Saturday, 30 August 2014

630m Trans-Pacific WSPR


Courtesy: https://www.google.com/maps/
It looks like the new 630m band may hold some surprising opportunities once the winter DX season is upon us. A recent posting to the down-under 600m Yahoo Group by David (VK2DDI) in New South Wales, Australia, set off a flurry of excitement when he announced his August 25th (0950Z) reception of the 475kHz beacon signal from WG2XIQ, operated by John (KB5NJD) near Dallas, Texas.

This is particularly noteworthy in view of the relatively low power used for John's beacon....around 200W. With the typical backyard antennas being used at these frequencies, efficiencies are very low and John's actual ERP is less than 5W. The transpacific reception of John's signal by VK2DDI confirms what most LF'ers already know....that small suburban lot amateur installations can have positive results on 630m without the need for huge antenna systems.

The WG2XIQ beacon was operating in the WSPR mode, which has become very popular amongst 630m experimenters as well as those just interested in listening-in. WSPR is not a QSO mode but strictly a one-way 'beacon' mode. Although two stations may each spot each other, it is not considered to be a valid two-way QSO. A check of evening  WSPR activity will often reveal dozens of stations actively spotting what they are hearing.

Like most LF stations, John's is mostly homebrew.

WG2XIQ/KB5NJD

I'll let him describe the details:

"I have a few ways of making RF in the shack. I can do CW with a very nice waveform using the GW3UEP VFO/Driver coupled with a GW3UEP 100w amp with waveform shaping. The other way is via the MF Solutions transmit downconverter, developed by John Molnar, WA3ETD/WG2XKA. I have two of those boards, one is a backup. I use a GPSDO for the LO and use that signal to drive two parallel GW3UEP amps with max power at 125 watts each. The W1VD Ø degree hybrid combiner brings them together in phase for close to somewhere between 200 and 250 watts TPO depending on how hard I drive and how close I match the TX levels entering the combiner. I filter the output with the W1VD KW LPF that was built by Dave Robinson G4FRE (ex WW2R). I power the amps with a pair of BK Precision 30V 6Amp variable power supplies (variable current limit threshold also). Scope match is used to resonate and match the the impedance. IF Rig on 630m is typically a Yaesu FT920. These days RX antennas are the VE7SL multiturn loop or the TX vertical, both of which have their own merits depending on the conditions at the time."



John's 630m Vertical




"Antenna is an 80 foot asymmetric T-top marconi with 100 foot and 200 foot legs....radial system is almost 3 miles of radials connected via various busses. 26 ground rods around the property. I monitor current in the shack and sample via a Bauer current transformer from an AM BC ATU."


630m Radial System

630m Antenna Loading Coil & Variometer
"As far as my system is concerned, I am the poster child for "If I can make it work, anyone can!" 

John's system does indeed work well...just last year at this time, his 630m signals were copied by KL7L near Anchorage, Alaska.

Of course, equal credit must be given to VK2DDI for having a system good enough to hear John's signal all the way down on Berry Mountain, New South Wales, Australia! It is there that David has set up a fine LF station, 500m above and overlooking the Tasman Sea...an ideal location for weak-signal LF work.

VK2DDI - Berry Mountain, NSW



David's receive antenna at the time, feeding and SDR-IQ receiver, was a simple non-resonant 90' vertical wire, with no ground radials and no tuning. It seems that the old real-estate adage, "location, location, location", can also be applied to LF reception!

 
WG2XIQ Signal As Heard in VK
David's screen capture of John's WSPR signal, although very weak, is clearly visible at 09:50 and apparently, strong enough for a solid decode.
David also runs the Berry Mountain Grabber, providing other VK and ZL experimenters a handy way of checking their system progress or propagation conditions.

If you have been doing any WSPR work on HF, you might be surprised at what you can hear down on 630m, even without a dedicated antenna for that band. Surprisingly good results can often be had with a non-resonant antenna as the signal to noise ratio can often be better even though signals may sound weaker. Give it a try and spot what you hear!

