The G3XBM Experimental Blogs

G3XBM's 5W Earth-Mode Tx (courtesy: G3XBM)

My interest of late has been piqued by the ongoing VLF experimental work by several European amateurs.








Recalling that Roger, G3XBM, did some VLF experimenting a few years ago, I have been reviewing some of the excellent hands-on information gathered and published in his ham radio blog and to some of his other VLF pages.

It's not the first time that I have found project-inspiring reading within Roger's blogs. They really are a treasure-trove of useful information, construction notes and accumulated test data gathered from his methodical approach to so many interesting topics ... experimental amateur radio at its very best.

A few years ago I was immediately hooked by his experimental lightwave work, both line-of-sight and clear-air / cloudbounce scatter ... so much so that I also became involved in some lightwave work with other locals who were also inspired by Roger's information, culminating in our own West Coast Lightwave Adventure.

Roger's VLF experiments are also proving hard to resist, especially those of the earth-mode type and I may find myself falling victim to his detailed Sub 9kHz Amateur Radio pages and the Earth Mode pages in particular.

It seems that most amateur VLF work is being done in the vicinity of 8kHz since this part of the frequency spectrum is unassigned. I gather that one can conduct earth-mode tests in any portion of the VLF spectrum since no signal is being 'radiated' as is typically done via antennas. Further investigation remains to see if I need a 'developmental licence' to conduct some radiated (non-earth-mode) experiments in the 8kHz range as well.

Getting a VLF signal from here on Mayne Island across Georgia Strait via earth-mode or via conventional methods would make an interesting challenge and would certainly result in some new homebrewing opportunities.

courtesy: https://www.google.ca/maps

Here on the island, I often hear audio associated with the container terminal and ship-loading operations near Tsawwassen, directly across the strait from here. I feel that this may be aided somewhat by the solid sandstone of the island being directly connected to the other side, so perhaps an earth-mode system utilizing the ocean as one-leg of a buried loop might be an interesting experiment to tackle ... or groundwave transmissions across the ocean via an antenna, to the other side, providing I could find someone to listen.

I see just two Canadian amateurs experimenting on VLF ... VO1NA (Joe) and VA3VVV (John) near Toronto. Any VE3's in the area who are interested in VLF may wish to contact John and exchange notes. He has a Facebook page showing his VLF setup. Interestingly, Joe's 30W VLF signal on 8.270 kHz has just crossed the Atlantic! Joe is documenting his VLF experiments here.

All of G3XBM's VLF blogs can be downloaded for reading or for printing via this link. Similarly, his lightwave experiments can all be found here ... both links will yield several pages of material if you click on the 'Older Posts' link at the bottom of each page.

The best way to follow these is chronologically which requires going all the way to the end of the final 'OlderPost' link and follow along with Roger as he gradually develops, evaluates and improves the gear that he needs to make progress. This is fascinating reading.

But be suitably warned ... you may readily fall victim to his experimental work as well and suddenly find yourself with another exciting project!

Lightwave Madness

The 288 km path  courtesy: REAST

One of the local lightwave builders, Mark (VA7MM), brought my attention to some outstanding lightwave work conducted several years ago, by a group of very dedicated amateurs in Tasmania.

A pair of articles describes their successful attempts to send signals, via cloudbounce, over the astounding distance of 288km (180mi), crossing Bass Strait between the north Tasmanian coast and southern Australia.


What did it take to transmit lightwave signals over such a distance? Basically a system similar to the ones recently employed in our own local lightwave experiments but on a grander scale ... much grander!

The receiver is based on one of the KA7OEI designs, with modifications to increase its sensitivity. The receiver, and several other designs, can be found on Clint's website here, probably the best source of information on amateur lightwave available anywhere.

The lightwave receiver  courtesy: REAST

Although the basic receiver used a typical-sized fresnel lens, what really set it apart from most was the use of a large (10mm x 10mm) Avalanche Photo Diode (APD) for the detector, to maximize the field of view produced by the fresnel and gather every bit of light possible ... at a cost of $1200!

The 10mm x 10mm rx APD courtesy: Hamamatsu

The transmitter was also big, consisting of an array of 60 red Luxeon III LED's, similar to the Red Rebel Luxeons used in our own local tests. Each LED had its own 12cm square fresnel lens, heatsink and method of focusing. Certainly this was a mammoth project, by amateur lightwave standards.

