Friday, 14 January 2022

January's Crystal Radio DX Contest

 

The first time I was involved with a crystal radio DX contest was about 20 years ago when I built a well-performing crystal receiver for the Yahoo Crystal Radio Group's annual DX contest. It was a great learning experience and taught me much about circuit losses and how to overcome them. I originally built several sets but was unable to hear anything other than local stations until I eventually figured things out ... the system was only as good as its weakest link or links!


Fast forward to more recently when I obtained and wrote about the Heathkit CR-1 Crystal Radio, a simple but very well-designed tuner that has become popular with collectors. Using the CR-1 re-kindled my interest in the DX contest activity of years ago and when talking with two other amateurs that had an interest as well (one had also been in the earlier contests sponsored by the Alabama Crystal Radio Group), we decided to bring the contest back once again. The Facebook Crystal Radio DX Contest Group was formed last fall, a set of rules drawn up and the contest date set for the first week of January of this year. This gave interested participants plenty of time to build something they could use in the contest.

I spent all of December designing and constructing a new contest radio, hopefully one with enough selectivity to get around the 15 local flamethrowers (10-50kW S9++ signals) that plague the band for me and eventually drove me from crystal radio activities.

The new radio makes use of several 'traps' to null strong signals ... two are in the antenna line while one is loosely coupled inductively to the detector tank circuit. The two inline trap coils are wound with Litz wire on ferrite toroids (R40C1) while the third is a basket-wound Litz coil (660/46) on a 4" diameter form.


The antenna tuning stage also uses the same ferrite material but in the rod / bar form. I wound a low-end as well as a high-end coil for the tuner using the same high-count Litz as on the big trap coil. The low-end coil is wound on a bundle of three rods while the high-end coil uses a single rod.

Antenna tuner

The detector stage uses another Litz coil with this one being solenoid-wound on a 4" diameter form. Both the antenna tuner and the detector use excellent quality hi-Q ceramic insulated air variable capacitors (18-360 pfd). All components that handle RF are insulated from the plywood bases in order to reduce losses. Moving a capacitor from the plywood to the insulated standoffs makes a noticeable difference, something learned the hard way years ago but actually measured while using the new radio.

Detector stage
 

The detector also has provisions for comparing various diodes as not all diodes are created equal ... not even all diodes with the same number! When testing and comparing diodes of the same type such as the popular 1N34 germanium, every once in awhile one of them will turn out to be noticeably more sensitive than the others. In my built-in B-A-C diode test module, the hottest diode is always mounted in middle-position A, making it easy to quickly compare by switching to the left for B or to the right for C. So far the best one I have found is the vintage Russian D18 germanium diode but an old 1N34 removed years ago from a 1950s-era Heathkit has given it a good run for the money! I've still several hundreds of early germanium diodes, pulled from old diode matrix boards years ago, to test against the D18 as well as numerous Schottky diodes.

Also on board the detector module is a Selectivity Enhancement Circuit (SEC) that increases selectivity by unloading some of the diode's effect on the detector coil, similarly to tapping the diode further down the tank coil. It uses a small butterfly capacitor seen to the right of the main tuning capacitor in the photo above. I found it extremely effective when needed and is well worth the addition to a high-performance tuner.

The detector stage is followed by an impedance-matching transformer for the sound-powered headphones. This stage also houses a 50uA meter to measure diode current / signal strength levels.



 

 

The meter can be switch-bypassed to prevent needle-bounce on stronger signals. It is particularly helpful when using the traps to null a signal to the minimum level.

 

 

The three traps utilized have been very effective in eliminating what I had originally perceived as an impossible DXing situation.

Here are the daytime-power signal strengths of my 15 line-of-site blowtorch stations that, without trapping, very effectively block most sections of the band. Anything over 50uA is ear shattering and problematic, usually requiring the use of all 3 traps:

             KVRI 1600 50uA
             KRPI 1550 100uA
             CJVB 1470 40uA
             CFTE 1410 350uA
             CHMB 1320 100uA
             CJRJ 1200 400uA
             CKWX 1130 300uA
             CKST 1040 90uA
             CKNW 980 150uA
             KGMI 790 100uA
             CHMJ 730 450uA
             CBU 690 650uA
             CISL 650 200uA
             CKSP 600 100uA
             KARI 550 100uA

Overall I was very pleased and surprised at the good performance of the new radio. During the contest period I identified and logged 92 unique stations in 16 states / provinces. More than one station was logged on 9 different frequencies as the propagation varied from night to night.

Highlights of the DX Contest were hearing WHAS in Kentucky (2,007 miles), WJR in Michigan (1,970 miles), KXEL in Iowa (1,556 miles), WCCO in Minnesota (1,423 miles) and CBW-990 in Winnipeg, smack up beside local blowtorch CKNW-980! Additionally, hearing Washington state 250 watter KFLD-870 and 250 watt KWBY-940 in Oregon were great surprises.


I found the use of a spotter radio (Sony ICF-2010) to be very useful in locating signals to target and to zero-beat with an RF signal generator. The generator’s tone-modulated signal can then be tuned in and the xtal radio and antenna / detector stages optimized. 

From here, any pest signals are then tuned to and individually nulled using the traps while watching the signal meter. Antenna and detector stages are then re-tweaked before disabling the generator and listening for the desired signal. 

Often it is heard immediately following the above tuning procedures but if not, monitoring the frequency for several minutes often allows time for the weak signal to fade up to audible levels. 

Comparing programming audio with what is heard on the spotter radio will confirm hearing the correct signal as will comparing audio to the station’s own live-feed on the internet.


