Corsair II

An update on the original Corsair circuit which can be found here, The Corsair TX.

Dave Martin.
 

Experimental Gate modulated 48 Metre transmitter

Below is a experimental variation of the Corsair circuit. Instead of series modulating Q2 and using the final Q3 stage as a linear the gate of Q3 is modulated by by the output of IC1 the LM386.

You must use the 7808 voltage regulator otherwise the voltage to the gate of Q3 will exceed the safe level and destroy it.

If you already have a Corsair built, altering it to this circuit is easy.

If you build this please leave a comment letting me know how it went for you.

The original Corsair circuit is HERE.

 Click for full size

Below is a video of what a test transmission from the above circuit looked and sounded like received locally.

Dave Martin.

Alternative oscillator for Corsair and Commando.

One disadvantage of the original oscillator circuit was the lack of available frequency shift.
The circuit below addresses that problem for the versions that run between 5 and 7 MHz.
Depending on crystal used you may find a tunable range of 7 KHz.
Just replace the first 2 stages from the normal circuit with those below.
To use on other bands the windings on L1/L2 would need changing.

The Corsair Transmitter by Dave Martin

The CORSAIR transmitter was designed by
Dave Martin of W.N.K.R. in 2004.
It is a 10 watt AM short wave transmitter that does not need a modulation transformer,
thereby much simplifying the design and still only needing 12VDC allowing it to run from a vehicle battery.
The "Pierce" oscillator uses a common FeT, the BF245.
The driver stage is a BFY 51 and is series modulated by a LM386 Audio IC.
The output stage is a very robust MoSFeT,
the IRF530.
It is possible to achieve more
output power than 10 watts.
But to give excellent audio reproduction, the power has been kept to the lower level.
On these pages we will outline versions of the "CORSAIR" for use on different bands.
At present versions have been made and used on air on medium wave through to 32 metres (9.3Mhz)

A LM386 audio IC is used to series modulate Q2. The LM386's output on pin 5, sits at half the supply voltage. But is swung plus and minus with the audio being fed to it's input.In the high current version Q4 allows Q2 to draw more current without damaging the LM386. The PA, Q3, is a IRF530 which is configured as a linear amplifier. To set up you should, by adjusting RV2, set the DC voltage at the junction of L8 & R7 to 2.5 VDC. Then by moving the turns on L6 further apart or closer together, get the RF power to read 10 Watts. It must be noted that Q2,Q3 & Q4 must have heatsinks and that Q3 & Q4 should be mounted using a TO220 insulation kit.
The table below shows the component changes needed to the PA and Filter section to use the CORSAIR on other bands.

All the above coils are wound using 22 - 24 SWG,
enamel covered copper wire.

Click on any picture to view large size..