Comments on low-noise antenna
design in Sept '95 QST

The antenna reduces line noise very well. (John S. Hill)

The loop is *very* effective on TV and other noises. (Guy Atkins)

Fairly narrow bandwidth; you'll have to tune it remotely for tropical DX. (Steve Byan)

Why tune a receiving antenna? (W8JI, Tom)

Best against strong local QRN, otherwise may perform poorer than a regular antenna. (Bill Turner)

From: John S. Hill (nj0m@primenet.com)
Date: Sept 5, 1995
Original source: Usenet's rec.radio.amateur.antenna

I built one with only 17ft on a side and boy does it work as advertised where line noise reduction is concerned. I live in an old neighborhood in the city. My 3/8 wave vertical receives line noise very well. Unfortunately, the loop doesn't do well with atmospheric noise, so it'll be a while before I can assess how it does with weak DX signals. Listening to stateside signals, my line noise on the vertical was 10 over S-9 and only s5 on the loop. Signals from both coasts were down about 15db on the loop, so the reduction in line noise was greater than the reduction of desired signals. Can hardly wait for the winter to arrive.



From: Guy Atkins (gatkins@gatkins.seanet.com)
Date: Sept 10, 1995
Original source: Usenet's rec.radio.amateur.antenna

I've built this antenna as described by the authors. The only differences are that I changed the tranformer ratio to match the ladderline to some 75-ohm Belden cable I had on hand, and I also resonated the (25 ft. square) loop to 3.3 MHz, which is in the middle of the 90 meterband of interest to me for foreign broadcast.
After using the antenna for 4-5 days against my 350 ft. long terminated, matched mini-Beverage and my Carolina Beam, I'm impressed with this loop. It is *very* effective on TV horiz. oscillator noise, the occasional powerline RFI I get here, and other local noises here. Like the articles stated, there are some noises that the loop seems to have no effect on. However, I find than S/N ratio is usually improved 3 to 4 S-units or more (after signal levels are equalized). A good, low-noise preamplifier is helpful with this antenna.
Although my version of this loop is resonated for 90 meters, it has been helpful on the 75 meterband foreign broadcasters, too, such as RRI Pontianak on 3976.7 kHz (Indonesia). On all other bands and frequencies the signal levels are WAY down, and antenna performs poorly.
It was definitely worth the effort to construct this noise-reducing loop! I'd like to try another one for the 60 meterband, or maybe modify my current one for switchable 90/60 meterband use, similar to the 160/80 meter version described by the QST author.



From: Steve Byan (steve@hi.com)
Date: Sept 14, 1995
Original source: Usenet's rec.radio.amateur.antenna

Guy Atkins wrote:
The low-noise horizontal loops described in two articles in the September QST sounds very promising for improving S/N on the lower bands.
The theory sounds good. I plan to try something along those lines this winter. However, note that the antenna is a tuned loop with a fairly narrow bandwidth. For tropical band DX use, you'll have to tune it remotely, perhaps using varactor diodes.
Note that a small loop antenna, such as the design in Fine Tuning's "Proceedings" a few years back, has the same noise-reducing antenna pattern when mounted horizontally. Its disadvantage is a much lower signal strength, hence the need for the high-gain low noise loop preamp. I don't know if the preamp design in the Proceedings has a low enough noise figure for the small loop to be competitive with the QST design with respect to weak DX.



From: W8JI, Tom (w8jitom@aol.com)
Date: Sept 14, 1995
Original source: Usenet's rec.radio.amateur.antenna

Note that a small loop antenna, such as the design in Fine Tuning's "Proceedings" a few years back, has the same noise-reducing antenna pattern when mounted horizontally. Its disadvantage is a much lower signal strength, hence the need for the high-gain low noise loop preamp. I don't know if the preamp design in the Proceedings has a low enough noise figure for the small loop to be competitive with the QST design with respect to weak DX.
I had poor sucess with this in the past. The horizontal small loop close to the ground lost so much sensitivity it was useless with the best pre-amp. But I'm sure the sensitivity would be better over very poor soil.
Remember a receiving antenna really doesn't need to be tuned. You can make up for the lack of efficiency with a pre-amp at the antenna. I see no reason why the antenna couldn't cover octaves of BW. It's done all the time with receiving loop arrays.



From: wrt@eskimo.com (Bill Turner)
Date: Sept 16, 1995
Original source: Usenet's rec.radio.amateur.antenna

My K6STI antenna has been up for about a week now, and here are a few comments on it's functioning:
1. For comparison, my regular antenna is a full size 1/4 wave ground-mounted vertical with 25 1/4 wave (almost) radials, remotely tunable, max SWR = 1.3:1.
2. I installed the K6STI antenna at a height of 10 feet. It is 12 feet on a side and square +/- about one inch. Fed with 450 ohm transmitting type open wire line as shown in the article.
3. It really does reduce locally-generated QRN, just as claimed in the article (September QST).
4. At a height of 10 feet, used on 80 meters, it is NOT a DX antenna -- low angle signals are weak, as one would expect. No magic here.
5. No preamp was needed. Plenty of output when resonated. I'm in a typical suburban locale (Seattle), so a really quiet location might benefit from one.
6. Because of the smaller size, I needed more resonating capacitance than the example in the article -- about 150 pf.
7. Bandwidth is about the same as in the article -- the +/- 3db points are about 50 kHz apart. (Rough estimate).
Conclusions: It works as the author described, but it's best use is where a strong local QRN situation exists. If there is no QRN, it has no advantage over the regular antenna, and in fact is actually poorer. Keep in mind this applies only to my installation. If you install it higher or size it differently, YMMV. Again, it's only been up a week, so evaluation will continue.