VLF E-field probe design from DK7FC

DK7FC's VLF E-field probe antenna

Stefan DK7FC is well known for his experiments at VLF. Here is his circuit for the E-field probe he designed which is in use at many VLF grabbers around Europe. It is highly recommended.

Further 481THz G4HJW reception "over the horizon"

G4HJW received on 481THz over an 8.63km non line-of-sight path

Bernie G4HJW was 20dB S/N in 0.67Hz bandwidth earlier this evening at my local test site 8.63km NLOS from his QTH "over the horizon". Bernie was using his Phlatlight beacon with 1.082kHz tone. The sky was clear and starlit, so this was clear air scattering not cloudbounce.  About 15 minutes after I first copied him it seemed to get more hazy and I was struggling to find his signal at all.  Best results appear to be with a clear sky and aiming at the horizon. 

On 3 attempts copying G4HJW's optical signal it has been (1) 30dB S/N, (2) no copy and (3) today 20dB S/N in 0.67Hz bandwidth over an 8.63km NLOS path. I am still using the BPW34 detector in 100mm optics.

160m JT65 QSO with loft vertical

JT65 QSO with 2E0ZRQ this evening on 160m

Managed to work 2E0ZRQ who was running 20W to a longwire with my 5W to the tiny loft vertical antenna this evening on JT65-HF. This is my first QSO with this mode on topband at a distance of 148km.

160m loft antenna diagram

This is a diagram showing the arrangement of my 160m loft-mounted antenna. The ground connection is made to a hot water tank (copper) next to the upstairs shack. It connects via copper pipes in the house to the external ground and works very well. The top capacity hat should be as large as possible but in my case is just a couple of horizontal wires around 1-2m longh in each case hung horizontally in the top of the loft space.

160m JT65

My 4 year old grandson having gone home now, I have my shack back again so am able to play amateur radio again. I've several things to catch up on including:

1. Trying for a first 160m JT65 QSO.
2. Measuring the performance of my ST-3 JRC headphones that AA1TJ managed to find for me recently.
3. Another over-the-horizon 481THz test looking for G4HJW's beacon and my own.
4. Testing my iPod Touch SpectrumView application with an external audio input.

This evening I have been copied by G4HPW (87km) on JT65 on 160m but no 2-way QSOs with this mode are in the log yet on topband using my compact loft antenna.

10m good despite the flare

Today all the propagation forecasts were showing poor conditions on HF. Despite this, 10m was well open this afternoon to the Middle East, Africa and South America with good signals received. My only QSO so far has been with JY5HX when running 5W CW here.

The lower part of 10m had several Russian (?) CB stations including one operating almost on 28.060MHz, the CW QRP frequency. Use it or lose it folks.

160m JT65

As I appear to be having some success with WSPR on topband, I have decided to try JT65 on the band to see if I can manage a few QSOs.

UPDATE: after calling for around 15 minutes I gave up!

My 160m WSPR analysis

Since erecting my tiny 160m loft mounted vertical this last weekend I've used it on WSPR a few evenings with great success. The following tables show the unique reports received and sent on the band using (mostly) 5W. Most stations copying me can be copied here, despite the horrendous noise issues on the band at night.

160m WSPR reports received

160m WSPR reports given

So far, reports have been received from 9 countries with best DX being 1007km. Not bad with an antenna which is essentially a 1m long coil, a couple of top capacity wires and about 3m of feed wire from the loft to the upstairs shack and tuned against my central heating system copper pipes as a ground.

Elecraft KX3 manual

The soon to be released KX3 QRP transceiver

The preliminary version of the owner's manual for the latest Elecraft KX3 12W all mode 160-6m SDR portable transceiver is now available. The product is expected to ship very shortly now. Reading the manual it is clear this is a VERY impressive radio packed with features and facilities. Initial reports from field testers confirm performance of this little radio is up there with the very best, and all this in a size not much bigger than the control head of an IC703.