The 60 LED TX array courtesy: REAST

One of the biggest problems when using such a high-gain system, is the difficulty in pointing. They found that aiming in altitude was simply a matter of pointing a few degrees above the horizon but azimuth pointing was much more critical, requiring accuracy to within a half-degree.

Earlier long-haul tests out to 209 km used the digital JT65 mode for signal decodes but the 288 km test used a fairly esoteric weak signal mode called WSC built on the Spectrum Lab software. This mode is capable of digging almost 20 db deeper into the noise than JT65, down to almost -50db.

An in depth description of the two long-haul events, including equipment schematics, can be found in "288 km Cloudbounce from Tasmania to the Australian Mainland" and in "209 km with Narrow Beamwidth Transmitter".

The 288 km crossing project evolved over several years and is all very well documented, from the first early steps, at the Radio and Electronics Association of Southern Tasmania's (REAST) website here.

This adventuresome project was largely the work of VK7MO, VK7JG, VK3HZ and VK7TW. Their work is most inspiring and much can be learned from seeing what they discovered when transmitting into the cloudy nighttime skies.

Such an endeavour as this makes the local, much shorter Georgia Strait crossing, seem like a cake-walk, but I can't imagine using anything that big and bright here without causing trouble ... it would probably appear much too 'laser-like' to talk one's way out of a jam. Pointing anything resembling a laser light into the air these days is simply begging for trouble.

I can however, envision a scaled-down version, perhaps consisting of an array of four Luxeons ... at least on my end of the path, but even pointing one of those from the city could be problematic. Perhaps any NLOS lightwave attempts across Georgia Strait will need to be well away from Vancouver and its two-million sets of eyes.

VE7CNF's Lightwave Cloubounce / Scatter Tests

After our recent lightwave CW QSO, described here, Toby (VE7CNF) has been re-focusing on refining his lightwave system for weak signal non-line-of-sight (NLOS) cloudbounce and scatter mode experiments.

His testing to date has been limited to within his own suburban yard, with the transmitter being set up on the south side of the house and the receiver set up on the north, while basically pointing things straight up.

Several tests have already been done with exciting results, including audible CW being returned from a low (5,000') cloud ceiling and weaker returns noted on clear air scatter but readily detected in the CW QRSS mode. Toby has also interfaced his PC audio, via amplifier and FET driver, to enable him to use WSPR and JT9 modes, resulting in positive signal returns using these two digital modes of modulation.

Toby described some of his results and methodology in a recent e-mail updater:

I've done some lightwave backscatter experiments this last week. The transmitter is on my front deck, pointed straight up as verified using a level across the lens end of the box. The receiver is in the back yard and pointed up also. Between the two, the house is about 30ft high and blocks any direct light.

Last night May 8 UTC was clear and I was getting a QRSS10 level signal with the receiver pointed at elevations from 70 to 85 degrees, through the transmitter beam. There was nothing received from straight up, so the clouds were too high for cloud backscatter. At 80 degrees elevation I got the best signal. I've attached an Argo screen grab of QRSS10 (FSK CW with the 570 Hz tone as key-down). 

QRSS10 CW clear air scatter return signal

During my tests I used the QRSS3 speed setting of Argo to point the receiver around and find the signal. It was pretty weak but still visible at that speed. When I slowed to QRSS10 it became easy copy.

WSPR2 was decoding consistently and JT9 was about 70%. I tried JT65, BPSK31, and MFSK8 but the SNR was too low for those to work.

JT9 cloudbounce return signal 14,000 - 24,000 FT

Here's Vancouver Airport cloud data for last night:

May 8, 2016 UTC CYVR clouds and temperature/dewpoint data:
0500 FEW CLOUDS (1/8 - 2/8) 14000 FT, SCATTERED CLOUDS (3/8 - 4/8) 24000 FT, 14 C / 11 C
0600 FEW CLOUDS (1/8 - 2/8) 14000 FT, SCATTERED CLOUDS (3/8 - 4/8) 24000 FT, 14 C / 9 C
0700 FEW CLOUDS (1/8 - 2/8) 12000 FT, FEW CLOUDS (1/8 - 2/8) 22000 FT, 13 C / 7 C
 
... I'll try CW and digital again when there's some lower cloud conditions. That’s tough to get without rain at the same time.

