ADDITIONAL WA2NTK CIRCUITS |
The article that was the inspiration for this transmitter can be found here... Easy 6aq5 40M transmitter Since I had a few 6P1P tubes in the drawer I decided to
build the circuit with a few minor changes. I used a 47K (47,000) ohm resistor for the grid and substituded .001 for the by pass capacitors. I used a 8 pin octal socket
for the crystal holder and key jack. Use whatever you have in your junk box. The components are not critical. I measured 5+ watts into a 52 ohn dummy load
with 250 VDC on the plate and screen. Keying is very good when tuned slightly off of peak. The output into a wire will be somewhere around 4 watts and 5 to 6 watts
using a small antenna tuner into a dipole.
Even small QRP rigs with plate voltages in the 250Vdc to 300Vdc can have substaintail voltages actross the key. In most cases this voltage will cause
elecrtical shock and will be to high for some electronic keyers. This simple circuit is inexpensive and quick to build. When mounted to a aluminum chassis the
chassis will amplify the relay clicks. I mounted mine on a small circuit board and the used rubber grommets to isolate the PCB from the chassis.
I can still faintly hear the relay but the clicking is reassuring that all is well in the keyer circuit. The other option is to use a small solid state relay. The circuit is easly adopted to 12Vac filaments by substuting a 12Vac
relay
I needed a simple way to switch a QRP transmitter from receive to transmitt and back using a mechnical switching arrangement.
I use this circuit in the center tap of the secondary of the power supply power transformer, (280Vdc, key down) without any problems. This is how I
did it. Unless you have a muting circuit in your receiver you will still have to reduce the amount of RF getting to the receiver. Just turn down the,
Audio, RF or preselector. For higher powered transmitters you can substitue a relay for the switch and add grounding of the receiver front end.
Since we lost two towering trees last summer I no longer have the ability to erect a long wire antenna. I now use a small ground mounted
vertical antenna based on the High Sierra screwdriver design or an off center fed dipole, a Windom antenna at 25 ft. The Windom is fed through 52 ohm
coax to a 4:1 balun and then open wire feeder up the tower to the antenna. Both antennas are unbalanced. Because of the circuit design of my QRP rigs they did not load up very well into these antennas
The following inexpensive antenna tuner is a result of not wanting to redesign the QRP outputs circuit to accomodate the unbalanced antennas.
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