AmateurRadio.com

A recent posting on the Yahoo ndblist Group page, by veteran LF/MW DXer and front-end guru, Steve Ratzlaff (AA7U) in Oregon, described his thoughts on LF/MW antennas and his experience with phasers:


Some years back at the other place, I experimented with phasers, trying
all the various ones I could find or build. I had a long term loan of
the DXE NCC phaser as well. I compared them mostly at MW where a phaser is generally most useful; but also at LF and HF. In all cases and all
frequencies, without exception, the Dallas Lankford "MW Phaser #2" was
significantly better. I have placed that article in the ndblist Files,
under "Aerials and Technical Files" section should you have an interest
in looking at that article.


For LF use I never found any reason to use a phaser for trying to
optimize the level of a signal. Usually LF signals are short-lived and
often you only have a short time to catch an ident before it fades away.
You can easily waste 30 seconds or more just trying to optimize the
phaser; by that time the signal is usually gone. For those with a local
noise problem from a single general direction a phaser could be useful
in nulling out that noise, though of course you would lose the signals
from that direction too.

I also had room for antenna experiments, being able to compare them with
my longwire antennas. For those with the room, I believe it's hard to
beat an elevated longwire of approx. 400 feet or longer. I was very
fortunate to be able to string two E/W 1600 foot longwires, on either
side of the property about 400 feet apart and roughly parallel; and a
much shorter 400 foot N/S longwire. But even the N/S short one enabled
me to log a number of Greenland beacons (of course this was back when LF
conditions were still excellent, not like now).

Some folks have good results with the K9AY type antenna--Doug in TX has
good results using that antenna. But it's a ground-dependent antenna and
many areas don't have ground characteristics that support such antennas.
My area was one of those--the K9AY never worked very well for me. But an
elevated vertical loop worked very well, using the Wellbrook ALA100
preamp. 

I had several rectangular loops up at one time, 120-150 foot
circumference using the ALA100, about 10 vertical feet distance between
the top and bottom wires to give a good capture area. These were very
sensitive at LF and a couple of times I was able to (barely) hear
distant South Pacific beacons that I was also hearing on the 1600 E/W
longwire. And of course the loop antenna is ground-independent so can be
used anywhere. It's bidirectional so can help in nulling noise too. And
such a loop doesn't take up much room as long as you can get it away
from local AC noise (which is true for all LF antennas, especially for
active whips).

Mark Connelly is a prominent east coast MW DXer and has a lot of info on
antennas and phasing on his webpage here.  All his applications are primarily for MW DXing but the principles apply equally
well to LF.

The Dallas Lankford phaser article described by Steve, can also be downloaded from here.

LNV phaser, John Bellini in Colorado, also chimed-in with some additional thoughts based upon his own experience:

MW DXer, John Bellini in Colorado, has recently posted another interesting set of YouTube videos describing the mechanical construction and operation of his cool, and somewhat stealthy, Low Noise Vertical (LNV) as well as his phaser in action against some IBOC and local blowtorch signals.

  His use of the phaser is particulary interesting. Here he demonstrates what two LNV's can do when phased correctly. The second antenna being used is one of his wire LNV's located further back in the yard.

The first video shows phasing against local IBOC crud.



The second video shows the phaser in use to knock down the sideband hash from a strong local (KOA) signal, 25 miles away.


For those that like to DX in real time (unlike those using SDR overnight samplings), the phaser has much to offer.

The one being used in the videos is the Quantum Phaser and more information about it may be found here.

More on phasers next time.

This week, three items for the workbench arrived...one of them the wrong item, but instead of complaining, I'll keep it.

First off were some 40-pin male pc board breadboard header strips, standard spacing. These will come in handy for making connections to both pc boards or to perfboard. At a cost of ~8 cents per strip and free delivery, hard to beat.



Next were some 2-pin screw terminal block connectors ... nice for a finished-look on a pc board or perfboard power connection. These came in at ~12 cents per connector.



The third item I had ordered was a small pre-built LM317 regulator board as I hate building these and they do come in handy.


However, this was not what I received (a first!). Instead I received a similar-looking AF amplifier board. It is easy to see why they might get easily mixed up by someone quickly throwing orders together for shipping. The AF board was about twice the cost of the $1.43 LM317 board and I can probably use at least one of them in my next lightwave receiver project.


A final item was ordered, from the U.K., some 250 solder lugs for just under 6-cents each, including shipping.


These are becoming very pricey domestically and are even difficult to find at a good price on e-Bay. With the Canadian dollar taking a big hit lately, bargains are even harder to find ... but I think I did OK.

This morning I completed the wiring of the test-bed MOPA's Hartley oscillator circuit. I was using the 80m tank at the time, wound with 3/16" copper tubing. Oscillator keying is about what I expected ... stable but with some ripple on the note. Even with DC on the filaments, many of these open-breadboard oscillators suffer from RF-modulated notes. Sometime wrapping the power supply or keying leads in a ferrite toroid help or eliminate the slight rasp. On the other hand, some builders prefer to have a note that sounds more '29-like, as in all likelihood, not many notes sounded like pure DC back in the day.
I'm really having second thoughts about my construction method and may just jump to the next (final) construction phase rather than slog through completion of the test-bed model. I've already learned much about the layout by getting to this stage and the extra work involved in completing the test-bed model may not tell me anything new.