VLF test by OE3GHB

OE3GHB's VLF loading coil and transmitter

OE3GHB has reported on his 8.97kHz VLF tests this weekend. He was copied by several stations in W.Europe. Gerhard's signal was clearly detected by OK2BVG, DF6NM, DK7FC and by Paul Nicholson in Todmorden. There was a trace seen by G3ZJO. At the moment my VLF system is out of action so I was unable to take a look. The picture shows Gerhard's enormous VLF loading coil. Antenna current was around 600mA and his antenna was a vertical on an 18m fibre glass pole with a 100m horizontal top wire with 600pF capacitance.

Mixed results on 160m

The small loft antenna for 160m has produced some impressive results tonight with spots from all over NW Europe of my QRP signal. Best was GM4SLV in Shetland at 5W and OZ7IT at 2W.

But the real reason for erecting the antenna was to allow QSOs on QRP AM over a 3km path to G6ALB so we could use topband for a talkback link when doing other tests. Now, at 9.30pm we went onto 1.973MHz AM to see how easy it would be. It wasn't easy at all! In fact it was very hard work copying even a few watts of AM. The killer is the noise floor that is around S9 both at Andrew's home and mine. On WSPR, with its much narrower bandwidth this is not such an issue, but on AM it ruins the band for what we'd intended. There is no way that 0.25W of AM would make it, certainly not easily with simple rigs as we'd planned. 10W would be OK, but that defeats the purpose. On 70cm AM (yes AM) we had armchair copy between us with about 1W. On 160m FM it was better copy until we dropped the power down and the signal was drowned by the QRN/QRM.

So, what will we do? There is now no point in continuing with the 160m AM transceivers as this isn't going to work at our noisy QTHs with QRP over 3km, sadly. The most probable choice will be 6m AM using my SixBox rig at my end.

The lower HF bands like 160m are radically different from 30 odd years ago when the noise floor was some 20-30dB lower.

160m loft antenna erected

160m loft antenna

Today I erected a small loft antenna for 160m use. The prime purpose is to allow me to test my QRP AM transceiver (that is under construction) with G6ALB in the next village. The idea came from an old RSGB book called, "Practical Antennas For Novices" by John Hayes G3BDQ. It consists of a long coil wound on a PVC pipe about 1.5m long with a couple of wires along the top of the loft as a top capacity hat. In John's design he used 21mm pipe but I chose 32mm instead and my inductance measured 590uH. Just a little more inductance in the shack was enough to make the antenna resonant when tuned against ground (my copper hot water tank and pipes in the house). Now it is time to find out how well (or not) it works. Incidentally without the additional loading in the shack it was a good match on 40m and 15m too.

UPDATE: My first 2 WSPR reports on the new (indoor) antenna were from OZ7IT at 853kms! The antenna must work, HI. Shortly after PA0A spotted me.

DMR products

My old company, Sepura, entered the Digital Mobile Radio market last year (as an addition to the TETRA products they already design and make) and are, as we speak, designing DMR products for sale in the near future. In recent days they've had a wake-up call from their major competitor Motorola in the form of two new DMR radios that set the benchmark. See http://www.motorola.com/Business/XU-EN/Product+Lines/MOTOTRBO/SL4000+Series/SL4000_SL4010. These look very attractive products and I am glad I no longer have the task of trying to beat them! Instead I can tinker with lightbeams and VLF.

Getting Going on "Bottom Band"

Well, guess what, I am a year younger (amateur radio wise) than I thought. Having looked up some old RSGB Bulletins this evening I see that I actually joined the RSGB in 1963 and not 1962, so I've only been a member for the last 49 years. Suddenly I feel a year younger!

I was looking for an article about lightbeam communications that was in the very first RSGB Bulletin (later Radcom) I ever received and this was in April 1963 and not 1962. It was called "Getting Going on Bottom Band". The article was an April Fool's one but I didn't realise this and got the reference books from the library. But, the fascination with communicating a long way over a beam of light was kindled in that very article and only now am I giving the subject proper attention, some 49 (and not 50) years later. I feel as if I have a whole year extra in which to enjoy the hobby, HI.

SpectrumView for iPod/iPhone

SpectrumView 0-24kHz displays of waterfall and spectrum

Looking around for useful (free) software to help me with VLF and lightbeam tests I came across SpectrumView yesterday. This is a fabulous application for the iPhone, iPod Touch and iPad which provides a 0-24kHz spectrum analyser and a waterfall display.  The app is produced by Oxford Wave Research.