I did get dew on the receiver last night, so I'll be adding heating resistors inside the boxes to keep the lenses warm. Electric heating has worked great to keep dew off the optical surfaces of my telescope. I'll also look at adding shrouds to shield the lenses from the cold sky.

More from May 15th:

Last night was good for backscatter from low clouds, at 1300 to 1900 ft according to airport weather. I had to stay up late though, as the cloud didn't move in until midnight.

I've attached a couple of CW recordings. Early on the signal was weaker with QSB. Later it was strong and solid.

I've also attached a screen grab of WSPR2. Signals were up around 0dB this time. 

WSPR cloudbounce return signals 1300 - 1900 FT

I played with a bunch of digital modes and FMHELL and SSTV. Everything was working pretty well off the clouds.

 

SSTV cloudbounce return signal

The nextstep is to move the rx farther from home, then to try sending signals over to John or Steve by cloud bounce.

You can find more information and all equipment details, including schematics, on VE7CNF's lightwave web pages here.

Toby's nearest lightwave neighbour, VA7MM, is in mid-build and is working to complete a system capable of running overnight cloudbounce / scatter tests between their two respective backyards ... the NLOS distance is about 15 km. Although the path includes some bright commercial lighting QRM, with narrow-band modes such as QRSS or WSPR, it may not be a problem. I suspect one of the biggest problems will be getting suitable weather as, here on the west coast, dense clouds usually turn into rain very quickly, especially near the coastal mountains where Toby and Mark are located.

I find Toby's results to be both encouraging and exciting! It will be interesting to try some cloudbounce between their respective stations and my own and maybe hopping the NLOS path across cloudy Georgia Strait. It may well be possible to do this in one of the quicker QRSS CW modes such as QRSS3 or QRSS10, both of which can have fairly fast exchanges of the required information (calls, signal report and final confirmations). Failing that, slower QRSS30 or one of the weak signal digital modes such as JT9 / WSPR which have the ability to dig deep (-30db) into the background noise may be the answer ... there is much to learn yet!

A Second West Coast Lightwave Adventure

51km Path courtesy: https://www.google.ca/maps

Toby, VE7CNF, successfully inaugurated his lightwave station earlier this week, on Monday night, completing a nice two-way CW contact between West Vancouver (CN89) and Mayne Island (CN88). The distance spanned was approximately 51km (32 miles), crossing atop the western edges of Vancouver and then across the Strait of Georgia, the body of water separating mainland BC from Vancouver Island.


The details of Toby's homebrew lightwave equipment are described on his web site here and are similar to the station at this end ... also described in earlier blogs. This was the same path covered in my two previous lightwave QSO's with Markus, VE7CA, described here.

Monday evening's weather was clear and calm but at this time of the year, true darkness is a long time coming. With a full-moon just a few nights away, the sky never did get very dark it seemed. I set up my end of the path late in the afternoon, just in front of the house.


            VE7CNF/7 end showing the busy-looking site in operation.

Accompanying Toby to the mountain lookout location were VA7MM, his YL VA7MAY and Markus, VE7CA who initially scouted out and found this nice site for our original lightwave contacts. Thanks to Markus who snapped a picture of the diehard lightwave crew!

VA7MM, VA7MAY and VE7CNF

One thing that I noticed on Monday night was the very loud QRM coming from the sodium vapor lighting used on the ski hills just above Toby's location. The resolution of my Fresnel lens was just not sharp enough to be able to isolate Toby clearly without also being saturated with the lighting noise ... from my end, the ski-hill lighting appeared just above his deep-red LED.

Although Toby's signal was very strong, the lighting hum was strong enough to cause some receiver front-end desensing and slightly modulate Toby's CW signal with a touch of AC ripple. I did not notice this hum when working VE7CA at the same location a couple of years ago. It's possible that there was no snow on the ski-hill at the time and the lights were not turned on.


Moving the receiver just a few degrees to the west made a huge difference, as the hummy background noise level returned to the quiet hush of a dark sky.

Toby's recording of my signal is much cleaner as there are no bright lights when looking towards Mayne Island. It is really interesting to hear the rapid fading, almost a flutter, on my CW signal, as the light passes through various levels of ever-changing haze above the water.


