One of my plans after I finish my PhD is to take some time off and travel the world. Being an engineer at heart, I don’t just take “regular” holidays – I need to bring my hobbies and experiments along. For radio enthusiasts, some take holidays just to chase down signals, something they often term a DXpedition. While I am not as dedicated as that, I still think it would be nice to sample the radio spectrum at different places around the world “while I’m there”, laws permitting (of course).
A particularly challenging portion of the spectrum is HF or shortwave. As I’ve mentioned several times before, Australia isn’t really the target of many signals, so hearing things down here can be a little difficult compared to Europe, where signals are ample. Even highly sensitive portable radios, like the Degen DE1103 of which I have two of, struggle to bring in any intelligible broadcasts with their 1 meter whip, or with the included ~10m of wire strewn across the room or even out a window. Some targeted broadcasts are “listenable” but hardly pleasurable.
The bigger issue in HF is noise. That part of the spectrum is particularly vulnerable to natural and man-made sources of noise – with cheap switching converters, computers, monitors, solar garden lights, poorly design light globes and Ethernet over Powerline (HomePlug) devices amongst others spewing out noise across the band which masks the signals we want to hear. Sadly, there is little we can do about this, and where signals are weak, a longer longwire antenna can end up picking up just as much noise as signal, resulting in a signal that is stronger but not any clearer.
My saviour has always been the Wellbrook Communications ALA-1530L – a shielded magnetic loop antenna that looks a little like a shiny rigid aluminium basketball hoop, of about 1 meter in diameter. It pulls in signals which are buried under the local noise much better than anything else, but it is very expensive (especially due to our falling exchange rates) and it is, for the most part, not something you can pack in your luggage and fly off with. It would be nice if it were possible though! Since then, there have been numerous improvements to the design, although tempting, I don’t quite have the pockets for it at this time.
So what is a traveller supposed to do? If you’re in a hotel, chances are that there’s a million LCD TVs, variable speed lift motor drives and light globes in close proximity spewing noise to oblivion. This means your regular telescopic antenna is probably hopeless, along with amplified regular whips. Often, because of vertical construction, you don’t have more than perhaps a balcony to use to put an antenna out, and hanging a wire over the edge just doesn’t seem like a good idea.
While trying to work out the answer, I came across several amplified loop antennas designed for travelling. One is the cheaper Degen 31MS, which is made with a soft wire loop, is about AU$30 but looks flimsy with a touchy tuning wheel and mixed reception. Aside from that, there is the Sony AN-LP1 Active Loop Antenna, which has better build quality, some innovative features and better reviews, but is only available in Japan and is much more expensive. Luckily, we have eBay, so AU$130 and about a month later, I managed to buy one and run it through its paces to see what it is capable of.
Unboxing and Set-Up
The product, similar to some other Sony products, comes in a relatively bland cardboard box with monotone printing. The box itself is around the size of a hard-cover novel. Rather encouragingly, the product is Made in Japan, so we’re definitely expecting quality. The J on the label, I believe, indicates Japanese market product – the AN-LP1 doesn’t appear to be available anywhere outside of Japan. The antenna claims coverage from 3.85Mhz to 21.95Mhz.
Included inside the box is two carbon-zinc style AA batteries (so you can get started immediately), a telescopic whip adapter, and a drawstring bag containing the antenna units.
Also provided is several pieces of paper, including an instruction manual copyright dated 1997 (making this product design 18 years old), a warranty registration card, some warning and support guides and an instruction manual for the included filter module.
Inside the bag, we find the antenna module itself, which has a suction cup for mounting on windows, or a clip for hanging on blinds. The clip itself is very sturdy and capable of hanging onto most things. The antenna itself seems to be modelled on a foldable car sun-shade, and is shown in the stowed and clipped position. To the right is the in-line filter unit.
Also included is the antenna controller unit, roughly the size of two stacked cassette tapes. The big wheel is the retractable antenna cable winder, with a slide switch and LED for power, and a rotating selector to choose the centre frequency of reception. It feels relatively solid, and the winder is smooth to operate.
The unit is powered by two AA batteries (included, as above), and internally stores the antenna cable in a spool (about 4m length). The output from the unit is fed out to a mono 3.5mm plug via a cable that wraps around the edge of the controller and nestles in a cut-out in the bottom right of the image.