To make best use of this I need to connect an external audio input into my iPod Touch 4g.  A 4-pin jack plug when inserted, rather than a 3-pin one, allows an external audio input (or a mic) to be connected so I can feed my VLF receivers, used for both 8.7-9.1kHz earth-mode comms and for lightbeam baseband/sub-carrier detection, directly into the iPod.  Resolution will be down to around 2Hz at best, so this will be of somewhat limited use, but certainly easier than a laptop for quick field tests or quantitative measurements.

The mic input (on a 4-pin jack) is on pin 4 (nearest the plug cover) and the ground is the next one down the connector (pin 3). The tip (pin 1) and pin next to the tip (pin 2) are the two audio outputs for a headset.


UPDATE 16.3.12: to tell the iPod Touch 4g that an external mic is connected you seem to need to have a 4k7 resistor to ground across the terminals. See later post for details.

RSGB member since 1962

Next month is an historic occasion for me as it will be exactly 50 years since I joined the RSGB. In those days applications had to be supported by 2 existing RSGB members and living in the wilds of Devon I had to look hard to find two!  One of the two who supported my application was Roger Thorn G3CHN, now SK, who later overhauled my ex-military DST100 radio and thereby opened up the world of shortwave listening to me. Roger worked at the local Decca Navigator station and I remember being thrilled when he showed me around the station.

Many people are critical of the national society, but behind the scenes the RSGB does a LOT for the UK amateur population. A society is only as good as its members and the contributions we make towards its success. A lot of hard work is being done currently to get the society back onto a firm footing after a turbulent period. It deserves our support.

472-479kHz available Jan 1st 2013 in UK

G3XBM's 500kHz transverter. Ideal for 472-479kHz.

OFCOM are now going to renew NoVs for the 501-504kHz band for existing permit holders and this will be possible via an on-line webform on the RSGB website.

"Following the agreements concluded at World Radiocommunication Conference 2012, Ofcom has started discussions with the RSGB and others about the timescales for implementation of the new secondary allocation to the amateur service between 472 and 479 kHz which, it was agreed at the Conference, would be effective from 1 January 2013.
Ofcom has therefore determined that, to allow these discussions to be completed, the current NoVs to allow experimentation between 501 and 504 kHz should have their validity extended to 31 December 2012. This notice confirms this fact."

See http://www.rsgb.org/operating/novapp/500.php. So plenty of time to get an antenna up and a TX or transverter ready. You might like to start by looking at http://sites.google.com/site/g3xbmqrp/Home/500k where I describe my 5W QRP transverter which will work on 472-479kHz. I've plans to make a Mk2 version of this during the summer with higher power and other improvements. It would be nice to make a PCB this time so that others could build it.

A very tiny Chirpy from Eldon WA0UWH

WA0UWH's version of Chirpy

Eldon WA0UWH has built an SMA version of my 10m Chirpy transceiver on a VERY tiny PCB. He is currently debugging it. See Eldon's blog at http://wa0uwh.blogspot.com/2012/02/my-xbm-10-2-chirpy.html for more details.

Optical RX schematic

Schematic of the G3XBM optical RX

Several people have asked for the schematic of the optical receiver used in the recent "over the horizon" red LED 481THz tests. Here it is. The BPW34 photodiode does not have any bias and is connected directly (in the air) to the gate of the FET. I have tried reverse biasing but it made little noticable difference to sensitivity. The cascode "head" is from KA7OEI and this is followed by an op-amp buffer and gain stage which feeds the PC. There is an additional stage of gain to drive a small crystal earpiece. I am sure the circuit can be further simplified and optimised but it has allowed me to copy a baseband scatter signal at 8.63km by ear and is as sensitive as any receiver I have yet tried.

Successful 481THz NLOS test (8.63km)

8.63km non line-of-sight reception of 481THz optical beacon

Bernie G4HJW set his high power optical beacon running a 1.082kHz tone this evening pointing in the Burwell direction on a non line-of-sight path from his home QTH at Little Wilberham. He then came over to Burwell to compare his RX and my own from a test site on the edge of the village clear of the village lights. Distance was 8.63km.