If you are interested in learning how to receive WSPR, here is a nice tutorial by ZS6SGM. 

Should you be interested in knowing more about obtaining a Part 5 licence to transmit on 630m, John will happily guide you through the process. He can be contacted via email or you can find him hanging-out most nights on the ON4KST kHz (2000-630m) chat page.

To keep on top of what is happening or who is on-the-air, most LF'ers rely on three sources:


Radio amateurs in Canada have had 630m as an amateur band since May of this year but unfortunately are not allowed to contact any of the experimental stations. Hopefully the U.S. will also obtain 630m as a ham band some time soon. In the meantime, a Part 5 licence for any U.S. amateurs would be a good way to be  all set when that day eventually comes!

Thursday, 28 August 2014

Alaska's NDBs Awaken!


Courtesy: http://www.alaskacooling.com

This past weekend saw another of the monthly "Co-ordinated Listening Event" (CLE) activities sponsored by the Yahoo ndblist Group and organized by Brian Keyte, G3SIA. This is a group of dedicated low frequency NDB DXers that enjoy hunting down new catches as well as keeping track of NDB activity in general. These low powered beacons make excellent propagation indicators and are always a good measure of one's LF receive capability.
As often happens, the monthly events seem to coincide with poor propagation periods for some unexplainable reason, as was the case once again. As well as the generally poor propagation, North America was plagued with high levels of lightning activity making any weak signals very difficult to hear through the steady din of QRN.

In spite of the poor conditions, two nice catches from Alaska (ELF and TNC) heralded the fast receding midnight-sun in the 49th state and the start of another Alaskan NDB DX season!

The NDB at Cold Bay is 'ELF' and transmits on 341kHz. Cold Bay is located on the Alaskan Peninsula, at the top of the Aleutian chain.


Courtesy: http://pics3.city-data.com

Built as a military airfield in WWII, Cold Bay's traffic is now mostly cargo and its long runway serves as an emergency 'alternate' for flights in the north Pacific.

A search of Google Maps shows the NDB itself is located several miles north of the airport and appears to use a large vertical and an extensive ground system. With the transmitter power listed as 1000W, ELF makes an excellent target for DXers looking for their first Alaskan NDB.


Source: https://maps.google.ca

The NDB at Tin City is 'TNC' and transmits on 347kHz. Tin City is located in northwest Alaska next to the Bering Strait and, unlike most places in Alaska, you really can 'see Russia from here!' The airfield is not open to the public but is owned and operated by the USAF and used to support their long-range NORAD radar facility northwest of Nome.

Source: https://maps.google.ca
TNC is located right at the airfield, west of the gravel runway. Although the power is not indicated, I suspect it is running more than the typical 25 watts as its signal is often fairly good copy, as heard here early one morning.

Like 'ELF', the antenna appears to be a vertical but possibly of smaller size.


Source: https://maps.google.ca
If you are listening for these targets, remember to tune with your receiver in the narrow-filter CW mode and listen for either the upper or lower sideband keyed modulation tone.

For ELF, listen on 342.030kHz or 339.968kHz. The carrier will be on 341.0kHz.

For TNC, listen on 348.034kHz or 345.968kHz. The carrier will be on 347.0kHz.

For a list of all active NDB's in Alaska, complete with accurate frequency-spotting information, visit the beacon-reporting RNA website. Put 'AK' in the 'States' window and pick 'All Results' in the 'Show' window. There are presently at least 60 or more NDBs known to be operational in Alaska.

As mentioned before, please exercise caution should you decide to jump-in...chasing NDBs can quickly become addictive as anyone in the 'ndblist' Yahoo Group will tell you.

On the other hand...Alaska is waiting!

