Crystal Radios Of The 2004 Contest Entrants
I have attached a photo of the set that I used during the contest. Daryll Boyd posted a picture on his site. I humorously called it "The Bondini". The most interesting feature is that this uses 4 inch basket weave coils with 9 points- double tuned.
The wire is 2 solid strands of twisted wire. I use a schotty diode and sp phones with a Bogen matching transformer. I wired it in as many combinations of coil and cap as time would permit.
Here is Bob's DX set.
Hobby Class Single Tuned Crystal Radio Capable Of DX My antenna consists of 70 feet of 18 gauge plastic insulated tinned copper wire oriented in a North East and South West direction with the lead in pointing North East. The far end is elevated over 40 feet while the other is only 12 feet high. A cold water pipe ground connects to the receiver via 15 feet of insulated 14 gauge solid copper wire.
A 250pF ceramic frame air variable capacitor couples the antenna to the receiver. The tank circuit is composed of a 365pF phenolic insulated air variable capacitor and a coil of 60 turns of 21 gauge wire wound on a 2¾ inch PVC form. It is tapped at 30, 40, and 50 turns from the ground end.
To combat the QRM generated by WXEM, only a mile away, the wave trap has to be closely coupled to the tank circuit. The trap is composed of a 250pF phenolic insulated air variable capacitor in parallel with a 60 turn coil of 26 gauge wire on a one inch diameter form.
Best sensitivity and selectivity is obtained with the 30 turn tap. Usually a single Philmore crystal earphone and a selected germanium diode were employed. Some improvement was noticed when using two earphones in series, probably a better impedance match.
I attribute my success with such basic equipment to mostly quiet RF environment, many hours spent DXing, and listening well into the night and the morning on one occasion. Furthermore, I was fortunate to acquire some high scoring stations. Somehow I heard two different stations on 630 25 minutes apart. WAVU was only 203 kilometers away but running a mere 28 Watts! Still, this does not compare to KEYH on 850. It was 1,211 kilometers away and transmitting at a power of just 185 Watts! The remaining acquisitions were locals, 50 KW Clear Channel, or not too distant 5 and 1 KW stations. I received one Canadian and one Cuban station, both 50 KW. The furthest catch was WBZ, Boston. A station on 1260 identified itself as Radio Disney but I was unable to obtain a call sign. Out of three possible candidates, I am fairly sure it was WWMK. Using a spotter set to ascertain direction,the station was either from Chicago or Cleveland, certainly not Boston. 5,000 Watt DX from 800 kilometers away is certainly not uncommon for me, but anything else would be. Besides, I did log a few stations running 5,000 Watts from Ohio.
My crystal radio is a design that has evolved after many years of searching for a good design. Most of the ideas used in this radio came from internet sites. No litz wire here. Just old cotton covered 20 gauge wire wound in a basket weave form. No sound powered headphones here. Just my trusty old magnetic Trimm Dependable's.
Yes, the meter is in the circuit all the time. It is a 50 µA movement in series with the headphones. It is helpful in maximizing design of the circuits, selecting the best crystal to use, and in tuning taps and caps for maximum signal reception. It indicates carrier strength of the received signal. The carrier contributes nothing to the audio heard in the headphones. A signal of 1ua is 100% readable. One local station gives a reading of about 500 ua.
My antenna is 18 gauge solid magnet wire. It is basically a Windom antenna that is insulated at the supports which are at the ends and at the lead-in point. It is 180 feet long and runs due east and west. The wire to the receiver comes off at a point about 60 feet from the west end and is about 55 feet long. The lead-in take off point is up 36 feet with the ends up about 24 feet.
The radio is made in a 20's battery radio wood cabinet. It uses three Atwater Kent variable capacitors. It uses Atwater Kent knobs with two sets of antique switch points mounted on a black plastic front panel. Genuine Atwater Kent copper emblem at the center top of the front panel. Antique connectors are on the front panel for antenna and headphone connections. Wiring inside is all by 16 gauge bus bar. 1N34A diode. The primary and secondary coils are 4 1/2 inches apart with no electrical connection between them. I have not found a trap circuit that helps enough to talk about.
2004 XSS DX Contest Information (SW, Open Class)
My 2004 contest log containing 156 SW stations (incl. 5 of uncertain ID) suggests that conditions in Central Europe are still more different from those in the USA than on the MW band. There are a lot of high-power SW/BC stations of 100 to 1000 kW in the numerous European countries and the neighbour areas, and particular networks that operate on rather many frequencies - like R.Free Europe, R. Liberty, VoAmerica (partly R.Sawa), VoRussia, etc. with their various programs. It is mostly possible to ID the received stations of these networks, but often difficult to determine the site (country) from which the particular tx operates. Only a few real DX stations are in my log with China/Peking being the most distant one (9500 km). So, is it really fair to compare my results with those obtained e.g. in the US if one gets one point,also for every "nearby" SW station?
