QRP Labs
CW Transmitter: 2-way ECL82 QSO recording PDF Print E-mail
Written by Hans Summers   
Saturday, 25 April 2009 07:21

Here's a recording of a QSO between my ECL82 transmitter TX (QTH just south of London) and a similar transmitter built by Bill G4KKI (QTH nr Manchester). His project was started when I sent him my spare ECL82 valve after several CW QSO's on 80m. The two ECL82's which are communicating here are therefore brothers! He built two versions of the transmitter, the 2nd version uses an EZ81 rectifier valve in the power supply in place of the solid state rectifier diodes. Thanks to Bill also for giving me a nice GZ33 rectifier for my all-valve tranceiver PSU.

The recording also shows what signals sound like in my HF receiver. During the QSO I was using the normal bandpass CW filter at all times, but on occasion in the QSB I additionally switched in the phasing filter. This makes the received bandwidth considerably narrower which increases the signal to noise ratio, very useful sometimes for receiving weaker signals. But it is difficult to tune and subject to ringing, therefore I tend to use it sparingly. It also creates a slightly muffled sound which makes signals sound less shapr or crisp. This effect can make it harder to copy some stations, particularly when QRQ.

Visit Bill's transmitter page!

During another QSO Bill recorded my signals. The recordings can all be downloaded in MP3 format by clicking here to visit the web page of Mike Andrews W5EGO. Mike kindly offered to host the files since I have limited space on this server and in any case it does not allow me to host MP3 files. Thanks Mike! Be sure to take a look around the rest of Mike's interesting website.

A QSL card prepared for this special occasion

Here's a screenshot from my audio editor program showing the entire QSO. The vertical scale is linear not logarithmic. QSB on the received signals can be seen easily. QSB can be quite deep on 80m but was not particularly severe on this occasion.

My "sidetone" can also be seen. In fact I have no sidetone on my receiver (yet), I just incompletely mute the receiver during transmit. The TX/RX relay in the TX switches the antenna over, and another relay simultaneously switches the input to the audio amplifier to ground via a 100uF capacitor. With this arrangement I can hear my own transmitted signals in the receiver at a comfortable low volume.

In this QSO are transmitters were somewhat offset from one another, due to both of us being rockbound (using crystals). This means when receiving my own signal during my transmissions, the CW filter attenuates them to be weaker than usual. In my second over you can see my signals at even lower amplitude, this is because at this time my phasing CW filter was switched in and provides a narrower CW bandwidth and therefore higher attenuation of out-of-band signals.

A closeup on "G4KKI", showing the nice clean keying waveform, with a little QSB. Both stations were using traditional straight morse keys.


Here's an "F" transmitted by G4KKI, showing the nice keying characteristic. I have received many on-air compliments on the CW tone, entirely free of any chirp etc.

"G0UPL" as sent by my TX. The spikes at the start of each morse character are most probably not a real effect, but a distortion introduced by the receiver. Bear in mind that plenty of RF is flowing around during transmit and the receiver is drasticallly overloaded compared to ordinary signals, even though the antenna is disconnected during transmit.

Here's a "C" sent by G0UPL. Note the presense of 50Hz mains hum. Almost no audible hum is present in my HF Receiver which is powered from an ex-PC switched mode PSU. The 50Hz hum on the recording probably originates in the cable between the radio and the PC. The length of the cable was approximately 4m, of which only 2m was proper screened cable. The remaining 2m was made from two lengths of multi-stranded hookup wire.

Click the image of Bill G4KKI's TX to see his website!

Last Updated on Saturday, 25 April 2009 07:52
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