Tuesday, 16 June 2009

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.
.





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8 comments:

Anonymous said...

hi dave, it's very nice job to make it.

but i wonder what's the frequency alocation for this rig ?

this rig for comunication or for broadcast ?

and how long distance the result trnsmitied ?

tnx,

adiis, jakarta, Indonesia

Anonymous said...

Does anybody know where VC1 and RV1 are being used for? Also, where is TP1?

Thanks!

Anonymous said...

VC1 fine tunes the crystal frequency.
RV1 is the input volume control for the audio.
TP1 is the gate of Q3

Anonymous said...

PUEDO YO USAR TOROIDES DE PLACA MADRE DE PC FOR ALL (L) ???

Anonymous said...

HOW CAN I' BUILD THE ALL 'L' ???

I HAVE A MOTHERBOARD TOROIDS

I NEED MORE INF ABOUT ALL 'L'

Anonymous said...

I NEED THE ALL INFORMATION ABOUT HOW TO BUILD ALLA L
SEND ME THE INF. lsedr@hotmail.com

PLEASE I DON'T SPEAK ENGLISH, MY ENGLISH IS NOT GOOD.

I SPEAK SPANISH

Anonymous said...

hi dave just in the middle of biulding a corsair is there any way of turning the output power up and down as you need it and how low can you go or is there a limet meny thanks richard.

Anonymous said...

For some reason Dave hasn't used an impedance step up transformer, the IRF530 can do 70 watts with out distorting the audio.
The IRF530 needs a low impedance on the front and back end to achieve the optimal power that can be obtained. A simple 5 ohm to 50 ohm impedance transformer is needed before the LPF, which I assume has been calculated for a system impedance of 50 ohm, which is not the impedance the IRF530 wants to see if optimal power is required. Your also fine the bias voltage won't need to be so high, which is the cause of the distortion to the audio. I have an IRF520 amp doing just under 50 watts @ 19vdc with only 500 mW drive. Also note the operating temperature of IRF5xx's if working at near optimal power should be around 105c, maximum rated continuous operating temperature is 176c as stated on the data sheet.

 
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