AmateurRadio.com

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.

Mike Tuggle's Lyonodyne 17 Crystal DX Tuner

The use of integrated circuits can be interesting in that one IC can be used to build a full superhet. The use of an IC means that the set will not qualify for the 1AD nor for the 2AD bonus points."

The challenge was too hard to resist for many and the contest was popular for several years running. Some of the inventive entries for individual years may be seen here. The contest logbooks  also make for interesting reading and demonstrate the capability of some of these simple radios.

Although the contest has not been run for the past few years, there is still much interest and discussion of "1AD" radios on Dave Schmarder's "RadioBoard" forum.

Mike's LF tuner is a prime example as he uses it daily and continues to post some amazing DX to the Yahoo "ndblist" Group. His furthest ndb catch in North America with the regen has been "YY" in Mont Joli, Quebec.
Now, "YY" is a good catch for me, from B.C., but Mike is listening from Kaneohe, Hawaii !

You can read about Mike's original design here, while his latest version shown below, incorporates a dedicated LF antenna tuner.

LF Regen (Courtesy Mike Tuggle)



LF Regen Schematic (courtesy Mike Tuggle)

A recent posting to the ndb list by Roelof Bakker(PAØRDT) of mini-whip prominence, described his recent construction of his own LF regen, based largely on Mike's design but with a few interesting changes.

Courtesy: Roelof Bakker, PAØRDT

Roelof has also published a nice write-up describing the project which sparked a lot of "must build" discussion within the group.....even enough to make Mike get out his soldering iron and build the European-version!

As old and as simple as they are, regenerative receivers still hold much fascination amongst radio builders and dollar-for-dollar are amazingly good performers, especially on LF.

My own surface mount version of the Pixie2

This page provides a guide to Pixie and related kits in a table format. These are simplistic single-band transceivers which are fun to build, yet they perform well enough to be used, although with some effort, for real contacts.

The idea of using the power amplifier transistor as a mixer seems to come from George Burt – GM3OXX – whose five transistor FOXX was described in 1983 in SPRAT. The basic design of the oscillator, PA/mixer and the simple keying has been more or less unchanged since RV3GM – Oleg Borodin – described the four transistor Micro-80 in 1992 in SPRAT. Later the Pixie 2 by WA6BOY replaced two of those transistors with the LM386 audio amplifier (QRPp 1995). Most later versions are variants of these designs.

Foxx
Foxx-3 kit from Kanga, £29.95	Incorporates a sidetone oscillator, changeover relay and low-pass filter. Different versions for the 80, 40, 30 or 20 m bands
Micro-80
Kit from QRPme, $35.00	Micro80D. Updated version with choice of  high or low impedance headphone, polyvaricon tuning cap and board mounted connectors, 80 m.
Pixie2
Kit from HSC Electronic Supply, $14.95	For 80 and 40 m. Eham review
Kit from Kenneke, $29.95	Includes 80 m crystal
Kit from QRPme, $40.00	Lil Squall Transceiver ][. Several components and the output low pass filter are on sockets. Comes with a crystal for 40 m.
Ali Express Ham QRP DIY Kit Shack 40 m, $15.07	40 m version. Tuning pot for VXO.
Radi0kit, £22.00	Enhanced Pixie2 which comes in 80, 40 and 20 m versions. Judging from the PCB layout it has an improved pin 7 muting circuit.

What can we say to characterize these designs? One the one hand they are very simple to build and get to work. One the other hand they are also simple in the sense that they do not always perform very well. Therefore I don’t think I would recommend them to any novice ham. It takes some understanding of frequency offsets and sidebands in order to make real contacts. But many have had great fun with this minimalist transceiver which in its basic version puts out some 2-300 mW. And it encourages experimentation and modifications. Also, it should be remembered that it isn’t really necessary to get a kit, as the Pixie 2 is quite simple to build from scratch also. I did that myself.

The original designs and many variants and modifications are documented in the Pixie file document of SPRAT. There are many, many more clever modifications out there and I have my share on this blog also. To sort out and link to all the other pages is too daunting a task, so therefore I have focused on kits here. Finally I wouldn’t be surprised if the table is incomplete so I would appreciate comments if you think that something is missing.

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.

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

"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:

• the RSGB LF Group reflector
• the Lowfer list
• the LWCA Message Board 

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!

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".

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.

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.....