Midway through our one hour QSO, Toby reported that my signal had dropped measurably as had his signal on my end. Although I could see no obvious clouds in the path, I did notice a red glow out in the Strait that had not been there earlier. When I turned off my transmitter, the glow disappeared, indicating that there was indeed some low level haze that had crept up on us, and enough to cause some signal absorption on the path. Thankfully signal levels returned to normal, and actually were a bit stronger, about fifteen minutes later, when the haze thinned and the skies had grown a little darker.

Towards the end of our QSO, I had the chance to test out my #2 receiver. It was built so that I could do some NLOS cloudbounce testing here on the island, without having to separate my main system's transmitter/receiver pairing. At the time, there were no lenses available from the overseas manufacturer, so my quest for a suitable lens led me to a local 'bargain style' hardware importer (Princess Auto), who had a good supply of $5 lenses. The lens seemed to function well in my local tests but it had never been put side-by-side with the higher quality lens in my main transceiver. As it turned out, the $5 lens worked very well, easily detecting the 51km signal although it didn't sound quite as loud since the receiver I built for it was intended to interface with my laptop and lacked the additional audio amp I had built for the main system.

A final interesting observation was made, when on a whim, I placed a large cardboard shield over the bottom quarter of the transceiver's receiver lens. The signal strength didn't appear to change at all. I gradually blocked more and more of the lens but astonishingly, was still able to copy Toby's CW with all but a 1" strip of the lens completely covered! This would tend to indicate that we would be able to communicate with a very much smaller Fresnel or optical glass lens, such as a 4" or even a 2" inch magnifier. As I commented to Toby on CW, the possibilities for experimentation are endless.

All-in-all it was a very successful evening and the mountain-top gang seemed to enjoy the outing as much as I did, and ... the QSL is in the mail.

Hopefully there are other VE7's in or around Vancouver that might be interested in throwing a signal over this way some night ... I'll leave the light on for ya!

Local Lightwave Activity / A New 630m Resource Site

Toby, VE7CNF, has sent me some mail indicating that his new lightwave system is ready for a two-way test!






His system is very similar to the ones built and deployed by myself and Markus, VE7CA, in late 2013. The culmination of that activity is described here, in 'On Making Nanowaves - Part 6'. Our lightwave QSO and homebrew gear were later described in a 'how to' article in the 'The Canadian Amateur' as well as in the newest edition of  'The Radio Amateur's Handbook' (2016).

Toby describes his most recent pre-QSO backyard testing:

The lightwave gear appears to be working well. Focus looks good and the
finder scopes are doing their job. There's a reflective sign high up on a
hydro tower 170 meters away that's handy for testing. It lights up bright
when the transmitter's on it.

Back scatter off the clouds above my house worked too. I heard my CW beacon, audible 339, off a patch on the clouds about 1 degree wide. I don't really know if it was clear air scatter from closer by, or scatter off the clouds, but the spot was small. That's with the tx on the front deck, and rx in the back.

I used Spectran to check the noise from city lights in my area. At QRSS10
speed there are spectral lines at 540, 600, and 660 Hz. They aren't too
strong, but those are some frequencies we should avoid.

VE7CNF's lightwave system - TX (L) & RX (R)

As well, Mark, VA7MM, is also putting together a similar system to join the fun ... it's great to see new local activity!

Hopefully the weather will co-operate enough to allow us to make a two-way QSO later this week. Plans call for Toby to set up near the same location in West Vancouver used by VE7CA as it offers a clear LOS path to Mayne Island, 54km to the southwest.

54km Georgia Strait crossing (courtesy: https://www.google.ca/maps)

 *****************************************************

Rik, ON7YD, has set up a new website devoted to information specific to 630m. His 472kHz.org site looks as if it will be a valuable resource for those looking to get information and a start on our new band. At present, there is some really great information regarding transmitters, antenna systems and calculating E(I)RP levels. Have a look!

More VE7 Lightwave Activity

Two more VE7's are well on their way to getting in on the lightwave fun in the Vancouver lower mainland region. Toby, VE7CNF, and Mark, VA7MM, are constructing stations similar to the ones built by myself and Markus, VE7CA.

Toby and Mark live close enough that a clear-air scatter QSO between them might also be a possibility. Having another near-by amateur, or even in the same city, is a great source of motivation ... not to mention having someone else to actually talk to, once the system has been built.

