New Lightwave Modulator

Yesterday I completed the construction of the crystal-controlled tone generator which will be used to modulate my lightwave transmitter during future clear-air / cloudbounce tests.




It was installed on the lightbox, right beside the original 556 CW beacon / tone generator.

The crystal-controlled oscillator uses a CD4060 IC as an oscillator-divider and produces a ~550Hz or a ~1098Hz squarewave from the 4.5MHz crystal.

4500KHz xtal divided by 8192 showing 549Hz output

The original 556 tone generator will be kept for aural CW and beacon modes as it provides a stable enough signal for this purpose but for the very narrow bandwidths that I plan to use when digging into the noise with Argo, I reasoned that the signal needed to be more stable.

As can be seen by comparing the two oscillators (crystal on the left and 556 on the right), the 556 has a lot of drift (although it looks like it might eventually stabilize) and, as well, produces several spurious signals ... probably robbing power from the main tone. The crystal-controlled signal is rock solid and doesn't appear to generate any parasitic signals in the process. The trace below the crystal signal is unrelated to the oscillator.

When I first wired the unit up, I found an unstable low frequency oscillation from the 4060 during key-up conditions, due no doubt, to the lengthy leads inside the box. This was cured by adding a pull-up resistor to the keying line as shown in the final schematic below.

Now it's on to building another fresnel-lens receiver box which will be needed for any field work here on the island.

Lightwave Scatter

Looking down the road at possible future 'clear-air scatter' or 'cloudbounce' lightwave tests with stations (VE7CNF and VA7MM) on the other side of Georgia Strait, I spent a few minutes breadboarding a more stable modulator for my lightwave system.


As it is at present, the modulator consists of a 556 tone generator, capable of either a steady tone for CW keying or a two-tone FSK 'beaconing' signal used to help the other station in aiming alignment.

For the slow QRSS CW narrow-bandwidth modes required for the scatter tests, I've always known that a tone which is much more stable and of precisely known frequency would be needed. The tone from the 556 does well as an aural CW keyed tone but would probably be all over the place when viewed in a very narrow-bandwidth and not nearly as stable as it sounds by ear.

The little modulator uses a 4500 KHz crystal (pulled from a old VCR several years ago) in a 4060 oscillator-divider. In this case, output from the chip is taken from either the 'divide-by-8192' pin 2, which outputs a precise frequency of 549 Hz or from the 'divide-by-4096' pin 1, which outputs a frequency of 1099Hz.

courtesy G3XBM: http://g3xbm-qrp.blogspot.ca/search/label/nlos

This tone is then used to drive an IRF 540 power MOSFET which controls current through the 1W Luxeon Deep Red LED in the transmitter. The 4060 modulator will be keyed via a QRSS software keying program that I have used for many years to key my LF transmitter.

The lightwave receiving station will look for the QRSS audio signal with an audio spectrum viewer such as Argo or Spectran. The ability to make automatic overnight screen captures will allow the receiving operator to get a good night's sleep while the system diligently watches for any traces of a signal.

An example of a strong signal capture showing a repeating "SL" identification is shown below, as it would appear in a perfect world. In this case (QRSS3), the short 'dots' are 3 seconds long while the 'dashes' are 9 seconds.

Huge signal gains (the ability to dig into the noise for signals) can be had by slowing things down and using narrower receiving bandwidths. Just going from a normal 12WPM speed CW (aural copy) to QRSS3 yields a gain of ~15db. At QRSS10 (10 second dots), an additional 5db is gained while slowing to QRSS60 (60 second dots), a whopping 28 db over 12WPM CW is gained!

Of course all of this extra 'hearing power' comes at a cost and in this case, the cost is 'time'. On an overnight of automated computer monitoring, time is not much of an issue ... it only becomes critical in 'QSO mode' when some QRSS QSOs can take several hours to complete. In any case, it will be interesting to see if any traces of lightwave signals will show up while bouncing around in the clouds.

The Georgia Strait scatter tests will not take place for some time but in the meantime, I hope to do some local tests here, from one side of my island to the other but will build a new portable receiver for these tests and leave my main system intact.

A 630m QRSS Test

A few days ago, the power of the slow speed QRSS mode was nicely demonstrated by Mark, VA7MM (Coquitlam, BC) and Jack, VA7JX (Campbell River, BC, on Vancouver Island).

Mark was transmitting on 630m at a power of just 144mW output, while Jack was receiving on his normal 630m inverted 'L'. Mark tried various QRSS speeds ranging from QRSS3 (3 second 'dits') to QRSS60 (60 second 'dits'). One can clearly see the difference between the three speeds.

