Mike Tuggle's 2010 Entry
Mike Tuggle, WY3B, Kaneohe, Hawaii
Stations Heard: 117
Commentary. What a fun event! Reception conditions were better than usual for mid-summer. The receiver I finished up with was a far cry from the one I started with. The receiver started out as a "concept" set -- just to see what could be done with a single tunnel diode active device and hopefully to have some fun along the way. What I wound up with approaches "competition grade." The soldering iron didn't go cold the whole time. A big 'thanks' to Dave and Rob for sponsoring this event and stimulating continued interest in crystal radios and simple active device receivers.
Basic Receiver. This direct conversion receiver is built around a homebrew diode-ring doubly-balanced mixer. It takes a modular approach to radio design.
– The local oscillator (LO) or VFO is a 1N3717 tunnel diode Hartley oscillator.
– The radio frequency input (RF) was direct from my external antenna and ground. Later, a passive tuner was added.
– The 'intermediate frequency' output (IF) is audio frequency to the phones.
When the LO is tuned to the same frequency as an incoming amplitude modulated RF signal, mixing takes place and the difference products, the audio frequency sidebands, appear at the IF output.
Balanced Mixer. A previous version of this type receiver used a 1-JFET Hartley as the local oscillator. See the "Brianodyne", at http://www.crystalradio.us/1adradios/1ad-2006-1.htm#tuggle The set here is the same idea with a different local oscillator. Below is the homebrew doubly-balanced mixer used in that set and this one:
During the RadioBoard Homebrew Radio listening event, this set saw three major improvements
1. RCA Big Cans phones replaced U.S.I. UA729's. The RCA's are an order of magnitude more sensitive.
2. A fine-tune variable capacitor was added to the oscillator.
3. Passive front-end tuning was added to the mixer's RF input.
These are described in more detail below.
Tunnel Diode. When the tunnel diode is operated at a point in the red-line region (175 mV, 2.5 mA), an increase in voltage causes a decrease in current -- and vice versa. This gives the diode its negative resistance characteristic. The tunnel diode, operating in its negative resistance region, negates the loss resistance in the oscillating LC tank, and thereby sustains the tank's oscillation.
Local Oscillator (LO). The LO's function is to switch the DBM diodes into and out of conduction. At the low level output characteristic of a tunnel diode oscillator, the diodes are not being switched sharply at all. At best, they are being biased slightly into more conduction in one direction than in the other.
LO output is taken directly off the top of the LC tank and fed via a 27 pF capacitor to the low impedance "LO" port of the DBM. No regard was given to matching, other than we know it is bad. I tried feeding the LO directly from the low impedance coil tap point, but the harmonic content of the oscillator went way up, rendering the set almost useless. Link coupling the oscillator coil to the LO port fared no better.
Operation.
Quirky Tuning. The most striking feature of this set is the quirky operation of the tunnel diode oscillator. At certain frequencies, as the set is tuned through the band, the oscillator abruptly jumps some 40 kHz. Two jumps landed the set on my two strongest local stations. It really seemed like a case of strong stations somehow "pulling" the local oscillator. But then a shift was noted that landed on a weak station's frequency. And, the shifts also occurred when no signal was applied to the RF port. Finally, on the oscilloscope (no load), the LO operates beautifully across the band -- no glitches. I'm still pondering this one . . . .
Anyway, if the tuning "jumps" over a station I'm tuning up to, I can always tune down to that station from a higher frequency. So, all frequencies are available, but a smooth dial calibration curve is not.
Harmonics. Like all simple oscillator sets, this set necessarily has a good deal of harmonic content. This means that stations at 2X, 3X, etc., the frequency being tuned to are also being directly converted to audio frequency (although not as loud) and being heard as QRM.
Front-End Overload. When the set's oscillator is off, a mish-mash of local stations appear at the phones. Presumably the diode ring is detecting much like an ordinary crystal set would. With the oscillator powered up, selectivity increases, and many of these local stations go away. But, my very strongest locals pervade the entire band. Extra care was needed when listening for a weak DX station to make sure it was not some local QRM.
Well into the RadioBoard Homebrew Radio listening event, it dawned upon me that a possible fix for this overload and for the harmonics might be passive front-end tuning at the RF port of the mixer. I opted for a double gang capacitor front-end design with simple link coupling to the RF port.
The improvement from front-end tuning was stunning. Harmonics and strong station overload disappeared. I still get splatter when parked next to a strong local. Whether that's a selectivity shortcoming or simply the local station misbehaving awaits future investigation.
Audio Quality. Operating in oscillation, plus fairly narrow bandwidth, make for enhanced DX ability but wretched audio quality. Distorted voice is recognizable, but music is unrecognizable and unlistenable -- unless -- the set is tuned exactly to frequency, nearly impossible, even with the vernier dial on this set. I added an 0.8-to-1.5 pF butterfly capacitor across tuning capacitor C as a fine tuning control. At the high end of the band, even this small capacitor's tuning is touchy.
Future Improvement. A FET buffer/amplifier stage between the high-Z oscillator output and the low-Z mixer LO input seems to hold promise. This adds another active device to the circuit -- something I wanted to avoid for the present. Maybe next time.
