-2008. The auction ends next weekend.

I have an almost complete set of SPRATs from the early 1980s to today that may be listed soon: as I have the CD, the paper copies are taking up shelf space. Paper copies are easier to thumb through though, so I may decide to keep these. We'll see.

There are a few other books and some baby clothes too if you, or your XYL, are interested. My aim is to declutter the shack as much as I can before the house move. The other books include some on disability related subjects, psychology and the Galapagos Islands (the latter is a very nice BBC book).

Last week's auction was very successful with all the books (and the fireplace surround!) finding new homes.

eBay is quite fun in small doses: I don't like to do this all the time - too much trouble packaging and labelling things and making the trip to the post office to send them off, but from time to time it is fun, especially watching the last minute rushes!

More books, including a few more obscure non radio related ones, will be listed next month.

More K1 fun

http://www.elecraft.com

Since getting my Elecraft K1 out of "hibernation" a few days ago I've had some lovely contacts with it on 40 and 20m as well as plenty of reverse beacon reports on 40, 30, 20 and 15m CW. I'd forgotten quite what a gem the K1 really is. No great DX - all the QSOs have been around Europe - but all at 5W with just the fairly basic Par 10/20/40 end-fed antenna. The receiver is lovely with signals just appearing nice and clearly, even QRP signals, out of the quiet background. This is not a synthesised rig and it sounds more like my old FT7 which had an excellent receiver.  Sensitivity is pretty good, and certainly fine for working other QRP stations around 7.030 and 14.060MHz, the QRP centres of activity.

FT817ND prices at Waters and Stanton

Looking on the Waters and Stanton website I notice they have increased the price of the FT817ND by around £30 to £565.95, despite the Yen exchange rate improving (in W&S's favour) by around 10%. I was rather hoping that the revised price might be nearer £499 i.e. downwards.

Would W&S care to comment on why the price has gone up suddenly by so much?

Perhaps there is a very good reason. To help everyone understand what I mean, see the BBC currency graph for the Yen over the last 12 months.

http://www.bbc.co.uk/news/business/

Looks to me like the UK pound buys a LOT more yen than in the summer of last year. Come on W&S, tell us what's going on.

UPDATE: I am being told the price in the USA has risen by $50 recently so maybe the rise is being driven by Yaesu? If so then they could be in trouble: falling handheld sales as a result of Chinese competition may be forcing them to squeeze for profits elsewhere? The slippery slope to niche markets and ...?

What happened to Wireless World?

When I was younger, and that was a LONG time ago back in the 1960s, Wireless World was an amazing monthly magazine: it was around 10mm thick and packed with articles and information. My old girlfriend's dad had a WW collection going back to the late 1940s and I used the excuse of looking through these to go to see her during summer holidays. Not that much reading took place on those visits!

My question was what happened to Wireless World? It was still around a few years ago in a rather sad state about one third as thick as the editions I recall in the 1960s and earlier. I presumed it has died a death as I'd not seen copies for some time in the shops.  A little more searching shows that Wireless World is now known as Electronics World and this April marks the 100th anniversary of its foundation as Wireless World back in 1913.  Can't say I've noticed copies in W.H.Smith.

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"

A solar peak in late 2013 and another in 2015?

Some experts at NASA are predicting some strange behaviour in the next few years with the possibility of a twin peak for cycle 24 but with one peak being this year and the other on 2015. A similar twin peak occurred in cycle 14 in the early 1900s.  See http://www.arrl.org/news/solar-cycle-24-may-have-double-peaks-says-nasa-solar-physicist.  If this happens we may have (half) decent conditions for several years yet in this current solar cycle.

Conditions in this peak really are very different from the massive peaks in the middle and late 20th century when worldwide DX was workable with ease on the higher HF bands and even 6m. OK, it is still possible to work all over the world but, believe me, it WAS a lot easier back then.