Going from the relatively slow CW rate of 6 WPM to just QRSS3 alone, produces a healthy 12db increase in signal level. Going from there to QRSS10 produces another 5db, while going all the way to QRSS60 produces a whopping 24.8db over 6 WPM CW! The trade off, of course, being the amount of time it takes to send the needed information.

In practical terms, contacts can be made relatively quickly at both QRSS3 and QRSS10. After that it becomes a bit of a chore as conditions need to be very stable for long periods of time ... as well, you'll need several hours to complete a two-way exchange.

courtesy: https://www.google.com/earth/

VA7MM - QRSS3

VA7MM - QRSS10

VA7MM - QRSS60

This is over a 120 mile (192km) path but what is remarkable is the rugged nature of the path as shown here:

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

Although mostly over water for the second portion, the initial launch of Mark's signal is into a hellish 60 mile path of rugged coastal mountain peaks, with most of them in the 3,000 - 4,000 foot range! If this is an all groundwave path, and I suspect that it may be, it surely demonstrates the amazing groundwave capability of 630m. If there were any skywave involved, I would expect to see some fading on the signal path ... but the QRSS60 signal looks rock-solid and fade-free.

I should add that Mark's transmitting antenna is very minimal at the moment, consisting of an 80m dipole fed as a vertical 'T', tuned but not impedance-matched and ... no ground radials. Pretty remarkable actually.

630m Resources - Part 2

Using the transverter approach offers the advantage of providing a higher-stability signal generated by the main station's transceiver oscillator system. Most of the digital modes require a higher stability than would be needed for straight CW.

If your main interest is normal speed CW, then a digital VFO, such as the one devised by GW3UEP, would do the job.

If you are content operating on 475.0 kHz, then an inexpensive 7.6MHz crystal, in a divided-down oscillator will work well, and with good enough stability for some QRSS work as my earlier "GW3UEP Transmitter In QRSS Mode" report indicated.


The other option for frequency generation is a DDS.

N3ZI DDS

For several years now, I have used an inexpensive N3ZI DDS to drive my 2200m transmitter and, more recently, my 630m system. The N3ZI DDS is an affordable option should you decide on a non-transverter style of transmitter.

For those wanting something a bit more robust, W1VD describes a very nice high-power transmitter. His website is packed with useful circuits and ideas for both 2200m and 630m.

W1VD Dual-Band Kilowatt : http://www.w1vd.com/

Another practical way of generating moderate power, certainly enough to meet the Canadian 5W EIRP limit, is to combine two or more 100W transmitters, such as the GW3UEP transmitter. It is reasonably simple and inexpensive to combine several modules with the use of a homebrew power combiner, as previously described.

Homebrew 630m two-Port Power Combiner / VE7SL

Of course, none of this would be of any use without thinking about suitable 630m antennas...ones that will fit in your backyard!

GW3UEP 630m Tx Complete

I was finally able to put the finishing touches on the new GW3UEP Class-E transmitter by mounting the hardware on a small 19" panel.

Added to the panel were a 5A DC meter to monitor drain current, a keying jack and a key shorting-switch for keydown testing. This is the third version I have built using the design on Roger's page, with all three performing pretty much as advertised. It is an inexpensive, easily reproducible design.

 

I made one small change in the third version (above) by adding an additional FET in parallel with the single IRF540 thus cutting heating dissipation as described in an earlier blog. At normal CW keying speeds, no heatsinking seems needed on this particular version, when operated on 12VDC. Anything a little higher or any QRSS modes would require heatsinking. I did eventually add two small heatsinks in case I chose to run QRSS at some point.

 

 

When operated at 12-13V, the measured output power is around 25W while at 22-23V, the output is around 70W. I suspect that you could get in excess of 100W out, at higher voltages and larger heatsinking or by blowing the sink with a small fan.

 

The main function for the new transmitter will likely be as a semi-permanent beacon as well as for a small signal source when tuning the antenna. I may also use it in the WSPR mode with a modification to the oscillator section. One particularly nice feature with the Class-E design is that with no load at all, the current drops to almost zero, should the antenna suddenly fail.

 

If you live in VE7 or across the border in W7 land, please have a listen on 475.0 KHz and let me know if you can hear the "VVV" beacon over the next few days!



 

Smoke Testing The GW3UEP 630m Transmitter

Drain (top) vs Gate (lower) on testbed Class-E GW3UEP TX

I've just completed the Muppet-styled printed circuit version of my previously breadboarded GW3UEP 630m transmitter. The earlier version was built "ugly style" in order to optimize part values and measure circuit parameters.