Both on Bernie's RX kit and my own we got solid copy by ear of the beacon at a distance of around 8.63km NLOS using 100mm optics. Once found, the signal was solid.  I then set up the optics on the tripod and fed the signal into Spectran where the signal was 30dB over noise in a 0.17Hz bandwidth. Listen here for a recording (best played back using Spectran with 0.17Hz bandwidth settings)

G4HJW's beacon TX

There was hardly a cloud in the sky, so this was largely by scatter from the mist/dust in the air. Bernie says signals have been stronger on other nights. Best reception was with the RX aimed just above the horizon, maybe 5-10 degrees at most above.

This was very gratifying as it is the furtherest NLOS signal I have copied and it verified my RX kit is now working at good sensitivity.

When I got back home I did try to copy the beacon by ear out of the bedroom window but the tree cover and lights made copy not possible. However I will try again later in the week with Spectran running and narrow bandwidth.

Failed cloudbounce 481THz optical test (7.6km)

Possible weak 481THz reception at 7.6km NLOS

This evening I tried a 7.6km non line-of-sight (NLOS) path between Burwell and Newmarket Heath with the 0.7W input red LED beacon running QRSS3 on an 820Hz subcarrier (at home) and modified KA7OEI receiver at the RX end, both with 100mm optics. My PC was running Spectran.

The best I can say is reception was very doubtful:  the screen capture above shows a signal at the correct subcarrier frequency in the right direction, but too weak to identify CW characters. The recent 3.6km NLOS test produced good 10dB S/N signals in 0.67Hz bandwidth - much easier.

With a largely clear sky, few clouds and a slight haze, not ideal conditions for cloudbounce testing. This test will be repeated when cloud cover is better and visibility is clearer. QRSS30 would give me another 10dB so this may be worth a go if QRSS3 doesn't work on a second try. There are several variables that make weak signal forward scatter detection difficult: (a) what vertical angle to use at both ends, especially with few clouds (b) amount and height of cloud cover, (c) horizontal direction of aim.  With QRSS3/30 modes it is a case of small aiming increments and wait to see if a signal appears on the screen. It is quite hard work.

The result is disappointing, but there will be plenty of other occasions to repeat this test and do others. All good  fun.

Some 160m AM QRP rig links

Looking around for some ideas for a local natter box, I came across these links for simple AM transmitters and receivers so far:

http://www.gameangler.eu/delboy/m0dad/construcion/poppet_top_band_am_transmitter.htm
http://www.angelfire.com/de/RadioAnarchy/
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/1.65MHz_AM_QRP_TX.gif
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/AM_RX_Superheterodine_NE612.gif

If you are aware of other, simple, ideas for 160m QRP AM rigs please let me know.  I've still to go through my old SPRATs to see what is there and there have also been some ideas in Practical Wireless.

A 160m AM local natter rig

Further to my post a few days ago about possible bands to use for a very local "natter link" over a 3km path between G6ALB and here, my thoughts are turning to 160m, partly for nostalgic reasons. This is where I first started my ham radio operating with a small 400mW AM transmitter from Practical Wireless (Dec 67 I think).

Although 160m is VERY noisy now, especially at night, I figure that 100mW AM will be enough to kill the QRM/QRN over such a short distance. So, I am gathering ideas for something incredibly simple to build.

For the TX the most sensible rig would be a crystal oscillator (or ceramic oscillator) followed by a buffer and series modulated PA using the modulation circuit from the 2m AM Fredbox. On receive, either a regen receiver (operating just out of oscillation) or even an MK484 (like the ZN414) single chip receiver are worth a try.

This would be no DX rig, just a very basic transceiver to get me into the next village and not much further. I'll keep you posted. Incidentally I am unable to do much building right now as my house is in the middle of some redecoration. I can't find anything!

