Crystal receiver 2019

Also in 2019 I`m still busy with my crystal receiver. Towards the end of the year I`ll listen what still there on the Medium Wave now most of the big transmitters are gone in Europe.

I took the spiderweb coils for that I made around 2006. Those are 440x46 Litz wire coils on a PolyEthylene coilform with an induction of around 215µH. Capacitors used also the same as back then. Coming from a 60`s tube radio. Cleaned again using circuitboard cleaner, ultrasonic cleaning and flushed using brake cleaner.

As a match to my soundpowered headset I do not use those 4x Adastra`s with a total of 320KΩ this time. I got something new, audio transformers made in germany by "Reinhofer Elektronik" (Gerd Reinhofer SK).
For my transformer I have the 53.48RA version. Input impedance: 100/250/450/700/1000KΩ.  Output impedance: 200/500/1000/2000Ω. Soundpowered decktalker headset of around 200Ω impedance.

For my audio transformer I made a small box to put all parts in. Two ceramic switches, a "benny" (named after Ben Tongue).
I call it my "Super Übermatch", because Dave Schmarder made a Übermatch.
The Benny will restore the high dc resistance to the detector circuit.

 


Coupled the LC circuit together and measured its Q again. This time not using the -3dB method and my FET amplifier and scope. But a completely new gadget to measure Q.

 

This Q meter is designed by a Chinese amateur (Mr. Guo) and sold in the USA through the radioboard by Mr. Mak.
This Q meter is not for sale commercially. At the right a picture of the meter as a setup on a breadboard.

The DUT is being measured using the "Ring down method". 




By measuring my LC circuits the Q factor are around 830 by 525Khz and 276 by 1600Khz. I also made around 15 other measurements between these two so I could calculate the impedance of the circuits at all these points. I need these later.

The antenna:
In the past I did not measure the antenna, but put it through a big variable C to the circuit. But now we have the "SARK 110". I didn`t use "My Favorite Junk" MFJ259C for it. That one is bulky, has no range,not stable, eats batteries, belongs in the garbage.

Here a screenshot of my wire antenna, values Rs and Xs seen here. These vary from 24-J252KΩ by 525Khz till 34-J221KΩ by 1500Khz. Export to excell also possible for further use.


Now I know the values of my antenna, and those of my LC circuits, I can calculate the match between the two. Because of the changing values of the two parts I need variable capacitor between the LC circuit and the antenna. If these calculations where neagive, it could be a variable inductor.

The value of my matching capacitor will be 98pf at 525Khz till 28pf by 1100Khz and up to 40pf at 1600Khz. So a small C of 10-120pF will do.
Because i have all my measurements in excell I can also make a small scale for that C with frequencies on it.
The calculations are partly made using Dick Kleijers website.

I`ve put all things together, not on my radiodesk, but on a clean desk without metals and wires in the neighborhood. Even not a AC outlet.
First half of the MW band is doing fine. Lots of stations. Also some real DX. A shame there are still some "Big Guns" from the UK spitting lots of dirt into the air so nearby frequencies are very hard to get. And some frequencies with nothing on it now, even listening using my kenwood TS450 and FD4 antenna.

See some results in PDF