Testbed (Ugly-Style)

The "ugly version" performed well at 12V and during overnight beacon testing was aurally copied as far east as Kansas. Although the final version has yet to be mounted on its small 19" rack panel, along with a meter to monitor final amplifier drain current, all indications show that it too works well.

Final Version (Muppet-Style)

This version, based on the GW3UEP design, has a few small changes, the main one being the addition of a second parallel-connected FET ....described in an earlier blog.

Running the TX at 12.8VDC on the drain(s) at 2.3A produces an input power of 29W. The measured power out, after the LPF, is 23W into a 50 ohm load. This represents an efficiency of 80%. When run in the normal speed CW mode, the FETs run cool enough that they would probably not even need a heatsink but if run in any of the QRSS (long keydown periods) modes, would certainly benefit from  heatsinking.

Running the TX at a higher voltage of 22.6VDC (on the amplifier only) yields a current of 4A for an input of 90W. Measured output power is 71W for an efficiency of 79%.

Heatsinking would be required at this power level, even for normal speed CW but the finals seem to run just slightly warm. A larger heatsink or possibly a small fan as well would be required for any QRSS CW modes.

I suspect that the efficiency could be further improved yet with very fine tweaking of the output circuit L/C network but the extra few watts gained would not be significant.

At either power level, this easy-to-build transmitter would make a great "first 630m transmitter" for anyone wanting to get started on our new band.

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".

630m QRSS30 Last Night

Before dismantling the little 25W GW3UEP test board in order to repackage it, I tried one more night of beaconing on 475.050 KHz, this time at a little faster speed compared with the previous night. Apparently the thunderstorm activity was at a much lower level as well, resulting in improved reception reports all over.

From Garry, K3SIW, in Illinois:

Andy, KU4XR in Tennessee, set up a 630m grabber to watch for my signals which quickly popped-up shortly after my local sunset:

JD in Kansas also had much improved reception over the previous test:

Thanks for the reports and the fun!

It sure would be nice to see some more Canadians getting on the band!!!

Overnight 630m QRSS Beacon

After completing the QRSS tests with the GW3UEP 630m crystal-controlled transmitter, I decided to let it stay running overnight to see how it would hold up and if 25W was enough to 'be seen' on 475KHz. In the morning I received three reports...from Kansas, Illinois and Alaska.

As well as sending along an Argo screen capture, Garry, K3SIW in Elgin, Illinois reported:

"Your signal was in and out here the whole night until local sunrise neared "



courtesy K3SIW


The QRSS60 signal is weak but discernible in the thunderstorm QRN at a distance of 1300 miles / 2100km.


John Davis in Kansas was battling even worse QRN but managed to catch a small glimpse of the weak signal just before his sunrise.

courtesy John (JD) Davis

Laurence, KL7L north of Anchorage in Alaska also sent a nice screen capture after setting up one of his many Alaskan Snapper low frequency screen grabbers to watch for my signal.

 

courtesy KL7L

Laurence commented:

"Nice signal on both arrays - a little weaker on the K9AY ast its suffering from the tx loop coupling at the moment -; this shot taken on the omni and shows occasional small Au doppler spread not seen on the beam - nice signal - AOS 0712 LOS 1105Z"

The path from Mayne Island to KL7L is almost exactly the same as the one to Illinois (1300 miles / 2100km) but unlike the eastern path, this is mostly 'over water' and one with little thunderstorm activity.

It seems that the 25W transmitter can do a credible job when run at QRSS60 (something it was never intended to do) if not a bit chirpy.



The GW3UEP 630m TX In QRSS Mode

By all accounts, the little transmitter designed by GW3UEP and detailed on his website, is an efficient performer and would be a great 'first' rig for 630m CW. I had the chance on Thursday to run some checks with my GW3UEP xtal-controlled 630m transmitter. Typically crystal oscillators sound stable to the ear but when pressed into the slower QRSS modes where the signals are being observed in very narrow bandwidths, any drift caused by crystal heating will show up pretty fast. I think that anyone building this transmitter would more than likely want to use it for normal CW or perhaps as a beacon transmitter but being able to use it in some of the slow speed QRSS modes would offer significant improvements in geographical coverage compared with straight CW....but, would the little fifty-cent HC-49 crystal have the stability needed for the slower modes?