40m regen receiver kit from OK land

OK1CDJ's version of my simple 40m regen receiver

Ondra OK1CDJ has been in touch again recently and he mentioned that he had built a version of my 40m regenerative receiver and is now supplying a kit of parts in the Czech Republic via www.hamshop.cz. There are some nice photos of Ondra's version built into a small tin box.  My original circuit is at https://sites.google.com/site/g3xbmqrp/Home/regen although I admit I was inspired by W2UW who used this circuit before me in his amazing FET-1 transceiver.

Commercial QRP: KX3 or FT818?

CQ Ham Radio Book

As I've said before here,  I just can't understand why an FT817 successor has still not yet appeared. The KX3 pre-release spec (now nearly 12 months old) gives a good idea of what is needed and Yaesu surely could beat Elecraft on price. Also, Yaesu's alternative is likely to win on size and looks.

Here in the UK, once import duty and tax are added, the KX3 will be expensive, so I am still hoping the FT818 will appear soon and be a more cost effective alternative. I love Elecraft kit but not sure that too many over this side of the pond will shell out over £1000 for a commercial QRP radio. An FT818 at, say, £599 would be a more cost effective investment. I say investment as my FT817 is now 11 years old and been the best amateur radio investment I have ever made.

So, I am still on the look-out for some HARD news from Yaesu Japan i.e. specs, price and release dates. If there are any leaks I promise you that the news will appear on this blog as soon as I get wind of anything. And of course, unlike the KX3 I expect an FT818 would be available as soon as an announcement is made.

The image above is linked from http://www.cqpub.co.jp .

Optical cloudbouncing (stage 2)

With my QRSS3 success last weekend over a 3.6km non line-of-sight path at 481THz (red light) I've been looking at other possible NLOS cloudbounce paths that start from my home QTH where I can set up my 100mm optics 0.7W input beacon pointing out of a bedroom window.

There are several different paths out to around 8km away that will be tried shortly.  I need to do a quick check at the RX locations to see that there are no issues e.g. trees very close and that I can safely park the car off the road at night. The tests can't start for a few days as I have grandchildren with us over the weekend. Maybe the first test will be on Tuesday evening.

Simple local ragchewing rigs

The Sixbox 40mW AM transceiver for 6m. Maybe a Fourbox will follow?

The experiments last week by G6ALB and I confirm that to talk over a few kilometres, very little power is needed. Indeed, below 1mW is all that would be needed on any mode, at least on 144MHz. Andrew and I are now thinking about rigs that we can use to simply keep in touch whilst we get on with other QRP tests on bands from VLF to light. One idea is a 4m version of my Fredbox/Sixbox QRP AM transceivers to be called the Fourbox. This would be extremely simple to build and ideal for communication between a couple of stations in adjacent villages. Activity levels on 4m are not that great so we would be unlikely to suffer much interference issues if a super-regen receiver was used as on the original designs. A simple wire dipole in the loft would be fine for an antenna at each end. At 6m I was able to use T37-6 toroids, but at 70MHz I think these would be just beyond their intended design limits. Small airwound coils would probably be OK.

How little power do you need to communicate?

Last night G6ALB and I did a test on 2m to see how little power was needed to communicate between the two of us. Andrew is 3km from me. We both use V2000 triband vertical antennas. We started the test with Andrew using about 0.5mW pep from a simple DSB rig. We then switched to CW (from a decent low leakage signal generator) and G6ALB reduced power in 10dB steps. The lowest level I could still copy his signal was -55dBm which is around 1.8nW. The screenshot above, taken from Spectran, shows his signal at that level.

This sort of power level could be generated by power harvesting, even rectified RF from the HF antenna. Now there's a thought - a free power TX.

Non line-of-sight optical path profile

This is the path profile of my successful 3.6km QRSS3 cloudbounce non line-of-sight 481THz (red light) test on Feb 12th 2012. Sorry it is in feet and miles. The vertical scale is exaggerated, but it shows how non line-of-sight the path was. I used http://www.heywhatsthat.com/ to produce the data. This is a very useful site.  It is fascinating that such paths can be used successfully for optical frequency communications.

A new MF ham band agreed at last

472-479kHz was officially agreed as a new secondary allocation for radio amateurs at WRC-2012 today.  See http://www.arrl.org/news/amateur-radio-gets-secondary-mf-allocation-at-wrc-12 .

