Almost all MW DX listening is done at my residential metro area home. The high signal area environment necessitates higher Q passive tunable loop antennas, and physically larger radios. This approach is different to using an expensive communications receiver, and 200 ft random wire strung out over a rural property. Such a broadband antenna pickup setup would overload the MW band at my home. The RF noise would also be unacceptably high.

There has been only a few times that I have been away on a MW DXpedition away to rural areas. The overall DX reception results excelled what is ordinarily received back at the house.

The first objective was to see if smaller overall size portable radios could perform at least near equally well to a reputable larger size radio such as the Drake R8B. The R8B was my reference radio that all others were compared to. AC powered PC SDRs were never an option at home or away due to the high 50 Hz RFI generated. When propagation conditions are unusually favourable, the Drake R8B and 40" loop is occasionally used at home.

One of the first reference sources consulted was the radiojayallen AM portables comparison review page. After purchasing portables of various sizes from near-ULR size (Tecsun PL-390), intermediate size (Sangean PR-D15), to large size (Sangean PR-D3 // Crane CC-2E approximate equivalent), extensive testing using daytime pure groundwave, and evening skywave, confirmed that within reason, physically larger receiver / antenna setups provided the best overall weak signal SNR and audio fidelity combination result.

The radiojayallen webpage allocates 5 stars for some of the physically larger portable radios. This matched my own observations. Longer length internal radio ferrite rod, larger internal physical size spacing, and larger size speaker(s), all contributed to less internally generated spurs, higher SNR, and improved audio fidelity. On the most distant daytime pure groundwave signals, the difference is significant between a Sangean PR-D3, and PL-390. This also applies to evening skywave. With no personal bias for overall radio physical size, larger sizes excelled. The signals fill a large size room with remarkable bass and treble clarity.

Because of the high local MW signal levels at my home, a passive high Q loop design was essential. I constructed Gary's 4-leg PVC 9-turn 40 inch side length table top with excellent results. A smaller 2 ft side length PVC circular 'hula hoop' compliments the larger loop for more frequent kitchen benchtop monitoring. Based on certain other DXers' reports, the general DX pickup results compare favourably with 5" or 7" FSLs.

During the 1960s in England, the scope for international MW was greater than now for various reasons. Mainly influenced by the research of 1950s U.S. MW DXers, the 40 inch side length square loop became the UK MW DXers' favourite antenna. It became the replacement for the earlier ubiquitous backyard random wire. The loop was directly connected to large Trio, Eddystone, and other communications receivers. 

On Sun, Oct 2, 2022 at 04:35 PM, Todd wrote:

Because of the high local MW signal levels at my home, a passive high Q loop design was essential. I constructed Gary's 4-leg PVC 9-turn 40 inch side length table top with excellent results. A smaller 2 ft side length PVC circular 'hula hoop' compliments the larger loop for more frequent kitchen benchtop monitoring. Based on certain other DXers' reports, the general DX pickup results compare favourably with 5" or 7" FSLs.

Thanks Todd,

The PVC-frame tuned passive loops do indeed still have a place in portable and Ultralight radio DXing, offering high gain at a relatively cheap price. Before the introduction of modern FSL antennas in 2011, this type of antenna was my primary gain booster for transoceanic DXing.

For those who have never investigated this type of antenna, the construction details for Todd's 9-turn 40 inch side length( table top) model are contained in the major 2009 article, "The PVC Loop-- Low Cost Ticket to High DX Gain, " posted at 
https://dreamcrafts.box.com/s/28nwynjluvrtr00nwzkr27x4ek9ha7w5
Any one of these PVC loops will make you wonder how the Tecsun AN-200 ever got out of China. You can even use the article to build a 9 foot 1 inch box loop, if your wife (or partner) has superior tolerance.

Gary DeBock (in Puyallup, WA, USA)


 

Perhaps it's time for the (semi?) annual plug for the IRCA Reprints (https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf) which include not only this article of Gary's but also many further articles by him as well as other authors.   Many of the Reprints concern ultralights and auxiliary equipment, so the index can be a worthwhile one-stop browsing companion.

best wishes,

Nick

Hi Gary,

Thanks to your online PDF construction articles, I was able to replace my run down 1984 home built wooden frame 40" MW box loop with your superior design 9-turn 40 inch side length table top PVC loop in late 2016. All new parts were purchased. This has proved to be an excellent antenna for MW DXing from my home. But due to its large size, not convenient at present to transport anywhere else.