I used my 2003 contest set (see Wuggy´s 2003 Contest site) which I extended for SW reception. This consisted in installing an air coil of 4 uH (fore in photo) for the 13m and 16m bands, a pair of Epcos pot cores of SW material K1 with solid-wire coils of 5.5 uH for 19m to 25m (marked by broken circle), and pot cores with 45/46 Litz coils of 10 uH for the 31m to 75m bands (full circle). Except for the air-coil tank I generally employ double tuning. The principal circuit layout for SW is the same as in the 2003 set (Ben Tongue approach). With the 5 SW coils there are now in total 13 coils in the set (LW, 3*MW, 3*SW), not counting those provided for triple tuning on extra boards (Boschodyne Plus).
At SW frequencies the obtainable tank resonance resistances are much lower than those at MW. Consequently sensitivity is a serious problem, and more often than on MW one hears two or even three stations at the same time. For improving the situation I employed a modified MFJ tuner 901B in front of the set (not shown in photo) to squeeze the last dB of power out of the antenna and trade it for selectivity. The tuner can be wired to act as a SPC or SL pre-selector, an "ultimate transmatch", or a capacitively-coupled third tank circuit (for triple tuning). With triple tuning I measured for example at 41m a loaded (i.e. with A/G and phones connected) -3dB bandwidth of 23 kHz and a -10dB b.w. of 47 kHz. -- I use a Schottky diode BAT 62 (as in photo) if high sensitivity is the prime goal, and 2 or 3 paralleled 5082-2835 if it is selectivity. The outdoor loop that I described last year in my contest report served as antenna.
For finding and then logging stations I employed two methods:
(1) First I scanned the band with my spotter radio ATS-404. When the scan had come to stop at a station, I tuned the xtal set to the particular frequency with the help of a loosely-coupled signal generator. After turning off the signal generator I then listened if I could hear that station in the SP phones of my set.
(2) When I had the xtal set tuned-up to a particular frequency within the SW band investigated, I slowly moved the sig. generator about 50 to 70 kHz around this frequency while watching for beat notes. When I found a strong beat I tuned the set to zero this beat, then turned off the signal generator, and listened whether I could hear the particular station. This was done repeatedly to scan various parts of the band. If I had been able to definitely hear the station in methods (a) or (b) I partly switched-on the spotter radio again for helping to identify the station received on the xtal set.
During this concentrated listening on SW, I found the rule of thumb again confirmed that Mike Tuggle formulated in a recent paper: "If you can hear them on a radio, you can hear them on a crystal set" - nearly always in my case.
2004 DX CONTEST SET DESCRIPTION
This is basically a Lyonodyne with some differences, such as:
1. The complete set has been built on one chassis and all controls are at the front panel.
2. The C1-C2 coupling is double: by means of rotation and changing the distance, and wave-trap is coupled only by rotation.
3. Using one or both sections of the C2 spreads the upper BCB.
4. There is one built-in detector diode with the possibility to experiment with other types of detectors.
5. Audio transformer is home-made and together with the impedance-selection switch allows the use of different impedance headphones, as well as a sensitive speaker.
I am aware of all the imperfections which are subject to experimental improvements. I want to thank Mike Tuggle who invited me to join the Contest and gave me many useful advice. My gratitude also goes to Ben Tongue for helping me to improve my impedance-matching transformer.
N.B.: The switch s1 is not shown on the photo (introduced after the photo was taken!).
Five Litz 4.5” O.D. coils are in use at all times. The detector and antenna coils are controlled by the three 8-1 vernier dials mounted in plexiglass. The antenna circuit is a modified Tuggle front end approach with one TRW cap (C1) in series with the antenna with C1’s stator linked to C2’s stator. C2 is tied to the antenna coil and earth ground. C3 is tied to the detector tank. All caps are TRW’s previously available from Fair Radio. This offers the set more flexibility in tuning than its previous traditional Tuggle Front end which used a dual ganged cap.
The three inductive traps surrounding the detector tank are driven by one gang each of three five ganged traps with right angled 120-1 drives from Fair Radio. Hand capacitance is controlled by use of empty plastic wire spools, slotted to accept the dials of the right-angled drives. The stand-alone TRW cap with vernier dial controls the inline toroid trap. The three inductive traps are permanently set to trap locals 1400, 1290 and 1230. The inline trap is used trap two local stations at 630 and 900 when in their vicinities. Otherwise it is used to assist swatting down 1230. Untrapped, 1400, 1290, and 1230 will show up all over the band because of their proximity to my location. The phones are DLR5s matched to the set via an STM designed by Steve Bringhurst. The set uses 3 paralleled Agilent 5082-2835s and a 3RT 12101 which are selected via a switch. To the right of the set is my frequency spotter Radio Shack DX 398. The antenna is an end fed wire, approximately 140’ long, with a 90’ horizontal run, up 50 feet. A post-contest improvement by adding three 8’ copper-plated ground rods to existing water main ground has noticeably improved selectivity, sensitivity and my ability to control the qrm of locals 1230, 1290 and 1400. The new ground system has also opened up about 150 KHz previously lost to the above three locals.