Recent Crystal Radio DX Group 'Listening Event'

Crystal Shortwave Receiver of Al Klase (N3FRQ)

The Facebook Crystal Radio DX Group’s fall listening event was held two weekends ago over a two-night listening period. Unlike last year’s event, this was not a contest but rather a leisurely opportunity for members to take some time to see what they could hear with their setups. Also unlike last year, this one introduced and encouraged members to see what they might hear on shortwave! Since circuits losses are measurably much higher as you climb above the broadcast band, audio amplification (AF) was permitted to encourage members to give it a try as this was a whole new region to explore for most of us.

The addition of shortwave inspired much discussion as well as construction, the main objectives of founding the group.

Shortwave crystal radio was all new to me as well and I struggled for several days, right up to the event’s starting time, to even be able to detect a signal. I had chosen to follow a similar path as described in WU2D’s excellent video, using simple link coupling into the detector tank circuit. I reasoned (probably incorrectly) that my end-fed 80m halfwave inverted-V would be close enough to resonating on the 5, 6 and 7 MHz SW bands to provide enough signal into the detector. After playing with this system as well as other antennas for several days, I eventually abandoned the concept and tried a different approach.

I added a loosely coupled tuned antenna input using my 630m inverted-V wire, bypassing its large loading coil and low-impedance matching system. Essentially it was a big vertical long wire tuned against a number of buried ground radials. I also added an LM386 audio stage between the detector and headphones, something I had not tried with the previous system.

This simple approach immediately produced signals … just in time for the start of the party at sunset!

Obviously, from just the physical appearance of my own SW tuner, there is a vast amount of room for improvement! As crude as it was, the following signals were all heard and verified on a separate SW spotter radio.

Oct 1

0250 10000 WWV Colorado

0255 7365 Radio Marti, Greenville, NC - Spanish

0305 9850 Radio Romania Int'l, Tiganesti, Romania - English

0310 9790 China Radio Int'l (CRI) Quivican, Cuba - English

0315 7375 Radio Romania Int'l, Tiganesti, Romania - English

0320 7335 Radio Marti, Greenville, NC - Spanish

0355 5000 WWV Colorado

0400 5935 WWCR, Nashville, TN - English

0408 5085 WTWW, Lebanon, TN - English

0429 4840 WWCR, Nashville, TN - English

0435 6000 Radio Habana Cuba, Quivican, Cuba - English

1411 6075 China National Radio 1(CNR), Baoji-Sifangshan, PRC - Chinese

1416 5980 Radio New Zealand, Rangitaki, NZ - English

1420 5965 CRI, Xianyang, PRC - Korean

1424 6125 CNR1, Beijing, PRC - Chinese

1426 6175 Voice of China, Beijing - Chinese

1428 7200 National Unity Radio, Tamsui District, Taiwan - Korean

1434 7410 CRI, Jinhua, PRC - Japanese

1436 7395 CRI, Kashi-Saibagh, PRC - Chinese

1437 7365 Voice of China, Shijiazhuang, PRC - Chinese

1452 9410 Voice of America, Tinang, Philippines - Korean

1741 12095 BBC, Kranji, Singapore - Korean

1745 11870 CRI, Urumqi Hutubi, PRC - Russian

2045 15000 WWV, Colorado

2312 11780 Radio Nat'l Amazonia, Brasilia, Brazil - Portuguese

Oct 2

1212 7245 Radio New Zealand, Rangitaki, NZ - English

1214 7310 CNR1, unknown tx site - Chinese

1220 7325 CRI, Jinhua, PRC - Japanese

1230 7355 KNLS, Anchor Point, AK - English

1240 7490 WWCR, Nashville, TN - English

1300 9675 CRI, Shijiazhuang, PRC - Russian

1307 9350 Voice of America, Tinang, Philippines - Korean

1311 9435 Voice of Korea, Kujang, N. Korea - English

1350 9265 WINB, Red Lion, PA - English

1740 9580 KNLS, Anchor Point, AK - Russian

1800 15580 VOA, Selebi-Phikwe, Botsawna - English

Reviewing many of the vintage radio magazines from the late 20s and early 30s, there appears to be very little published material from this era. I found this somewhat surprising but then perhaps not ... maybe most radio-buffs were still entranced by the new regenerative circuits popping-up every month and had little appetite for crystal SW receivers.

It would appear that even today there has not been much investigation or experimentation in building an efficient low-loss crystal receiving system for shortwave … somewhat of a golden opportunity for today’s crop of crystal radio builders!

In view of the above, along with a surprising amount of interest in SW during our recent listening event, I’d like to include SW in all future events going forward and possibly encourage even more new interest in developing efficient circuits. Is it practical to consider non-audio amplification for such circuit’s? Time will tell but already, several members are having measured success with just bare headphones!

Some of the BCB and SW construction inspired by the recent listening event is shown below. For more information and more sets, please visit the Facebook Group and consider taking part in our next event, sometime in December ... maybe you can build the perfect SW tuner!