24 hours with 1mW output on 40m

Well, that was fun: a 24 hour period with my WSPR beacon running at just 1mW RF output on 40m into the Par 10/20/40 antenna at just 5m up in the garden and yet still plenty of reports from around western Europe. Best DX reports were from F6HTL (737km) and F1ING (581km) with reports from G, PA, and F.  I shall now have a try at the same power level on 10m or 20m and see how it goes. It was interesting that there were few reports last evening and overnight on 40m, possibly because my 1mW signal was being crowded out by others running "high" power like 1-2W, HI.

Some of the reports with 1mW on 40m WSPR

A WSPR beacon TX at the 1-5mW power level is feasible with just one transistor and a single balanced diode mixer and may be one of my next "just for fun" projects.

UPDATE 1700z: on 20m WSPR with 1mW output I managed just one report this afternoon from F1JRC/2 at 971km.

Chinese FT817 a step closer?

Steve G1KQH has alerted me to a new Chinese HF SSB/CW transceiver kit called the KightKit KR-10 that retails in the USA for $259.95  Although this is a kit, it is available ready made for just $30 more. That is less than $300 for a built HF QRP rig.

The rig doesn't look very pretty, in my view, and I/ve no idea about its availability in Europe including the UK.

The spec is:

• RX frequency range: 0.1 ~ 30MHz
• TX frequency range: 0.1 ~ 30MHz
• Operating Mode: SSB / CW
• Receiving sensitivity: better than 0.45uV,
• RF output power: ≥ 4.5W
• Frequency stability: better than 0.5ppm
• Operating voltage: 12.0 ~ 14.0V DC
• RX Standby Current: 0.5A
• TX current: 1.5A Max
• Dimensions: 97 x 40 x 155 (mm)

See http://www.kightradio.com/X1M-QRP-SSBCW-Transceiver-Kit_p_305.html for more details.

Now, there are clearly signs that the Chinese are coming up fast on the HF QRP transceiver front. It surely cannot be long before a Chinese company launches an FT817 competitor. They have a tall order to exceed its spec but they've had 13 years to dissect and analyse the Yaesu radio.  

1mW (0dBm) TX on 40m WSPR

Just for fun I'm having a go at QRPp WSPR on 40m. The set-up is the FT817 on 500mW going directly into a 26dB attenuator that feeds the Par 10/20/40 end-fed longwire antenna in the garden at around 5m above ground. So far, after about 10 minutes a few spots received: G3XVL at 61km being the best DX with reports also from G4IKZ and G4NRG.

Amazing NLOS 481THz reception tonight!

This morning I realised that I was 2.5 degrees out in my aim last night with my optical beacon, so this evening I repeated the over-the-horizon optical test, moving instead to a new location fully in the beam at a distance of 4.8km. The difference was astounding! Last night I was struggling to copy the signal even with a long carrier. Tonight it would probably have been audible in 10wpm CW!

Excellent NLOS 481THz copy this evening

I ran QRSS3 tonight and was rewarded with signals 20dB over the noise in 0.34Hz bandwidth when beaming just above the horizon. At higher elevations the signal was weaker. With this strength I am very confident that with QRSS3 the signal should be copyable non line-of-sight (NLOS) out to at least 10km by forward scatter and possibly much further, even with my 1W LED running at 250mA in 100mm optics.  This was an excellent result and I am now confident the RX is working very well indeed.  Cloudbounce is another mode I have yet to properly exploit. The reception tonight was as a result of clear air scattering presumably from water droplets or dust particles.

This time I made recordings which are linked from my website. These can be played back through Spectran or Spectrum Lab software and further analysed. See https://sites.google.com/site/g3xbmqrp3/vuhf/optical/481thz-nlos .

Rapidly I am learning the absolute importance of accurate aim: 2.5 degrees out last night probably reduced the signal level by around 20dB. For serious tests over longer ranges a means of very accurately aligning the TX and RX is essential. Unlike with line-of-sight where the red dot can be seen by eye usually, NLOS requires careful alignment from map features.