Source: http://www.dstarcomms.com/GW3UEP/472kHz.htm

Previous on-air testing between G3YXM and G3NYK has shown the theoretical gains to closely follow actual gains when comparing CW speeds of 12 wpm with QRSS rates of speed. Simply going from 12 wpm to QRSS3 (3 second dots and 9 second dashes) will garner a whopping 12 db improvement at the receive end. Slowing from QRSS3 to QRSS10 yields another 7.6db. If the crystal controlled transmitter is stable enough at QRSS10, almost 20db improvement in readability could be realized....it would be the equivalent of staying on CW but increasing the little transmitter's output power from 25W to 2500W! This is one of the main reasons so much Low Frequency DX work is done in one of the various QRSS modes....to overcome the extreme inefficiency of most backyard antennas used for LF and the subsequent low effective radiated power.

Using the VA7JX 630m screen grabber, I was able to observe the stability characteristics of the xtal-controlled oscillator at various speeds as Jack followed along, switching his Argo receive speed to match my own.

As can be seen below, the oscillator stands up nicely at QRSS3 (3 second dots) while sending "SL".

Slowing to QRSS10 (10 second dots) shows things still looking pretty good.

At this speed, we are now running the equivalent of 2500W on 630m at normal CW speeds but lets see if it will hold up at even slower speeds and to the scrutiny of even smaller bandwidth filtering. Here we are at QRSS20, giving another improvement of almost 2db or the equivalent of 3900W

At this bandwidth and long key down periods, the drift caused by crystal heating is now beginning to show up and although certainly usable at this speed, it would appear that anything slower than this speed would be even worse.

Moving down to QRSS30 will gain almost 2 more db, now at the 6200W normal CW speed. Although more drift is apparent, the signal is still easily readable.

QRSS60 (60 second dashes) yields another whopping 3db and the 12WPM CW equivalent of 12.4KW.

In spite of the rigours placed on stability, the signal is still surprisingly useful although very 'chirpy' at this speed.

The huge improvement in effective equivalent power is of course realized at the expense of time, where just sending my call alone takes about 45 minutes! Two-way contacts have been made at this speed in spite of the time needed to exchange calls and signal reports. Faster speeds of QRSS3 or QRSS10 offer a much more realistic rate of exchange, allowing two-way QSO's to be completed fairly quickly, along with that very helpful 12-20db of signal improvement.

I didn't expect this small crystal to perform as well as it did but working in its favour is the fact that any actual drift in frequency is divided down by a factor of sixteen when going from 7.6MHz to 475KHz. As well, the method of keying used during the test was probably the worst one possible as far as stability goes as the entire 4060 oscillator was being keyed on and off for each sequence, requiring the crystal to constantly heat and cool for each character sent. Although keying this way is the easiest method, letting the oscillator run continuously and keying an intermediate stage such as the driver or the final itself should yield even better results.

In its present form, it seems that the little GW3UEP transmitter will stand-up very nicely in the faster QRSS modes, and would still be usable at the much slower ones if one was prepared to accept a little drift. With a different keying method and some Styrofoam insulation protecting the crystal, I suspect that further improvements at QRSS30 and slower could yet be made. 

Over The Horizon DX....On Lightwave

I was excited to read an article by Roger, G3XBM, in the June issue of Radcom magazine describing his experiments in non-line-of-sight (NLOS) lightwave work. Last fall, VE7CA, VE7BDQ and myself built LED lightwave stations, mainly due to Roger's inspirational blogs describing the development and progress of his own lightwave system. Our local work resulted in two exciting CW contacts between myself on Mayne Island and VE7CA in North Vancouver, about 54km away and on the other side of Georgia Strait. 

Our Lightwave QSO Path

The details of our system and contacts will be the subject of an upcoming article in 'TCA', the Radio Amateurs of Canada journal.




Although VE7BDQ did not build a transmitter, we did have one unsuccessful NLOS attempt, hoping to catch a signal from the bottom of a somewhat unstable cloud layer.

Roger's article describes the results of his low power 'clear air scattering' tests and levels of signal detection at varying distances. His success in this mode has given me renewed hope of eventually being able to cross the water via this method and maybe even doing it without the cloud layer!

Our systems used a 556 tone generator to produce a keyed 600Hz tone, but I think Roger's approach of using a crystal oscillator / divider as the tone source will likely produce a much more stable signal and one that would be easier to spot on a slow speed Argo or Spectran screen, as any attempts would be run in slow speed CW QRSS mode.

For more on Roger's excellent lightwave activities and NLOS experiments, visit G3XBM's Lightwave Blog pages that cover these topics.

If there are any others in the Vancouver lower mainland region who might be interested in joining in the lightwave fun, we would welcome your help....this is one activity where "the more, the merrier" is surely the case!