VLF E-field probes compared?

Both the PA0RDT and DK7FC E-field probes antennas are suitable for detecting weak VLF amateur signals around 8-9kHz when used with the right PC software. See https://sites.google.com/site/sub9khz/antennas for the schematics of these and others.

What I'm wondering is has anyone done a "like-for-like" test to compare their performance? With a near identical test set-up (same height above ground, same ground and PSU noise conditions) it should be possible to compare noise floor, sensitivity (S/N of Alpha beacons, VLF MSK signals), and by looking for the intensity of the intermod line at 9kHz from broadcast signals in Europe get an indication of dynamic range. Has anyone done this test at VLF? If not, it looks like I shall have to do it and "suck it and see".

Incidentally, the PA0RDT voltage probe antenna makes an ideal antenna for shortwave, medium wave and long wave DX SWLs. It is essentially a high dynamic range wideband receive antenna which is tiny, yet capable of excellent results if mounted in the clear in a low noise environment ideally away from house electrical interference.

More optical tests looking for elusive GB3CAM

This evening, thinking it would be a good opportunity to look for the GB3CAM optical beacon (yet again) I took the trip to nearby Nine Mile Hill (32km from the beacon) with the kit recently used to detect G4HJW's Phatlight beacon over the horizon at 8.6km. My RX is now pretty sensitive. However, I failed yet again to detect anything of GB3CAM. Actually it was a little hazier than my first tests (when I had sensitivity issues) but I was disappointed not to detect a thing. All I managed was a chat with the farmer in whose field gate I'd set up my optical kit and PC: he seemed happy with my explanation.

I've asked the beacon keeper if the beacon was actually on-air - it could have been off I guess. 

My other question of Bernie G4HJW, the beacon keeper, is what the ERP of the GB3CAM beacon is compared with his phlatlight beacon at home that I'm consistently able to copy at 20-30dB S/N in 0.17 - 0.67Hz bandwidths non line-of-sight, whereas I've so far been unsuccessful receiving the Wyton optical beacon line-of-sight. At 32km haze will matter more and it may just be that on the occasions I've tried I've either had insensitive kit or poor optical conditions. I did try very carefully scanning the horizon this evening after sundown for a good 15 minutes without detecting a thing and I had a very good idea where to aim.

160m WSPR this evening

If JT65 is hard going on 160m this definitely cannot be said about WSPR: having switched on just a few minutes ago I am seeing and have been seen by plenty of stations in northern Europe with my 5W to the tiny loft vertical.

MSF 60kHz off air until April 6th

If you use the 60kHz LF signal from MSF Anthorn to lock your frequency reference or digital watch you may have a problem for a couple of weeks: it is off the air!  It is scheduled to be off air until 20:00 UTC on April 6th. See http://www.npl.co.uk/science-technology/time-frequency/time/products-and-services/msf-outages.

PA1B's QRPp website

Bert PA1B has an excellent website describing his experiments with very low power on HF. Using his FT817 with various simple attenuators he has been able to work some remarkable DX with powers ranging from 1mW to 500mW. His website explains how he has achieved this. It is an inspiring page showing just what is possible.

QRP JT65 to HB9 on 160m with indoor antenna

Just seen that HB9FX has copied my 160m QRP JT65 signal at -24dB S/N. Still finding it hard to make 2-way QSOs with this mode on 160m, but it proves the tiny indoor loft vertical antenna is radiating OK. Best DX report on JT65 is still the SP station about 10 days ago at over 1000km.

10m DX

This evening there were some interesting west African stations coming through on 10m.  6V7Z in Senegal on SSB and J52HF in Guinea Bissau on CW. I did not try to break pile-ups with my QRP and instead worked CT9/DL3KWR on QRP CW. Following this I moved down to 12m and worked N1WPU on CW also with QRP.

First ever 2-way international ham QSO on VLF

From Marcus DF6NM via the RSGB LF reflector earlier today:

"Today between 7:30 and 14:00, Lubos OK2BVG and I successfully completed a two-way contact on 8.97 kHz. We believe that this is the first international QSO ever on VLF.

The distance between Breclav (JN88KS) and Nuernberg (JN59NJ 69es) is approximately 424 km. The weekend before, Lubos and I had found that we could see each other's VLF transmissions from our small home antennas in a slow spectrogram, using about 0.45 millihertz FFT resolution ("DFCW-6000"). This long integration requires about 2000 seconds of continuous non-interrupted carrier to reach full sensitivity.