Successful over the horizon 481THz test at 4.6km

This evening, in the freezing cold, I attempted a non line-of-sight (NLOS) optical test using my beacon TX (1W 10mm LED at 250mA in 100mm optics) at home in the bedroom firing out through the double glazed bedroom window and my new improved receiver (SFH213 detector in 100mm optics) at a new test site 4.6km away towards Cambridge. The path is obstructed by rising ground some 10m above the TX and RX height around mid path.

481THz signal (top line) at 4.6km over the horizon tonight

This time, I used a lower TX subcarrier tone frequency of 572.3Hz and a continuous carrier transmission so that aiming would be easier (!) than with CW or QRSS3. I am pleased to report successful reception of the signal in 84mHz bandwidth using Spectran, but aim was extremely critical and the signal was not solid, probably because of  aiming issues and possibly changing sky conditions.

When I got home I checked the frequency to make absolutely sure that this was my carrier, which it was beyond any doubt. The signal was totally inaudible in the headphones and there was no sign whatsoever of the red beam in the sky. The most probable propagation was by scatter off dust particles in the atmosphere.

This was MUCH harder than I expected: I honestly expected to hear quite reasonable signals by ear, but as the plot shows, the signal was only just copyable in 84mHz. When I received my signal NLOS last year at 3.5km on a different path signals were 10dB over noise in a wider bandwidth on QRSS3.

At the moment I am still aiming the TX and RX as low as possible on the horizon, but I need to try greater elevations to see if this gives better to worse results over this sort of distance.

Another 6-10dB ERP from the Phlatlight LEDs (still to be fired up) would certainly help.

Practical Wireless (April 2013)

G3XBM in New Zealand (Abel Tasman National Park) Feb 2009

For the second month in a row I have an article in Practical Wireless. This time it is one submitted several years ago describing my operation on 70cms FM when on holiday in New Zealand in 2009. New Zealand has an excellent internet-linked repeater network that links repeaters all across the country, so one can work from the very south of South Island all the way to the top of North Island and talk to anyone on this linked network.  I found this invaluable when on holiday.

Sadly the exchange rate is not as favourable now as in 2009, but New Zealand is a wonderful place for a once in a lifetime holiday, with very friendly and welcoming people.

If you get PW, I hope you enjoy the article.

Optimised 481THz receiver

As the weather was miserable here today, I decided to work on the K3PGP derived 481THz optical receiver this morning. I wanted to ensure it was working at maximum sensitivity with subcarrier tones around 100-1500Hz. With some adjustment of the coupling capacitors and the addition of an HF roll-off capacitor on the collector of T2, the sensitivity now appears to be excellent. My test is an AF modulated red LED on the ceiling of my building shack, in almost total darkness, with the test receiver (less any lenses) on the bench about 1.5m away. If the receiver is working credibly then the tone can be heard in the headphones when the LED is barely lit. In the case of this latest receiver I cannot even see the LED lit at all in a darkened room, yet the tone is audible in the receiver. When comparing this with my previous best optical receiver there is around (guess) 6dB more sensitivity. This design uses "blog standard" components: nothing selected for low noise, and not an IC in sight. I am now waiting for some decent weather - and no snow please - to test this on my NLOS test path.

K3PGP receiver for 481THz

One of the simplest, yet highly sensitive, receivers for optical communications is one designed by John K3PGP. The G8CYW design in Practical Wireless in the March and April 2013 editions is based on this. This works really well in darkness, but is easily overloaded in any light. Many circuits are optimised for speech communications but this one works really well with digital modulation at very low frequencies where the detector sensitivity is highest.

http://k3pgp.org/Construction/Frontend/preamp.gif

Today I've been building a version and I am in the process of optimising it for subcarrier frequencies below 500Hz. I have added an extra transistor gain stage after the basic K3PGP design but want to see if lower noise FETs and transistors make a worthwhile improvement. When satisfied that it is working optimally I shall be trying this at the RX end of my over-the-horizon tests. I am quite excited about trying much lower frequencies in the next test using QRSS3 and continuous carrier.