I'm using a VT-25 version of the somewhat pricey and hard-to-find type '10' tube. The final version will be built in a similar fashion to my Tri-Tet-Ten, on an aluminum sheet atop the breadboard. Hopefully having the groundplane and shorter leads, will lead to a cleaner note in the final version.

I'm rather dreading this next final phase as there is little room for error. The aluminum sheet must be precisely pre-drilled, as well as the breadboard, and protected at all times (especially when making soldered connections) to prevent any finger marks or scratching on the aluminum sheet. There are still several drilling details to be worked out before I can move forward.

Yesterday I had the chance to have a closer look at the two lenses recently purchased for a new portable lightwave receiver. The initial testing procedure of the page-size fresnel (actual size is 200mm x 270mm) proved incorrect and required more space than the bench top could provide. Eventually the focal length was measured as ~ 368mm +/- for an f/d, or F number, of 1.36 ... a convenient value and much better than the 'other' common fresnel page reader focal length of ~ 600mm. This jibed nicely with the recommendations given in Clint's (KA7OEI) website optical information:

"For practical reasons, it is recommended that an optical system using Fresnel lenses be designed using lenses that have an F-number in the range of 0.5 to 1.5 - that is, around 1. Remember: The "F-number" is the focal length divided by the diameter of the lens, so for an F-number of unity or one, the diameter of the lens would be the same as its focal length."

The lens was able to bring a small LED flashlight (consisting of an array of 21 white LEDs) into surprisingly sharp focus although the shot below does not reflect that due to my camera's poor focus in the darkened room.



The glass 4.5" magnifying lens proved to have a focal point of 203mm for an F number of 1.8. This lense produced an even sharper image of the same light source and may be the best candidate for the portable receiver although the larger aperture of the fresnel might not be worth counting out at this point.

The fresnel may work well for a transmitter and will likely require a small (inexpensive) secondary focusing lens between the LED and the fresnel, in order to have the LED efficiently illuminate the fresnel. The secondary should effectively gather and focus as much of the emitted LED light to just within the boundaries of the fresnel without any wasted light energy being lost to spill-over at the edges.

It would be great to have a permanent lightwave 'beacon' that one could test various receiver lenses and combinations but at present there is very little activity here in VE7 land ... although that is changing, with the interest of another local, VE7IGH (Greg) near Vancouver and right across Georgia Strait from my location. Grant has already built a receiver and will soon start on transmitter construction ... way to go Greg! 

Courtesy: http://www.arrl.org/

I've now completed a set of tank coils for the new'29 MOPA project. These were wound with 3/16" copper tubing which has become very difficult to source. Luckily, after much searching, I was fortunate enough to find several rolls locally at a very attractive price. Although I do see it quite often on e-bay, sellers either refuse to ship to Canada or their shipping charges are far too high to make it worthwhile. The larger 1/4" rolls are still readily available, but for any given inductance, will take up a lot more room on the breadboard if space is an issue.

These coils cover the amplifier tank, the Hartley oscillator's tank, and the antenna coupling link. Respectively, the coils measure 4.9uH, 4.0uH and 1.9uH.

Winding these is always fun but the method used requires that the needed length be predetermined and cut from the roll beforehand. The first time I did this, when building my TNT transmitter, I learned the hard way to always add at least another foot to cover the additional length eaten-up by turn-spacing and for coil end flattening and mounting.


While visiting Vancouver for a few days I was able to find a couple of pieces needed for my non-line of sight (NLOS) lightwave experiments.

I purchased a nice 4.25" magnifier lens, with suitable focal length, as well as an inexpensive page-size fresnel magnifying lens. What is particularly pleasing is that the fresnel is a rigid lens, about 2 mm thick, unlike most page magnifiers that are thin and floppy. I have yet to test its blur circle or determine its focal length.

I plan to use one or the other of these lenses in a small, portable lightwave receiver module that I can carry to the other side of the island to listen for the main large transmitter, aimed slightly above the horizon, in beacon-mode. If the smaller fresnel does the job, it will be an inexpensive source for anyone else needing a simple lens for either transmitting or receiving.

If the deep-red light tests prove successful, I'll switch the system to IR light but at this stage I'm not sure how focusing and optimizing receivers and transmitters can be done with a light source that is essentially invisible? Perhaps using an IR source that is right on the edge of deep-red will still have enough visible light to allow finding the optimum focus more easily.



More information on NLOS experiments can be found in Yahoo's Optical DX Group as well is in G3XBM' s 481thz blogs.

As well, anyone in the Vancouver lower mainland (as far as the northern Sunshine Coast area) that might be considering lightwave ... I'd love to work you! Pretty well any high spot in this region is direct LOS for me.

'29 MOPA Plan

I have completed manufacture of the three RF chokes required for my new MOPA project. Two of the chokes (the ones in the amplifier) are broken into three sections, presumably to reduce stray capacitance or unwanted resonances while the choke for the Hartley oscillator section is one single winding.


The choke forms were first turned on the wood lathe, using Mahogany hardwood scrap, to a diameter of 3/4", and then stepped down slightly, for the space occupied by the windings. The windings, using single silk enamel #31, were then done, still on the lathe, while rotating the spindle manually.





I've always been surprised at how little inductance is really needed for effective choking on HF and it would seem that the 'standard' 2.5mH is much more than is actually required. The single-ended version is just 190uH, while the three-section chokes measure just 240uH, about 10% of what normally might be specified today.