The connectors themselves are moulded and Sony branded, and is generally “idiot proof”, however, the wires are quite thin, so care should be taken when pulling them in and out. It also seems that the antenna cable has been waxed for additional lubrication, and when rewinding, wax accumulation can be seen at the edges of the casing. It’s nice to see the attention to detail.
When set-up, the antenna looks like a sun-shade or an oversized microphone pop-screen.
Connecting it Up?
As the output of the antenna controller is to a mono 3.5mm jack, intended for Sony portable receivers, connecting it to serious reception gear that has a BNC or SMA coax connector seems to be something that’s not straightforward.
I reasoned that the connector is often used for external long-wires to be connected to the radios, thus, is a high impedance input. So therefore, we should probably treat the output of the antenna as a high impedance signal. This means we should use a longwire adapter. It’s probably clear why I bought another one … to modify. First step was to remove the banana jack, and replace it with an old fashioned 3.5mm mono jack (from my scanner discriminator mod days). The hole itself has to be drilled to 6mm to accommodate the jack, which is then screwed into place and soldered.
This does leave the question, what about the ground? In fact, the ground should be common to both jacks, so I decided to get a piece of short insulated wire to bridge them together.
With this interface, the 3.5mm mono plug can be converted to a BNC output for feeding a proper receiver with convenience. I decided to go one step further and fill the inside of the box with silicone, except the area around the 3.5mm jack so that it can still fit in. This will provide mechanical rigidity to the ferrite toroid and wires, so they don’t break under mechanical shock.
Of course, I thought I did the right thing, so I tested it out with my Tektronix RSA306, using it “directly” connected to the analyzer input (top) and via the longwire adapter (bottom).
As it turns out, the signal seems to be marginally stronger with it directly connected. The high frequency noise also seems to be lost with the longwire adapter. Hmm. Maybe the amplified nature of the antenna has an output impedance low enough to drive a 50 ohm input directly … and all of this is in vain?
Of course, if you’re using a portable receiver, it may well have an external antenna jack which would be the right fit, or you can use the included conversion clip which clips onto the telescopic antenna itself.
While I was at it, I decided to compare the two longwire adapters with the output from the Sony loop, flipping between the tuning settings – in all, it again seems to confirm that the WiNRADiO is marginally better, but not in any big way.
The included filter unit did arouse some of my curiosity – did it have any noticeable effects? The Tektronix RSA306 seemed to answer that with a definite yes.
It seems there is a spike of interference at about 8.5Mhz which is much attenuated by adding the filter module in-line as described by the yellow leaflet. This may be because this is local electrical interference which is getting into the retractable antenna cable which is not shielded and the filter is acting as a choke.
Frequency Selector Operation
Lets see what happens as we twist the frequency selector dial.
It’s clear that changing the frequency selector dial does impact on the peaking of the signals from the loop. In this way, the loop itself acts as a pre-selector, only really amplifying the frequency band which is selected. The bands are narrower towards the low-end of the spectrum, and it seems more gain is available, whereas towards the higher end, the bands are wider and the gain is somewhat reduced. It seems that the loop also handles decently strong MW transmissions just fine, with them attenuated to a satisfactory level (although, this unit is not specified for MW reception at all).
As the tuning switch is fixed in its selections, it is not possible to continuously drive the peak to any frequency from the controls provided. This may mean that the reception is sub-optimal for some frequencies within the bands, and possibly, very sub-optimal for between-band frequencies.
A quick electrical check of the connections – of which there are five – had me concluding the following:
- 3.5mm mono jack – tip is battery +’ve, ring is ground.
- 2.5mm stereo jack – tip is tuning voltage +ve, ring is tuning voltage ground, and sleeve is the antenna signal.
Therefore, the 3.5mm plug carries power from the batteries (it’s always ~3v regardless of the frequency selection), whereas the front two contacts of the 2.5mm plug carries a tuning voltage – 1v at 4Mhz, and 14v at 20Mhz. This is probably used to drive a varactor or similar to control the frequency peaking – which theoretically could be anywhere provided a continuously variable voltage is produced.
As the unit is powered by two 1.5v cells, there must be a switching converter of some sort inside the unit to provide the higher voltage required for tuning. This leads me to believe that some of the observed interference spikes may not be local interference from electrical appliances, but could also come about due to leakage of the switching waveform harmonics into the RF chain.