10m WSPR today

Today I've been running either 50mW or 2W on 10m WSPR. 50mW was enough to get to 4X1RF but 2W was needed to be seen in Uraguay at 11127km using the Par-10/20/40 endfed antenna. The jury is still out on how performance on the 3 band antenna compares with the 10m halo, which is currently down pending a rebuild.

Source of BRIGHT red LEDs

Some have asked me what LEDs I've been using so far for my optical experiments. Well, these are 10mm diameter "conventional" style LEDs from a source in Hong Kong. They are 1W devices capable of 280000mcd output and look like a normal LED on steroids in that they come in a standard looking clear package with 2 thick leads.

They are available via eBay at £9.30 for 10 off from Hi Tech LED World.  The supplier delivers promptly and with good packaging (and a nice collection of attractive stamps on the package). They also have a range of other devices available.

Use the link http://www.ebay.co.uk/itm/350347623711 .

As mentioned before, I also have some even more powerful LEDs called Phlatlights which are intended for overhead projectors. I've still to fire these up. These are about 10dB more powerful than the 1W LEDs, so are potentially dangerous.

Gaps in my knowledge

Sometimes I feel a complete fraud: people drop me emails and ask me questions and I am completely at a loss how to answer. The reason is there are an awful lot of things that I should know about that I don't. As an example, PIC programming: many of the things I want to do, like make a simple VLF frequency generator with FSK keying could probably be done very easily with a PIC, but I have never, ever, used a PIC and certainly never programmed one. There are whole areas of circuit design in which I'm very weak, for example digital logic, microprocessors etc.  Even my RF knowledge is frankly far from expert.  In my professional life I managed to get promoted into management roles where my "hands on" RF skills were not an embarrassment! You'd be surprised how many managers in RF jobs are not actually that hot at RF design.  Mind you, it helps to have a "jizz" (instinctive feel) for RF and I did (and still do) have this.

The reason I raise this is to give others hope. Even without knowing too much a lot can be done and we are never too old to learn new tricks. There are far too many things to know about to be experts in everything and the best we mortals can do is try our best in a limited area. This is why I concentrate on simple HF and low VHF QRP projects, optical and VLF work which I can get my head around. I'll leave the complex stuff to people far better than me.

http://uk.farnell.com/productimages/farnell/standard/1701537-40.jpg

At some point I may have a go at PIC programming but writing software was never my strong point. Neither was maths for that matter. Talking about PICs, if I wanted to have a go at PIC programming what do people recommend for going about it? What is the best (simple please) book and what is the best development kit on which to try out the programmed devices?

Rockmites

Some years ago I bought a Small Wonder Lab Rockmite-20 from QRPshop in Germany. As I didn't have a suitable antenna at the time, the project got shelved and the complete kit has been sitting, unbuilt, on my shelf. Now I have a Par-10/20/40 end fed antenna up covering the band I've no excuses. So, maybe next week in between other experiments I'll build it and try it on the air.  The reviews of the project on eHam.net are very good with a score of 4.9 out of 5 from 79 reviews. It is a clever design with a full keyer built in and using a couple of crystals with one as a front end filter to keep out the broadcast breakthrough.

Aiming high

This evening I caused a few curious looks on our road as I adjusted the optics on my latest 481THz beacon in the dark.  In order to carefully align the powerful red beam, it is important to ensure the cross hairs on the gun sight telescope used for aiming are precisely aligned with the tightly focused red beam.  I beamed onto the rear of a distant car and made some adjustments. As I was doing this, someone walked down the road with a dog and stood, puzzled, at why this car number plate was glowing red very brightly!  The beam was aiming slightly too high, but after adjustment is now precisely in the centre of the cross hairs, so next week, weather permitting, it will be time to try again at the NLOS test.

New 481THz QRSS3 beacon ready for action

Completed 481THz beacon electronics

This afternoon I finished off the electronics build of the new dual frequency optical beacon TX for 481THz (red light) over-the-horizon (NLOS) tests. In the end I opted for QRSS3 on a choice of 2 sub-carrier frequencies selected by toggle switch together with the option of a continuous sub-carrier transmission on either frequency to help beam alignment. I have not incorporated an FSK facility at present. All that remains is to align my sighting scope with the optics so that I can use this to help with aiming. Currently the beam appears off-centre in the spotting scope cross-hairs.

