AmateurRadio.com

ZVR - 368 Vancouver -  Middle Marker Rnwy 08R - reported as far as California

Now that CLE186 has come and gone, worldwide results will soon be posted by e-mail (to all those submitting reports) as well as to the CLE website. CLE organizer and data-cruncher Brian Keyte (G3SIA), indicates that 50 logs (and over 2,000 reports) have been submitted, including two first-timers - Graham (VE3GTC) near Ottawa, ON and Hans (BX2ABT) in Taiwan. It's always great to see new activity, especially on LF!

As is usually the case with CLE's, propagation conditions begin to deteriorate shortly after the announcement of the upcoming event. By the weekend's arrival, conditions are usually much worse than earlier in the week and such was the case once again! In North America, lightning activity and mediocre propagation dominated the three-night event, with the consensus of opinion giving the nod to Saturday night and early Sunday morning as being the best period.

Courtesy: http://www.lightningmaps.org/

Here on Mayne Island, Friday night was pretty much a wash and only the stronger signals made it through the din and into the log. A twilight check on Saturday evening indicated improving propagation and less lightning, renewing optimism that the entire weekend would not be a wipeout.


Since purchasing the Perseus SDR earlier this year, I have been using it exclusively for the past few CLE's. I have been exploiting one of it's main features....the ability to record the entire band overnight and then tune through the band the next day, as in real time. I no longer had to prop my eyelids open until 0100 or later, or to leave a sound sleep to journey out to a cold shack to hunt the pre-sunrise band for anything new....yes, Perseus has made it possible to DX while I sleep!

Now the very concept of this horrifies many of the 'purists' and I myself held-out for several years before venturing over to the darkside...but...embracing new technology along with its associated new learning is what is important. If I get to sleep-in because of it, even better!

So....that's the way it is supposed to work, but due to operator error, Perseus failed to launch on Saturday night, and the best conditions of the CLE were missed altogether. Having seen the error in my ways, the perils of Perseus will, hopefully, not strike again!

Conditions on Sunday night were noisy once again, although not as bad as Friday, and the following log was gathered after parsing through my overnight recordings.


I have, over the years, logged all of these beacons before, except for one..."OKT" in Yoakum, Texas...new catches are always nice and are harder to find  it seems. The Google Map's 'street view' shows what appears to be a nice top-loaded "T" antenna at OKT:

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

My CLE186 beacons - Courtesy: https://www.google.ca/maps/

It was nice to salvage Sunday night but I'm still a little bummed about missing the best night of the weekend...at least I had a good night's sleep.

The Mini-Whip at University of Twente's (Netherlands) Remote Receiver

I think many hams believe that they need big antennas and lots of space to operate on 630m or even to listen on the band. I can assure you that big antennas are definitely not needed to listen or for that matter, even to transmit effectively.

You might be surprised at just how well you can hear on 630m using one of your low band antennas, such as an 80m or 40m dipole. Best results will be had with the coaxial feed's shield lifted from ground and connected to the center pin. This, in effect, allows your dipole to act as a top-loaded 'T', with the coaxial feedline now acting as the vertical element and the dipole section as a capacitive tophat. With a few ground radials, such an antenna can even be used for transmitting, if suitably resonated, but that's another topic altogether. Even untuned, this system will allow you to receive suitably on 630m providing your location is not inundated with high noise levels. High noise levels can often be overcome by using loops, either resonated or broadband. Loops can be very effective at nulling noise, particularly if it is coming from one direction, and vastly improving LF receive-capabilities.

Another popular solution and one that can be quite effective at lowering noise levels and improving overall signal-to-noise is the use of a short active (amplified) whip antenna. One very popular and proven design is that of Roeloff Bakker, PAØRDT. His simple-to-build active whip has been employed around the world and is being used by many LF'rs for dependable reception on the NDB band as well as on 630m. Roeloff himself operates from a noisy urban area yet manages to hear amazingly well on LF and MF with this simple antenna. Unlike a much larger wire antenna or large loop, the small active whip can be easily positioned in the quietest part of your backyard or rooftop. Often just moving such an antenna a few feet one way or the other can make a huge change in the noise level if you are operating from a typical city or suburb location....the PAØRDT whip may be all that you really need for long-term, reliable LF reception.