It may be some months, or even a year or so, before the band is available in the UK. I already have kit to use on the new frequencies (my 500kHz tranverter) but may update it with a better antenna and a bit more power.

7kHz doesn't sound much but it is much better than the 3kHz available by NoV around 500kHz currently. Also it is likely to be available in most countries with EIRP somewhere between 1 and 5W depending on footnotes and location.

Simple Home-Built Radio Projects page

The website of Rick Anderson KE3IJ is one of my favorites as it is filled with simple circuits, mainly simple receivers, that can easily be reproduced and that work well. See http://www.ke3ij.com/radios.htm. What I like is that on many pages there are little extra bits of circuitry that can be used in other projects too.  Lke me, Rick loves the humble 2N3904 transistor which is useful from audio to VHF.  They appear all over the place in his novel circuits.

The universal scale of things

http://images.4channel.org/f/src/589217_scale_of_universe_enhanced.swf

This quite wonderful website brings to life the scale of things in our incredible universe from the smallest strings and branes to the largest galaxies and nebulae in the cosmos. And we are somewhere in the middle of all this.  Zoom in both directions (smaller and larger) and be amazed.

Successful non line-of-sight 481THz test tonight by cloudbounce

QRSS3 signal at 3.6km by non line-of-sight cloudbounce

Armed with my simpler QRSS3/CW beacon (see earlier post) I did a very successful non line-of-sight (NLOS) cloudbounce test this evening using my 1W red LED in 100mm optics (run at 340mA). TX was my "G3XBM" message in QRSS3 (3 second dots CW) at 820Hz subcarrier.

With the beacon aiming out through the double glazed shack window at nearby Burwell windmill (as an aiming point) I set off for a road at Landwade which was 3.6km away "over the hill" and on a NLOS path from here. At Landwade I set up the 100mm optics and my variation of the KA7OEI head feeding into my laptop running Spectran. Immediately I got a good signal from the beacon 3.6km away. Signal was around 10dB S/N in 0.67Hz bandwidth. The signal was neither visible as a red glow nor audible in the earpiece despite listening quite hard and panning around for best signal.

This was my first proper NLOS test and it is extremely encouraging. I did try to elevate the RX to higher points in the sky but best reception was with the optics aiming at the lights of Burwell village in the distance i.e. as low as was possible in elevation. At the TX end I was aiming to just clear the slight rise in ground to the east of me near Burwell windmill.

Weather conditions were light patchy low cloud with pretty decent visibility. I did notice QSB as cloud cover varied.

I'm really lucky finding this test path as I can put the TX beacon on the bedroom shack windowsill and fire towards the windmill. In daytime I would be able to align the RX better as I was having to guess the best direction with only Burwell church visible. I had to tweek the alignment to what I thought was the right direction. I did not spend a lot of time trying to peak the signal and better copy is possible.  In all honestly I did not expect this test to be successful.

Simpler 481THz beacon TX

This afternoon I built a simpler CW/QRSS3 beacon for lightbeam experiments. Rather than use a crystal divided down in a 4060 IC I simply used my K1EL keyer IC's sidetone output to drive an IRF640 which drives the 1W LED. 10wpm CW or QRSS3 beacon message is therefore produced on an 800Hz subcarrier. The stability of the sidetone from the PIC keyer is quite sufficient for QRSS3 although not good enough for QRSS30 or 60.

Homemade 45rpm disc recording

Handmade disc recording made on a coffee tin plastic lid

Whilst clearing out a cupboard the other day I chanced upon a piece of my history in the form of a small 45rpm disc recording that an old school friend and I made in 1969. Using an old record turntable with a very large horn as the acoustic microphone we recorded me saying some words and poems onto the polypropylene lid of an old coffee jar. Shouting VERY loudly, the sound is imprinted onto the disc in just the same way old gramophone records were made back in the 1800s. The metal foil inner lids of cocoa tins were also quite good for this as I recall. Francis Wood, my school friend went the whole hog and put the record into a homemade sleeve (with suitable handwritten text) with inner cover and the disc finally inside. I did play this disc some years ago and it was still intelligible (just) but nowadays I have no 45/78rpm kit to play it on. I remember the first time we made such a disc back in 1962 how amazed I was that it worked.