My old 1984 MW loop was discarded on the council clean-up. Even the 365 pf tuning capacitor was unusable.

My initial unintentional step towards URL DX was when I purchased the Tecsun PL-390 for 64 - 108 MHz VHF FM DX back in early 2011. For such a small portable, the FM DX performance was indeed impressive. But I soon discovered that MW performance was also impressive. The next step was to try my old wooden frame MW box loop inductively connected with the PL-390. As expected, a 40 inch 9-turn loop provides a tremendous signal boost to a small portable. By mid 2012 I had first discovered the advantages of portable radio monitoring for serious MW DXing. I liked the convenience of quickly setting up a portable receiving system that out-performed a Drake R8B and outdoor random length backyard wire. As a consequence, the Drake R8B then took a back seat.

In 2016, I started to research other alternative AM/FM portable radio options. Based on Jay Allen's, and others reviews, I bought the Sangean PR-D15 in Dec, 2016. This was another important improvement. The PR-D15 permanently replaced the PL-390 for MW DX, but I still occasionally use the PL-390 digital numerical strength meter to determine the lowest RF noise areas inside and outside my home. RF noise from different sources tends to cluster in tight physical areas. Very useful for knowing where to position any portable radio, or antenna for maximum signal-to-noise performance. 

The Sangean PR-D3 was purchased in Nov, 2019. This replaced the physically smaller PR-D15 for general DX due to the improved sound quality. I suspect that both radios use the same, or similar DSP chip. Sangean seem to have chosen 4 KHz bandwidth for the PR-D15. This explains why the AM audio is relatively muffled. But when looking for overseas TP 10 KHz channels, I always use the PR-D15.

Due to variations in design, parts, and component layout, portable radios perform differently for MW DX. But suppose a DXer had the funds to employ an experienced RF engineer to design the best possible performing portable radio based on the Silicon Labs Si 4735 DSP chip. The first consideration would be adequate internal space to keep internally generated phase noise to a minimum. In other words, the familiar 'birdies' spurious tones that can be heard on both my PL-390 portables. This would require internal shielding as is common with the most expensive communications receivers. The IMD is a function of the DSP chip, hence that cannot be further reduced via physical design modifications. The next consideration is a larger speaker (or twin speakers) that combined with a physically larger radio cabinet enclosure, provides the best possible sound reproduction as displayed on a spectrum analyser, and subjectively to listeners. Another improvement is a longer and/or wider diameter internal ferrite rod. This would increase both 'barefoot', and inductive coupling signal pickup to nearby loop antennas. Other potential improvements include front control placement, and physical size of digital frequency readout. This would prove to be an expensive exercise. With R&D, part sourcing, and construction time, the end cost would be potentially thousands of dollars. But there are commercially available portable radios that do somewhat approach the theoretical ideal. Among a large universe of options, it takes someone like Jay Allen to identify them.

Regards,

Todd

 

Would Shawn's loop be the one described in IRCA Reprint A-129, Art?

https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf

also now mirrored at dxer.ca     http://dxer.ca/images/stories/2019/irca-reprint-index.pdf



best wishes,

Nick

Yes it would.
I am glad it is still out there.
Only difference is that mine does not tilt. It is always vertical.

They are great performers. Only issue is that they are large, bulky and tough to transport.
I have had my 2 since 1997 and 2000. Built in Texas, moved to Arizona, then to Oregon and in 2 weeks back to Texas 😎

73 Art K7DWI

This I built this time last year. Coil former is a 30 inch maple drum hoop. Coil is a twin pair of 3000/46 Litz, 120 uH, capacitor is a Comet 10-1000 pF vacuum variable. The inner loops are 1/2 inch copper tape on inside of drum hoop, for feedback, and the pickup is 1 turn of shielded RG174. There is a gap in the coax shield at the apex, and a balun at the base. Behind the support are a Mini-Circuits low noise amp and a Mini-Circuits signal splitter. The regeneration control is a 500 Ohm 10-turn pot behind the small black knob to the left of the capacitor’s shaft extension.

It sits on a big lazy susan I built. The loop sits on a hanger built into the base, and has a tilt knob.

It works REALLY well unless you factor in the cost of the parts. I would have been better off building an array of terminated loops with Wellbrook flag amplifiers and a dxe phaser with that money. Live and learn.