Courtesy: PAØRDT

Common practice is to mount the PCB inside a small weather-sealed PVC pipe and erect it atop a mast, after taking the time to "sniff-out" the quietest location for its placement.

Courtesy: http://www.leeszuba.com/projects/

With very few parts needed, the whip can be built for just a few dollars...even less with a good junkbox and the needed transistors.

Courtesy: http://www.leeszuba.com/

You can read Roeloff's own information on construction of the active whip here, with additional information here.

I even see the parts and PCB available on e-bay. As well, Roeloff himself, can provide finished units ready to mount in the air.

Courtesy: http://countingradios.blogspot.ca/2014_01_01_archive.html

There are plenty of informative Mini Whip articles and construction stories on the web should you wish to learn more:

• Fundamentals of the Mini Whip  by PA3FWM

• A Compact Active Wide-Band Receiving Antenna  by G3GRO

•  PAØRDT Mini Whip - Commercial & Homebrew Versions Tested  by GØKYA

• The PAØRDT Mini Whip  by DL1DBC 

• The Mini Whip Antenna  by Lee Szuba

If you're stuck with limited space for an LF-receive antenna, this may be just the answer!

It's often easier to achieve high power on 630m or LF by combining lower powered amplifiers than it is to build a single high-power rig. A simple Class D push-pull switching FET amplifier can readily produce 400-500W when operated in the 35V range. Combining two such amplifiers, both sharing a common oscillator / driver stage, would yield 800-1000W output...probably much more than needed on 630m.

The low parts-count of the amplifier stage in the GW3UEP Class-E transmitter should easily produce 150-200W when run at a slightly higher drain voltage and proper heatsinking. Combining two such modules would yield 300-400W output at very low cost.

Combining can be done with a Two-Way (3-port) Wilkinson Splitter / Combiner. Splitters and Combiners are one and the same, depending on which ends are used for input(s) / output(s). When used in the 'combine' mode, insertion losses are virtually zero and mainly due to the miniscule resistive losses of the coils.



Combiner component values can be calculated the old fashioned way or by using one of the numerous online calculators. This excellent online video by Sebastian (KF5OBS) explains exactly how to calculate component values for the truly dedicated amongst us:

Courtesy: https://www.youtube.com
He also has a new video showing how to calculate values for combiners having more than two outputs, should you want to combine three or more individual amplifier modules.

The first combiner I built was for my 2200m kW and combined the output of two 500W Class-D modules:


The air core coils are high-Q, cheap and easy to produce. If space is important, the inductors could just as easily be made using frequency-suitable powdered iron toroids, but at more expense. In actual operation, I have never been able to detect any heat from any of the combiner components, even when running a full kW at lengthy keydown periods of several minutes during QRSS transmissions, affirming the almost 'zero' insertion loss when used in the combining mode.

When I decided to use the same amplifier on 630m, a suitable circuit was designed and built for that band as well:


The terminating / balancing resistor (R) is used only as a safety device in case one of the two amplifiers fails during operation. It allows the still-working amplifier to safely dump some of its power into the load without destroying itself. Under normal operation, no current flows through this resistor so no power is wasted, assuming both inputs are equal. I have read of some schemes that will sense any current flow through 'R' and immediately shutdown the entire transmitter, thus allowing a resistor of lower dissipation to be used for 'R'.

Another benefit of the Wilkinson L-C Combiner is its filtering capability, as it works extremely well as a LPF. Neither my 2200m kW or 630m kW use any low-pass filtering other than that provided by the combiner's L-C network. It also seems to work well as a buffer of sorts, as both myself and VE7TIL noticed with our 2200m systems. We immediately stopped blowing FETs mysteriously when operating at full power. The amplifiers did not seem to react any longer to reactive components suddenly appearing in the antenna system or somewhere in the output network....everything was 100% more stable and reliable it seemed.

I can envision an exciting project consisting of a pair of GW3UEP finals feeding a toroid-based combiner, all in a very small footprint.

Should you choose to combine a pair of amplifiers for 630m, here are the values that were used in my own combiner:

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.

Several hours were spent yesterday finishing off the new 630m antenna matching transformer and installing the new loading coil with built-in variometer.