Thanks. — to Richard O'Neill for the beautiful J-Bros. var. cap. in the antenna tuner. -- and especially, to Brian Hawes for not only much helpful advice and insights but also for the tunnel diodes!
Enlarged View
Contest Log -- LW-MW Class
Mike Tuggle
Kaneohe, Hawaii 21.4 deg. N, 157.8 deg. W
Times/dates are UTC (HST + 10 hours)
Date # Time Call Freq Dist Location Notes
2010 UTC kHz miles
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07/23 1 2237 KSSK 590 7 Honolulu, HI pop music
" 2 2248 KRTR 650 16 Honolulu, HI "All New 6-50 AM"
" 3 2301 KHNR 690 9 Honolulu, HI pollutalk
" 4 2304 KGU 760 9 Honolulu, HI relig. talk
" 5 2306 KHVH 830 7 Honolulu, HI "News Radio 8-30"
07/24 6 0336 KKNE 940 16 Waipahu, HI Hawaiian music
" 7 0801 KTLK 1150 2570 Los Angeles, CA "AM 11-50"
" 8 0808 KWAI 1080 9 Honolulu, HI "AM 10-80, K108"
" 9 0810 KNX 1070 2547 Los Angeles, CA "KNX 10-70"
" 10 0813 KIPA 1060 215 Hilo, HI Hawaiian music
" 11 0819 KTCT 1050 2401 San Mateo, CA sports talk
" 12 0825 KFAX 1100 2401 San Francisco, CA preaching
" 13 0831 KPNW 1120 2523 Eugene, OR "11-20 KPNW"
" 14 0841 KMVI 550 93 Wailuku, HI ESPN sports
" 15 0850 KSFO 560 2391 San Francisco, CA C2CAM
" 16 0901 KMJ 580 2493 Fresno, CA "NewsTalk 5-80 KMJ"
" 17 0907 KQNG 570 109 Lihue, HI C2CAM
" 18 0914 KFI 640 2566 Los Angeles, CA news-talk
" 19 0924 KIRO 710 2662 Seattle, WA ESPN sports
" 20 2059 KNUI 900 97 Kahului, HI Valley Isle news
" 21 2101 KLHT 1040 11 Honolulu, HI religion
" 22 2105 KHCM 880 9 Honolulu, HI Chinese pgmg.
" 23 2117 KUAI 720 116 Eleele, HI rock
07/25 24 0834 KHBZ 990 7 Honolulu, HI medical talk
" 25 0847 KZOO 1210 9 Honolulu, HI Japanese pgmg.
" 26 0849 KNDI 1270 7 Honolulu, HI Filipino pgmg.
" 27 0851 KUPA 1370 11 Pearl City, HI Fox Sports Radio
" 28 0855 KREA 1540 7 Honolulu, HI Korean pgmg.
" 29 0901 KAOI 1110 97 Kihei, HI "96.7 FM"
" 30 0908 KEX 1190 2590 Portland, OR "11-90 AM"
" 31 0911 KPTK 1090 2662 Seattle, WA local talk
07/26 32 0800 KHNU 620 208 Hilo, HI pollutalk
" 33 0803 KKON 790 180 Kealakekua, HI ESPN sports
" 34 0807 KHLO 850 215 Hilo, HI ESPN sports
" 35 0825 XESDD 1030 2613 Puerto Nuevo, BN ranchera
" 36 0827 KTNQ 1020 2570 Los Angeles, CA Spanish pgmg.
" 37 0846 KUAU 1570 105 Haiku, HI contemp. Chr. music
" 38 0851 KBLA 1580 2555 Santa Monica, CA Spanish pgmg.
" 39 0852 KGST 1600 2505 Fresno, CA Spanish sports
" 40 0858 KUMU 1500 7 Honolulu, CA rock
" 41 0900 KFBK 1530 2461 Sacramento, CA "NewsTalk 15-30"
" 42 0916 XEKTT 1700 2612 Tijuana, BN sports talk
07/27 43 0856 XEW 730 3787 Col. El Vergel, DF Spanish pgmg.
" 44 0901 KPUA 670 210 Hilo, HI CBS news, C2CAM
" 45 2055 KPHI 1130 14 Honolulu, HI "KPHI AM 11-30"
07/28 46 0905 CHMJ 730 2702 Vancouver, BC talk
" 47 0922 KTRB 860 2419 San Francisco, CA "Xtra Sports"
" 48 0927 KKOB 770 3221 Albuquerque, NM C2CAM
07/29 49 0738 KRTA 610 2488 Medford, OR Spanish, ranchera
" 50 0742 KEAR 610 2397 San Francisco, CA rel. talk/music
" 51 0853 KSL 1160 2976 Salt Lake City, UT talk, NBC news
" 52 0901 KTKZ 1380 2470 Sacramento, CA news
" 53 0913 KHRA 1460 7 Honolulu, HI "Radio Korea"
" 54 0918 CMBT 1180 4769 Villa Maria, Cuba Spanish pgmg.
