Review: LF Engineering H800 Skymatch Active Antenna
Last updated Aug 24 2005
Review: LF Engineering H800 Skymatch Active Antenna
Last updated Aug 24 2005 |
Review
I compared a LF H8000 with a random long wire hanging in my attic
(see above) using a Sony 2010 portable receiver. Despite my initial
misgivings about the antenna, which looks like a
plastic baseball bat attached to a 50-foot cable, the LF H8000 was
a great improvement over the wire. There is a small preamplifier
hidden inside the bat part, which gets power from a small unit at
the other end of the cable that couples the antenna to the radio.
The manufacturer doesn't say what is inside the antenna, but
claims it's not a whip.
The LF H8000 gave the greatest improvement in the MW band, where the radio has poor sensitivity. Stations that went undetected with the radio's ferrite loop or the longwire were clearly readable when the H800 was attached. When I hooked up the antenna to a VLF converter, and unplugged a number of electrical appliances to reduce the power line buzz, the antenna was easily able to pick up the WWVB coded signal at 60 kHz, the huge LORAN-C signal at 100 kHz, and air navigation beacons throughout the LF band, along with a bunch of other unidentified bleeps and squeals. However, depending on location, when the antenna was indoors the performance in LF was not always as good as the receiver's internal ferrite loop, and the greater sensitivity to the E signal compared to the ferrite loop caused a few problems. This was particularly evident when I moved the antenna to the basement, which is the farthest point from my computer (do not even suggest turning off my computer!). In this low-noise environment, the Sony's ferrite loop picked up the nearby Gaithersburg beacon at S6, while the signal from the LF H8000 was only S2-S3, and was unable to completely null the powerline noise. This illustrates the importance of elevation for good performance of this antenna.
In MF and HF, performance was much better than a random wire. All signals were increased by at least 2-3 levels (using the Sony's scale of 0-10 LEDs); more importantly, many signals that were previously entirely drowned in receiver noise were loud and clear. When the antenna was mounted in the attic, MF signals were comparable in strength to the signals received using the Sony's large ferrite loop, but had lower powerline noise. Mounting the antenna outdoors produced the best result, with WWVB and European shortwave signals pegging the signal strength LED display at 10. LF reception was also improved; however, at some frequencies, the faint European signals that were detected between 150 and 250 kHz were mixed with images of strong HF and MF stations. The LF H8000 also had some deep nodes, especially between 7 and 10 MHz. Wrapping a 10-foot wire around it as suggested in the instructions improved this somewhat. Not unexpectedly, the antenna was of no value for higher frequencies and VHF.
Unlike other active antennas that are shaped like a giant hula hoop, this one would be inconspicuous enough to go unnoticed attached to your roof. Although the antenna is waterproof, the instructions are a bit vague on the subject of lightning protection, saying only that it has "extended ESD and RF protection". A close strike would probably fry the antenna's electronics. I highly recommend it, however, as long as it's mounted at a high enough location.
Final Setup
After trying unsuccessfully to get noise-free MW and LF signals from
this antenna when it was mounted in the attic, I finally gave up
and mounted it outdoors on top of a wooden fence about 20 feet from the
house. At this location, it was inconspicuous enough not to cause any
problems with our Homeowner's Association, which forbids outdoor
radio antennas. I also got rid of the thin coaxial cable that was
supplied with the antenna and connected it to a 250-foot length of
RG58 using BNC connectors.
This setup produced an excellent signal/noise ratio throughout the LF, MW, and shortwave bands up to at least 15 MHz (note: I have not yet tested this setup below 150 kHz). In my area, reception on the LF band is normally very difficult because of the neighbors' electrical appliances. Even a tuned loop antenna (which gives a much stronger signal in LF than the LF H800) can only be used in my location during the daytime due to interference from halogen lights and light dimmers, because it can't be located far enough away from the house. However, the LF H800 gave a signal on LF that, while not as strong as that from a tuned loop, was often almost free of buzzing, even during times when the receiver's ferrite loop could not pick up anything indoors but a loud buzz. The selling point of this antenna is its compact size, which allows it to be mounted in a better location than most other antennas.
To fix the problem of low LF signal strength, I added a model L-202 LF preamplifier between the active antenna and the receiver. This preamp has adjustable gain and a cutoff filter that attenuates MW broadcast signals. This filter is not adjustable, and MW signals below about 700 kHz still leaked through. This is inevitable in any good filter, but it's a problem in my area, where we have a large BCB station at around 570 kHz. With the preamplifier, the signal strength of LF signals was almost as high as with a medium-sized loop antenna, without the need for manual antenna tuning. The tradeoff, of course, is that some MW signals that the filter doesn't block may still get through to your receiver and show up as images. Although the preamp eliminated the image of the Chinese-language shortwave station that had been showing up in the LF band, MW broadcast stations were still audible at several points on the LF band. However, with this combination, something other than receiver noise was finally detectable throughout the 150-400 kHz band.
Adding a wideband preamp was a disaster, however, in the higher MF and HF regions. With the preamp, which was rated for 1.8-30 MHz, the range between 2 and 3.5 MHz was populated almost entirely with MW BCB signals, sometimes two at a time. This would probably happen with any active antenna. But if you don't have the real estate for a real antenna, the LF H800 is an excellent alternative. With an active antenna, there is only one variable in antenna placement: getting the antenna as high above the ground and as far away from electric appliances as possible.