My BTTF 2006 Crystal receiver.
2005 is here.


The Crystal receiver I made for the 2006 BTTF contest is seen here, now I re-measured the LC circuit again with my newly made FET amplifier like it is seen on the site of "Dick Kleyer". The 20Mhz  DDS signal generator I use is bought at ELV in Germany.

The measured LC circuit is the antenna tuning circuit, this one is identical to the detector circuit (same L and C). Here I came to a bandwidth of 6.9Khz at a frequency of 1.6Mhz. Lowest frequency at the -3dB point is 1.598Mhz, Upper -3dB point is 1.6017Mhz.

Measured at 1600khz measured at 531khz

BW= fh - fl       
BW= 1,6017-1,5948
BW=6,9khz
The Q factor of the circuit is:
Q= f.res / BW
Q= 1598,5khz/6,9
Q= 231

BW=fh-fl
BW=531,8 - 530,7 
BW=   1,1khz
The Q factor of the circuit is:
Q=f.res / BW
Q= 531,3/1,1
Q=483


Parallel resistance RP of the circuit at the two frequencys are:
 

Rp at 1600khz Rp at 531khz
Rp=2∙pi∙f∙L∙Q
Rp=2∙pi∙1598500∙0,00025∙231
Rp=579KΩ
Rp=2∙pi∙f∙L∙Q
Rp=2∙pi∙531300∙0,00025∙483
Rp=402KΩ

 

The resistance RL has to be three times Rp, the headset/speaker has to be matched to the this value, the diode Rd also needs a value of RL, I took the average of 519KΩ and 402KΩ , 460KΩ x 3 = 1380KΩ. So I came to the conclusion to use  the HSMS286K diode with a Rd of 1476KΩ, according to Dick Kleyer`s diode table.

The last measurement at 531khz also gives an improvement in the Q-factor of my coil , this is due to the setup I used to measure and my FET amplifier. Here the Q went up from 175 to 483,..this because the circuit has lesser loading.

The Q also will go up more if I clean up my desk more,...but hey,...all the crap is also lying there when I use the crystal receiver,...so why bother to get a higher Q just for statistics.



The FET amplifier.

With the FET amp I noticed the effect of hand capacity and surroundings very clearly when I measured my coils when looking at my scope (Tektronix AN/USM281A). So it was a very good idea to build that FET amplifier to measure my LC circuits.

 

Long wave crystal.
150-280KHZ

While at it I quickly build a "Long wave" crystal receiver. I used a 1000pF var.Capacitor and a coil of 900ÁH. This one is wound on a 5cm diameter cilinder using 0,5mm thick enameled wire. On one side of the LC circuit is connected the antenna and on the other side earth. Crystal (diode) used is a schottky diode. Audio transformer connected, headphone,...results... about 6 stations at 16.30 in the afternoon.
 

 

Anither new thing I came across as a detector was a MOSFET, a "zero voltage-threshold MOSFET ". It is the "ALD110900A" DIL with two mosfets in one housing, the "ALD110800A" is the same thing with 4 mosfets in one housing.

click here for a description for a crystal receiver using these mosfets.

 


My references for my calculations: the site of Dick Kleijer

The "Woods metal" or "Cerrobend" I got from the UK: DGR design.
The "Galena" I got from Ebay: http://www.ebay.com  search with "galena"
Shellac I bought here in my neightborhood: http://www.dekwast.nl , but
you can get it much cheaper at Ebay for about 10 euro`s/kilo.
 

 

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