International broadcasting is a shadow of its former self, and my hearing is down about 10 dB.  I'm using an software-define-radio to find stations and tune the antenna. The grid-dip oscillator and freq. counter allow me to positively identify stations by frequency.



The Facebook group is running one of their listening events later this fall, and they allow "one stage of audio amplification" for short-wave crystal sets.  Part of me says that that's cheating, but then again I'd like to hear a few more stations.  So, I designed an amplifier.



This is a straight-forward "source follower" using a common 2N7000 MOSFET (see Amazon).   Component values are not overly critical, but you want the  bias resistors to be a high value, 1 Meg in my case.  The source resistor (680 Ohms) establishes the output impedance and current drawn through the transistor.  You might want to go lower on the source resistor if you're using low-impedance phones.  I'm drawing 2.2 mA from a 6-volt supply.  The 2N7000 is good for 200 mA so you have some leeway.  I tried the same circuit with a MPF102 JFET, and it seemed to work OK.

The source-follower has a voltage gain of a little less than one, so it delivers a little less than the input voltage to the load.  However because of the large difference in input and output impedances, there is a LOT of power gain.  I'm seeing more than 20 dB.

The high input impedance allows the diode to be connected to the top of the tank circuit, where its sees maximum signal voltage, without putting too much of a load on the tuned circuit.  The low output impedance makes it easy to use sound-powered phones or ear buds without the expense of a transformer.



You should alway bread-board experimental stuff.  I added a green LED to remind me to turn it off.  A power switch on a crystal set.  WTF!



My variable cap has a built in reduction drive, that's nice.  With light coupling like the one-turn primary in this case, it's worthwhile calibrating the dial.

Here's the log from the first evening's listening from Jersey City, NJ :

HDSDR software on a PC  to "bird dog" for the crystal set and adjust the antenna tuner.



Signals about 5 dB over S9 (S9 = 50 uV, -73 dBm) are easily copied.

Here's a useful short-wave-listening link:

Enter the frequency, and they'll tell you who's on.  https://www.short-wave.info/

Here’s some info on my recent short-wave crystal-set experiments.  The basic conclusion is that SW crystal sets are quite worthwhile, and need not be unduly elaborate to give gratifying results.  This is especially true on the US east coast where the “prime time” broadcasts are really strong.

A word of warning:  You’re likely to hear strong, clear English broadcasts from the likes of The BBC, The Voice of Viet Nam, and Radio Taipei.  Don’t believe it!  These are rebroadcast from nearby sites in US and Canada.  To sort this out, there is a good frequency list available at:  http://www.primetimeshortwave.com/

I the short time I’ve been at it, I have heard Radio Exterior de Espana , Swiss Radio International, and The Voice of Russia from my West-central NJ location. So intercontinental DX is entirely possible.  I even heard a “numbers station” on about 13.5MHz.

This is a simple double-tuned radio built around Air Dux coil stock.  I used this because it was handy, but solid bare wire of about 14 gauge on 2” PVC should work just fine.  (Strip a length of #14 Romex.)  The primary tuned circuit is Tuggle style and offers a reasonable compromise between  effective, flexible antenna matching and ease of use.  I bent down every other turn on L1 to make it easy to tap with an alligator clip.  I equipped the secondary coil with a separate “primary” winding so the set can be used in the single-tuned mode to do a quick band scan.  Coupling is controlled by moving the two sections around on the table.  The “ground” end of the coils face each other.

Some additional observations:  A secondary coil of about 4 – 4.5 uH will tune 5-18 MHz with a 365pF cap.  That’s where 95% of the action is, so band switching can be avoided.  As with most double tuned sets, a calibrated dial on the lightly-coupled secondary really helps sort things out on the air.  I’m using sound-powered phones, but signals are strong, so a modest headset will be ok for starters.  Just elininate T1, C3, and R1, and connect the headset between the diode and ground.