Due to the larger and much better antenna (inverted-L 70’ x 100’) on the crystal radio, I would often hear good audible signals on it and not on the spotter (something that I found surprising) so often times it was productive to just tune around the band on the crystal radio, tweaking stages as required.


I’m looking forward to further improvements of the tuner as well as to the next DX Contest whenever that will be scheduled ... hopefully you can join in as well!

 
CONTEST LOG (pests in red)

                    FREQ UTC    STN    LOCATION    MI      

540    3:50    CBK    Watrous, SK    764      
550    1:04    KARI    Blaine, WA    25      
560    1:30    KPQ    Wenatchee, WA    168      
570    3:45    KVI    Seattle, WA    107      
580    3:42    KIDO    Nampa, ID    492      
600    1:17    CKSP    Vancouver, BC    32      
610    4:15    KONA    Kennewick, WA    271      
620    1:22    KPOJ    Portland, OR    241      
630    3:40    CHED    Edmonton, AB    530      
630    21:10   KCIS    Edmonds, WA    87      
650    1:05    CISL    Richmond, BC    24      
660    3:30    CFFR    Calgary, AB    693      
660    21:23   KAPS    Mt. Vernon, WA    52      
670    3:25    KBOI    Boise, ID    807      
690    1:06    CBU    Vancouver, BC    19      
710    3:21    KIRO    Seattle, WA    108      
730    1:02    CHMJ    Vancouver, BC    22      
750    3:55    KXTG    Portland, OR    243      
760    4:01    WJR    Detroit, MI    1970      
770    3:17    KATL    Miles City, MT    831      
780    4:00    KKOH    Reno, NV    658      
790    1:07    KGMI    Bellingham, WA    39      
810    4:05    KGO    San Francisco, CA    786      
820    1:59    KGNW    Seattle, WA    106      
830    2:20    WCCO    Minneapolis, MN    1423      
840    4:10    CFCW    Camrose, AB    530      
840    4:00    WHAS    Louisville, KY    2007      
850    4:20    KOA    Denver, CO    1118      
850    1:12    KHHO    Seattle, WA    121      
860    3:48    CBKF    Saskatoon, SK    758      
860    1:04    KPAM    Troutdale, OR    226      
870    4:30    KFLD    Pasco, WA    266      
880    1:17    KIXI    Seattle, WA    102      
890    4:35    CJDC    Dawson Creek, BC    494      
900    4:38    CKBI    Prince Albert, SK    810      
910    4:40    CKDQ    Drumheller, AB    468      
920    4:42    KXLY    Spokane, WA    285      
930    1:50    KBAI    Bellingham, WA    37      
940    4:45    CJGX    Yorkton, SK    940      
940    0:58    KWBY    Woodburn, OR    256      
950    4:50    KJR    Seattle, WA    106      
960    4:52    CFAC    Calgary, AB    444      
970    4:55    KBUL    Billings, MT    722      
980    1:08    CKNW    New Westminster, BC    32      
990    4:58    CBW    Winnipeg, MB    1156      
1000  3:45    KOMO    Seattle, WA    105      
1010  4:59    CBR    Calgary, AB    453      
1020  0:54    KWIQ    Moses Lake, WA    216      
1030  5:06    KTWO    Casper, WY    918      
1040  1:09    CKST    Vancouver, BC    23      
1050  5:10    CJNB    N Battleford, SK    707      
1060  5:07    CKMX    Calgary, AB    441      
1070  5:10    cfax    Victoria, BC    33      
1080  0:33    KFXX    Portland, OR    232      
1090  1:40    KFNQ    Seattle, WA    109      
1100  3:55    KFAX    San Francisco, CA    779      
1110  5:15    KRPA    Oak Harbor, WA    48      
1120  0:48    KPNW    Eugene, OR    340      
1130  1:10    CKWX    Vancouver, BC    22      
1140  5:20    CHRB    High River, AB    443      
1150  5:50    CKFR    Kelowna, BC    185      
1160  5:53    KSL    Salt Lake Cty, UT    781      
1170  1:11    KPUG    Bellingham, WA    39      
1180  5:09    KOFI    Kalispell, MT    416      
1190  5:55    KEX    Portland, OR    241      
1200  1:12    CJRJ    Vancouver, BC    23      
1260  5:58    CFRN    Edmonton, AB    522      
1290  6:00    KUMA    Pendleton, OR    306      
1290  6:00    KGVO    Missoula, MT    449      
1320  1:13    CHMB    Vancouver, BC    23      
1360  6:12    KKMO    Tacoma, WA    115      
1370  4:32    KXTL    Butte, MT    535      
1380  6:16    KRKO    Everett, WA    88      
1410  1:14    CFTE    Vancouver, BC    22      
1460  1:55    KUTI    Yakima, WA    207      
1470  1:15    CJVB    Vancouver, BC    25      
1480  1:20    KBMS    Vancouver, WA    227      
1520  1:05    KKXA    Snohomish, WA    88      
1520  1:13    KQRR    Oregon City, OR    241      
1530  4:30    KFBK    Sacramento, CA    698      
1540  1:50    KXPA    Bellvue, WA    102      
1540  4:46    KXEL    Waterloo, IA    1556      
1550  1:16    KRPI    Ferndale, WA    31      
1560  1:14    KVAN    Burbank, WA    272      
1580  6:25    KGAL    Lebanon, OR    297      
1590  1:22    KLFE    Seattle, WA    91      
1600  1:00    KVRI    Blaine, WA    25      
1620  1:30    KYIZ    Renton, WA    111      
1640  6:45    KDZR    Lake Oswego, OR    239      
1660  0:56    KBRE    Merced, CA    812      
1680  1:35    KNTS    Seattle, WA    91      
1690  0:53    KFSG    Roseville, CA    705