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2.4Ghz 20 Watt PA

Some pictures and info on some recently acquired PA's for the 2.3Ghz to 2.5Ghz bands.

Written by: G4RFR ( FRARS ) Sunday, 21 July 2002

Click for full size imageThe tests for this unit were carried out by Andy - G4JNT. I'd like to thank Andy for his tests.


These PA units were found at a UK rally this year for the sum of 18 UKP each! A bargain if I may say so.

The version with a 9 pin connector has the following connections :
Pins 1 , 6 +12.6V
Pins 2 , 7 Gnd
Others, signalling and control, not identified yet.

At 13.8 Volts, the current consumption is quiescent 6A, The DC supply to devices inside, 9V on drains of PA indicating some sort of active regulator circuit inside, but we couldn't see where the 3V at high current is dropped - must be a resistor hidden under the PA, probably for Id. monitoring. Bias on the PA devices is -2 V and very likely active biassing is in use, so the suply range of 12.6 +/-0.3V is a dissipation issue in the regulator rather than RF device limit. Would have thought the lower limit could be less with 9V Vd, need to test this.

RF Tests: 2.4GHz, Drive 6dBm (4mW) gives greater than 6W output, and with increasing drive, we saw power up to 14 Watts. In fact briefly tested to around 20 Watts output but as my load is only rated at 3 Watts and the PA was drawing 11A didn't keep it there for long ! At 2.32 GHz, gain is 3dB lower needing 8 - 9dBm for >6 Watts , but the same power output is possible, in fact I may have even seen slightly more during a quick test at 20W. Current for a given power was marginally higher, but only by 0.4A or so. So it looks as if most of the gain is falling off in the low power driver stages rather than the PA itself. which is just slightly less efficient at this freq. Current stays at 6A to around 5 W output indicating linear class A operation to this point, then increases above this figure as the PA operates in class AB.

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