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Practical Wireless Technical Review: Alpha Loop 10-80m Magnetic Loop Antenna


Practical Wireless Technical Review: Alpha Loop 10-80m Magnetic Loop Antenna

As featured in January 2018, Practical Wireless
Author: Carl Gorse 2E0HPI 

Carl Gorse 2E0HPI takes a look at yet another antenna suitable for portable operation.

Having used many antennas for operating portable around the UK, I decided to contact Alpha Antenna USA to try out one of their latest products. I’m talking about the Alpha Magnetic Loop antenna, available in the UK from PW advertiser Moonraker. I wanted to try this loop because of the extra bands available compared with the Alex Loop that I have been using recently. The latter covers 7 to 30MHz (the 40 through 10m bands) while the Alpha Loop continuously covers from 3.5 to 30MHz (80 through 10m, including the 60m allocation). Alpha Antenna were very supportive, organising delivery via Moonraker UK. I have now had the opportunity to try out the antenna from locations throughout the UK, with some excellent results.

The Alpha Loop in its 40-6m form is a magnetic loop antenna consisting of a single (Faraday) loop of LMR-400 low-loss coaxial cable. An SO-239 connector on the smaller loop, which also consists of LMR-400, couples to your feeder. There is a tuning box, Fig. 1, with a 6:1 Vernier drive to make tuning easier, and other associated hardware. For 80 and 60m operation, along with improved performance on 40m, an additional length of cable (a so-called Booster cable, which attaches with Velcro straps in series with the 10-40m outer loop) can be added, resulting in a two-turn loop some 120% longer than the single loop. The antenna is rated at 30W PEP (SSB) or 15W for CW and continuous (data) modes.
The antenna comes with a tripod, Fig. 2, carrying bag, Fig. 3, and ‘Selfie stick’, Fig. 4.
A more detailed description, taken from the Alpha website, appears in the sidebar. See also the Alpha Antenna website

Setting Up and Tuning
Although the promotional material says that the antenna deploys in five minutes, in my experience it is more realistic to allow 10 to 15 minutes to set everything up when out portable. The tuning is done in the same way as with many other loops, manually tuning for maximum noise and then fine tuning for best SWR. Tuning is easy but very sensitive, hence to the 6:1 vernier drive. It is necessary to tune slowly and carefully – the peak will be very sharp and the loop will need retuning if you move frequency by more than a very small amount. I would recommend tuning at low power (say 5W or less) to avoid any damage to the transceiver.

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Comparison with Other Antennas
I tested the Alpha Loop against a vertical on a recent visit to Blackpool where I met up with Dave G4AKC who operates from the shores of the Lancashire coast and always manages plenty of nice contacts. We used the same power, 30W, and were roughly 500m apart and on the 20m (14MHz) band. On the vertical, signals were much stronger than the loop by around four S-units, which is probably about what you would expect. However, the loop performed very well with contacts into VK7 Australia (via the long path) with a report of RS45 and to PY7 Brazil with a 57 report. For a loop of its size, I consider those contacts to be an excellent achievement. I also operated using 15W from the Ribble Estuary and worked roughly 95 contacts around Europe as well as K1RO on the east coast of the USA.
In more recent activity, during the CQWW Phone Contest (reported in this month’s HF Highlights column), I was pleased to work 8P5A in Barbados and the PJ4Q team on Bonaire.

Other Results
On the 80m band (where, of course, the loop is very small relative to a wavelength, even with the Booster Cable), I have successfully made a number of contacts around the UK. Although the specification says that the antenna works right across the band, I was only able to tune it successfully from 3.650 to 3.785MHz. However, in subsequent discussion with Steve of Alpha Antenna, it seems that the trick is to have more separation between the two loops.
On the 40m band, adding the Booster loop, Fig. 5, appears to improve performance by two to three S-points and I also noted when using the loop from home that it was significantly quieter on the 40m band than my half-wave dipole.
At the time of writing, I have tried the loop on 80, 40 and 20m on SSB and on 40, 20, 17 and 15 on the FT8 digital mode, all with good results both from home and out portable. 

Quality of Construction
The Alpha Loop is made from high quality Times Microwave LMR-400 with high grade silver-plated PL-259 and SO-239 connectors. The main tuning box is fully waterproof and the fixing hardware consists of stainless steel nuts and bolts.
I did find that the Selfie-stick and the main tuning box were a little top-heavy, causing the tripod to tilt and fall over a few times so I took to using some short guy ropes and pegs where needed. I thought that the tripod was a little on the small side given the size and weight of the antenna. However, Steve at Alpha Antenna tells me that the tripod I have been using (and as supplied by Moonraker) is intended primarily for indoor use and that the heavier (HD-FMJ) version is available for outdoor purposes (see the Alpha Antenna website). This is not currently sold in the UK but other options are available such as photographic tripods and the like (see Carrying on the Practical Way in this issue for a discussion of exactly that topic).
Incidentally, Steve also recommends the use of a little grease between the tripod and matching box, especially when out portable, to avoid threads binding when subject to salt, sand and the like.

Price and Availability
The Alpha Loop retails at £399.99 from Moonraker UK who are the main UK dealer for Alpha Antenna USA.

The Alpha Loop has been a really nice antenna to use with some excellent contacts on all bands. For me, it wins over other loops I have used, if only because of the size of the loop and the high quality of construction, making it very suitable for extended or repeated outdoor use. So even taking some minor criticisms into account, I feel it represents good value for money and it’s an antenna I would definitely use on future trips. Indeed, I am planning for it to be part of my kit for a visit to Jersey next year.

Alpha Antenna have other portable and base station antennas in their range, including a directional antenna that can also be used as a vertical and that requires no additional tuning unit. I hope to be taking a look at some of these over the coming months. For now, I would like to thank Moonraker UK and Steve at Alpha Antenna USA for the loan of the antenna for the purposes of this review.

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