Tuesday, 26 August 2014

'CQ Crossband' - 630m

 
First 630m contacts
In early May, VE7BDQ (John) was my first contact on our new 630m amateur band! Soon after, I had QSO #2, with VA7JX (Jack), on Vancouver Island. So far there appears to be only one other station in Canada on the band... VO1NA in Newfoundland!
 
Where are the rest of the Canadians? It's not too late to be the 1st VE6, VE5, VE4, VE3, VE2 or VE1 on the new band!

Hopefully there will be more stations active before the winter DX season gets underway!

In an attempt to keep my own interest level up as well as  trying to get the word out to others about our new band, I've completed crossband contacts with three other VE stations. Two of the contacts were on Vancouver Island....VE7DAY (John) in Campbell River and VA7FC (Perry) in Courtenay. The third station was VE6TA (Grant), near Edmonton, Alberta. A fourth crossband contact was completed when I worked W7WKR (Dick) near Lake Chelan in Washington state. John, VE7BDQ, also completed crossband contacts with VE6TA and W7WKR giving those two stations a 'VE7 two-fer'.







Both John and I would love to do a lot more crossband work, especially with stations in the U.S.A. who presently cannot transmit on the band but may still be very much interested in 630m. A recent overnight beaconing session at 25 watts output clearly indicated that under fairly normal conditions and with a good receiving system on 630m, my normal speed CW signal can cover a wide geographic area during the hours of darkness. Having up to 500 watts of power available for CW, my signals should have good coverage to all of the western and central states at this time of the year.

Such crossband type contacts are perfectly legal between any and all stations in the "amateur radio service" and at one time, this was the only mode available between Europe and North America on the 50MHz band, as this tantalizing review of Cycle 19's amazing propagation explains.

If anyone, anywhere (both U.S. or VE), would be interested in attempting a crossband CW QSO, I would love to try! Please contact me via the comments section below or via e- mail.

I would also be interested in hearing from any Canadians who are planning to get on the new band as I am trying to keep track on my website's LF page.

Sunday, 24 August 2014

On Making Nanowaves - Part 6

After several weeks of reading, planning and homebrewing, both the transmitter and the receiver boxes were finally finished....at both ends of the path!


After the transmitter and the receiver had been accurately focused (the receiver's photodiode at the fresnel's focal point and the transmitter's secondary lens properly positioned) both enclosures were screwed together and mounted on a tripod.



Markus, VE7CA, had checked-out a suitable location not far from his home QTH on the road to one of the local ski-hills. This gave him an unobstructed view to my location on Mayne Island, about 54km to the southwest. I had planned to set up in my front yard, about 15' above sea level and on the eastern shoreline with a direct shot to Markus.

Even though we were using LEDs rather than lasers, I still felt somewhat uneasy as our path crossed directly over the runways at Vancouver International (around the path midpoint) as well as the main ferry lane between Vancouver Island and the B.C. mainland. Considering the distances involved, I probably need not have worried as the light, although bright, would cause no physical harm other than possible momentary distraction or curiosity. If one of the ferries had been approaching the path, I had planned to shut down until it had passed as it would have been hard to convince authorities that the light really was not a laser, before they carted me away!

After waiting for the usual winter B.C. rain to subside, we finally had a promising evening shaping up, although somewhat cold. Markus, accompanied by Jim, VE7BKX, loaded his vehicle and headed for the mountains. With neither of us having 2m portable radios, we somewhat guiltily reverted to cellphones to announce setting-up status.

VE7CA/7
Shortly before dark, I aligned my light boxes to point at what I was pretty sure was Markus's location and turned on my FSK beacon.... the bearing was taken from Google Maps and alignment aided by my I-Pad's Commander Compass Lite app. The plan was for Markus to sweep until he (hopefully) heard me and then turn on his beacon so that we could then both tweak our final alignments.

Almost immediately I heard his beacon signal although there was no visible sign of his light.

Before final alignment I made a quick recording of his signal.

