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Tricks in the art of nulling

By Mark Connelly
hcdx list, September 4, 2000

On Saturday, September 2, 2000, I stopped in at Vern Brownell's QTH (W1VB) on Eastward Road in Chatham, Cape Cod, MA.
Vern has recently become interested in medium-wave and his house is right on a private beach: ideal for DX.
One purpose of my visit was to consult on a good antenna system for medium-wave DXing. There's a reasonable amount of land between the house and the beach, certainly not enough for a Beverage but adequate for two 50 m (160 ft) wires, one northeast and one southeast. This is the first system we rolled out.
I had a phasing unit with me and I told Vern that by combining the two wires through the phaser we could generate a good east- west cardioid pattern that, if set up for the west null, should give a good 120-degree wide sweep of DX targets from Europe and the Middle East on the northern end to Africa and Brazil on the southern side of the optimum pick-up zone.

It soon became apparent that electrical noise carried on house wiring was too high in amplitude - about S8 - for the wire antenna system to work. The noise could be totally nulled with the phasing unit, but using phasing for that took away the real objective: nulling out pesky New York stations and other unwanted broadcast interference from the west. Sometimes a noise null might coincide with a "pest" station null, but more often it didn't. Maybe you'd even be nulling desired DX instead. The results would just turn out to be a "crap shoot" with little predictability.
Connecting the two wires through a balun reduced the noise a little (down to about S5) but that took the nulling option away unless a third antenna was introduced. Vern and I concluded that even this level of noise was excessive. We connected the "beach ends" of the two wires to change the "vee" into a horizontal triangle. Signal levels were slightly higher but the mains noise still wasn't low enough for weak-signal DXing such as during aurora or during initial (1 hour or more pre-sunset) Trans-Atlantic fade-ins. Certainly it wasn't good enough for 160-m ham DXing where the signals are orders of magnitude weaker than the big European medium-wave broadcasters.

I still knew that there were some "tricks of the trade" that could work. Even that "mecca" of MW DXing Cappahayden, Newfoundland had some electrical noise issues that had to be solved. One of the visitors at Vern's mentioned that he used to work for a power company in Pennsylvania chasing down sources of electrical interference. All of us know that the degree of cooperation that power companies give to hams and radio listeners can vary greatly. It is often in the power company's interest to find and eliminate noise sources, more because the noise often emanates from their own equipment that may be in the early stages of a possibly catastrophic, dangerous, expensive, and service- interrupting failure. The threat of FCC intervention (in these days of a relatively toothless agency) is probably a secondary concern at best.

Vern and I went around the house with a transistor radio to see if the noise peaked up at any single spot. The worst of it was at the circuit breaker box (unfortunately quite close to the ham shack) and we concluded that the RFI was probably riding in on the mains from an outside source. The power conduits are underground but that didn't seem to make much difference in the immediate vicinity of the house. Perhaps Vern's friend can help him eventually deal with the power company.
In the mean time, I knew that I had a good chance to eliminate the noise pick-up by using a balanced loop antenna at least 15 m / 50 ft. behind the house. I installed the 1.8 m per side square single-turn broadband loop (BBL-1) that I use on the roof of the car during beach DXpeditions. The loop was aimed for east-west and positioned about 15 m behind the house along the border between the lawn and a low cluster of pitch pines and red cedars just above the beach. We turned on the Drake R8A after deploying the loop and "voila": very low noise. Weaker daytime groundwave stations were now out of the "muck".

We still wanted to have another antenna available to allow nulling of domestic stations to the west. The wire antenna that we'd installed was too much of a noise "picker-upper" to be of much benefit. I knew that a right-angle two loop system: one aimed northeast and the other southeast would work very well into a phasing unit adjusted to knock out westerly stations. I've used a similar set-up at other house locations where longwires were totally useless because of local electrical noise.

By this time it was about 6 p.m. local (2200 UTC) and skip was starting to build. I had the broadband loop feeding channel 1 of the phasing unit and the noisy wire arrangement going to channel 2. For cruising the dial, I left the unit set for reception from the loop only. Not surprisingly, Saudi Arabia - 1521 was the first Trans-Atlantic "out of the box" with a heterodyne against WGAM/WWKB/WTHE-1520 at 2210 UTC and good room- filling audio by 2225. This is about an hour before sunset. Other early arrivers included Algeria-981 and Libya-1251. Vern had a R9000 receiver on the other side of the room. He brought up good Libya audio on that: just about as clear as what I had off the loop on the R8A. I asked him what antenna he had attached to the R9000: after all it didn't seem to be picking up much noise. The antenna was a ham band (VHF, I think) coax-fed vertical groundplane. I said "Let's phase that against the loop". Noise problem solved ! We could now DX seriously. I "walked up" to one NYC station after another and then "bam !" nulled them into the dirt. I had Croatia/Spain-1134 louder than "next door" WBBR-1130. Morocco-1053 was blasting in at S9+30 next to a feeble remnant of nulled WEVD-1050. We were ready to rock.
Vern and I cruised the dial from 7 to 9 p.m. EDT (2300 to 0100 UTC). I didn't write anything down, but I know we heard, as a minimum, the following signals: Algeria-549, Spain-585, Canaries-621, Spain-639, Spain-684, Spain-774, Egypt-819, Azores-836, Canaries-837, Italy-846, Spain-855, Egypt-864, Canaries-882, Algeria-891, UK-909. Spain-918, Spain-954, Spain-972, Algeria-981 (and later possible Greece), Spain-999, Canaries-1008, Spain-1026, Morocco-1044, Spain-1044, Morocco-1053, Spain-1080 (almost equal to WTIC !), UK-1089, Spain-1107, Spain-1116, Spain-1125 over Croatia, Spain/Croatia-1134 even mix ... huge!, Spain-1143, Spain-1152 over possible Romania, Canaries-1179 slightly over a big jumble (Sweden?, Greece?, Romania?), Spain-1197, unID-1206 (low audio), Spain-1215, UK-1215, Spain-1224, unID-1233 prob. Morocco, Libya-1251, Spain-1296, Spain-1305, Spain-1359, Spain-1413, Germany/Algeria-1422, Spain-1485, unID (Saudi Arabia or Belgium)-1512 in WNRB slop, Saudi Arabia-1521, Spain-1521, Kuwait-1548, Algeria-1550, unID-1557 (France ?) in WQEW hash, Spain-1575, Spain-1584, Spain (EI)-1602 big (stronger than WUNR/WWRL-1600).
The best signals were in the mid-band (1000 to 1200 kHz) segment. Low band conditions were poorer by comparison.
Latin Americans were weak: even RVC-530 wasn't too good.
I left a bit after 9 p.m. so Vern could get back to his guests and I could get over to W. Yarmouth to sleep before going home early the next morning. I'd been up since 5 a.m. and would be arising at the same time on Sunday.

Most likely Vern will have me install a phasing unit and at least one low-noise loop over at his place on a subsequent visit. He told me that he'd probably join the National Radio Club soon and that he's likely to show up at some of our monthly Boston Area DXers meetings in Lexington, MA. The mind boggles at the DX logs that will be possible from Vern's excellent location on the shore in Chatham, not far from old (now-deactivated) WCC. Who knows - maybe a "delegation" of the Boston Area DXers might show up down there in the winter for a DXpedition. They used to go up to Chamberlain, ME for this.

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