This year's contest gave us some pleasant surprises, not the least of which were much higher station counts and some really super DX. Bill Wilson checked in with a whopping 117 stations in the Open Class, but placed third, mostly due to a number of unidents - he will probably resolve them by next year, so watch out! Mike Tuggle placed #1, using large litz wire coils, basket wound, from a favorable location - he is in Hawaii, and scored a bunch of west coast stations at 2500+ miles. Now for some specifics:
Antennas: Lots of wire "out the window" seemed to be a significant factor, as did getting the flat top portion high in the air. Mike Tuggle had room for only a 50 foot flat top section, but used 3 parallel wires to give him some more capture area. Antenna tuners were allowed in the open class, and were the norm. Separate antenna tuning was not an option in the Hobby class, which only allowed one tunable coil. My solution was to use a big antenna with a fixed loading coil to transfer signal to the set's tank circuit; I played with the turns on the loading coil until I was able to get pretty much across the band. It worked pretty well with the 4 inch diameter coils and some 200 feet of antenna wire. The most successful sets used inductive coupling between the antenna and tank coils.
Coils and variable capacitors: For the most part, large diameter (3+ inches) coils using large wire, on the order of #20 and larger, were found in the top scoring sets. The litz coils used by Mike had measured unloaded Q in the range of several hundred. Air variable capacitors were also the norm. Mike used the best high Q capacitors he had, and wound his coils to match the value of the capacitors; in so doing, he bucked conventional wisdom a bit, which suggests that a high L to C ratio is preferred. His coils were under 200 uH.
Detectors: This year saw the use of transforming the detector and headphone circuits to take advantage of high level tapping of the detector on the tank coil. Ben Tongue and Al Klase convinced us that this was the way to go; if you can effectively match the impedance of the detector/phones to that of the tank circuit, you get a higher signal voltage to play with without loading down the tank circuit. This also led to some searching for the best diode(s) to use for detectors, and a variety were used, from the ubiquitous 1N34 type to Shottkys.
Phones: For the most part, the balanced armature design phones used for sound-powered applications pretty much ruled the day. In all cases, getting a good impedance match with the most sensitive pair of phones in your inventory was critical to maintain selectivity and get the best sensitivity. All of us have realized by now that there is nothing magic about 2000 ohm phones; in fact, my least sensitive set of phones is a 2k pair of recent construction.
Other set tidbits: While air core solenoid or basket wound coils were the most used, Mike Tuggle chose to wind his antenna tuning coil on a ferrite rod with litz wire, and then put it parallel to his tank coil instead of axially aligned to it as most do. This allowed him to place an inductively coupled trap coil on either side of the tank coil. The results speak for themselves. Richard Budny used bias with all his detectors, and claimed improved sensitivity in all cases. In the hobby class, one contestant got a nice mess of local contacts using only a large indoor loop, and another picked up some locals using only a ferrite core antenna.
Location, location, location: Mike showed us what a clear shot over open water can do. Other favorable factors seem to include (1) few strong local stations that mask the distant ones (2) wide open spaces around you (3) ability to point the antenna at the dx stations.
Operating: Know your rf environment.
Get acquainted with the stations that you can normally hear, and use them
for "band markers". This is particularly important when you do not
have any dial calibration. Keep a log of stations heard. Listen at all
times of the day, particularly in the early morning and late afternoon.
There is no set time for dx to come in, although the night time hours are
best. Listening during daylight hours can sometimes yield those stations
that only come in occasionally. Play around with wavetraps close
to the strong locals. An inductively coupled wavetrap placed between
the antenna coil and the main tuning coil can add another level of selectivity.
Use a superhet with a digital readout to help you identify both frequency
and identity of dx stations. It will also let you quickly determine
what's out there. Sometimes new stations will only appear for a few
minutes, and you need to be able to hop right on them.