I decided to remove two turns from the bottom half of the coil, lowering the tuning range from 177-330uH to 165-313uH. Still not ideal but slightly more efficient. In reality, any losses from the variometer inefficiency are minuscule compared to the overall ground-system losses and probably unmeasurable. As it stands, the inverted 'L' resonates on 473kHz with 185uH of inductance and ideally the variometer should be operated closer to its total maximum inductance.


The new matching transformer is similar to the one that works so well on the 2200m system and wound on two TV flyback ferrite cores.




Once everything was cabled-up, I returned to the shack and plugged the coax into the KØLR antenna meter (VFO) and tuned it to 473kHz. I then went back to the variometer and tuned it while watching the meter through the shack window, looking for the sharp rise in current that would indicate resonance. I swept from one end to the other but saw no change! I eventually realized that I had not attached the antenna downlead to the top of the loading coil...duhh!

Once in place, the sweet-spot was quickly located and I returned to the shack to switch to the transmitter and scope match. For starters I had set the matching transformer to the 50ohm tap but the Scopematch indicated a resistive impedance of about 25 ohms. Moving to the 25 ohm tap resulted in a perfect match as can be seen here with both the current and voltage waveforms in exact phase and amplitude.


The Scopematch truly makes things easy, once you remember to attach the antenna!

The antenna tuning systems for 2200m and 630m are now separate and independent of each other, each with their own coaxial feedline and tuning system but I really wonder if I'll ever be active at all on 2200m again as there just appears to be no real interest amongst Canadian amateurs in our new 'topband'. It's really a shame since so many people worked very hard to obtain 2200m for Canadian amateurs...for me, its been a wonderful learning-ground for building and experimenting, as is 630m.

With the 630m system all ready to go at maximum EIRP, things are all set for the late October 630m Activity Night (hope you will be there). In the meantime, while awaiting new Canadian activity (come on guys!), I'm open for business.

Anyone wishing to try a two-way crossband contact please let me know. Both myself and VE7BDQ would love to work you!

Courtesy Roelof Bakker PAØRDT

Anyone experimenting with the LF regen circuits described by Mike Tuggle and Roeloff Bakker in my recent  "Tuggle-Style LF Regens" blog, might be interested in some helpful 'building notes' posted to the Yahoo ndblist by noted NDB/BCB DXer and exceptional RF guru, Steve Ratzlaff, AA7U of La Grande, Oregon.

                                                     ..........

I've managed to complete my new 630m loading coil / variometer combination but will need to wait for the completion of my impedance matching transformer before I can test it out on the antenna. From earlier tests on 475kHz, it seems that my inverted 'L' needs about 190uH for resonance on 630m so just a small loading coil was needed. The built in variometer will allow the system to be tuned to resonance easily, without the need for playing with taps. Once I had started to wind the main coil, I decided to put on a few more turns than I had originally planned, reasoning that it would be easier to remove turns if less inductance was needed than it would be to add more turns if I fell short.     My matching transformer will be similar to the one used on my 2200m system for the past several years. Construction details may be found on the GW4ALG web site. This method of matching, rather than tapping up from the grounded end of the loading coil to find the correct impedance match, is much easier to use and readily allows for changes to be made as the seasons change from winter (wet) to summer (dry).

Source: http://www.alg.myzen.co.uk/radio/136/ant_xformer.htm

 

Source: http://www.alg.myzen.co.uk/radio/136/ant_xformer.htm

To avoid core saturation at 1kW, my 2200m transformer was wound on two pieces of 'street ferrite', a phrase coined by VE7TIL  to describe the abundance of these free flyback cores often to be found in discarded TV's and computer monitors. The ferrite usually has a very high permeability and works well in this application as well as for switching FET amplifier output transformers...and, the price is right!  

Source:  http://leoricksimon.blogspot.ca/2007/05/flyback-driver.html

The challenge is removing the core from its encapsulated shroud without damaging the core. Once you get the hang of it, it is fairly easy to do, but you must work carefully with the brittle ferrite. With the proliferation of LED TV's and monitors, this source of free cores will not be around  much longer so grab them while you can ....this ferrite is just too good to throw away!