We decided to use absolute frequency encoding of characters ("MFSK-37" mode), which has a simple structure but is significantly more efficient than two-frequency DFCW. The software signal generators in SpecLab were used to create 30 minute dashes by editing the frequency in 1 mHz steps every half hour. This can be automated by opening a textfile which is read by the "periodic actions" function. Between transmissions, additional half-hour gaps were inserted to let the FFT ring down, and allow for TX-RX reconnections.

Characters are identified by reading the frequencies above 8970.000 Hz, with 8970.000 to .009 assigned to the numbers, .010 idle or space, and .011 to .036 the letters A-Z. Lubos used a Rubidium standard to lock his transmit samplerate, while both receivers and my TX were synchronized by military MSK signals from GQD (22.1 kHz) and DHO (23.4 kHz).

With about 80 watts from an audio amplifier, I could get up to 0.38 A antenna current into my top-loaded vertical 9 m above the roof, radiating on the order of 10 to 15 microwatts. I believe that Lubos is using similar equipment, perhaps a couple of dB stronger. For receive, my soundcard was connected straight to the loading coil and antenna, whereas Lubos has an active probe at a quiet site remote from his TX location.

We wanted to go for a "full QSO" format with reports and confirmations, beyond the rudimentary three-dash "micro-QSO" format which was used in June 2009 between DJ2LF and myself. With single-letter suffixes, we ended up proceeding as follows:

07:30-08:30 "NB" ;Lubos' call: df6Nm de ok2Bvg
09:00-10:30 "BNM" ;my reply and report: Bvg Nm M
11:00-12:00 "RO" ;his confirmation and report
12:30-14:00 "RTU" ;my confirmation and thank you

Although today the noise was not as low as it had been before, we managed to exchange the essential information in 5.5 hours until 13 UT, after which QRN from lightning in southeast Europe became strong enough to obliterate further copy.

Attached image contains captures from Lubos' grabber at Apollons temple (top) and my receiver (bottom), with screenshots from the DK7FC and OE3GHB grabbers pasted inbetween. The original captures are at http://df6nm.bplaced.net/VLF/ok2bvg_df6nm_120325/. All spectrograms were stretched to the same timescale (5 min/pixel). On the left hand side, you can see a MFSK pre-test from Lubos, sending his call to hs own grabber at very low power. There was also a long dash from OE3GHB on 8970.030, and a carrier from DJ8WX on 8970.022 is visible at DK7FC.

The rightmost part of the captures shows the essential eight dashes from our QSO. You can see that I had almost lost Lubos' "B" when my noise blanker triggered heavily on local QRM, inducing me to give an "M" rather than "O" report. But hovering the cursor to 8:15 UT does show the peak at 8970.012 Hz in the spectrum graph. My final "R" is just barely visible at .028, whereas the following "TU" at .030 and .031 ended up drowning in the increasing noise.

During the lowest noise period (9 - 12 UT), the dashes were visible (though not decodable) in 4.5 mHz "600" spectrograms. At that time, our symbols also appeared on Paul Nicholson's spectrogram http://abelian.org/vlf/fbins.shtml#p=1332712800&b=110&s=sp

Thanks again to Lubos for the effort and patience! Although exchanging half-hour symbols is tedious and may sound boring to some, both of us enjoyed it and actually found it quite exciting.

Best 73,
Markus (DF6NM)"

DX reports with JT65 on 10m QRP

This evening I called CQ on JT65 on 10m as the band was closing (I thought) and was surprised to see a couple of reports appear from LW9DC (Argentina) at 11272km. No QSO resulted, but a report of -16dB was quite good with the 5W and halo antenna. A little later I got reports from LU2XPK (13419km) and LU2XPL (13426km). Again no QSOs, just reports from these stations on http://jt65.w6cqz.org/freceptions.html.

VLF activity this last week

Whilst I was away on holiday there was considerable activity around 8.970kHz from Europe with Henny PA3CPM now putting a consistant signal from his small home station antenna on the G3ZJO grabber. Activity is continuing this weekend.

One of my priorities in the next 2 weeks is to get my VLF receive set-up back in full working order as this has been off-air for a couple of months. I will try a new E-field probe this time around and see how results compare with my 80m square wire loop. The PA0RDT or DK7FC E-field probes are well proven designs that work well if mounted high and in a low noise environment. See https://sites.google.com/site/sub9khz/antennas for details. Antenna size is less important than S/N and dynamic range on VLF RX. This is why tiny voltage probe antennas can work so well.

160m WSPR

Just back from a week away on holiday and sorting out things like washing, post etc. So, whilst this is going on I have set the WSPR beacon running with my 5W into the short loft vertical to see what is about.  In the next couple of weeks I have some work to do on antennas in the garden.