Cambridge Club Talk - a good turn-out

This evening I gave my talk "VLF Amateur Radio" to the CDARC in Cambridge. The turn-out was excellent, especially considering the very cold weather here at the moment. It was -10deg C coming home in the car.  At the end of the talk there were plenty of interesting questions. It was fun to share my enthusiasm for VLF things with such an appreciative audience. Click on the link if you'd like to see a copy of the slides I used this evening.

Reliability of radio gear

Tin Whiskers on an IC contact

When I mentioned the eHam review of the KX3 on the GQRP reflector last night most of the replies focused on the reliability of complex modern electronics equipment. Some people believe that with fewer parts and SMA components reliability is higher today than in earlier times. Others, including me, were more circumspect and feel that, unless production processes are well controlled, the danger of failure is higher. There are also potential issues with leakage in small geometry ICs as well as the dreaded "tin whiskers" issue where metal dendrils can grow over time between IC balls. My own experience in mobile radio design and manufacture may have coloured my views. We got it right in the end i.e. getting production processes well honed, but you cannot take process control for granted, ever. The slightest drift in quality can spell disaster, field failures and a ruined reputation.

One thing many people agreed on was this: if you want to be sure of the reliability of your amateur radio equipment then build your own. A simple QRP transceiver, easy to make from many published designs in QRP books, should last a lifetime and will be easy to fix in the unlikely event of something going wrong. There is also nothing quite as satisfying as making contacts with something you have built. Even a simple crystal controlled TX and direct conversion receiver are likely to give FAR more satisfaction than a rig costing £1000 with all the bells and whistles. I still recall the thrill of my first ever hombrew contact across the Atlantic with 800mW CW on 15m using my little Pipit transceiver with 7 transistors total and a handful of parts. This rig was so effective that it was my main station rig for many months. Every QSO, and there were lots, meant something special.

KX3 review on eHam

http://www.eham.net/reviews/detail/10271

This is the first ever review of the Elecraft KX3 by one of the field testers using SN-0006 sample fitted with internal batteries and the optional roofing filter. The field tester was mightily impressed.

Optical cloudbounce propagation theory

Bernie G4HJW and I are interested in carrying out some "cloudbounce" tests using our 481THz optical kit and we both are none to clear about the physics of scattering of signals from water droplets and dust in clouds or the sky. However, today a new tool to help our understanding was shown to us on the UKNanowaves Yahoo Group in a posting by Barry Chambers.

The free software is available at  http://www.philiplaven.com/mieplot.htm and allows us to work out the intensity of a scattered optical signal as a function of scattering angle, droplet size and wavelength. Scattering is best when the angle of incidence is at grazing incidence and the droplet size is small. If I've understood the results correctly, aiming at the underside of a cloud at 45 degrees would result in a scattered signal some 50dB weaker than if at grazing incidence. So, depending on how far apart the 2 stations are and the angle at which the optical signal hits the underside of a cloud then signals can be quite strong or extremely weak. This is why weak signal modes like QRSS60 may be needed to work a given path by cloudbounce.

A novel QRP power source

FreeCharge 12V is a small, portable generator, similar to that used in portable hand-cranked torches. The output is regulated to give 12-14.2V DC although the product datasheet does not state the available current. I suspect it is in the low milliamps as its main use appears to be to power/charge mobile phones in an emergency.

This could make a novel power source for low power QRP transceivers as no batteries would be required, just a few seconds or minutes of cranking.  Figures given are 360 turns (approx. 3 min wind) gives 9-11 minutes of mobile phone talk time and a 60 second wind gives 2-4 minutes of talk time. Price is £19.99 and it is available from Freeplay or via Amazon UK.

The sales blurb says:

"The Freecharge 12V provides emergency power to a mobile phone, PDA, iPod, GPS receiver, or any other electronic device for which you have (or can get) a cigarette-lighter adapter. Wind its hand crank to generate electricity and put power straight into your device. Never be unable to use your mobile phone, or other important device, just because its battery has run down."