Except for the LED focusing sled, Toby's fine-looking transmitter box and LED driver / modulator, are now complete. The receiver is next on the list. I believe this will use one of the inexpensive ($5) fresnels lenses, purchased locally at Princess Auto, that seems to work very well for the price.

photos courtesy VE7CNF

At this pace, perhaps a four-way VE7 lightwave QSO will soon be in the making!

Clear Air Scatter Tests On 458THz

After patiently waiting for the bright moon to clear the early evening skies, I was finally able to venture out for my first clear-air scatter test this past Sunday night. I had plotted the path on my Mayne Island map and determined bearings as best I could, but the path was going to be very tight. If the path plan was right, my signal should just clear the high beachfront bluffs at the chosen sea-level receiving site.

After carefully aiming the light, I set off for the receive site at around 7:45PM and was all set up with the new lightwave receiver about 30 minutes later. The site appeared fairly quiet and the Argo screen confirmed that there was little QRN coming from the local houses up on the bluff. I listened for over an hour, trying various slow changes in pointing ... varying the azimuth a few degrees at a time, and then the elevation. Unfortunately not the slightest indication of my ~549Hz tone was seen. I was confident that the system was working as several strobes were heard from distant aircraft (near Vancouver), as their flashing lamps skimmed the edge of the far treeline.

It seems likely that either my aiming or bearing calculations (or both) were off and that the signal was probably slightly to the west of me, with the bluff blocking any hope of reception ... I knew it was going to be close but was hoping for a little luck.

I left the transmitter outside overnight (it was set up two properties to the SE) and decided to try a second shot on Monday night. This path, although shorter by a mile, would require the signal to pass over two high hills ... the first topping out at 667' and the second at 567'. The overall direct-path distance was 1.7 miles (2.7 km). A cross-section of the signal path is shown below as it hugged the edges a little lower than the peaks:

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

I have been using a 'compass' app on my I-Pad to determine directions when aligning the transmitter and receiver setups. I'm not 100% convinced of its accuracy at all times, as readings can sometimes be a bit flaky. Before doing any more testing, I'll need to solve this, either with a better app or with a real compass.

The transmitter was set up just before darkness, pointing right at the edge of the treeline along the 667' ridge and elevated at a 28 degree takeoff angle. The deep-red, 640mw LED, was switched-on just before departure at around 8:30PM.

It didn't take long to get set up in the back of the CRV, with the receiver temporarily set in no particular direction and plugged into the computer.

When Argo came to life, I went to the front of the car to grab the I-Pad so that the receiver could be aligned but was surprised to see a bright line at 549Hz when I came back! It seems that my 'rough' placement of the receiver was spot-on, and not exactly where I had originally intended. In fact, there appeared to be about a 10 degree error in where I had planned to point. I later traced the error to my path drawn on the paper map as it was difficult to determine my exact receiving location on the older map, which didn't show the new road where I had set up on.

Monday night's path

I was eventually able to fine-tune the aiming and hone-in on the best spot but was surprised that there was a broader degree of acceptance in both azimuth and altitude. At around 8 degrees of elevation, and although I was pointing well into the nearby trees, the signal was still observable with just tiny patchs of sky poking through behind the trees. At 10 degrees I was above the trees, with a solid signal. Surprisingly, the signal was not lost until pointing past ~ 15 degrees ... I had expected sharper pointing.

With the strength of signals recovered on this path, two-way communication could have easily been established on any of the CW QRSS modes ... if quieter, probably on normal audible CW. Signal strength indicated that there was still plenty 'left in the bucket' for greater distance paths, probably much further than I am able to test here on the island.

This was the first thing I saw, at the QRSS60 mode in Argo ... a fairly narrow passband and a ~25+ db dig into the noise.

Backing off to a wider bandpass (less sensitive) but faster QRSS10 mode showed the signal still very apparent:

The almost 'real time' QRSS3 mode, although showing a much weaker signal, indicated that the signal would have been almost audible had it not been for the high level of background noise at this site. Don't confuse the lightwave signal with the much stronger 9th harmonic of 60Hz on 540Hz!

The ferry terminal was just down the hill about 1/2 mile and with several kilowatts of spectrum-polluting 60Hz sodium vapor lighting, the cloudy skies were a sea of bright-pink. There was a high level of audible hum in the phones, right from the start, that unfortunately, masked any hope of an audible detection. The waterfall screen capture shown below, illustrates the massive QRM at this otherwise nice site!