As I now have the option of a lower sub-carrier frequency, I need to revisit the improved RX to see if I can better optimise sensitivity at the lower frequency. Theoretically the detector should be several dB more sensitive at a lower sub-carrier frequency which should help with NLOS tests where signals are weak.

The beacon is powered by a 19.5V 4.5A ex-Dell laptop SMPSU, although I only need around 300-400mA with the current LED, which is exceedingly bright.  In the picture above you can see the BACK of the LED and that is pretty bright. At least with the PSU the whole beacon is self-contained.

Progress on the new 481THz beacon TX

Today I made a start on the new optical QRSS3 beacon. This time, the circuit has some improvements: a continuous sub-carrier option and a choice of audio subcarrier frequency. Also, the frequencies are now derived from an HF crystal so stability will be excellent.

The part completed new 481THz QRSS3 beacon

The oscillator/divider is a 4060 IC and this is enabled by the output of a K1EL keyer IC programmed to send "XBM" in QRSS3.  The square wave output from the 4060 feeds the gate of an IRF510 FET which switches the 280000mcd, 10mm diameter, LED in 100mm optics.

A possible refinement will be to pull the crystal using the keyer output signal so that I have a continuous carrier but FSK keyed. This would mean I'd always have a signal to aim at, but with FSK QRSS3 CW on it. I'm not sure how much pull I'd get after dividing down if I just changed one of the capacitors loading the crystal. I shall have to experiment and see. Even as little as 5Hz would be enough, but that would need 50kHz shift at crystal frequency! A better way may be to key the frequency out of the 4060, so mark is, say 550Hz and space 1100Hz or vice versa. Plenty to try tomorrow.

Frustrating day at both ends of the spectrum

Today I tried two experiments. Firstly a continuation of my tests with the loop and E-field probe out in the fens on 8.977kHz and then tonight, another over-the-horizon test on 481THz.

Failure 1 at VLF: whereas in the past I've had a decent signal at my test site at Tubney Fen 3.5km from home on the loop antenna on 8.977kHz, today I could copy nothing. There was some strong interference and I thought that may have been the problem, so I moved on to a second test site 5km away where again I usually get a good signal. Again nothing. In the past this second site has given me signals so strong that I could copy 10wpm CW from home on 1kHz by earth mode. Now around the village and in nearby Swaffham Prior the signal levels were (as far as I can recall) similar to past levels, so what has changed? One theory is that the wet winter has saturated the fenland soil so conductivity is much higher, resulting in much higher attenuation at VLF.  Another possibility is some utility has changed - a change of pipe type or a re-routing of an electricity cable? My TX and RX equipment is largely the same as in previous tests.

Optical QRM on the 820Hz sub-carrier frequency

Failure 2 at 481THz: I tried a third attempt at my over-the-horizon QRSS3 reception of my signal on a 820Hz sub-carrier. This has been successful in the past. The 100mm lens TX was carefully aligned just to the right of our local windmill on "the hill" and I traveled to what should have been a direct line path (but over the horizon so the signal has to be scattered) about 3.5km away. Optical conditions looked good with clear visibility of street lights in Burwell. Well, I am pretty certain that I was able to hear my signal by ear in the headphones keying away slowly, but because of a lead failure (later fixed) and then a strong interfering signal very close to the 820Hz sub-carrier, I failed to see my signal with Spectran and make a screen capture. I think this QRM signal is related to new street lighting as panning the horizon brought up this interference on most street lights at around 3km range. The solution will be to choose a different sub-carrier tone frequency. BTW, it is fun to hear the strobe lights from aircraft: these are very strong and can be copied well off the direct path by scattering.

My next immediate priority is to change the optical beacon TX so that I can use a range of different sub-carrier frequencies all derived from an HF crystal divided down with a 4060 divider. This will also allow me to run a continuous signal which will help with alignment and I can avoid QRM by moving the HF crystal frequency if needed. I could also arrange DFCW modulation by FSK keying the HF crystal: this will allow a continuous signal for audible alignment yet be detectable with software packages like Spectran in QRSS3.

