December 14, 2017

Homebrew Crystal Radios
with Basket Weave Coils for Medium Wave DXing and Shortwave listening.
Also crystal radio projects with ferrite bar antenna,  radio waves hotspots, and others.

日本語ページはこちら  >>>

■ Coil Projects   ――――――――――――――――――

Shortwave crystal radio (2014)
 A Proof-of-concept model of crystal radio with basket coils.

Short Wave Radio

RCX - Proto (2015) 
 Homebrew crystal radio
for MW DXing. Prototype.
 I posted an article of making and testing of RCX-Proto in QEX JAPAN NO.17 (below).

別冊 CQ Ham radio QEX Japan NO.17  (2015.12)
  My article in this edition( pp. 80-89, Japanese )
  " Improve selectivity and sensitivity by devising coils.
  Designing and making of crystal radio with basket coils : Part 2 "

 ※ For the information of basket coil winding method, please refer to the article in
 " 別冊 CQ ham radio QEX Japan No.15 (2015.6)", "
Designing and making of crystal radio with basket coils : Part 1".

RCX - 61000 (2016) 
 Homebrew crystal radio
for MW DXing.
 After testing of RCX-Proto for a year, I tried to design a new set with higher performance and easy to use.
 Result: Very satisfied.

61000 02  

handout_smll    A handout (PDF, Japanese)  at JARL Ham Fair 2016, Tokyo.
circuit diagram   Circuit diagram ( PDF, Japanese )
JOGB_small   Daily reception of JOGB (Kumamoto) in Tokyo from Jan. 1 to Dec. 14, 2017 with RCX-61000, (PDF, Japanese).

RCX - 61000  MK II  (2017)  
 Homebrew crystal radio
for MW DXing
 Exibited at the J
Ham Fair 2017, I enjoyed a pleasant talk with many people. Thank you !

MKII_03   RCX61000MKII_01

MKII handout small   A handout (PDF, 4 pages, Japanese)  at JARL Ham Fair 2017 ( Ver.5 Revised on Sep. 30 ).
MKII Circuit   Circuit diagram ( PDF/Ver.4, revised on Sep. 11 )

■ Crystal Radios with Ferrite Bar anntena  ―――――― 

RBM - 100 (2016)
 This is the second set of my portable crystal radio projects for the hotspots exploration ( see below ).
 It has 3 ferrite bars (18 cm long) with
litz wire coils for the main antenna. A rod antenna is also mounted.
Also, it carries red and blue LEDs as a detector in addition to germanium diodes.

 rbm100_01 rbm100_02 rbm100_03

RBM - YR (2015)
 The first set of my portable crystal radio projects.
 I made it for my wife so as to use it during the hotspots exploration.
It has 5 ferrite bars (18 cm long) with litz wire coils for the main antenna. Also, it carries red and blue LEDs as a detector in addition to germanium diodes.
 It appears in the footage of the " TAMORI Club ( See below ) ".

 YR01 YR02

・Prototypes of RBM series (2014 - 2015)
 Each sets can use MOSFETs, LEDs, and diodes as a detector by replacing on the socket easily.

 proto01  proto02  proto03

 proto04  proto05

■ Reports on Radio Waves Hotspots  ―――――――――

What is Radio Waves Hotspots ?
    There are places where you can hear the broadcast on a crystal radio without a big external antenna - like a long wire antenna, while those places are surprisingly several kilo meters  to well over 10km away from the transmitting antenna.
    We call those places radio waves hotspots.
    There are possibilities of hotspots, such as near tall building pillars, utility poles, guardrails, fences, crossovers, big bridges and so on.
    In order to qualify as a hot spot, it is subject to (1) while it depends on the power of transmitting antenna, it should be far enough from the transmitting antenna, and (2) you might be able to receive and enjoy the broadcast on a crystal radio without an big external antenna.
    On hotspots, you can enjoy the broadcast even with dynamic headphones or speakers, with loud sounds. With ceramic earphone, you could hear it at such a high volume that the ear might hurt.
    Also, even with an LED that has high forward voltage, detection can be done and you might see an led light up brightly.
     In addition to medium wave broadcasting, hot spots exist also in shortwave broadcasting band and FM broadcasting band.
    We frequently conduct field surveys on hot spots in Japan since 2014.

・Hotspots of Magnetic field type in Tokyo

・Hotspots of Electric field type in Tokyo
  Tokyo Big Site - Feb 2017  (Report in Japanese)

<<<<< Caution !!!   >>>>> 
· Do not explore in places where you can not secure your own safety.
· Do not enter private  property or restricted area without permission.
· Do not disturb other people while exploring on streets and other places.
· Be careful not to be mistaken as a suspicious person.
· Common sense and good manner are the most important things you should know while exploring.

Hotspots links
HD logo
全国・電波ホットスポット探検隊 - Radio Waves Hotspots Detectives (Japanese site)"
全国・電波ホットスポットを探せ (Japanese site)

Hotspots Detectives on National Television !
 We were featured in the famous Japanese TV show, " Tamori Club(タモリ倶楽部)" on February 12, 2016 (24: 20 - 24: 50).
 Title :  " A Thorough Survey of Radio Waves!  We are Radio Waves Hotspots Detectives"
 You might find
the footage on Youtube by searching with " Tamori Club 2016.02.12 ".

■ MW DXing and SWL  ――――――

   (Produced by CQ Publishing Co.,Ltd. with the cooperation of )
 uz8cq  Order UZ-8CQ at CQ Web shop, CQ Publishing Co., Ltd.. 

QEX NO23 2017 別冊 CQ Ham radio QEX Japan NO.23  (2017.06)
My article in this edition(pp.85-92, Japanese)
" Product review : UZ-8CQ - Large wooden loop antenna for medium wave reception "
In this article, you can check the great performance of UZ-8CQ in MW DXing with Tecsun PL-360ET, SDR#, or in the reception of NAVTEX Japan.

■ Gallery  ――――――

          (coming soon)


Crystal Radios with Basket weave coils for MW DXing and SWL.
Amature Ham Radio(JJ1DIS), QRPp, Morse code.
SDR with RTL-SDR dongles, SDR#, GNUradio, RasPi, Arduino.
A member of "全国・電波ホットスポット探検隊 - Radio Waves Hotspot Detectives (Japanese site)"

twitter @imp_radiotech

IMP 2017. 12. 14
Tokyo, Japan
All rights reserved. (c) 2017 by IMAMURA Akira / JJ1DIS