The night was not going to be complete without a strobe signature, captured on Argo from a high passing jet aircraft:

strobes

All-in-all, it was a very successful outing, considering the obstructed path and the $5 fresnel lens used in the portable receiver! I've examined the island map for any other possibilities and there are not many suitable candidates. I had hoped for one other possibility towards the west, which would stretch the path by almost another mile, but I'm not really sure that I can get a clear shot without hitting the very close treeline at this end.

I think the next round of testing will be in the other direction ... across Georgia Strait, with John, VE7BDQ, who has expressed interest in doing some deep overnight Argo searches for my signal in the clouds.

I'm not sure which mode would offer the best chance ... 'clear air scatter' or 'cloudbounce'. John has a very good receiver, with a slightly larger and better-quality fresnel than the one used in these tests. Working from his suburban backyard, directly across the strait at 13 miles (21 km) distant, his direct path to me is somewhat obstructed and will require an elevation angle of around 30 degrees at his end. I think, ideally, we would both like to be skimming just above the ocean, with only a slight elevation. A lower and less obstructed shot from his yard would mean an oblique path so this also remains a possibility. We will play with what we have and hope for the best ... even just a trace of signal would be a measured success.

I think that a non-line-of-sight (NLOS) contact would make an exciting challenge and a great project for two amateurs living in the same city or town, and ... you really don't even need a ticket!

For more technical details on the equipment used in this test, see "A West Coast Lightwave Project" describing the activities between here and Markus, VE7CA. We have just learned that this article will be published in the 2016 Radio Amateur's Handbook ... hopefully inspiring  more new lightwave activity!

Lightwave Scatter Planning

Over the past few days I've been trying to figure out some possible pathways that might be covered when transmitting from home.







The only real directions that I can go any distances are towards the southwest and to the southeast because of two large hills (500' and 900') to the south.

courtesy: https://www.google.ca/maps

courtesy: http://www.jeffstopos.com/

The challenge will be to put a signal over this 500' hill, about 1.5 km to the south ... I'll need to go around it on either side or over the top. Going around it at its edges will allow me to keep the light beam on a fairly low angle.

The main obstacle is my lot ... it is heavily treed in these directions and aiming would have to be too high of an angle to get over the trees. I do however, have one small gap between the trees which has turned out to be close to the right bearing (220 degrees) for the southwest test. For this, I can set the transmitter on my back sundeck and shoot through the gap without bothering anyone. For the southeast shot, or one over the top,of the hill, I'll need to move the transmitter two lots to the east of me, and use the neighbour's clear view of the hill.

This should work out OK, as the neighbour spends the winter in Boston and the house is vacant ... but the outside power sockets are alive. This path though, has me shooting across a small bay and above several houses. Most are summer residents only but there are a couple that are permanent. I'll need to contact them and give them a 'heads-up' before I run any tests, so they don't call the RCMP!

The June 2014 edition of Radcom has an inspiring article by G3XBM, "Over The Horizon At 481THz", where Roger describes his early clear air scatter tests and excellent results over an 8.5 km path. This is a very impressive distance considering the small LED transmitter and 4" magnifying-glass lenses used.

Unfortunately, the distances here, on both paths, are not very much ... about 5 km. I'm  fairly limited to how far I can go here on the island. I'd be very happy to cover this comparatively short distance and a lot will depend on being able to keep a low enough angle and still get over the hill.

With the right weather, I may start as one reader has suggested, with a short almost vertical incidence shot and set up a few blocks away to test out the system.

Lightwave-Portable Progress

On Tuesday, I completed the plywood enclosure for the new portable lightwave receiver and mounted the optics and the electronics. My plan is to use this here on the island for some clear-air scatter / cloudbounce tests, once suitable listening locations are determined.



As with my main system, I used a homebrew mount capable of movement in three directions.

The photodiode needs to be mounted precisely at the focal point of the fresnel lens, and all three directions need to be juggled for correct alignment. Shown below is the setup used on the shop floor for alignment. The signal source is a 1W red LED about ten feet away.

I covered the photodiode with a small piece of paper which made it a lot easier to find the point of sharpest focus. Once this had been found, everything was tightened and, hopefully, locked into position.

I then constructed a simple mount which allows the receiver to be tilted in altitude so it can be set to point at the desired region of sky. Once this was done, there was nothing else I could do but wait for darkness, so that the receiver could be tested.