Neither if us had any real idea of what type of signal strength to expect and we were both very surprised to hear how strong the signals were. Once we had both aligned and our lights were now visible, we switched to CW mode and proceeded to work each other in typical QSO mode.

Hear is a recording of Markus sending my RST report.

Signal reports as well as grid squares were exchanged just to make everything 'official'. We then settled into a nice twenty-minute ragchew until the cold winter air took its toll on our fingers forcing us both to close down and pack up for the night.

Markus grabbed a short cellphone video from his end which shows the still fairly bright twilight skies and the LED signal source:


Earlier, John (VE7BDQ) had made the decision to not build a transmitter as he preferred not to go portable. Both of us were interested in pursuing a possible non-line-of-sight (NLOS) path by using either 'cloudbounce' or 'clear-air scattering' which would allow John to set up in his backyard. The path between us is much shorter than the VE7CA/7 path as can be seen in the map below:

Courtesy: https://maps.google.ca/
To date we have made one test at this mode, trying various takeoff angles at my end, but cloud conditions were not optimal, and as yet, I am not totally certain of what type and height of cloud would be best. Perhaps we should be looking for the typical very light fog that often forms over Georgia Strait for enhanced water molecule scattering? As well, I think our best chances for success would be the slow speed QRSS mode, possibly QRSS3 or QRSS10 which could offer as much as 20db signal gain over normal speed CW.

For one-way beaconing, I plan to add a more accurate crystal-controlled tone module so that my CW signal's frequency is precisely known and can be watched for in the very narrow bandwidth window of Argo or Spectran over a given period of time. Even at these slower speeds, QSOs exchanging the minimum required information can still be made relatively quickly. Hopefully any reception at all of my signal at John's location will excite him into building a transmitter as well. Completing a two-way contact using the NLOS mode would be a very interesting challenge.

In the meantime, Markus and I have been seeking out possible new locations for his remote work, using "HeyWhat'sThat Path Profiler" web site. This site quickly indicates the distance and headings between any two points and draws a geographic contour of the path showing any obstructions.

Courtesy: http://www.heywhatsthat.com/profiler.html

Markus hopes to get out to one such favourable location in the Fraser Valley mountains, before the weather turns nasty once again.

If there is anyone in the Vancouver lower mainland region that might be interested in building a lightwave station to join us in the fun, please do not hesitate to make contact with any of us...we would love to hear from you!


If you are a member of the Radio Amateur's of Canada (RAC) and receive their 'TCA' journal, please watch for our upcoming article in September's issue..."A West Coast Lightwave Project".

Friday, 22 August 2014

On Making Nanowaves - Part 5

With the fresnels in hand, a pair of plywood box enclosures were built...one for the receiver and one for the transmitter. Eventually they would be coupled together so that both would be pointing at the same distant spot.



The next step was to use John's design to mount the receiver and transmitter modules so they could be locked into position once aligned properly. His system used the 1/4" split shaft locking mechanism removed from an old Allen-Bradley potentiometer to hold a short length of rod fastened to the module's case.







This allowed the shaft to be moved forward and backward for focus while the slot in the mounting plate allowed for vertical centering. The plate mounting mechanism itself allowed for lateral centering. This system allowed for the locking of the receiver's photodiode at the exact focal point of the fresnel lens.The same scheme was employed for the transmitter's LED as well, since accurate focusing was critical there also.







In order to focus as much of the LED's light onto the primary fresnel lens, a small inexpensive (secondary) collimating lens was required. This assured that the fresnel was properly illuminated out to its edges and no further. Any light spilling over the edges of the fresnel would just be wasted.


Our particular fresnel had an effective aperture of 260mm and a focal length of 200mm, producing an F-number (f/D ratio) of .76.... Clint suggested that our collimating lens should have an F-number of ~ 1 - 1.2 and be a PMN (Positive MeNiscus) type and that we hedge our bets by trying lenses above and below that value. Ideally the collimator should be at least 25mm in diameter for ease of mounting and, when perfectly illuminating the fresnel, be as close to the LED as possible, if not touching it. Just placing a less than ideal secondary too close to the LED would end up over-illuminating the fresnel, while having it too far away would under-illuminate it.

