BTTF listening contest, 2005


Between Christmas and Newyears 2005 there was the Dutch BFFT listeningcontest for crystal receivers. This means you can only participate using a passive radio,...no amplifying or input power is allowed, only the energie from the antenna.

I already had some experiance building honeycomb and other coils for crystal radio`s,..so it was time to make a contest receiver. I used a diode (1N34) instead of a real crystal .

And there is also a description of the picture above,..from left to right:

Left you see the antenna tuner capacitor,..unknown origin but 2x500pF in series,...so 250pF.

Next the first LC antenna circuit, a spiderweb coil with 45 windings made out of 440/46 Litze on a polypropylene coilform and measures 215ÁH. Parallel on the coil a Hammerlund variable C of 300pF, operated through a 1:5 reduction with a ceramic insulator in between to reduce hand capacity.

I measured the circuit on its bandwide and Q factor. Bandwide is aprox 4.7Khz, a Q of around 212.
Q=res.freq/bandwide,    Q=1000Khz/4.7Khz,  Q=212.
Impedance of the circuit: Z = 2 x pi x f x L x Q.      Z = 2 x pi x 1000000 Hz x 0,000215 H x 212.    Z =286,242KΩ.

Next you see the detecor circuit, made from a identical coil with a value of 215ÁH. Tuning capacitorparallel on the coil and is also from an old tube radio and the value of that one is 500pF.

I also measured this circuit at 1Mhz (1000Khz) and the bandwide is here 6.4Khz. The impedance of the circuit is: Z = 2 x pi x f x L x Q,    Z = 2 x pi x 1000000 Hz x 0,000215 H x 156.    Z = 210.631KΩ

The LC on the right is the wavetrap made out of 45x0,007mm litzewire and measures 230ÁH, the capacitor is a Hammerlund and measures 230pF. Q of this circuit is around 95. Its low because of the used litze wire,..the more little wires,..the better the Q.

Headset is a real old one, from around 1920/25. It has a resistance of 3KΩ with a impedance of around 15KΩ. This is ways to low in combination with the impedance of the detector circuit. But it has to do the job when you don`t have anything else.

This radio can still be improved,..so perhaps next year a better one.

Here the  loglist of what I heard with this set during the contest.
 

Couple of months later...

Saturday morning, 1th of April, 2006  (no kidding)

I think I`ll go teo the BTTF homebrew day at the town of "Kootwijkerbroek", lots of noce things to see there I hope,..and I send in a log of the last BTTF contest, so let`s see where I ended.

Coming inside I just missed the opening speech, so I wnt to the bar to get a nice hot cup of coffee, as I came on my motorcycle and it was cold outside. Well, they announced that the homebrew/contest prizegiving started so I went to that hall and took a seat.

Homebrewers with there radios were around 5 or 6,..not many. Listeners there were 7,..so I got the 7th place was my opinion,..as Dick Kleijer also participated and he is gooood. Well I had no 7th place,..5th place,...Dick Kleijer,...hmm,..not his style I thought,...did I log more stations as he did?? Third place,...Lisa Leenders.  What the....? Did the lost my log or did the forget about my log. In the end I took first place,...me?..first time in a contest with a crystal radio.

Well, you hear your name,..so I went in front of the crowd,...bit dirty hands and old trousers as I was repairing my car at home and also went to get some parts afterward here. So I went to collect my prize and to say how surprized I was and I thanked the organisation of the things the accomplished and doing. Hopefully I`m here again next year.

Rest around it was not big, homebrew projects, QRP. Sweets for the eye and lot`s of things you can learn from,..also the things other people had to say. Lotsa ragchewing face to face. It was worth it to go there.

Hopefully next year there will participate more people, so get a more contest like feel.


73.
Frank, de PD2MRX (now PA2MRX)
 

 

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