As regards the VLF earth-mode tests, for now I am going to draw these to a halt and will try again in a month or so when I hope the fen soil conductivity has reduced. If things are unchanged then I suspect that something in the utilities metalwork out in the fens has (permanently) changed.

Projects update

It is some time since I summarised my projects list and progress. This is the current "ideas list" for the coming months. As we are in the middle of a house renovation/move project over the next 3-6 months it is quite likely that my amateur building work will have to go slow.

• VLF earth-mode - optimising the E-field probe and loop antennas for mobile coverage tests
• 481THz Optical NLOS tests - testing new RX and then trying the 10dB higher powered PhlatLED TX and seeing how far over the horizon I can reach.
• WISPY 10m WSPR beacon - combining the TX and RX boards into a full WSPR/PSK31 transceiver. Separate modules made and tested but yet to combine.
• Tenbox - I still need to finish either the AM transceiver or modify the design to a DSB transceiver.
• 2m horizontal omni antenna - I need a simple horizontally polarised omni antenna for the new QTH. I'm tempted to organise a pair of stacked big-wheels with around 5dBd gain.
• Simple test equipment for the shack at the new QTH - I want to build a number of pieces of simple test gear such as a frequency counter and simple spectrum analyser 
• Rebuild of the 10m Homebase-10 halo - the wooden frame structure is showing signs of age, so a fibre-glass support may be less visible and more durable 

Now, knowing the way things work with me, I 'll wake up one morning and think of something completely different to work on. That is the fun of simple homebrew amateur radio experimentation: no-one tells you what to do, unlike when at work, and each day is one filled with opportunities.

Double or single peak for cycle 24?

At the moment the jury is still out on this. We've seen activity slide since the peak around Nov 2011 but there may be signs that the trend is upwards again leading to a second peak as has happened in a few recent sunspot cycles. This NASA video gives some insight into the thinking.

More analysis with Spectrum Lab software

Spectran is a very easy package to use but it has its limitations when analysing weak audio signals. A more powerful package is DL4YHF's  Spectrum Laboratory which is an extremely powerful piece of software. The problem is that if I've not used it for months it takes me hours to remember how to drive it. A secret is to store ".usr" configuration files so one can go back instantly to a set of settings e.g. a given frequency to analyse with a specified bandpass filter and bandwidth.

Faint line at 8.9775kHz visible at greater range (43mHz bandwidth)

Anyway, to cut a long story, this evening I set up some config files to allow me to look again at the recordings of my 8.9775kHz VLF earth-mode signals made during recent drive around tests locally. Although the original analysis was done at 180mHz bandwidth I can now replay the recordings and look in bandwidths down to 34mHz. What happens then is that signals present but too weak to see now appear above the noise floor as a faint line. The net result is that the signals can be detected in some of the "in between" locations that were not apparent from the 180mHz (wider!) bandwidth analysis.

I intend to use Spectrum Laboratory and narrow bandwidths for the over-the-horizon 481THz optical tests if Spectran proves not up to the job. However, when bandwidths are very narrow there is a time-lag before the trace appears on the screen. This is less than ideal when trying to align weak optical signals with beamwidths measured in a degree or less. What is needed is an accurate beam heading and then allow the trace to build on the screen. I don't have enough experience yet to know how much beamwidth spread a cloud or free space dust scattered optical signal gets. When looking for G4HJW's signal over the horizon in clear skies last year the alignment was quite critical, but his signal was audible in headphones so the optics could be peaked by ear before analysing with Spectran or Spectrum Lab. I had more luck with my own QRSS3 signal over the horizon on a shorter path, managing to align by eye on visible landmarks enough to see the trace on the PC and then peak it.

Mobile 8.977kHz VLF loop tests started

Today I started to do my tests on 8.977kHz using my 5W earth mode transmitter at home but using a mobile loop antenna on the car connected to my PC via a tuned preamp. The idea is to be able to drive around and measure signal levels with Spectran software whilst actually on the move.

