Crystal Radios Of The 2009 Contest Entrants
Ralf Siemieniec, Open Class, SW Class, and Below BCB Class Entries
In the (broadcast band/mw) contest, I used my latest receiver which was just finished right in time. The schematic features a double-tuned circuit with an additionally antenna matching cap and probably does not show surprises. The whole device was designed to gain highest Q values within my possibilities. I used polystyrene coilformers of the german manufacturer Reinhöfer which already offers the possibility to gain high Q values.
The coils have 185µH and were wound with 460 x 0.02mm litz wires. Measurements of such a coil show increasing Q with frequency up to 1550kHz and a maximum value of app. 830. A noteworthy improvement was reached by drilling six holes in each segment of the coilformer, now the Q increased across the frequency range of interest (in Europe, station in the mediumwave band cover a range from 531kHz to 1611kHz). Moreover, also a maximum Q of app. 1020 was found. Therefore I decided not to use contra-coils since I wanted to avoid the use of any (more or less lossy) switch in the RF section.
To preserve the high Q, I used TRW silver-plated air variables in the antenna and detector circuit. Coupling of the coils is made variable by a somewhat old-fashioned technique as used in old tube radios. Anyway, it is working very smoothly and reliable.
Housing is done by low-loss polypropylene sheets which keeps the Q up (refer the measurements of Dick Kleijer at http://www.crystal-radio.eu). In difference to most constructions presented so far, I completely enclosed the device. The main reason is to keep dust away from the caps - if you ever did Q measurements of high-quality aircaps with dust in between the plates, you will understand why. The dust probably kills more Q than the housing might do, providing the use of appropriate materials (thus, no wood, PVC, metal, acryl glas or most colored plastics).
All variable caps are completed by 6:1 vernier dials made by UK Jackson Brothers. 5082-2835 schottky diodes are used as detector diodes and provide the best matching between detector circuit and audio transformer I was able to realize. The matching transformer with an input impedance of 500k was also manufactured by Reinhöfer. The radio is completed by a pair of balanced-armature headphones Baldwin Type C as well as the usual benny circuit.
The real backdraw of my receiver is the limited antenna. I live in a five-storied house which not much chances for long antenna wires. Thus my best option was a 10m wire between my balcony and the roof of the next garage. Compared to my other set which I used in the last sprint contest and still used for the longwave and shortwave band in this year, selectivity and also sensitivity was noteworthy improved. The 6:1 vernier dials are already a minimum requirement, 12:1 or more would be favourable.
In all, I was surprized about how many and how distant stations I was able to receive during the contest.
Shown below is the set used in this contest for SW and LW. It is the same set used in the 2008 Sprint Contest.
Dan McGillis, Open Class Entry
My entry this year is a simple loop-stick crystal set - something the grandkids can play with. It's been described at the RadioBoard.
I used a little antenna tuner that's also been described before. Click here for the RadioBoard link for the tuner.
The set didn't do too bad for only a few days of listening. A big 200' antenna certainly helps :-) It makes a nice progressive set. I started out using Mike Peebles's cat's whisker detector stand It's very smooth & works well. Substituting a FO-215 diode perked things up. Adding a Bogen+Benny for some audio matching made a big difference. Coupling-in a simple antenna tuner really brings-in the DX and kills the SW ghosts.
Mike Tuggle, Lyonodyne-17, Open Class Entry
This year's effort was something of a disaster. The night before the start, our annual Kona winds blew the antenna into the mango tree and ripped it to shreds. I spent opening day out in wind and rain, in true ham fashion, getting the antenna down and re-erecting a simple longwire in its place. Conditions throughout the contest were blah. I don't know whether the original 4-wire flat-top was really that much better, or if conditions were simply that blah.
Jack Bryant, Open Class, Two-Way Shortwave Class, and Below BCB Class Entries
I only worked the first 24 hours of the contest on the broadcast band. I had copied one navigational beacon at 529 kHz, and decided to build a simple set for LF. I copied four more stations for a total of five. The stations are: DIW, CLB, BH, YYW, and LYQ.
I worked a few contacts on 75m AM using the xtal set as a receiver. My transmitter VFO had bitten the dust, but I got a crystal for the transmitter on Saturday, and that worked fine.
I used essentially the same set for the broad cast band that I used in years past, with minor mods to the antenna tuner. I did use Schottky diodes for the fist time. I used two in parallel during the day, but moved to just one at night due to the overload I experienced using the pair.
This year I used a different set of phones made from SP mic elements. The earphones were made of hard plastic, but the headset band placed the phones on the back part of my ears. I did not experience the ear pain of previous years, but I made sure to move my glasses far up on my head, or not use them at all to eliminate pinching the nerve beside my ear.
I have used a Realistic DX-398 for several previous contests, and I used it for this one, too. I used a PC for logging along with paper copy backup. I used a four foot table from Lowe's as my listening post.