The fresnel lens used was purchased locally for just $5, so I had my suspicions regarding its optical quality. As well, it is 20% smaller than the bigger lens used in the main lightwave system. The bigger lens is 650 sq.cm compared to the inexpensive 'page-reader' lens of 530 sq.cm. The 2mm thick rigid plastic lens is an 'Enkay 2950-C'. The larger lens has a focal length of 20cm while the page reader has a focal length of 45cm. This gives them 'f' numbers of .78 and 1.6 respectively.

Once it was dark enough, I took the receiver to the ocean side of the house and sat down with the receiver. From here I have a clear view of the mainland coast, on the other side of Strait of Georgia. The nearest point of land on the other side of the Strait is about 20km.

courtesy: https://www.google.ca/maps/

Much to my delight, the new lens / receiver appeared to work just as well as the bigger more expensive fresnel. As I swept the receiver across the far coast, I heard about twenty different signal sources. As usual, the strobe lights on aircraft were plentiful and very loud as planes lined up to the far north to land on runway 08 at Vancouver International. These signals were about 55km away. Several planes were followed as the climbed out into the clouds further to the east over Surrey. As I lost them visually in the clouds, the strobe signals were still quite strong in the receiver. Several signals were heard coming from Washington state, including a particularly strong 'growler', repeating about every two seconds, coming from Cherry Point south of Bellingham, about 80km away. There were many signals that had no apparent visual source (to my eyes) but were easily heard in the receiver. It appears that the $5 lens is a real bargain and should work well for my scatter tests. It seemed also, that the smaller lens, having a higher 'f' number, has a narrower field of view as aiming was a little sharper than with the bigger lens.

To hear similar signals, recorded on my first receiver, go to the links at the bottom of this blog from 2014/08.

The next task will be to determine suitable listening locations here on the island. Unfortunately, the island is dominated with two high (600'+) peaks, one right behind me to the south, which will make it challenging to get a signal from one side to the other. Hopefully I can find a clear spot somewhere that will allow me to shoot a signal over the top ... and of course, the fall weather must co-operate.

courtesy: https://www.google.ca/maps/

Portable Lightwave Receiver Progress

Yesterday, between dabbling in the Arkansas State QSO Party on CW, I manufactured and assembled the PCB for the new 'portable' lightwave receiver. When building PCBs, I use the printer-toner method, after drawing the design with MS Paint. Compared to some of the freeware PCB design software now available it is fairly crude, but it more than meets my needs and could even work for designing SMD boards if needed. I've also made the switch from using the messy and corrosive Ferric Chloride etchant to a weak solution of Hydrogen Peroxide and Muriatic acid. The latter seems so much cleaner, faster and overall produces a better-etched board. Boards can be completely etched in around three minutes, compared to the much longer Ferric Chloride.

I chose to use the same receiver circuit as the one in my main system, garnered from the design shown in Roger's, (G3XBM) blog. If you have an interest in getting started in lightwave experimenting, you will find Roger's blog of his lightwave adventures to be both informative and inspiring.

courtesy: http://g3xbm-qrp.blogspot.ca

As before, I made a couple of minor changes to the receiver, substituting a BPW34 optical pin diode for the one shown as well as subbing a 2N5457 JFET for the MPF102. In addition, 2N5089s were substituted for the 2N3904s. The newer JFET is lower in noise as are the higher gain 5089s. In all likelihood, the differences are only minor but I like to think that every little bit helps when all system-losses are considered.

Note that it is important to make the connection between the diode and the JFET's gate lead 'floating' in the air as any contact with the PCB could introduce unwanted loses at this point.

As in my original receiver, a locking split-shaft, removed from a junk box potentiometer, was mounted to the back side of receiver box. This will allow the receiver box and its pin-diode to be aligned forward and backward for focus and then locked. Once built, the focusing carriage will allow the receiver to move laterally, left to right as well as vertically, up and down. Positioning the optical diode at the exact focal point of the lens and maintaining this position is crucial. The finished carriage, will look similar to this one, used in my main system's receiver and transmitter box.

So it's on to the plywood receiver box and then the focusing carriage. It will be interesting to see how my $5 fresnel lens page-reader, purchased from Princess Auto, compares with the slightly larger (and probably better) lens in the main system's receiver.