" 55 0935 KHTK 1140 2466 Sacramento, CA "AM 11-40", sports
07/30 56 0846 KOGO 600 2609 San Diego, CA "Kogo" C2CAM
" 57 0901 KWVE 660 2534 Oildale, CA synd. religion
" 58 0909 KTNN 660 3083 Window Rock, AZ Navajo chant/pgmg.
" 59 0914 KNBR 680 2394 San Francisco baseball game
" 60 0932 CBK 540 3476 Watrous, SK grammar lesson
07/31 61 0800 KNEW 910 2397 Oakland, CA "9-10 AM" Fox News
" 62 0801 KOXR 910 2508 Oxnard, CA Spanish pgmg.
" 63 0806 KXTK 1280 2443 Arroyo Grande, CA sports
" 64 0813 KLBS 1330 2459 Los Baños, CA Portugese pgmg.
" 65 0821 KLIV 1590 2410 San Jose, CA "15-90 KLIV"
" 66 0823 KAHZ 1600 2584 Pomona, CA Chinese pgmg.
08/01 67 0807 KDIA 1640 2405 Vallejo, CA relig. teaching
" 68 0815 KUBA 1600 2458 Yuba City, CA oldies
" 69 0828 KYOS 1480 2484 Merced, CA talk
" 70 0838 XERCN 1470 2613 Tijuana, BN Spanish pgmg.
" 71 0838 KUTY 1470 2576 Palmdale, CA talk
" 72 0844 KUHL 1440 2444 Santa Maria, CA financial talk
" 73 0855 KWKW 1330 2549 Los Angeles, CA Spanish pgmg.
" 74 0910 KPAY 1290 2465 Chico, CA "12-90 KPAY"
" 75 0910 KKDD 1290 2613 San Bernardino, CA Disney
08/03 76 0847 CBX 740 3203 Edmonton, AB CBC, jazz
" 77 0854 KFQD 750 2773 Anchorage, AK talk
" 78 0900 KTRH 740 3914 Houston, TX C2CAM
" 79 0925 KSLR 630 3728 San Antonio, TX talk
" 80 0937 KPLY 630 2560 Reno, NV ESPN
" 81 0941 KIDD 630 2400 Monterey, CA "Home of SF Giants"
08/04 82 0809 KAVL 610 2567 Lancaster, CA sports talk
" 83 0839 KLFF 890 2443 Arroyo Grande, CA relig. teaching
" 84 0918 WOAI 1200 3728 San Antonio, TX talk
08/05 85 0800 KKOL 1300 2672 Seattle, WA "New 13-00 KKOL"
" 86 0805 KSRO 1350 2387 Santa Rosa, CA "13-50 KSRO"
" 87 0835 KPUG 1170 2710 Bellingham, WA sports
" 88 0852 KCHJ 1010 2518 Delano, CA "El Gallito"
08/06 89 0843 KMKY 1310 2395 Oakland, CA Disney
" 90 0848 KCTC 1320 2466 Sacramento, CA "ESPN 13-20"
" 91 0856 KOKC 1520 3735 Oklahoma City, OK trucker radio
" 92 0900 KABC 790 2548 Los Angeles, CA "KABC L.A."
" 93 0904 KKOH 780 2564 Reno, NV "NewsTalk 78 KOH"
" 94 0908 XEROK 800 3223 Ciudad Juarez, CH Spanish talk
" 95 0917 KCBS 740 2392 San Francisco, CA news
08/07 96 0818 KERN 1180 2515 Wasco, CA "Kern Radio" talk
" 97 0834 KLOK 1170 2411 San Jose, CA "KLOK 11-70 AM"
" 98 0850 KLAC 570 2558 Los Angeles, CA sports
08/08 99 0840 KGDD 1520 2589 Oregon City, OR "La Grande"
" 100 0900 KLLK 1250 2381 Willits, CA Spanish pgmg.
08/09 101 0902 KVIN 920 2474 Ceres, CA oldies
" 102 0906 KJR 950 2658 Seattle, WA ESPN sports
" 103 0914 KKGN 960 2396 Oakland, CA talk
" 104 0915 CFAC 960 3120 Calgary, AB "Sports Radio"
" 105 0918 KHTY 970 2534 Bakersfield, CA talk
" 106 0922 KINS 980 2379 Eureka, CA talk
" 107 0927 CBR 1010 3114 Calgary, AB CBC pgmg.
08/10 108 0827 KOAC 550 2538 Corvallis, OR talk
" 109 0833 KGO 810 2401 San Francisco, CA talk
" 110 0852 KOA 850 3345 Denver, CO "KOA, Denver"
" 111 0900 KJOP 1240 2504 Lemoore, CA religion
" 112 0906 KDLG 670 2601 Dillingham, AK NPR pgmg.
08/11 113 0750 XEMO 860 2614 Tijuana, BN Spanish pgmg.
" 114 0823 KRVN 880 3634 Lexington, NE talk, C&W
" 115 0900 KHPY 1670 2615 Moreno Valley, CA musical ID
" 116 1511 WQAG957 1610 9 Honolulu, HI Conv. Ctr. TIS
" 117 1840 KKEA 1420 7 Honolulu, HI sports talk