Holidays and light

Starehole Bay near Salcombe today

Being on holiday in South Devon at the moment it is a good time to do some walking on the cliff tops in the spring sunshine. Now, most people looking at the beautiful coastal scenes will think, "this is a beautiful view" or "aren't we lucky having such good weather".

So do I, but I find myself looking out to sea and thinking how would a 481THz light signal scatter off waves in the sea? Would my beacon be copyable around the coast by aiming a few miles out to sea and aiming a receiver (located down the coast) at the same spot in the sea? How would my QRSS3 light beam beacon signal scatter off those metamorphic schist cliff formations? 

I need a holiday .....oh, I'm on one!

All for the want of an SMA-BNC adaptor

This week my wife and I are on holiday at my brother's home in South Devon. I don't bring much ham gear with me these days, but I packed my VX2 dual bander and a small mag-mount to erect when static on the car roof.  Packed the rig, charger, several whips, mag mount  ......but I forgot to put in the essential SMA-BNC adapter.

Never mind, there are plenty of things to do instead of amateur radio including seeing the house in Island Street, Salcombe where my dad used to live in back in the 1920s now on sale as a second home for rich bankers at £325k. The house has no views, is tiny, has nowhere to park the Rolls and floods when there is a very high Spring tide.
 

KX3 - more pictures

Some nice shots of the new Elecraft KX3 QRP transceiver at http://www.worldwidedx.com/elecraft-kx3/134267-elecraft-kx3-hands-preview.html.  This rig has still to start shipping nearly 12 months after first announced although the first units should be on their way to happy customers within weeks now. There were some late changes following extensive field testing and some supplier issues.

QRM on VLF?

DK7FC, PA3CPM and DF6NM have all been TXing today around 8.970kHz with reception reports coming in from many of the western European grabbers. DF6NM is running some 20dB less ERP than Stefan yet is appearing on UK grabbers quite well just HF of DK7FC. PA3CPM is a much weaker signal although he has been copied by Paul Nicholson in Todmorden UK. Activity is likely to continue over the weekend. Here is a screen grab from Eddie G3ZJO's VLF grabber today showing 2 of the active stations quite clearly. Notice the timescale on Eddie's grabber: between markers it is 4 hours in his DFCW6000 window, so don't expect snappy QSOs on VLF.

Dropbox Windows Registry issue - NOT fixed!

Having struggled to get Dropbox files sharing working on my main WinXP PC I today did a full uninstall and loaded a new version 1.1.45.exe from http://dl-web.dropbox.com/u/17/Dropbox%201.1.45.exe and I was back in business for the first time in 3 months. Within 10 minutes though, the same "unable to access vital Windows registry data" message reappeared! What the heck is going on???

iPod Touch external audio - success!

Thanks to some input from Robin G7VKQ I have now managed to get an external mic to work with my iPod Touch 4g. He referred me to http://www.blackcatsystems.com/ipad/iPad_iPhone_iPod_Touch_Microphone_Wiring.html which shows that a resistor to ground is needed to make the device recognise the external mic is in place. In the end I found a couple of ways to make the connection work (shown below).

When used with the Spectrum View app from Oxford Wave Research I was able to connect my lightbeam receiver to my iPod Touch 4g and record QRSS3 and CW transmissions. This is 10wpm CW being received at home between rooms by scatter in broad daylight.

iPod Touch 4g repair video

Ever wondered how one would go about repairing an iPod Touch 4g if one went wrong? I chanced upon this video describing how to disassemble it. This Apple device is quite remarkable as it does so much in such a small space and having seen just how it is constructed inside I am even more impressed. However, even having seen this excellent video I think it is beyond my skills to repair it if it went wrong.

iPod Touch, SpectrumView and external mic input

A few days ago I mentioned SpectrumView as being a very useful package for the iPhone and iPod Touch 4g for audio measurements and spectrum analysis. Well, I've now got a 4 pin jack plug and wired it up (according to the best published data I can find) as an external mic input. To my great disappointment nothing happened and the internal mic was still being selected. I am wondering if something has to be asserted to select the external mic input? Anyone know please? What did I do wrong? The ring nearest the jack body is the mic input and the next ring down is supposed to be the ground. I checked the plug was correctly wired. Help!

New personal DX record on 160m JT65

SP3CUG has just spotted my 5W QRP 160m JT65 signal from my tiny loft antenna at a distance of 1063km. This beats my best DX so far (a report at 1007km from SM on WSPR) on 160m using the small indoor antenna. I cannot see him TXing which is a pity as he may be able to work me.

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.