Saturday, November 03, 2012

Tiny CW transceiver for Feld Hellschreiber

This morning I had a Feld Hellschreiber contact with Stephen, VK2BLQ on 40m. Here's how he looks to me:

And here's how I look to him:

Comparing the two waterfalls above I think I have too much RF gain which is leading to a noisy receive display.

My goal here is to be able to use a very simple, very small, CW transceiver with a digital mode. Next step is to get an audio driven keyer working.


I've now got this working with the tiny CRK-10 CW transceiver via a simple audio keyer interface.

I'm using a little USB audio adapter and then you can see my simple audio transformer, full wave rectifier and 2N2222a transister to key the CRK-10. In the video below I test transmitting into a dummy load.

Stephen wrote "Good to work you on 40 Hell again.

The CRK10 has a very narrow filter, I was calling you back on 7030 several times, but not until I QSY to 7131.2KHZ that you heard me.

Your RST was about S3-5 but letters were good. Goes to show a microrig and pc  has possibilities.

The narrow filter kills the noise and makes the letters clearer.

I dug out  a couple of older T/R  boxes to mod for keying the tube TX directly. Don't think a relay is fast enough and is noisy. I'll use a powerfet rated for 100v and 1 amp as the Cathode current is 100mA and key up volts is quite high."

Here's how the QSO looked to me:

So aside from the fact that I'm off frequency, my reception is superior to my main rig.

Here is the simple keyer circuit. Small signal diodes, a 2N2222a and a few 0.1uF caps. The transformer is a little audio transformer, not sure what ratio.

I added a 3.5mm socket to the CRK-10 and connected it to the top of C22 where the transistor pulls low to key the carrier.

Thanks again to Stephen, VK2BLQ, for all his help at the other end but it looks to me that a truly minimal Feld Hell transceiver is quite practical.

1 comment:

VE9KK said...

Very nice, I used to be into the digi modes but once I changed out my PC and had to set up the PC and rig communications it became very frustrating!! BUT as the conditions on HF go into the barrel I will put my nose to the grind stone and set up the digi modes once again.