30t 80cm loop mounted behind the car

The loop was mounted behind the car in such a way that it would detect any ground propagated signals. The loop is about 10cm off the ground.

A drive test to Swaffham Bulbeck was carried out and signals were detected more or less continuously out to 3.5km from home before they disappeared in the noise. Bandwidth used was 0.18Hz with a continuous carrier. Although coverage was as I anticipated, signal levels were not as great as when the loop was actually laid directly on the ground. At one of my usual test sites 3.5km out in the fens there was no copy with this loop arrangement yet there was a decent signal copied with the loop on the ground a few days earlier. I need to do some direct comparisons between the loop on the ground, the loop mobile mounted 10cm above the ground and with the E-field probe on the car roof. Initial indications are that the difference between the EFP and the mobile loop is probably no more that 5-6dB.

Signal received with Spectran and the mobile loop

Revised UK Frequency Allocation Chart

From the OFCOM email newsletter today:

UK Frequency Allocation Table

Ofcom has published a revised UK Frequency Allocation Table. This details how various frequency bands are used in the UK, and which bodies are responsible for planning and managing them – including frequencies assigned to individual users or installations at particular locations. It also shows the internationally agreed spectrum allocations of the International Telecommunication Union. 

The table shows frequencies below 8.3kHz are unallocated in the UK but there are some footnotes in the ITU frequency allocation table that require administrations to ensure no harmful interference to services above 9kHz and to notify other administrations about research below 9kHz.

My understanding is therefore that below 8.3kHz the UK administration "does not care" what happens as long as interference to allocated services is avoided. This is my interpretation and not a legal statement.

VLF earth-mode mystery deepens

This afternoon I did a larger coverage test with 5W  8.977kHz earth-mode, driving in several directions locally in the car with the roof mag-mounted E-field probe RX antenna and with a PC in the car monitoring the signal. I drove for several kilometres in different directions recording where the signal could, and could not, be copied. The best reception distance with the E-field probe was 3.2km.

The map shows the results. Yellow shows where I drove and red shows where there was signal present and recorded on Spectran. I have recordings of the whole trip which I will more carefully analyse later.

5W 8.977kHz earth-mode coverage using EFP RX antenna

The interesting thing is that the signal could be copied in 4 local villages (Burwell, Reach, Exning and Swaffham Prior) but there was almost zero coverage once outside of these villages. This is NOT the case when looking with a magnetic loop RX antenna, where the signal can be copied more extensively in the rural areas at even greater distances.

It would appear that the E-field signal needs to be strong above ground to be copied with the EFP and this only happens where there are buildings i.e. in the villages. It suggests I'm detecting the signal from cables or pipes in houses.In more rural areas the signal is weaker above ground and not detected, at least not with 5W TX.

Mobile on 8.97kHz VLF

Route taken from A to F (about 4km)

Today I did a fascinating experiment on 8.977kHz VLF using my 5W earth mode transmitter and a mag-mounted E-field probe and laptop running Spectran in the car. Basically I did a "drive around" test to see where the signal could and could not be copied.

Signal strength on 4km run between 2 villages

A continuous carrier was transmitted and I continuously monitored the received signal in the car. The drive was from the middle of the next village (Swaffham Prior), out through to the main road, then back along the main road to Burwell, around part of the village and then back home to the TX location. The signal was visible in Swaffham Prior at 5-10dB S/N, then disappears and returns on approaching Burwell where it is up to 40dB/S/N in 0.18Hz bandwidth. Within Burwell it is almost solid copy. The red timing ticks are every 30 seconds.

What I am detecting (I think) is the local E-field from the VLF signal in the ground, no doubt aided by local utilities. What puzzles me is why there is NO copy in between the 2 villages when there are, I think, pipes and cables in the road.

In the coming days this test is worth repeating locally in other directions and further afield. Fascinating to think a 5W VLF signal injected into the ground can be copied on a 19 inch whip on the car roof like this.