A quick check of current consumption showed that the unit consumed 10.07mA at 3v, thus a set of alkaline batteries can be expected to last well over 160-200 hours of operation.
From connecting the antenna to my Degen DE1103’s external antenna jack, it seems that the signals are received less strongly than with the telescopic whip indoors. This might be due to the relative gain difference, as using the telescopic whip adapter seemed to provide better results, although interference was troublesome with the DE1103. Throwing out a long piece of wire indoors picked up more noise – so the loop antenna seemed to have an advantage when it comes to local interference.
Using it with the longwire adapter and my Icom IC-R75, I could easily compare the performance of the loop indoors (ANT 1 input) and the 15m longwire outdoors (ANT 2 input). On the whole, the longwire outdoors beat the loop indoors every time, and the difference was quite noticeable even on local broadcasts (i.e. Bureau of Meterology weather voice and fax). This is particularly disappointing when we consider that the Wellbrook loop, also outside, outperforms my 15m longwire with a noticeable margin too. As a result, the Sony loop doesn’t seem to collect enough signal to be a good candidate for even receiving lower-powered local transmissions. This is clearly reflected in this local radiofax received with periodic antenna switching from internal (noisy, dark fades) to outdoor longwire.
On broadcast transmissions targeting Australia, the performance was acceptable and the audio was intelligible, although the noise level seemed higher than the longwire.
Using it with the longwire adapter and my WiNRADiO G31DDC was also possible, although it clearly showed the problem with “peaking”, as SDRs can have wide-band operation which exceeds the peaked reception bandwidth of the loop. The peaks seem optimized for broadcast bands, so hams and utility monitors may find lower gains where they need it most. The broadband Wellbrook is very much preferable for this reason. The signals were of no real difference, with the Wellbrook and 15m outdoor longwire preferable. If I would have to say, the performance of the Sony loop is probably about a 7.5m long-wire roughly.
The convenience is that it is easily packed, easily set-up and less sensitive to local noise, but for DXing, it is a bit disappointing. Although, that being said, as the service manual seems to be available online, there may be potential for modifications and improvement.
It’s no Wellbrook loop, nor is it even a match for a 15m longwire placed outside which is noticeably worse, but to compare it to those would be rather unfair given the Sony sits indoors – closer to sources of interference.
When using the antenna, at least in Sydney, it seems it struggles to bring in enough signal. Compared to the telescopic on the DE1103, the performance is much better. Signals which are barely discernable on the telescopic are listenable under the loop. It’s a shame it’s not “clear as a bell” like it would be on the Wellbrook. Part of the reason probably comes down to the smaller loop aperture of 50cm diameter, which reduces the collected signal. Being closer to interference is a disadvantage as well.
The tuning dial can be seen to act as a pre-selector, eliminating one of the issues with lower cost receivers in their rejection of out-of-band signals. This in itself can be of a benefit for portable low-cost radios, but is a disadvantage if you are intent on using it with wide-band SDRs. Because the tuning dial is “stepped”, accurate peaking of the signal is not possible, and only pre-tuned peaks can be selected. Broadcast-band listeners are probably not going to see significant disadvantages from this, however, outside of broadcast-bands, the reception might not be optimal.
Of course, the antenna is designed for use with Sony equipment, specifically, some models of their Word Band receivers. I did try it with the DE1103’s Ext Ant input, but found the signals to be worse than the telescopic (probably due to low gain on the external input), and thus the telescopic antenna clip seemed to work better (but then you do get some local interference to boot). Using it with more serious gear proved to be an interesting challenge – using my gut feeling of putting in a longwire adapter for impedance matching seemed to provide no real benefit to the signal output compared to direct connection, which was not particularly strong, but it was still usable with my Winradio G31DDC and Icom IC-R75. Some harmonic-style interference spikes were seen, which may be a product of local noise and/or the internal switching converter inside the unit used to generate the tuning voltage.
Regardless, it seems to be a niche product, which probably works well for its intended purpose – i.e. listening to target-area broadcasts with table-top portable receivers. For the DXer, it probably still has benefits over telescopic antennas because of its lower sensitivity to E-field interference, but it doesn’t have enough “copper” to pull in the weaker signals as a longwire would. If travelling in strong reception areas, it will probably be enough, but for DXing, it seems it isn’t really an optimal choice.