Mitsubishi brick amp - lead length

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Joined: Thu Mar 13, 2008 7:19 pm

Mitsubishi brick amp - lead length

Post by g4bbh » Tue Mar 06, 2012 2:48 pm

I have an amplifier using the Misubishi RA18H1213G which I built some time ago using the Mini-Kits board. This amplifier gives excellent power out but has consistently been at the bottom end of the quoted gain range at 22dB. I have used all the usual construction precautions and can only see one possible cause of loss.
The Mini-Kits PCB is made from a fairly thin (FR4?) board which has to be mounted flat on the heatsink tight up against the module. There is about 1.5mm or 2mm hight difference between the module lead-in and lead-out out and the PCB so there is about 2mm of lead from the module to the 50 ohm strip line on the board. Could this cause loss at 23cm? If so I will have to make an aluminium spacer between the PCB and the heatsink to raise it.
Dick G4BBH

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Joined: Sun Nov 20, 2011 3:44 pm

Re: Mitsubishi brick amp - lead length

Post by G3GJA » Wed Mar 07, 2012 12:32 am

I'd be very surprised if shortening the leads by 2mm would make that much difference Dick.

The datasheet gives a minimum power gain of 23dB with +10dBm in, i.e. 10mW in for 2W out with VDD=12.5V, VGG=5V, so you should check it with those parameters to see if your amp is OK.

It's also very frequency dependent. The datasheet shows typical power gains of around 25dB for +10dBm in at 1240MHz, rising to 31dB at 1240MHz. At 1300MHz it tails off again and is about 5dB down on 1270MHz.

Obviously the gain also drops off with increasing drive power / output power, particularly as you get past P1dB which is around 10W out. You need to take into account cable losses to / from the amp; a couple of feet of 5mm coax will easliy lose a dB or two.


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