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The new 'loop' is not really loop-shaped but is rectangular (10' x 20') and more like a Flag antenna shape. I considered a Flag but really don't need any back-end nulling capability since I'm mainly interested in listening to the east and to the north.


The main boom section is composed of two sections of 1" PVC thick-wall (Schedule 40) pipe joined at the center and reinforced with a 10' section of 2" x 2" Douglas Fir. In addition, the boom has a truss of 1/4" Dacron to take out any end-loading sag. The vertical end sections are 3/4" Schedule 40 PVC pipe, fastened with a T at the boom end. The center mast is made of 2" Schedule 40 ABS pipe with a long section of 1 1/2" ABS nested inside that telescopes upward to anchor the truss ropes and give some additional rigidity to the mast.

Main boom and mast construction

This type of construction would lend itself well to anyone interested in a rotating Flag antenna for the BCB / LF or 160m. The cost are very low, the structure is lightweight and the materials are readily available at most hardware outlets.



Looping E/W

Although the preamp is completely sealed and weatherproofed, I still decided to mount it inside a container. The container also provided a convenient anchor to terminate the loop end wires (PVC-coated #18 stranded) without putting any tension on the soldered terminals.

Although I have not had much time to listen, and conditions are still in 'recovery' mode from earlier disturbances, initial indications are that everything is performing as well, if not better, than expected. It certainly outperforms my 10' active shielded loop by a large margin. I have yet to do any serious S/N comparisons between it and my primary LF receive antenna, a large inverted L, which must be tuned to resonance for the desired listening range. I believe that the very quiet loop / Wellbrook combination will provide an overall S/N improvement.

I have always believed that smaller loops provide deeper and sharper front-to-side nulls so I was pleasantly surprised to measure (using Perseus) null depths from 25-30db, on various groundwave signals....more than expected. Skywave signals also deliver sharp deep nulls in the order of 22 - 25db...again surprising, but I'll take them! A brief listen pointing S-E last evening turned up good signals from 1 kw'ers KYHN (1650kHz) in Fort Smith, Arkansas and KKGM (1630kHz) in Fort Worth, Texas. An early morning listen revealed good audio from JOIK (567) Sapporo, Japan and JOAK (595kHz) in Shobu. Down in the ndb band, little 25-watter 'IP' on 210kHz was an all-time new catch from Mobile, Arizona.

There is still much to learn from this new antenna system but the biggest challenge will be keeping it up all winter. I did lose one of my 10' loops after several years, due to wind when the main (un-reinforced) PVC mast eventually failed from flexing fatigue. I will tie the ends of the new antenna down when the winds get strong to reduce as much mast flexing as possible. I could however, run the risk of violating another long-standing radio tradition..."if your antenna stayed up all winter, it wasn't big enough". I just can't win.

My present 9.5' active loop

During last winter's DX season I built and played with a number of different preamps for use with my (almost) 10' diameter shielded loop. I had been hoping to get the Burhans Preamp to play-nice above 500KHz so that I might use it for DXing the broadcast band with my new Perseus SDR radio. By bypassing the preamp's LPF, the level of BCB signal delivered by the 10' loop was just too much for the preamp's JFET front end to handle with the consequence being various strong intermod products showing up at several places inside the band. Several different toroidal input transformers produced varied results but none were satisfactory. Although I didn't try it, a smaller aperture loop might do just fine with the LPF removed and even better if there were no blowtorch BCB signals in the vicinity. My particular location, on the east coast of Mayne Island, looks directly across Georgia Strait to several 50KW BCB transmitter sites near the points of nearest landfall. Luckily, this direction is usually in the loop's null when pointing in my favorite target direction of SE/NW for the central U.S. Even so, it would be nice to not have to worry about loop orientation in order to guarantee intermod-free performance.

I did have much better success on the BCB using a version of the PA0RDT active antenna preamp, modified with transformer input to match the shielded loop's low impedance to the JFET amplifier input.

Courtesy: Aldo Moroni

Gain of the system was adjusted by swamping the transformer's output with various levels of 'R' until there were no signs of intermod products with the loop pointing away from the Vancouver blowtorch signals. The end result was a preamp that had good performance throughout the BCB, even with the big loop, as this recording of French language station, CJBC (860KHz) in Toronto(identifying as 'Radio Canada') demonstrates.



....but unless the loop was oriented in my favored SE/NW direction for most North American targets of interest, there were still a few frequencies that produced some very low-level intermod products. Again, had the loop been just slightly smaller, I think this preamp would do a great job as a wideband loop amplifier for the BCB and above. Although still usable down at 540KHz, performance dropped off rapidly as I went lower in frequency and was not considered usable for the LF NDB band. Perhaps more inductance in the input transformer as well as higher value coupling capacitors would improve LF performance. There is still room for further development of this circuit for LF use with a medium-sized shielded loop.

I recently ordered and received a Wellbrook ALA-100LN loop preamp, which I am anxious to install for the upcoming DX season. With its front-end of 8 JFETS in push-pull parallel, the Wellbrook boasts extremely good strong-signal handling capability within the BCB and below.

Please visit: http://www.wellbrook.uk.com/

My present plans call for a new and lighter loop frame, this time using PVC tubing in some sort of H-frame. I will aim to make the loop as large as possible while keeping within the Wellbrook's circumference limit of about 21m. Mid-summer doodling has produced one possible front-runner but no final decisions have been made.

10' x 20' LF / BCB Loop

I always savour the design and 'what-if' phase of any new project and the new loop is no exception. Any other ideas for possible frame configurations would be most appreciated.