Accordingly, four small glass collimating lens of various F-numbers were purchased from Surplus Shed at around $4 each. Each lens was then mounted on a drilled-out piece of PCB material using 'JB Weld'.


Once cleaned-up, the lens board was then positioned directly over the center of the LED on a machine-screw carriage mount. The carriage allowed the lens to be locked into position once it was correctly positioned. All four lenses were tested to see which one would correctly illuminate the fresnel while still being as close to the LED as possible.







The eventual winning secondary lens was #L10016 (.9 f/D) which allowed for a sharp and fully-illuminated fresnel while being just a few millimeters above the LED.



The next step was to adjust the entire LED and secondary carriage for the sharpest focus on a distant flat surface. This was done over a distance of about 200' and was a fairly fine adjustment.


Once done, it was actually possible to see the two fine wires connecting to the LED die on the distant projected image.


With the final focusing taken care of, the tone modulator and MOSFET LED driver were installed. This used an IRF540 switching FET, driven by the digital tone signal to control the current through the LED.


All we could do now was patiently wait for a nice clear evening to put the system to work.

Wednesday, 20 August 2014

On Making Nanowaves - Part 4

Researching suitable LEDs for our lightwave project forced me, once again, to the bottom of the learning curve. Like the variety of photodiodes being used in simple lightwave systems, there were a myriad of LEDs experimentally lighting up the skies both in the UK and in the U.S.

It seemed that the present flavor-of-the-day in terms of LEDs was the Luxeon III, a 3W / 1.4A device being produced by Phillips.....or rather.....was being produced. Apparently our new found interest in lightwave communications had been coincidental with the retirement of this popular LED and all stock had been depleted! Although still available in some wavelengths, there were none in the desired 'deep red' portion of the spectrum that we had chosen for our system.

Courtesy: http://www.luxeonstar.com/luxeon-rebel-leds


All was not lost however as a 'replacement', largely untested by the lightwave community, spec'd-out at a lower power but with a somewhat more efficient design. The new device was the Luxeon 'Red Rebel' and rated at 700ma. ....apparently no slouch at all.




I had also been watching the various offerings available on e-bay which provided a number of tantalizingly inexpensive options. Many of the LEDs from China appeared to offer good promise and may well be good performers, but most appeared to be lower-quality knock-offs of the name-brand models.

These higher-powered LEDs, on close examination, usually contained two or more separate LED die behind the lens. A single light source is required to achieve maximum focusing / lens illumination efficiency and although tempting, should probably be avoided. 'Safe' names to look for include Philips, Osram and Luminus and often, bargains can be found on e-bay when NOS is being disposed of.

Like most 'power' LEDs, the Rebel needs to be mounted on a heatsink otherwise catastrophic destruction would be immediate. The usual method of heatsinking is to attach the LED (by solder or adhesive) to a copper star-shaped interface which is then fastened to a small heatsink.






Courtesy: http://www.luxeonstar.com
 
The interfaces can be purchased separately but soldering the LED can be challenging without overheating it. They can also be fastened with JB Weld and enough pressure to ensure a firm bond without damaging the LED. An easier alternative is to procure the LED already mounted on the interface as shown here.








Once adequately heat-sunk, voltage can be applied to the LED after taking measures to limit the current to safe levels. Although these LEDs are very small, they emit an exceptionally bright light and must be treated with care. The Rebel is shown here, shortly after first applying voltage. The current in this test was just 100ma. Although they are rated at 700ma, I have run this one up to 1A without failure but it is normally run at the rated current.

