I assembled my QRPme Tuna Tin 2 50th Anniversary edition kit a couple of months ago, but then it has just been sat around. I fixed the missing keyer transistor issue and verified that the rig produced RF, but that’s as far as it went.
I knew that Rex (Mr QRPme) W1REX was making the trip over to Telford hamfest at the beginning of this month, so it spurred me on to make an end fed antenna for the Tuna Tin 2. The hamfest weekend was over in a flash and I hadn’t even touched the Tuna Tin 2.
I have been wanting to try the Tuna Tin 2 since I got back from Telford. I had been thinking about how to interface the receiver to the Tuna Tin 2 transmitter. I do have an RF sensed antenna changeover device (Tuna Helper), but the idea of the new Tuna Tin 2 kit is that everything is brought together on one can. The Tuna Tin 2 50th anniversary edition has a receiver feed tapped off the EFHW transformer and a receiver mute jumper. The idea being that you can just connect a QRPme Sudden Storm Receiver straight to the transmitter.
I’m haven’t got the greatest technical mind, but I thought that feeding the receiver directly from the transmitter was a bad idea - during transmit a potential 2 watts of RF could be fired straight into the receiver '612 mixer chip (depending upon setting of front end variable resistor). I thought I’d try the method I’d used before in a home brew rig, to use a pair of diodes to limit the maximum signal level into the receiver.
I made up some cables with the diodes, along with a capacitor and inductor, hidden inside the connector shell. A quick test with my oscilloscope showed reduction of the signal level.
Yesterday my work shift was very short, so I was home by early morning. I did some last minute tinkering and then loaded up my Tuna cans to take them up Hutton Roof Crags G/LD-052 for a test.
The weather was pretty gloomy but I put on a brave face!
I had swapped the Tuna Tin 2 50th Anniversary over to 20m as I had got some more low pass filter modules from Rex at Telford. The antenna is cut for 40m, but it also works fine on 20m.
I discovered that I couldn’t get the RX mute function to work, the RX would mute in all cases when I tried different ways of connecting it to the transmitter. I resorted to a switch soldered to some DuPont wires, which I carry with my stash of Tuna can connecting cables. For each transmission, I’d have to manually switch the mute for the receiver.
I shortly discovered that my receiver protection cables (band specific) seriously attenuated the receive signal.
Despite my challenges, I managed to make 5 QSOs with the Tuna cans. I’ll have to investigate the RX mute issue (it’s complicated a little bit because I don’t have a schematic for the TT2-50A transmitter, it’s a case of reverse engineering!) and I’m going to try to remake my receiver protection cables.
73, Colin
sandwich?