Luxeon Red Rebel at 100ma.
The next task was to tackle the 'antenna' which, in a lightwave system, is the lens. Many of the UK amateurs were having good results with inexpensive 4"-5" magnifiers mounted inside ABS or PVC tubing. The remainder, and those in the U.S., were using plastic Fresnel lenses mounted in homebuilt plywood boxes of various designs. Clint's (KA7OEI) website contains a vast amount of valuable hands-on info describing the latter and we chose to go via that route.

Like the large variety of both photodiode and LED selections, fresnels were no different. Once again there was a lot of information to digest while learning about the various types. Eventually, John, Markus and myself each purchased two plastic fresnel lenses from 3DLens in Taiwan. One would be used in the receiver box while the other was for the transmitter. These were 26cm square lenses, model A260.

Unfortunately I no longer see these particular lenses being offered....hopefully it is only a momentary depletion of stock. There are many different sizes and types of fresnels out there....some if them perfect for this type of use and others not so good, so think carefully before buying anything and know what you are getting. Studying Clint's pages regarding fresnels will help immensely.

Things to pay attention to are the focal length and groove 'pitch'. For a typical 10"-12" lens, look for something around 10-12" focal length, otherwise the mounting enclosure will get too deep and awkward to handle. Front surface 'groove pitch' should not be too fine...something around .5mm is good but our finer (.2mm) seemed to work well also.

Now that the LED had been mounted and the fresnel lenses were in hand, the next task would involve the focusing mechanism and alignment. Thankfully John had devised a smart method for mounting and adjusting focus a few weeks earlier, when we were still working on receivers.....

Monday, 18 August 2014

e-Bay PCB Thermal Transfer Paper

This past weekend I had the first opportunity to try my e-Bay purchased thermal transfer paper. It was to be used in my iron-on PCB work as a hopeful improvement over what I had been using...just ordinary printer paper. Supposedly the shiny photo quality papers were proving to be good performers but are expensive. Some have reported good results with glossy magazine paper but my one experience with that was not a pleasant one. Unknowingly, when I had removed the magazine page, a small amount of the sticky adhesive used in the binding process was still on the sheet. Running it through the printer caused it to melt and smear some of the laser cartridge's toner and for the next several weeks, any printing I did had a slight black streak along one edge...doh!

My new paper from China (free shipping!) was pretty inexpensive and if it offered even a slight improvement, would be well worthwhile. This first use of the paper would be a circuit board for my earlier test-bed GW3UEP 630m transmitter. I had finished designing a PC pattern for it, using MS Paint, and was anxious to see the results.


Courtesy: http://www.gw3uep.ukfsn.org/
I decided to use a small separate board for the crystal oscillator-divider so at a later time I could more easily swap it out for a DDS driver. Using a separate board would allow me to do that without disturbing the rest of the transmitter.



I know that a lot of folks turn up their noses at MS Paint but I have always found it to be a very versatile piece of software and have used it for making PC layouts for many years. I also use it for drawing all of the schematics appearing on my website.

After printing the pattern (printer set for maximum resolution and darkest print) and ironing-on the pattern , I allowed the board to cool for several minutes before immersing it, along with the now firmly attached yellow paper, into cold water. The first thing I noticed was how easily the paper came away from the board. It actually 'un-peeled', much like a good quality price tag sticker...you know.... the ones that don't take forever and come off in tiny bits and pieces. It peeled off smoothly with no paper residue left on the board. This was a huge improvement already. There were just a few traces of toner left on the paper as almost all had been transferred to the board.

Once dried, a close examination revealed that I had pressed a little too hard with the iron and there was some evidence of  'squeeze-out' along the edges of some lines. I also found one or two very small thinner areas that probably required going over with a permanent-ink black marker pen just to make sure that those spots did not get etched. Over all I was extremely pleased with the paper and will be using it from now on.

Another recent change in my PC etching regime has been a switch from the old Ferric Chloride standby to a combination of Hydrogen Peroxide and Muriatic acid. Not only does it seem to etch more cleanly (no undercutting) but it also etches very quickly and without any solution warming needed. This board was completely etched in just over 4 minutes.
  

The chemicals used in this method are inexpensive and are readily available at the drugstore and at the hardware store. There are numerous web-descriptions of this particular etching process but this site seems to cover the basics nicely.


The completed board turned out as shown here:


The CD4060 not only functions as a crystal oscillator but also as a versatile frequency divider. As well as fundamental frequency output, ten different 'divide-by' functions are available depending in which output pin is chosen. These range from divide-by 16,384 to divide-by 16. This circuit uses the latter, dividing the 7.6 MHz crystal down to 475 kHz at pin 7.


In summary, I can highly recommend the e-Bay yellow thermal transfer paper when used for this method of making PCB's and is much cheaper than buying photo-quality printing paper.

Saturday, 16 August 2014

On Making Nanowaves - Part 3

Having studied many of the receiving systems being used by others, it seemed that designs ran from the 'very simple' to the 'very sophisticated'. Once again I looked to Roger's experimental work involving receivers since the one he had been using had evolved over a period of several months and several tweaks. The design that he used was an adaptation of the original low-noise PIN diode laser receiver designed several years ago by K3PGP and shown here on K3PGP's Experimenter's Corner.

Roger's adaptation, shown below, appeared to be getting excellent results when used in his over-the-horizon clear air scattering tests.



Although Markus, John and myself all built the same design, it is interesting to see the end results, as each used a different construction method.

John chose to use perfboard and point to point-to-point wiring:

VE7BDQ's Perfboard RX
I built mine on a PCB....

VE7SL's PCB RX
...and Markus used 'dead-bug', also known as 'ugly construction' style, the preferred method of most scratch-build homebrewers:

VE7CA's Dead-Bug Style RX
I made a couple of small changes and used a 2n5457 JFET in place of the MPF102 as well as some 2n5089's in place of the 2n3904's. I think Markus swapped JFETs as well and used 2n4401's for the bipolars, while John built a stock version of the receiver.


All of us used the Osram BPW34 PIN diode for the detector after having it recommended by Clint in e-mail 'detector discussions' as being a good performer . It is still readily available from the usual places, at around eighty-cents.

BPW34 Spectral Range
The BPW34 turns out to be sensitive over a fairly wide range of frequencies. At our frequency of interest (deep red) at the edge of the IR range, the detector is operating at about 65% of its peak performance which is lower and well into the IR range.


Many silicon PIN photodiode detectors are available with filters that let them achieve maximum sensitivity at the lower IR range while blocking the unwanted higher frequency visible light sources. Such is the case with this one, available as the BPW34FA. If you wanted to run an all IR system, reducing visible light QRM, this detector might be a better bet.


BPW34FA Spectral Range






When it comes to diode detectors, there are always  new challengers appearing in the marketplace. There are still many opportunities for experimenting when it comes to optimizing the front-end of your receiver.









When coupled with its focusing lens in the final stage of construction, the receivers are amazingly sensitive. Even the slightest hint of a light source, often invisible by eye, would produce a response from the system....even starlight!

One of the first sounds detected was a low-pitched and repetitive 'thump-thump' which turned out to be the wingtip strobe lighting of jet aircraft activity approaching and departing Vancouver International Airport. After several nights of listening it was apparent that the strobe lighting could be detected from at least 70 miles out and from aircraft still above 10,000'. Panning over to the runway (about 25 miles away), I could often detect the strobes from departing aircraft even though they had not appeared above my sea-level horizon. Eventually I would see them rise above the horizon, about a minute after hearing them on the runway while on their takeoff roll. I suspect the propagation mode would be a form of clear-air scatter since there was no direct line-of-sight to the signal source when initially heard.

Panning the receiver slowly along the many miles of coastal mainland, on the other side of Georgia Strait, revealed many signals, most of them with different audio signatures. Some sounded rough and buzzy, like an unfiltered CW note, while others were T9 and very clean. Most had different repetition rates resembling radar sweep speeds but, once again, most sources were not visible to my eye...nor were they located when scanning the signal source with binoculars. I suspect that most signals were from various fixed lighting installations either strobe lighting or area flood lighting. Some targets appeared to be slowly moving and were found to be coming from tankers and container ships travelling along the far coast line. Hearing so many of these modulated lightwave signals was certainly an interesting experience and something I had not really expected. Even individual stars would produce a detectable 'hum' as the receiver/lens combination was aimed directly at them.

My one and only daylight test revealed extremely high levels of hum from the bright sky and, no doubt, front end overload desensitising....but the sudden sound of a buzzing bee in the headphones turned out to be just that, as the reflected light from its wings was being modulated by the rapid flap-rate....all very eye-opening to me and totally unexpected.

Here are some recent audio recordings made during a period of heavy cloud cover over Georgia Strait. All are on the far mainland coast or further inland and most sources were not visible to my eye.


    I think such a system would make a wonderful 'science-fair' project for a budding student, complete with recordings....but perhaps it has all been done before!

    For a very in-depth study of various current RX designs, see the Optical Receivers page of KA7OEI.

    With all three receivers working well, the transmitters would be next....

    Thursday, 14 August 2014

    On Making Nanowaves - Part 2

    Now it seemed that up until just a few years ago, most amateur lightwave work had been done using lasers. The UK boys, as well as others, were now using LEDs, whose technology had made huge strides in recent years. The 'non- coherence' of LED light, unlike lasers, offered a distinct advantage when used for communications. Fading and signal dropout during periods of poor visibility were significantly reduced with the non-coherent LEDs when compared with laser light's 'all or nothing' characteristics.



    Courtesy: KA7OEI
     
    As well, the thought of using lasers was somewhat scary in view of the growing amount of negative publicity from frequent reports of irresponsible use....combined with the fact that my path to VE7CA had to cross Vancouver International Airport!



    Shining just a low-powered laser across this region was not something that I felt even remotely comfortable about doing. I felt much better about the project the more I learnt about LED's and of the good results being had by other experimenters.


    Another exceptionally good source of valuable information (and probably the best on the Internet) is the 'optical' page site of Clint Turner, KA7OEI. Clint is an exceptionally gifted engineer-experimenter and is extremely generous in sharing his knowledge with others. As our local project developed over the course of many weeks, we exchanged several e-mails. My numerous questions would always result in very long detailed answers...and precise explanations for the reasons behind the answer or suggestions.

    Clint Turner, KA7OEI

    Just name any radio-related activity and Clint seems to be not only involved in it but has excelled in it. His willingness to share with others is just another example of why our hobby is so enjoyable!


    While still deciding on receiver / transmitter designs, I built a small audio tone generator that would be needed, no matter what type of transmitter was eventually built. The plan was to have some method of making our signals stand out when searching for them in the noise. A distinctive two-tone FSK alert tone was decided upon as it could easily be built using a pair of 555's or a single 556. The final module allowed for three separate modes...an FSK 'beacon' mode, a keyed 'CW' mode and a short 'dash' mode (less annoying than the 'alert' tones).

    
    Modulator mounted on TX
    Here is a recording of the FSK 'beacon' mode in action.

    
    Courtesy: http://electronic-projects.50webs.com/p1.htm
    The base tone was set at about 600Hz since we preferred the lower tone for CW work.
    No doubt there are other methods of building the FSK alert module but the 556 is simple and worked well.

    For very weak-signal CW work, likely involving slow-speed (QRSS) modes in future 'non-line-of-sight' (NLOS) 'cloudbounce' trials, something with a bit more accuracy such as a crystal oscillator divided-down to audio frequencies would be better. Such a system would be very stable and provide a more precise modulation frequency... necessary for the narrow bandwidth viewing windows required for Argo or similar DSP audio viewers.

    With the tone generator taken care of, the receiver was next on the list.